Author Topic: Is it possible to make a poor man's flat stones with a glass plate?  (Read 1005 times)

Offline nrml

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After watching Mr Renzetti's video
I am convinced that a pair of flat stones would be a handy thing to have around the home shop. Unfortunately I don't have a surface grinder or the money to buy a pair of ready made stones.

This got me thinking. If I get a float glass plate like this https://woodworkersworkshop.co.uk/products/scary-sharpening-glass-plate?variant=9040138371 and fix a sheet of abrasive paper onto it with spray glue and lap two Norton stones with it using the three plate method, what are my chances of getting a half decent pair of flat stones? I am thinking that lapping the two stones against the float glass first would save a lot of time and effort compared to attempting it directly with just 3 stones. I can lay the glass on top of my little Chinese granite surface plate to reduce flex. I don't really want to apply abrasives directly on my little surface plate as it is the only one I've got.

I'd be very grateful if someone would point out why this would be a waste of time before I find out the hard way.
« Last Edit: March 22, 2018, 02:13:10 PM by nrml »

Offline sparky961

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #1 on: March 23, 2018, 12:47:11 AM »
I've done this "by hand" using an inexpensive diamond file (the kind with the plastic backing and oval holes), a surface plate, and a pencil.  You use the surface plate with some fine paper as the reference.  The pencil serves as your "bluing".

Start off by marking a crosshatch pattern in pencil on the entire face of the stone.  Rub it on the fine paper on top of the surface plate (doesn't take much) to determine the high spots.  You can take the pencil and draw circles and such around the high spots to make them stand out more.  Then take your diamond file and work down ONLY the high spots.  Don't get carried away.  After the diamond file, go and rinse the entire stone with water and maybe some soap.  Keep repeating the process like you would for scraping until the high spots are dispersed and small.

When you get really close, just rub the stone directly on the surface plate.  This should make the graphite (pencil) shiny where the high spots are).  If you have the patience, you'll figure out a system that works for you.

Offline vtsteam

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #2 on: March 25, 2018, 02:58:12 PM »
Well first of all I never think an experiment like this is a "waste of time" even if it doesn't work out as I hoped. You always learn something interesting in the process.

Second, seems to me, and maybe only me, logical that the three plate method assumes three plates with similar wear characteristics.

Having two of them different to the third seems to me likely to defeat the entire reason it works. But what do I know?

People, like myself, who have never tried what they propose as "true"  (at least in this case) are just as likely to be wrong as right! :coffee: 

:beer:
I love it when a Plan B comes together!
Steve
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Offline nrml

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #3 on: March 25, 2018, 05:06:53 PM »
I have been ruminating over this for a few days and my initial thoughts were that  the difference in wear characteristics between the glass/sandpaper and the stone  would completely mess things up when swapping around three-ways. However, my research seems to suggest that float glass is usually exceptionally flat - often exceeding the flatness of budget surface plates. Where it loses out is in flex due to limited thickness and lack of calibration. It wouldn't be guaranteed to be reliable for measuring but for sanding / lapping it should be flat enough.

If I flatten out both stones as much as I can with reference to the the plate as suggested by sparky961 I should be almost there. As a final step if I lap the two pre-flattened stones against each other, flip and repeat, I should in theory get them to match quite closely.

The potential unevenness of the paper and glue layer is what is casting doubts in my mind about the practicality of this approach. Also, I am not an engineer or machinist, so I might be overlooking something elementary.

I'll give it a go over the next few weeks and report back.

Offline vtsteam

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #4 on: March 25, 2018, 06:56:20 PM »
You never know until you try......  :beer:
I love it when a Plan B comes together!
Steve
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Offline JHovel

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #5 on: March 26, 2018, 09:01:34 AM »
My understanding is that this approach would not work.
If I have it right, the idea is to grind off all the sharp points of the abrasive grains on the face of the stones. That way they will no longer remove metal by 'stoning' or abrasion.
However, the edges of the now ground flat grains are now sharp. The gaps between the grains are now crucial to the flat stones' function: anything sticking up from an otherwise flat surface will 'fall' or protrude into the gaps and will get sheared off by the edges of the grains.
To make use of this property, the stones need to ALSO be dead flat.
To achieve both at the same time, a surface grinder is used with a fairly fine diamond grinding wheel. It needs to be fine so as not to rip out any grains, but grind them down.
I've done that as an experiment with a few low-cost bench stones. I found the bonding resin or medium of the stones needs to pretty tough. Many stones have their grains bound by fairly soft and weak bonding. I guess that's a good idea if you want to expose new and sharp grains for stoning things. For this purpose, that's the exact opposite of the properties we want for flat stones.
A couple of very cheap stones I found in local hardware stores had very hard bonding and sure enough, they were crap at sharpening tools. Even using their coarse sides, they would quickly stop removing metal and just polish or burnish metal.
Once I ground them on the surface grinder, they behaved perfectly as flat stones.
I've made a few pairs of them for friends and myself now. They do exactly what Robin described and demonstrated in his YouTube videos.
Cheers,
Joe
Cheers,
Joe

Offline nrml

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #6 on: March 30, 2018, 01:19:34 PM »
If I my understanding of what you are saying is correct; if I went ahead with my plan, I might end up with 'flat stones' but the grain size would still be too big for it to work as a precision flat stone as the lapping process would only remove the binding matrix  and not shear the abrasive particles on the surface to a finer grain size.

That does make a lot of sense. Thank you for the information. I am glad I asked the question before jumping in feet first and wasting time and money like I usually do.

Offline sparky961

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #7 on: March 30, 2018, 04:50:04 PM »
It's been a while since I watched Mr. Renzetti's video on this, but I recall that he used the stone on something that was previously surface ground, and it highlighted how poorly that item was ground.  I've done the same using the method I detailed above to the stone, then taking the stone to a 1-2-3 block that didn't cost me much.  Sure enough, the previously unseen wavy surface texture was highlighted across the entire surface.  This may not prove definitively that my stone is flat, but I'm sure it's a lot flatter than when I bought it.

I suppose one could set up a test so that the surface of the stone is parallel with a known-flat surface plate.  Next you'd run an indicator of appropriate resolution over the surface to check flatness.  Now, I don't know about you, but I'd rather not grind down the ball on my nice Mitutoyo 10th's indicator.... but to each their own.

Offline nrml

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #8 on: March 30, 2018, 06:10:45 PM »
I don't think getting it flat will be an issue. Just the aggressive abrasive action of a hand lapped stone versus a much milder polishing action from a diamond ground stone would render it far less useful for finished surfaces.

Offline vtsteam

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #9 on: March 30, 2018, 10:59:23 PM »
This seems to be one of those long technically jargonized weigh-ins involving multiple statements of personal imagination that could more easily resolve itself in real life by just trying the experiment.

It will work or it won't. The answer will be evident in an hour.  :dremel:
I love it when a Plan B comes together!
Steve
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Offline Pete.

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #10 on: March 31, 2018, 02:53:35 AM »
'Flat' just means that enough evenly distributed points create an average plane. That wavy surface on the 1-2-3 block - that was still flat as far as it's function as a 1-2-3 block requires. Just 'seeing' waves in the surface doesn't mean it has been poorly ground, you can take a normal hand scraper and put any pattern in a surface that you can see without affecting the dimension to any degree that you could measure.

Offline JHovel

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #11 on: April 01, 2018, 08:32:30 AM »
I may not have communicated accurately enough, so here are a couple of doctored microscope images to illustrate what I believe Robin Renzetti proposed and achieved - and I copied, seemingly successfully:
Cheers,
Joe

Offline sparky961

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #12 on: April 01, 2018, 04:30:50 PM »
here are a couple of doctored microscope images

Not to be purposely argumentative, but I'd like to see actual unaltered images showing the same thing.  I don't think what you've illustrated is possible.  The abrasive grains will either be ripped from their bonding matrix and/or fractured in a somewhat random fashion depending on the material and orientation.

Of course, this entire discussion is hypothetical.  The original question, as I interpreted it was "is this a waste of my time"?, to which I emphatically say "no" until proven otherwise.  If it's proven otherwise by doing the experiment then it wasn't a waste of time, now was it?

Offline JHovel

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #13 on: April 02, 2018, 09:25:03 AM »
Well, sparky, sadly I don't have the means to do microphotographs....
The reason we use fine-grit diamond surface grinder wheels for this job is that they don't rip the aluminium oxide grain out or fracture them, but abrade them flat.
All I can tell you that my stones no longer work to sharpen anything, just slide across smooth surfaces. They will, however, make any tiny burrs shiny, so I can see where they are. By concentrating pressure a little on the shiny spots, they soon disappear and the stones slide again.
Since that is the intention of flat toolmakers' stones, I'm happy with the result.
Cheers,
Joe

Offline vtsteam

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #14 on: April 04, 2018, 10:28:15 PM »
Sigh, still no actual results.

Okay seems people don't really "get" the three stone method, and confuse it with "lapping" and confuse lapping with sticking sandpaper on some reference flat.

Three stones theory works like this. Rub with short circular strokes two reasonably flat same grit surfaces together enough, they become negative images of each other. One has humps where the other has matching hollows.

Then take a third, again same grit surface, stone and rub it against one of the earlier pair -- ideally and theoretically,  it now wears into a negative pattern of the second stone, and a matching pattern with the first stone.

Then rub those two together and again theoretically and ideally the matching high spots now remove each other to achieve a greater flatness than either had to begin with.

Theory and idealism depart if you realize the third stone actually imparts some new contours to the second stone. But by repeating the round robin process, all three stones gradually remove their combined differences and flatness is achieved.

That's the theory.

Whether this would work in the scenario first proposed, I again don't know the answer to, nor does anyone else who hasn't actually tried it.

Which is why it would be nice if the proposer actually did that and reported back.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Fergus OMore

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #15 on: April 05, 2018, 04:18:00 AM »
I would agree with Steve wholeheartedly.  Unfortunately, there is a continued failure of readers to access the information which has been suggested many times- and sadly never never acted upon.

One of arguably the most able writers on model engineering- who is still with us, wrote to me and admitted bitterly  about people asking the 'same damn fool questions' and receiving the same damn fool answers.

So the answers really are there to be found- without me perpetuating the same answers.

The classic answers are in Holzapfell, in Connolly's Machine Tool Reconditioning and a quite delightful and refreshing chapter on prisms in Smiths "Advanced Machine Tool Work'

Because they are free on the 'net, it only requires some persistence to 'read all about it' and then to prove or disprove what was so carefully explained------ at great length.

And there one has it!

Norm



Offline hanermo

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #16 on: April 08, 2018, 04:53:07 PM »
I have no great wisdom or vision to apply on stones..
but lots and lots of experimental experience on relatively high-flatness // semi-precision steel surfaces.

For flatness..
several good youtube videos illustrate the process.

I may be doing a commercial run of same, delivering lapped surfaces, within a few months, about 12" in size.
I could do upto 50 cm per size, but it has mass/handling consequences and costs.
As everyone said itīs a high-hour process in labour terms.

My plan is to do "some" good enough before real production.
My plan is to do "good" at a decent price.


Offline vtsteam

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #17 on: April 10, 2018, 09:41:17 PM »
And just to point out the reason for the three stone method -- it doesn't depend on a prior reference flat surface.

It has been by some proposed as the method that produced the first reference flat surface.

And it is useful to know should civilization reboot, you're setting up shop in the wilderness, or you just don't have the money for a surface plate, but are surrounded by flat stones.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline sparky961

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Re: Is it possible to make a poor man's flat stones with a glass plate?
« Reply #18 on: April 11, 2018, 12:43:04 AM »
And it is useful to know should civilization reboot, you're setting up shop in the wilderness, or you just don't have the money for a surface plate, but are surrounded by flat stones.

...And, of course, you have WAY too much time to kill... :P