Precision Ground Toolroom Stones

Like everyone else in this thread, I'm fascinated by the video.

I'll trust anything Robin has to say absolutely -- the man's a wizard.

But why was a diamond wheel in a surface grinder the only method that worked for him to make them? He didn't report what other methods he attempted, but the first that comes to my mind is lapping on a diamond plate like this one (it's how I used to flatten water stones for sharpening woodworking tools).

How flat do they have to be to work the way he shows in the video?

I'm very curious to see how flat you're able to get your stones. Please take the time after you grind them to measure them on a surface plate with a tenths indicator (use a gauge block on top to eliminate the surface roughness).

I'm curious to see how flat I can get a stone by lapping it on my diamond plate (not sure how flat my diamond plate is, but I'll check that first). If the diamond plate isn't flat enough, I'll follow up with sandpaper on a granite surface plate. If that doesn't work for some reason, I might try some coarse carborundum grinding grit on a temporary lap (just a piece of cast iron durabar that's been scraped flat -- not my box parallel!). (Somewhere I acquired several film tubes with different grits.)

If I have time, I'll try some experiments tomorrow. I'll report back how far I get without a surface grinder. I think I've got a couple stones I can experiment with.
 
Uh oh. I just rewatched the video and he explicitly mentioned that lapping didn't work.

I'm not exactly optimistic, but I'll still see how flat I can get them.
 
Rex, I have some ceramic stones and a few years ago I made one dead flat on a DMT diamond plate. It works great for many things, but does not appear to be in the same league as what Robin is doing. The ceramic stone is very fine, and it was flattened in the same interest of making a better stone for removing burs on hardened steel tooling. It does not leave visible scratches on the surface of the metal, but is also very slow to remove metal to repair the burs. Perhaps doing the same to a coarser stone would give a better result. Seeing the obvious complete success of Robin's work, I am inclined to follow his lead faithfully, and have purchased the diamond wheel and stones to do it. The man knows what he is doing...
 
Yup, since Robin said it can't be done any other way I'm not optimistic. I don't own a surface grinder, though, so figure it can't hurt to experiment.

For my next trick I'm going to climb in the ring and fight Floyd Mayweather. :)

I initially thought he was just getting them flat, but I now think the diamond wheel must do something to the surface of the stone. If anyone finds a link to the (U Penn?) paper he mentioned I'd be interested to read it.

I'm an engineer by training and inclination: if I can't measure something it doesn't exist! I just want something objective to measure to see what I'm after. Even if I had a surface grinder, I don't trust my skill enough to take a resulting stone to anything important without measuring or testing it somehow.

I don't appear to have any small India stones, though. Just slipstones, ceramic stones, and water stones. I'll order a couple before performing any experiments.

I also saw in the comments that he mentions using 3um to 6um diamond slurry to lap -- that's way finer than I expected (equivalent to P3000 to P6000 Grit lapping paper). I do have some lapping films that fine, but I don't think I'll be able to bring myself to use them with an India stone!

I'd have thought the pores of the stone were bigger than 3um!

His comments indicate he may be offering some for sale soon. I'll probably just get in on that. :)
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Rex
 
I would think that the grit would be carried by the stone instead of the cast iron because of the porous surface of the stone. I could be totally wrong :disturbed:
but I would think you'd be cutting more cast iron than stone with the abrasive. Interested to see what you get.
I did try to check the stones I flattened. The best I can tell, I'm well within .001 It's hard to get a good reading because of the porous surface. I tried using a ceramic gauge block to bridge the peaks of the surface. :cool 2:
 
One of the commenters (that Robin agreed with) said the diamond wheel actually shears/grinds the individual grit particles in the stone. If that's true then I can see how only high speed grinding would suffice.

I find that ... surprising ... though.
 
tyler machine said:
I tried using a ceramic gauge block to bridge the peaks of the surface. :cool 2:
Click to expand...

Put the stone on your surface plate and a 1-2-3 block or other precision ground part like a gage block or small parallel on top of the stone at each end, then indicate off the top of that. This will average out any surface irregularity in the stone.

Robin is almost certainly getting his stones within 0.0001" across the 6" length of his stone. (The man knows precision.)

Regards,
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Rex
 
Using a 1-2-3 block would just show overall parallelism. What you're after is and even distribution of bearing points. With enough bearing points being in contact with the surface no one point can generate enough force to cut.

Also I used slip stones to make my first sets. :cool 2:
 
tyler machine said:
Using a 1-2-3 block would just show overall parallelism. What you're after is and even distribution of bearing points.
Click to expand...

While I'm no expert, I do know a little about handscraping and testing your progress.

You can either attempt to measure each individual high spot (bearing point) on your stone directly, measuring each individual peak and valley, or you can rest a precise thickness part on top of the peaks and measure from that.

I'd suggest the later may be easier, is definitely the recommended practice, and will likely lead to more repeatable results.

I think your point is that the top surface of your stone can be flat but not parallel to the bottom surface. This is certainly true, but you can use the averaging of a gage block to map out the topology regardless. Just move the gage block to various locations and measure from there. A 1-2-3 block is a little big, but will still give you meaningful results if you move it to each end and the middle and take readings at each location. A small jo block would be better.

If you get a deviation of 0.001" at one end vs the other, and the middle doesn't show a deviation of close to 0.0005" then your part definitely isn't flat.

Regards,
--
Rex
 
The genius to the method that Robin is using is that it actually grinds the individual grains of the stone's abrasive dead flat and parallel. The result of that is that the grains cannot cut anything that is not sticking up above the surface that is being rubbed against. Any amount of imperfection in the stone's flatness will cause problems with the goal of cutting nothing but the high spots. Also, the reason it does not cut the flat surface of the work is both the flattened grains and their large area of contact, which together does not allow any cutting. Any imperfections of the stone surface, like scallops, wheel hop, or whatever else, even tiny, will degrade the results. That's how I see it, anyway, and that is what I understand from Robin's video. There are definitely ways to improve the surface by tweaking whatever method of grinding that is used, but it will not take much imperfection to ruin the results, at least the results Robin is getting, which is extraordinary!
 
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