Quartz Surface Plate?

[sparky961]

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]

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]

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]

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]

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]

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]

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]

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

David D

[sparky961]

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]

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

[sparky961]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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

[PekkaNF]

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]

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]

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