Author Topic: Quartz Surface Plate? (Read 26609 times)

sparky961 · « **on:** August 20, 2015, 07:43:47 PM »

I've been keeping my eye open for some used granite countertop pieces or a sink cutout or 3 so that I can make up a cheap surface plate (or 3). Tonight I saw an ad for some pieces of Quartz; any thoughts on whether this would be suitable for a surface plate? Or rather anything that would definitely exclude it?

In doing some quick searches I learned that apparently the better quality pink granite surface plates have higher quartz content which yields more abrasion resistance.

There's probably enough there that I could make like 10 plates for $40 or less. Waste of money or good project?

jcs0001 · « **Reply #1 on:** August 20, 2015, 08:08:13 PM »

Interesting project - I have no idea how flat they are.

I bought a granite surface plate from Busy Bee some time ago for around $35 - they were selling lots to people as headstones because they were inexpensive. I guess I should have put that in my will

So you may be able to recoup your investment if they aren't flat enough - just approach the local funeral home.

John.

sparky961 · « **Reply #2 on:** August 20, 2015, 08:39:12 PM »

A lot of my early tool purchases, including the mill/drill I use were from Busy Bee. It's a convenient place to get your hands on various grades of Chinese equipment. Some crap, some stuff that's stood the test of time so far. Unfortunately I've come to realize just how much a trip to Toronto ends up costing me when I do break down and go there for some reason. I haven't even bothered to check out the shipping price for a surface plate because I'm afraid to know.

Still, the current perma-sale price of $49.99 for a 12 x 18 x 3 black granite surface plate at Busy Bee doesn't seem that bad. Specs say it has an "accuracy" of +0.0001, which is questionable to say the least. Though admittedly it would probably be more than adequate for my home use.

I guess if I go the countertop route I could try my hand at hand engraving my own headstone....

gerritv · « **Reply #3 on:** August 20, 2015, 08:59:06 PM »

I was looking at using some marble tile from ReUseit but now that you mentioned the price at BB I might risk a trip to smoky Toronto.
Even if it is good for .001 it will suit my needs.

Gerrit (recently moved to St Catharines)

BaronJ · « **Reply #4 on:** August 21, 2015, 05:52:16 AM »

I must admit that I use a cheap 13" square porcelain tile for my surface plate. Since I have no desires to do any scraping and this would be for me the only reason to spend any money on a surface plate, having a flat surface over a relatively small distance as a measuring reference is all that I need.
Having said that, If I did need to use a surface plate there is a couple that I have access to. In one case a skilled instructor to teach me how to not to use it.

mechman48 · « **Reply #5 on:** August 21, 2015, 06:15:32 AM »

I have a piece of black polished granite worktop, 18" x 18" x 1" (countertop, sink cut out) that I got free gratis from a local manufacturer

; I measured from corner to corner in two planes with a digital DTI & all I got on one corner was a drop off of 1/2 thou' ... -.0005" the rest of it read .0000" at all points, close enough for what I need to do, not looking for light waveband flatness as I've long ago finished diamond lapping safety valve discs & nozzles. Any granite trivet from your local home ware or DIY store should suffice for ME work.

George.

John Rudd · « **Reply #6 on:** August 21, 2015, 08:10:23 AM »

Got my granite surface plate from Aldi....IIRC, was about £7.....and very heavy...
Measures about 12 x 8 x 1 inch thick....
I think it will meet my needs....,

Stilldrillin · « **Reply #7 on:** August 21, 2015, 08:20:26 AM »

A piece of granite floor tile, 12" x 6", has met all my needs over the past 10 years.......

David D

sparky961 · « **Reply #8 on:** August 21, 2015, 04:25:14 PM »

Sound like it will likely work well. I think I'll ask around a bit though and try to find a few sink cutouts for free.

Doc · « **Reply #9 on:** August 21, 2015, 09:50:43 PM »

Free shipping from Enco code AUG29
So the cost of a plate isn't too bad.

sparky961 · « **Reply #10 on:** August 21, 2015, 11:24:33 PM »

Any idea if their free shipping works for Canadian addresses too? With the very low Canadian dollar right now, it'd have to be one heck of a deal.

gerritv · « **Reply #11 on:** August 22, 2015, 08:20:39 AM »

Their 12"x9" is USD43.43 so the Busy Bee one is still a better value.
KBC Tools has them at CA$53 and seems to use $8.95 flat rate shipping for a 33lb lump. Might be worth a call to verify that?

You also could get a US Address in Niagara Falls, NY though if you want to use Enco. CBI is a good place.

And then enjoy some wine and lunch at one of the 50+ wineries in the Niagara Region on the way home :-)

tom osselton · « **Reply #12 on:** August 22, 2015, 02:38:28 PM »

I have been thinking about getting the busybee one and am wondering if anyone has asked about if a bigger size was available from them I'll ask next time I'm there.

PekkaNF · « **Reply #13 on:** August 23, 2015, 09:32:58 AM »

Has anybody measured or questimated how inaccurate substitute surface plates are?

I have trouble with my milling machine, basically screws/nuts etc are ok, but I have used all adjustement range on tapered gibs. That is not that big problem, but ways are way out of specs long ago.

I would like to asses the flatness of the milling machine table and only reliable way I can figure out where I can do it repeatedly is fairly large surface plate.

The milling machine table is 1000*250 mm and about 75 mm thick + dove tails etc.

This large surface plates are not something that are sent on mail routinely and the ones that are made for industry are not only wonderfull piece, but also way out of my buged.

Anything better than 0,01 mm / 1000 mm would be a big improvement. I have seen float glass mentioned. Also epoxy granite countertops. Granite countertops? They would need pretty substantial base because the milling table must weight something like 100 kg and the table should not deflect much under this load.

I have small 200*300 very thick surface plate that came with an inspection report and it is pretty close to flawless that I can tell. 1/10:th of accuracy would make verry happy on this larger scale.

Any suggestions?

Pekka

* Small update...I have about 250 *600 mm granite table top offcut in the garden. It looked straight, I put 600 mm long parallel to it and mounted DTI on magnetic base and run test...Showed close to 0,1 mm swing. Magnetic base was small and DTI was offset, but least that piece was not very flat.

sparky961 · « **Reply #14 on:** August 23, 2015, 06:38:57 PM »

My plan, if I find some decent pieces, is to lap three of them together in succession in order to end up with 3 "perfectly" flat surfaces. I figure starting with something reasonably flat will reduce the amount of lapping needed but it still may require some brew and media to make the process a bit more fun.

vtsteam · « **Reply #15 on:** August 23, 2015, 08:45:29 PM »

Pekka, seems like you could get within your level of tolerance with a straightedge. Some long carpenter's levels are ground to a reasonable tolerance, and might be used with some blue marking compound.

PekkaNF · « **Reply #16 on:** August 24, 2015, 03:16:02 AM »

I got one 500 mm long Flat straightedge, DIN 874/2 and two parallels, that are true to first one as far as I can tell. I also have 150 mm long hairline and according to that one these are pretty straight as well.

Problem is that this is essentially a line, I need plane that I can measure height of several points relative to each others and do it repeatedly.

I borrowed an accurate spirit level from a friend. It has graduation of 0,02 mm/m inclination and leveling the milling machine took some time. Took like a minute for the bubble to creep into final position (last few digits). Scary sensitive. Machine foot are 700*900mm grid and a fraction turn of the leveling screw sent the bubble often 5 divisions away.

I tested an 10 mm thick float glass piece and it's surface variation was a whole lot better than old granite kitchen counter top. Short distance accuracy was good, but it seem to need very stable/straight subtable to keep it straight. Placed it on top of the counter top and put only 600*50*10 and DTI /w base and it was not straight at all in 400 mm distance. Any 100 linear distance was pretty good tought, but it looked like it adopts shape of the table under when we are talking 0,01 mm or so reading when any load it applied onto it.

I have to test few objects and see how reasonable results could be obtained with far from ideal eguipment.

If the float glass or granite countertop turns out to be good enought, maybe I can build each measurement setting such way that the weight of the object (E.G. milling machine table of 50-100 kg) is suported on parallels, discs or such and the measurement table is supported right under these spots to prevent the flimsy measurement table from bending under the full load????

Dodgy?Maybe, but I don't think I have the skill/time to make three really big surface plates and then start scraping the heck out of the mill machine after that anytime soon.

The three palate method is something I should to in a small scale to make some support "discs". Is there a good guide where the method and logic is explained plainly and clearly?

Pekka

jcs0001 · « **Reply #17 on:** August 24, 2015, 11:03:13 AM »

Pekka:

Regarding supporting the float glass. I read some years ago about race car repair bays where they laid down a thick layer of epoxy which self leveled to give them a very flat surface to use for measuring suspension etc. on their cars. Can't seem to find it online but it may give you some ideas for supporting the glass.

A few years ago I made a small glass surface plate and bedded it in bondo (car repair filler) on a 3/4 in. plywood base. It did seem to "bend" a bit though. I actually made 3 and used valve grinding compound and a huge amount of manual work grinding them against each other. They turned out ok but still had low spots around the edges. I have one left and use it for a flat surface for lapping and the like.

John.

vtsteam · « **Reply #18 on:** August 24, 2015, 12:04:44 PM »

JCS description of 3 plate method using glass and bondo beddding on ply comes from the Gingery books. Gingery later concluded that the bondo and ply shrank and threw the plate off in flatness.

Pekka I think you misunderstand me. The ground carpenter's level is to be used as a straightedge, not a level, and it (or any other straightedge) would need to be longer than yourf milling table -- say 1200 mm, minimum. I believe that such a level can be found at very reasonable price ground to less than a .001" overall, which I believe fits your rquested precision.

You do not necessarily need a surface plate for a limited tolerance on your milling table. You can test with a 1200 mm straightedge laid lengthwise at front and back and crosswise, as well as diagonally. Even a conical (twisted) straight solid will register as nonlinear if the straightedge is not placed directly on a radial.

When i built my Gingery lathe bed I used a 4 foot long ground carpenter's level, with a guaranteed .001" edge straightness tolerance over that length. I believe it cost about $40 US at he time.

You can also make a straightedge using the method of threes from hot rolled steel stock -- say 1/2" by 2" by 4' (or similar metric).

The method of threes is simple:

Grind with lapping compound any two surfaces (called say A and B) until they conform. This may not be straight, but they will be mirror images. Then lap a third surface (let's call it C) to A.

It will now be similar to B.

Then lap C and B together. Since they will have relatively corresponding high and low areas, the lapping will produce a reasonably flat surface. This method can be repeated if extremes of accuracy are required, but generally one go is sufficient for home machinist's needs.

I made a straightedge for the new lathe I'm building, but used another method of comparing it to a surface plate I already had, and scraping.

Scraping or lapping a straightedge by the method of threes would be much easier and quicker than doing the same with 1200 mm square surface plates, and because of the low mass, a straightedge needs far less stiffening, for your limited accuracy puroposes.

PekkaNF · « **Reply #19 on:** August 25, 2015, 03:48:31 AM »

Thanks.

I'll get that. Works well on simple planes, but gets a bit more convoluted when there is a dovetail and other features stikking out.

See CoC.

I know there is a way, three points makes a imaginary plane, but it's easier to measure from the real plane nearby than from points of any real distance.

I was thinking of checking the table (worst part) first. It looks like table surface and dove tail planes should be parallel. This should be easy to check with micrometer. I hope there is few original/straight/pristine spots left I can establish this. Then I'll mount the milling machine table on top of the "plane" from these spots. Short paralles or such.

Then I could check the wear on dovetail guide surface that should be straight and coplanar to milling machine table and surface table. This measurement should be fairly straightforward with a comparator/scriber foot and DTI.

Primary goal is not perfection, but correction to the right direction.

Pekka

PekkaNF · « **Reply #20 on:** August 29, 2015, 02:35:08 AM »

I measured flex of two common materials:

30 mm thick granite table top 290*600 mm

10 mm thick float glass. Plate size 300*400 mm.

I placed the spesimen on top of the small surface plate. Overhang was 240 mm and measurement point c/300 mm and 200 mm overhang. DTI was zeroed when there was no load and read when a dummy weight of 1320g was placed behind/front of the central measurement point.

With 10 mm glass plate the deflection was 0,05 mm and with 30 mm granite plate there was no perceptible change. This clock had a reading resolution of 0,01 mm. I do have 0,001 mm clock, but not that good base that it would make here much real life difference.

Soo it looks like if proper Bessel points are used to support the load/surface plate it should support measurement apparatus.
https://en.wikipedia.org/wiki/Airy_points

Therefore hunt of 30 mm and/or 60 mm granite interior decoration material is on the way.

Pictures:
Initial try....too much uncertainty, but it showed that glass deflected and that measurement system was not rigid enough. Also initial 100 mm overhang produced reading on the glass plate, but absolutely not reading on granite table top.

For next round I INCREASED the plate overhang to 240 mm and measurement point to 200 mm overhang and on width on the middle of the plate. Load was placed off centre fore/aft.

Next two pictures are measured on the same setting.

Pekka

sparky961 · « **Reply #21 on:** August 29, 2015, 07:58:43 AM »

If you need even more rigidity, what about sandwichkng multiple layers of granite with epoxy between?

PekkaNF · « **Reply #22 on:** August 29, 2015, 11:18:49 AM »

I really don't know about epoxies enough, I think I would need a speciality epoxy that does not shrink etc.

One engineer at the work suggested of adding some more vertical offcuts, bit like I-beams under, glueing them together firs then mounting the embryo surfaqce plate on to of the real surface plate and glue the whole pagage with low shrink epoxy, but most of the surface would covered with release agent....epoxy would be there just even out all the surface features between rigid member and table top. I'm pretty sure the devil would be here in details, like where to mount it and how and how accurate hard points would be....

I have to see waht is available, it might turn out most cost effective to use 60 mm thick stone if I can get it with any decent surface quality.

Cheapest real surface plates even close to this size 1000*400+mm starts to cost serious money and shipping is a killer. On that behalf a good small 600 mm surface plate + and a half decent straight edge might come cost effective.

But let's see.

Pekka

Will_D · « **Reply #23 on:** August 29, 2015, 04:54:46 PM »

Ok, Its Saturday night and a wee drink has been taken!

This talk about surface plates etc leads to 2 different considerations:

1. The most stable surface I know of, (but not neccessarily flat) is an optical bench as used for holography. The home made variety consists of a concrete slab floating on a lot of car inner tubes suported by another massive structure. The keyword here is "floating" as it resists distortions caused by passing traffice and the like.

The mirrors and lenses placed onto this relativley are so light they cannot distort the "flat" surface. This allows the holgram/whatever to be created

2. If a very flat surface (like plate glass/granite) is expected to remain flat as a reference plane surface when loaded with significant loads then at a minimum a floating solution needs to be used to distribute the load evenly. That said the material also needs to be thick & strong enough to resist deflection given the applied point loads.

A long time ago I was advised to "float" my plate glass "surface plate" on a nice piece of carpet (itself resting on plywood) in order to erect my 3 1/2" gauge loco chasis.

PekkaNF · « **Reply #24 on:** August 30, 2015, 02:34:52 AM »

Will, you are right on those points. The "thing" with optical wizardy it timedomain, wibration and other time spesific disturbance would make absolute mess of holograms an othe laser stuff.

RPI (Rensselaer Polytechnic Institute) has least one sandwitch table on it's lab. I have seen one big one here in Finland it had a thick aluminium sheet peppered with holes on top and may layers of different material. No car tyres thoufh, but it was in a cave.

Anyway our needs are a little different. When lorry passes by, I'll notice it here houses are on caly and trafic nearby rumbles the house. Then I'll just repeat the measuremet. Also optic puts very little load on table. I'm planning to place about 100 kg lump of stuff and thay would distort most of the stuff I could wheel into my garage unless some consideration is placed on mounting the piece and reference.

Heck. If there were a lightweight, rigid, but weak straight reference (say honeycomb filled composite) plate I would not support any weight on it. Just use it as a reference.

I'm having a bad flu or something and I'm really to sick for the shop. I have had time to play with 10 mm glas plate and I'm starting to see where old instructions come from. Glass plate seems to have pretty good surface quality when it comes to measurement with 0,01 mm accuracy on short distance - say 100 mm. But it bends easily under load. It needs realatively flat surface under it. This understructure could have relatively rough or even abrassive, or soft surface that reders it uselees to measuremet. Glas does not respond well on local stress, therefore there has to be something flexible between the glass and this "rough" surface. However too much flex is not a good idea either, it could allow the glass to bend under piece you are trying to measure. Also, I don't think gluing the glass on any other material is a bood idea.

One idea that proably would work is to have rigid base, injection compound on top of it to even out all surface and conform glass undulation. This has few unknowns to me. Another is how accurate glass really is? How to prevent glass from gluing and still keep it on it's place. Is the glass waviness such that it will not mess up measurement due to thermal expansion or othe type of movement? This would need some iteration on smaller scale.

I'm checking the "rock" next and try to find some more samples. It looks like it would offer me beter chance for success than glass.

Pekka

BaronJ · « **Reply #25 on:** August 30, 2015, 06:50:40 AM »

Hi Pekka,

I'm sure that someone else will have said it, but it might pay you to have a chat with your local funeral director or headstone mason. I've had a chat with one near me (UK) and he says that unpolished granite slabs 4" thick are relatively cheap. However they are also quite flat ! The high cost is down to the amount of time and effort involved in polishing them. He has machinery to do this although I've not seen it in action, mainly because it's always in use and inside a very large enclosure. The fine slit that comes off makes a good lapping paste :-) He also gets broken and damaged headstones when he has to replace one. Some of these get cut down for plinths and other things. So its worth investigating.

PekkaNF · « **Reply #26 on:** August 31, 2015, 04:07:46 PM »

I have contacted two businesses both do headstones and table tops. But they don't have information on how true the tops actually are.

One is local and I'll visit it if I get from my work any time when they are open.

I have tried two method home:

1) Support good straight edge on top of the 0,05 mm feeler blade from both ends. Straight sample should allow a same gauge feeler gauge to slide under the straight edge. I found that same gauge feeler blade is just a tad tight....as it should be. I have 0,03 0,04 0,05 0,06 and 0,07 mm feeler blades. This shows pretty easy if there are any big problems.

On real surface plate 0,04 mm feler blade slid sweet, I could feel a little constant resistance. Same thickness feeler gauge was tight and tend to move the straight edge...pretty sure the DIN 874/2 straight edege has some 20 um variation....

On granite kitchen top piece 0,03 was tight on some spots and couple spots could place even 0,06 mm feeler gauge under the straight edge that was supported 0,05 mm feeler gauge at both ends, but it was nearly as bad as I tought.

Hair staright edge did emphasis high spots and walleys pretty clearly. Looks like colorful table top granite is not really a best choise. It might have harder and softer parts in it and it seems to show on surface quality.

2) I place straight edge on sample plate and imobilize it with a long parallels on both sides, Then I slide a magnetic TDI stand w/ clock on the side and indicate from top of the straight edge.

This was interesting...Real surface plate showed practically no clear movement on the dial...which was good, because it showed that the measurement can be used to indicate straight line and instrument was good for it.

On the othe had the checkered granite surface plate showed regular waviness and raising/dropping error trough the whole travel. Indicator base is relatively short, it would pick up easily surface undulation. Another thing is that DTI was at offset from the base amplifying the error greatly. I did not do math, but on real surface plate the indicator hardly moved at all and my sample of granite table top indicated worse than 0,05 reading, growing to 0,1 mm at the ends and also showed definite dip on the middle of the plate.

Now I have a way of field checking the embryo surface plate in a somewhat reliable way.

VT's comment on using a building aluminium straight edge is haunting me. I know that there are some very good aluminium straight edges, but I can't get my brain around the oxide layer/truing abrasion when used against feelergauge atc problems. But it could be cheap, rigid and lightweight. Can't really protect the soft edge with a steel strip from feeler gauge roll.

Took two solid hours to get repeatable results, but I think I have a method for testing now.

Pekka

vtsteam · « **Reply #27 on:** August 31, 2015, 08:04:43 PM »

Pekka, an aluminum straightedge certainly isn't resistant to wear and abrasion the way a cast iron straightedge is, however, if new, and you are careful with it (as I was) there's no reason why it shoud show any wear at all for some occasional jobs.

Now if you were rebuilding machinery every day, that would be different.

No guarantees that you will find a perfect straightedge at the store -- but it seemed you had moderate expectations for the tolerances you would find acceptable on your mill. I don't remember the brand I bought 14 years ago, and I doubt I, or you, might ever find it again. And I did not test it either -- I was only building an 20" bed length lathe with it (12" carriage travel).

One nice thing about a store bought level, though -- you can always return it if you find it isn't suitable. And in my case, I've been using it as a builder's level ever since. Not suitable any more for scraping ways, but I now have better equipment.

Good luck, if you do try it!

PekkaNF · « **Reply #28 on:** September 02, 2015, 03:02:13 AM »

I have home two builders straight edge. They are good enough for building, general standard seems to be +/- 1mm/2m or better and they are somewhat better.

I'm thinking of buying pretty good 1 m DIN 874/1 straight edge. I also bought Russian? 400 mm long camleback, let's see how does it compare when I'll get it from the mail. At 40€ price range I don't know what to expect.

I'm including here some pictures that relate to my previous message. Hope they are more clear than my text.

Pekka

DMIOM · « **Reply #29 on:** September 02, 2015, 04:26:36 AM »

Quote from: PekkaNF on September 02, 2015, 03:02:13 AM

......I'm including here some pictures that relate to my previous message. Hope they are more clear than my text.

Both are perfectly clear - thanks for taking us along on the journey.

Dave

vtsteam · « **Reply #30 on:** September 02, 2015, 01:53:19 PM »

I was thinking about that 400 mm long camleback, and I was imagining bolting three of them to a piece of bar or square tube to make a 1200 mm long straightedge. Set them on your granite surface plate at work (or wherever) and tighten the bolts so the camelbacks are all in line along the bottom.with the surface plate.

Then I was thinking, well heck you could do the same with (not camelbacks) but just short lengths of bar stock, bolted to a full length piece. As long as they were reasonably straight three of four hundred mm long pieces, and de-burred, it should work for your purposes.

Hey and if it ever warped or anything, you could just re-straighten it with the bolts on a surface plate again. An adjustable straightedge.

PekkaNF · « **Reply #31 on:** September 03, 2015, 02:29:33 PM »

Quote from: Baron on August 30, 2015, 06:50:40 AM

Hi Pekka,

I'm sure that someone else will have said it, but it might pay you to have a chat with your local funeral director or headstone mason. I've had a chat with one near me (UK) and he says that unpolished granite slabs 4" thick are relatively cheap. However they are also quite flat ! The high cost is down to the amount of time and effort involved in polishing them. He has machinery to do this although I've not seen it in action, mainly because it's always in use and inside a very large enclosure. The fine slit that comes off makes a good lapping paste :-) He also gets broken and damaged headstones when he has to replace one. Some of these get cut down for plinths and other things. So its worth investigating.

I checkked the local one and the machine was a little antique...and rock plates lookeed fine, but measured badly. One was better, but it is still marginal.

Pekka

jcs0001 · « **Reply #32 on:** September 03, 2015, 03:29:05 PM »

Pekka, Steve and others - thanks for the discussion about this. I was wondering how to check such items for flatness and you've provided some answers.

John.

BaronJ · « **Reply #33 on:** September 04, 2015, 06:38:23 AM »

Quote from: PekkaNF on September 03, 2015, 02:29:33 PM

Hi Pekka,

Quote
I checkked the local one and the machine was a little antique...and rock plates lookeed fine, but measured badly. One was better, but it is still marginal.

Pekka

I haven't been down that way for a while, I'll have to call on him and talk to him some more. Not surprised that the machine your mason has is a little antique, I suspect that the machine that my local mason has is an antique as well. I'll have to persuade him to let me have a look at it and maybe photograph it. I'll let you know when I get chance.

PekkaNF · « **Reply #34 on:** September 04, 2015, 03:23:57 PM »

Plate is pretty, but looks like as a whole it is not straight enough.

But I got three weird knife straightedges and one camelback. They sem to be pretty nice.

Pekka

sparky961 · « **Reply #35 on:** September 08, 2015, 05:21:20 PM »

So I just happened to be driving through a busy section of a larger city today and passed by a sign on a building that said "GRANITE COUNTERTOPS". I kept driving along for a while before it clicked that I should go back and check it out.

I very patiently waited in the showroom while the salesperson finished up with some actual customers before asking about their scrap; sink cutouts, broken pieces, whatnot.... and I was a little surprised when she directed be to a large green bin behind the building, saying "take as much as you want; we pay to get rid of it". It was filled with varying sizes and shapes of all different kinds of mostly 1-1/4" countertop material. There were lots and lots of long narrow pieces that didn't seem too useful at the moment (though I got to wondering about straightedges), quite a few smaller rectangles about 8 x 10 or so, and .... GOLD MINE ... a handful of quite large pieces, both rectangular and irregular or broken.

Just goes to show that it never hurts to ask. Especially when you ask nicely.

I'll try to get some pictures up for those who just like to oggle, but now I'm having to think about what to use as a cheap lapping compound. What's cheap and easy to source, very fine, and harder than granite? I'll do my own research in the meantime but anyone's experiences lapping their own plates would be a great addition to this thread.

Manxmodder · « **Reply #36 on:** September 08, 2015, 09:23:54 PM »

Sparky, I was just thinking about this kitchen worktop granite surface plate earlier this evening.

If you need to remove any high spots on the plate I reckon a steel backed diamond coated sharpening stone would be quite effective.

You would just need to keep checking with a DTI clock to keep track of your progress.

I have a couple of diamond coated steel backed stones that I bought a while ago on Fleabay.

Or may be one of these multi faced rectangular blocks would be worth considering.
http://www.ebay.co.uk/sch/i.html?poi=&adpos=1s1&ul_noapp=true&geo_id=32251&MT_ID=11&crlp=71010014297_807&keyword=diamond+sharpening+block&rlsatarget=aud-105106656306%3Akwd-6907918083&_nkw=diamond+sharpening+block&device=c&crdt=0&treatment_id=7&clk_rvr_id=894874226903

PekkaNF · « **Reply #37 on:** September 09, 2015, 03:30:09 AM »

Quote from: sparky961 on September 08, 2015, 05:21:20 PM

So I just happened to be driving through a busy section of a larger city today and passed by a sign on a building that said "GRANITE COUNTERTOPS". I kept driving along for a while before it clicked that I should go back and check it out.

I very patiently waited in the showroom while the salesperson finished up with some actual customers before asking about their scrap; sink cutouts, broken pieces, whatnot.... and I was a little surprised when she directed be to a large green bin behind the building, saying "take as much as you want; we pay to get rid of it". It was filled with varying sizes and shapes of all different kinds of mostly 1-1/4" countertop material. There were lots and lots of long narrow pieces that didn't seem too useful at the moment (though I got to wondering about straightedges), quite a few smaller rectangles about 8 x 10 or so, and .... GOLD MINE ... a handful of quite large pieces, both rectangular and irregular or broken.

Just goes to show that it never hurts to ask. Especially when you ask nicely.

I'll try to get some pictures up for those who just like to oggle, but now I'm having to think about what to use as a cheap lapping compound. What's cheap and easy to source, very fine, and harder than granite? I'll do my own research in the meantime but anyone's experiences lapping their own plates would be a great addition to this thread.

Very nice, have you measured any of them yet? I'm eager to hear how are the results?

Pekka

jcs0001 · « **Reply #38 on:** September 12, 2015, 10:51:30 PM »

Another possible source of granite countertops:

I was in our local re store (Habitat for Humanity runs them) and saw three pieces of granite countertop - two about 18 x 36 in. or so and one about double that size. As I recall they wanted $20 for the smaller pieces and $40 for the larger one. I was tempted to buy one of the smaller ones as a glueing table surface (it would definitely be flat enough for glueing wood pieces up). Don't have room in my shop for it however.

John.

Pete. · « **Reply #39 on:** September 13, 2015, 06:05:18 AM »

I might have some very nicely finished slate slab down here in Kent. I'll run a dial over them and if they are suitably flat I'll put up a photo.

PekkaNF · « **Reply #40 on:** September 13, 2015, 12:46:25 PM »

Good or bad, we need to know!

I haven't found any dead sure way telling the good and bad appart. They all look good and most of the ones that looked like a real surface plates were pretty bad.

Pekka

Pete. · « **Reply #41 on:** September 13, 2015, 01:31:37 PM »

A dial gauge and stand will tell you how flat they are.

DavidA · « **Reply #42 on:** September 13, 2015, 02:55:30 PM »

Pete,

How would you set about doing that ?

I would have thought that you would need to know that your dial guage stand was precisely square to the slab under test and that the vertical shaft was also dead on vertical at any position of the base.

Any error at all and the dial guage will move relative to the slab.

Dave

sparky961 · « **Reply #43 on:** September 13, 2015, 03:22:29 PM »

Funny, I was just going to pose a similar question.

I've done a fair bit of reading and watching videos on this subject. It seems that there are two checks, one for local flatness that uses a height gauge and DTI (or similar contrivance) and a more elusive overall version. The former I can do, but how do I know that the whole thing isn't concave or convex? Add to this the requirement that it be within the reasonable limits of a home shop budget and environment.

I did try some off-hand "lapping" of just two pieces; a smaller one on a larger one. I did this mostly to test the"feel" of the operation, which was interesting to say the least. When I was using water with toothpaste (yes, you read that correctly) it was smooth in some spots and then just sort of "stopped" as though a corner dug in, or the friction or suction became strong very quickly. It didn't slide smoothly as I expected, rather in a bit of a "jerky" motion. Dry was considerably better, but my selection of readily-available fine hard powders is very limited. I tried using talc, but I know this is very soft. I was thinking it would be more of a dry lubricant and the two granite surfaces would wear each other. Maybe it would work just completely clean and dry to start even?

I haven't put any measuring devices on there yet, save for an angle plate with a cross-hatch pattern drawn on it with a sharpie. The pattern didn't wipe off as consistently as I'd have liked, but this is all far from scientific.

I did notice that the formerly shiny surface has begun to take on more of a matte finish. I hope this indicates something beneficial, and not just some residual toothpaste haze...

Pete. · « **Reply #44 on:** September 13, 2015, 03:53:45 PM »

You can spot dishing or twist in a plate by trying the stand and DTI at different angles and directions across the plate.

krv3000 · « **Reply #45 on:** September 13, 2015, 05:25:58 PM »

well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat

sparky961 · « **Reply #46 on:** September 13, 2015, 10:42:40 PM »

Quote from: krv3000 on September 13, 2015, 05:25:58 PM

well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat

Hmm... indeed, but a bit of a paradox, isn't it? If I had a piece of glass I knew to be flatter than the plate I'd just use the piece of glass.

That said, are you talking about regular thin "window" glass, or thicker "plate" glass? If window glass is flat enough I'm sure I could rustle up some of that. The thicker stuff could be an issue.

sparky961 · « **Reply #47 on:** September 13, 2015, 11:12:06 PM »

So, I had a chance to take a closer look at my haul tonight. Spoiler alert: Don't get too excited.

Good news is that I was able to measure flatness deviation. Bad news is that it wasn't difficult to measure.

To start off, my setup is far from ideal so take everything here with that in mind. I have a shiny rock (could be granite, but how would I know?) about 26 x 26 x 1-1/4 sitting on a relatively rigid small table made of MDF. Between the rock (we'll call it "granite") and the hard place (the table), there are three strips of minicell foam about 1" thick and maybe 12" long, placed somewhat evenly to support the plate. Why? I had some left over and it seemed this would allow the plate to "float" the best way possible with available materials. With the indicator set up I pushed in various places and with a lot of pressure could move the indicator by about 2 tenths. As you'll see in the next paragraph, proper support is the least of my concerns at this point.

After cleaning the slab, I proceeded to jury-rig my DTI to my height gauge. Yet another tool/adapter thing to make.... The gauge base is about 5" long and my first setup put the indicator point about 6" from the end of the base. Moving this around the plate in no particular pattern yielded a rough average of +/-0.005" deviation over 6", with a maximum of about 0.008". The gauge base didn't slide nicely in many spots like you'd expect on a surface plate. This probably explains the "grabbing" I noted earlier while doing my lapping trial.

One of the pictures below shows the granite floor tile I picked up at Home Depot. It was more difficult to measure because there isn't a lot of room to move the gauge around. I shortened the reach to about 4" and deviation seemed a bit better, maybe +/-0.003". Given the smaller distance, this may or may not actually be any better.

So, in summary I don't think granite countertops are a useful surface plate as supplied. If you're ok with +/- 0.010 or so then go for it, but I'm looking for better than that.

I'm going to continue working with some of the pieces I have to see if I can't find an effective way to improve the flatness.

sparky961 · « **Reply #48 on:** September 14, 2015, 01:17:36 AM »

Man, I really should have gone to bed after that last post but I had an idea as I was writing it that I had to try. Yes, I'm sure lots of you here know the feeling.

So it turns out it was a great idea! Don't give up on granite.... more to follow.

Pete. · « **Reply #49 on:** September 14, 2015, 01:58:21 AM »

Quote from: krv3000 on September 13, 2015, 05:25:58 PM

well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat

The only problem with that is if you put a piece of glass on a surface plate it might well be flat but if you put it on anything else - especially with a chunk of iron on it - it will bend and not be as flat as it was when you checked it.

PekkaNF · « **Reply #50 on:** September 14, 2015, 03:15:47 AM »

Quote from: sparky961 on September 13, 2015, 11:12:06 PM

So, I had a chance to take a closer look at my haul tonight. Spoiler alert: Don't get too excited.

Good news is that I was able to measure flatness deviation. Bad news is that it wasn't difficult to measure....

I know

I had the same feeling. Now, after few measurements/samples I have concluded: Generally glass (compared to a rock) seems (locally) more smooth and flat, but has greater error over a long distance + flexes like there is no tomorrow.

Have you measured diagonally and on each side how much there is error from level, like I did on Reply #28 top picture on this thread page? There is hope, if the plate is relatively true, even though it has hills and walleys....if it is inclined or twisted - ahem.

Pekka

Manxmodder · « **Reply #51 on:** September 14, 2015, 07:06:36 AM »

Quote from: Pete. on September 14, 2015, 01:58:21 AM

Quote from: krv3000 on September 13, 2015, 05:25:58 PM
well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat

The only problem with that is if you put a piece of glass on a surface plate it might well be flat but if you put it on anything else - especially with a chunk of iron on it - it will bend and not be as flat as it was when you checked it.

Bedding the piece of float glass evenly down onto a piece of granite counter top with something like thin consistency tile adhesive or Plaster of Paris may work.

That way the glass is sufficiently supported to prevent bending/twisting distortion.....OZ.

PekkaNF · « **Reply #52 on:** September 14, 2015, 07:32:48 AM »

plaster of paris is not stable...shrinks forever

Thermal expansion of materials is different and on this scale it ads up. One material/piece if pretty sure.

I haven't found a relatively big piece of glass that is flat. We have a guy working here who used to make machines for a float glass mill and from discussion we concluded that this kind of accuracy is hard to obtain from a standard glass. You might get lucky and find a piece that is cut from the middle of glass (web?) and on the middle of the cycle. Edges are "crabbed" and restrained....you don't want from too close to edge, there is a little tilt. Not much but enough to ruin it for our purposes. When molten glass is cooled it's run over rollers - that produces waviness...you might see that when you run the TDI over the glass and see regular swing.

So, it might be enough to lap a lot of small objects and on many purposes, but I find it too hard to accept as a surface plate - unless ground and for a lightweight objects.

Pekka

BaronJ · « **Reply #53 on:** September 14, 2015, 08:27:29 AM »

Quote from: sparky961 on September 13, 2015, 03:22:29 PM

I did try some off-hand "lapping" of just two pieces; a smaller one on a larger one. I did this mostly to test the"feel" of the operation, which was interesting to say the least. When I was using water with toothpaste (yes, you read that correctly) it was smooth in some spots and then just sort of "stopped" as though a corner dug in, or the friction or suction became strong very quickly. It didn't slide smoothly as I expected, rather in a bit of a "jerky" motion.

While toothpaste is fine for lapping, maybe too fine for what you are trying to achieve, it needs to be kept wet otherwise as you have discovered dries out and grabs. Fine grinding paste in oil works well but it still needs to be kept wet.

Quote

I did notice that the formerly shiny surface has begun to take on more of a matte finish. I hope this indicates something beneficial, and not just some residual toothpaste haze...

Yes the toothpaste is starting to abrade the polished surface and take down high spots but bear in mind that the high spots on each surface will rub each other so you need a third plate to work against the other two. Eventually you will get one surface that is matt all over.

krv3000 · « **Reply #54 on:** September 14, 2015, 06:54:55 PM »

I see I will have to take sum pics at work we have a very very large bit of glass for testing bed plates on press tools to see if they are flat the plates are normally 10ft long by 4ft wide by 4 inch thick yes granted the glass its 12 inches thick and gets recalibrated every year but the principal is the same blue on the plate put the glass on and see watts watt as for the type of glass to use at home go to the scrap yard and get ether a side window out of a panel van as they are tuff end the bit I use at home is a old oven doer in sum old car books to check if your cylinder head is flat they just say any peace of glass big enough to do the job

krv3000 · « **Reply #55 on:** September 14, 2015, 06:58:25 PM »

if you intend to bond the glass to a suitable top just use builders adhesive comes in a variety of cullers and is made for the job

sparky961 · « **Reply #56 on:** September 15, 2015, 11:31:01 PM »

So, among the other things that life has required of me lately I've spent about 4 hours working on flattening one piece of counter top that I obtained. Considering that when I started I was seeing a 0.010" swing in some places on the indicator, lots of progress has been made. It's been going well enough that I've switched from the 0.001" indicator to the 0.0001" indicator to better discriminate the deviation. I'm down to about 0.0015" max, with lots of large areas not moving the needle more than 0.0005".

Two words: Silicon Carbide. That's all you need to know.

Maybe diamonds would cut faster, probably in fact. But I don't have diamonds. I did have an old green Silicon Carbide grinding wheel that was too small to mount but otherwise in good shape. I thought "what the heck, I'll see what it does". I used the side of the wheel to take down the high spots prior to lapping, not to mention leaving the abrasive grit between the two plates for faster cutting action. I've been going back and forth between the stone and another piece of countertop. I have three on the go now, and I'm using one of the larger pieces to span a greater distance across the largest one. I had noticed some dishing after the first session, which I hope to rectify with the larger piece.

I'd be very pleased if I could get this locally flat to within +/- 0.0002 or so using this method. I may start running into problems with deflection around that point though because that's about how much it deflects under it's own weight when you pick up an edge.

There's been lots of talk about bonding various things to others in this thread. What about making a stack of granite with epoxy between? I guess even something like builder's adhesive should be fine. Differential expansion shouldn't be an issue because it's all granite. The little bit of epoxy shouldn't affect that. Rigidity will be increased significantly.

There are some pretty distinct stages one can observe:
1. Smooth - Two pieces begin rough and offer little resistance to sliding over each other
2. Grabby (very scientific, I know) - When using a liquid with grit, this happens when you're starting to get pretty flat. There's strong suction that causes the plate to move with greater force or stop completely over irregularities. It seems to indicate that you're gotten rid of most really high spots and are starting to get flat.
3. Slick - The big piece of rock you're sliding around begins to feel almost like it's floating. It will just about spin on it's own.

My advice if anyone wants to try this is to have patience and perseverance. It's not the most exciting thing to do but it does seem to be working.

Manxmodder · « **Reply #57 on:** September 16, 2015, 06:22:08 AM »

Looking good,Sparky. I'm watching this effort with interest as I do have a few decent sized pieces of this granite counter top lying around looking to be used for something......OZ.

hanermo · « **Reply #58 on:** September 16, 2015, 10:23:28 AM »

I went through this exercise, to align my scratch built VMCs linear rails, 2200 mm long.

I found a vertex ground CI straightedge, about 150€, new in the UK. Accurate to 0.04 mm.
A better option is a granite long parallel, but they are about 600 for 1.4 m long iirc.
Still thinking about it.
Machine builders square spirit levels, == 0.02 mm/ metre, were about 70£. I got two, and they make aligning stuff quite easy.

Testing the straightedge on a real granite surface plate, 600x440 mm, proves that you can easily see errors of about 0.01 mm, with a light behind it.
Putting a cig paper as a shim on either end, shows the lift clearly.

Since you dont need perfect, testing from the center to the edges should get you close.
Its feasible to sand steel pretty flat, ime.
I used a big, heavy, large belt sander.

Marking with a spirit permanent marker pen and sanding it off, shows you can get decent control on maybe 0.02 mm depth or so.
The edges get rounded.
The rails are mounted, and very well aligned, except at one spot. Its either high, low, twisted, or wanders from the front rail in some direction.
Plan is to put a dti on the ram, and check for rail error in the 3 axes.
Then just use a screw-jack to push it straight, and then tighten the mounting bolts.

You can easily feel any error over 0.01 mm while pushing the ram back and forth. Asain, cig paper as shims proves this quite easily..
The blocks are strong, and wont come to any harm from hand-forces.
I used 35 mm linear rails and blocks.

Hope this helps.

BTW - Pics of the machines will only come once they are polished, for commercial reasons.
Machine is commercial quality, with commercial components, and costs, and I need to clean them up before pics.
Hope to get them polished inside a month.. but this is not a reliable estimate.

sparky961 · « **Reply #59 on:** September 22, 2015, 03:56:23 PM »

I've had the chance to spend a few more hours rubbing two stones together and I'm surprised to say that I wasn't really bored throughout the process. It's rather relaxing and very rhythmic; albeit very messy as well. It's to the point where I have one fairly large slab pretty much floating around on top of the other with little resistance. Actually, a few times it just about got away on me and slipped off the other side onto the floor! These pieces aren't light! It's a bit strange to spin one atop the other with almost no resistance. Hours of fun, in fact.

Now, the two issues I'm struggling with are as follows:
1. Flatness doesn't seem to be improving beyond around 0.001" max deviation over about 6". Lots of places sit closer to a few tenths plus or minus but not as many as I'd like to see.
2. How to translate indicator readings into "map" of surface, most importantly the high spots. The way I see it, a + or - reading could mean a small surface variation at the indicator tip, a large variation at the tip, or that the base is sitting on/in a variation that's causing the tip to erroneously read high or low.

How do you sort all of this out?
Is it possible without the fancy gadgets and software that professionals use?
Would 3-point contact of the height gauge base be of more benefit than the flat base that can rock a bit on imperfections?
Is this where it becomes easier to use a level?

For #1, I'm thinking it could be just that I haven't done enough work on it yet. But what I don't want is to keep working and not see any improvement. Hence #2, I want to be able to ensure its getting better, not worse or just shifting the variations around.

jcs0001 · « **Reply #60 on:** September 22, 2015, 06:09:32 PM »

Sparky:

Not sure if you've seen this. Evan describes using a cheap laser level (capable of generating a horizontal line) and a tripod to mount it on to get an estimate of the flatness of a surface:

http://bbs.homeshopmachinist.net/threads/18917-Qualitative-flatness-testing-cheap-%28pics%29

John.

PekkaNF · « **Reply #61 on:** September 23, 2015, 03:52:56 AM »

There is pretty good way, if you have time and good level. I have some proof that there is method for one spirit level and for two....Any solid information?

Procedure is somewhat like this:
http://www.mate.tue.nl/mate/pdfs/1698.pdf

There must be somewhere a punch list instruction, but this should give a good foundation on theory.

Pekka

BaronJ · « **Reply #62 on:** September 23, 2015, 10:46:37 AM »

Hi Sparky

Quote

Would 3-point contact of the height gauge base be of more benefit than the flat base that can rock a bit on imperfections?

Use three ball bearings to stand your indicator base on. If necessary a touch of super glue will hold them in place.

sparky961 · « **Reply #63 on:** September 23, 2015, 05:38:30 PM »

Thanks for the new info and tips. I'll give an update once I've made some progress.

News:

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