About cleaning slip stones..

[Bob Korves]

Of course, I am not into $400/pair precision ground stones, and if my little engineering adventures ever called for it, I would hope to have my own surface grinder with diamond wheel as well.

I made my own precision ground stones. It only requires a surface grinder, a diamond wheel, and careful work, which can all be used for many other tasks in the shop as well. The precision stones are now about the most often used tool in the shop. My old B&S surface grinder has been used for making stones for quite a few other local hobby machinists as well, with them doing the hands on work.

 

[Ianagos]

I bought a set of norton bench stones and they were surprisingly flat. I always thought about precision grinding them and I have a diamond wheel on the grinder but I just haven’t found it necessary the stones must be within a thou for how well they match up.

 

[Bob Korves]

I bought a set of norton bench stones and they were surprisingly flat. I always thought about precision grinding them and I have a diamond wheel on the grinder but I just haven’t found it necessary the stones must be within a thou for how well they match up.

The "magic" of precision stones is not just that they are flat. Each individual grain of the stone is also flat, and in the same plane as all the other flat grains. This ends up with a huge amount of flat and parallel plateaus with sharp corners and a large combined surface area, which cut anything sticking up above the work surface. When the high spots are cut down to a flat plane, the precision stone skates on the surface like it is ice, without abrasion. It only takes a couple uses rubbing a precision flat stone on a surface that you think is 'perfectly' flat to "feel" what they do and how. It is not abrasion, it is accurate, parallel cutting of burs and other imperfections. No matter how flat an ordinary sharpening stone is, it has a bunch of sharp points with a relatively small combined surface contact area, which individually gouge out small grooves in the work.

 

[graham-xrf]

I tried a Norton stone that I had gently rubbed against it's partner, onto the side of a (relatively old) gauge block. After a couple of rubs together, the stones slid over each other slippy, making a little squeak. Rubbing on the gauge block flat did not affect it at all, except maybe making it a little "shinier".

I think if the points of abrasive are all in a flat plane, and engage a nominally flat steel, they can be below the pressure threshold to be able to cut at all. They just glide over. Only burrs and irregularities sticking up can hit that pressure, and get cut. That is why the surface grinding ridges started to show up shiny on my 123 block.

 

[Ianagos]

The "magic" of precision stones is not just that they are flat. Each individual grain of the stone is also flat, and in the same plane as all the other flat grains. This ends up with a huge amount of flat and parallel plateaus with sharp corners and a large combined surface area, which cut anything sticking up above the work surface. When the high spots are cut down to a flat plane, the precision stone skates on the surface like it is ice, without abrasion. It only takes a couple uses rubbing a precision flat stone on a surface that you think is 'perfectly' flat to "feel" what they do and how. It is not abrasion, it is accurate, parallel cutting of burs and other imperfections. No matter how flat an ordinary sharpening stone is, it has a bunch of sharp points with a relatively small combined surface contact area, which individually gouge out small grooves in the work.

I have a set that I rub together and they act just like precision ground flat stones. I can stone gauge blocks and it does not disturb the mirror finish. After a point your precision ground stone are rubbed together enough that they are at the same point at mine as far as the grains. If you don’t rub your stones together every time you use them then you are not going to have a very flat stone for too long. I think the precision ground stone is a bit over hyped and you can lap your stones flat or any other method as long as they are flat.

 

[Bob Korves]

I think the precision ground stone is a bit over hyped and you can lap your stones flat or any other method as long as they are flat.

Compare them side by side and then see what you think... The real issue with the precision flat stones is that it takes considerable time to make a set. I made my set in my own shop, retired geezer with plenty of time to mess around making a set. At a typical shop rate, yes, it could cost hundreds of dollars in shop time, not to mention the other costs. Grinding them flat on a decent surface grinder will make a much more accurately flat surface than lapping them together or lapping them on less than accurate surfaces while not properly supported.

 

[Ianagos]

Compare them side by side and then see what you think... The real issue with the precision flat stones is that it takes considerable time to make a set. I made my set in my own shop, retired geezer with plenty of time to mess around making a set. At a typical shop rate, yes, it could cost hundreds of dollars in shop time, not to mention the other costs. Grinding them flat on a decent surface grinder will make a much more accurately flat surface than lapping them together or lapping them on less than accurate surfaces while not properly supported.

Well when I have some free time I’ll try to make a set or maybe just order a set up. A bit pricey in my opinion so I may just make them.

I’m a firm believer that a surface could be much flatter by lapping than a surface grinder could produce. With a few stages of cast iron laps loaded with diamond I think you could get the stone pretty flat. But I’d start with a surface ground stone unless I had a lot of time.

Remember things like optical flats are lapped not ground.

 

[Bob Korves]

Yes, I agree that very fine surfaces are produced with lapping. I do some lapping myself. The question of time and effort invested is often very high for lapped parts, though again for a hobbyist it can be all part of the fun. I do not think we will see production runs of flattened stones for profit anytime soon... It takes me several hours on my surface grinder to make a set of two to a nice and quite usable surface condition

 

[ACHiPo]

I was a skeptic of precision stones. Now I’m a convert.

 

[graham-xrf]

I was a skeptic of precision stones. Now I’m a convert.

I found this video that pretty much confirms it. What surprised me is that you can go at something round, or tapered, and get much the same effect. I think you have to be more gentle, because the pressure is along a line contact, not an area. This one also taught me that for for this trick, the stones are used dry.

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At 18:30, Robin mentions surface grinder arbors - something @ErichKeane may be interested in.