- Joined
- Jun 15, 2017
- Messages
- 525
I have been watching videos on precision-ground bench stones. For those who don't know, these are ordinary India (or other) stones that have been ground smooth with a surface grinder. They don't really have points on the abrasive crystals. Very strange. They remove burrs from stuff without scratching. They're amazing to watch.
To get them to work, you need a pair, because you have to rub them against each other sometimes to flatten the bits of metal imbedded in them. A pair will usually run $200 or so. The raw stones are $22.50 each on Amazon.
Robin Renzetti has a wonderful, informative video on these stones. I watched it, and now I'm confused, which is by no means unusual. On the one hand, he says the stones have to be flat (surface-grinder flat). On the other, he uses the stones on round work, meaning he applies them to things that can't possibly benefit from a flat stone. The side of a round object can't lie flat against anything. Some dude who commented on his video claims the stones don't really have to be flat, and although I know nearly nothing about the subject, it kind of makes sense to me, because when you look at a close-up photo of a ground stone, you can see that all the points have been polished off of the grains. You would think that the polishing of the grains is what really makes the stones work.
Adding to the confusion, machining guru Forrest Addy says that for deburring, he likes lapped stones that are slightly convex. Convex isn't flat. He said this in a discussion of burr files, however, so I don't know whether it's relevant to the use of precision stones.
For those who don't know, a burr file is a piece of a file which has been dulled deliberately on a flat stone. You can move a burr file back and forth on a metal surface, and as long as the surface is smooth, it won't remove anything, but if there is a burr, it will shave it off. That's the theory, anyway.
If you can get away with convex stones, then clearly, there is no point in paying someone a hundred bucks to grind them. Renzetti says it's extremely hard to create really flat stones without a grinder, and not all of us have one in the shop.
To make things more complicated, some stones come with a lip ground into them, along the long side. It allows you to put the stone up against a part and reach under it a little. I don't know how you would reproduce that lip without a grinder.
I kind of wonder what a local shop would charge to grind a couple of stones.
To get them to work, you need a pair, because you have to rub them against each other sometimes to flatten the bits of metal imbedded in them. A pair will usually run $200 or so. The raw stones are $22.50 each on Amazon.
Robin Renzetti has a wonderful, informative video on these stones. I watched it, and now I'm confused, which is by no means unusual. On the one hand, he says the stones have to be flat (surface-grinder flat). On the other, he uses the stones on round work, meaning he applies them to things that can't possibly benefit from a flat stone. The side of a round object can't lie flat against anything. Some dude who commented on his video claims the stones don't really have to be flat, and although I know nearly nothing about the subject, it kind of makes sense to me, because when you look at a close-up photo of a ground stone, you can see that all the points have been polished off of the grains. You would think that the polishing of the grains is what really makes the stones work.
Adding to the confusion, machining guru Forrest Addy says that for deburring, he likes lapped stones that are slightly convex. Convex isn't flat. He said this in a discussion of burr files, however, so I don't know whether it's relevant to the use of precision stones.
For those who don't know, a burr file is a piece of a file which has been dulled deliberately on a flat stone. You can move a burr file back and forth on a metal surface, and as long as the surface is smooth, it won't remove anything, but if there is a burr, it will shave it off. That's the theory, anyway.
If you can get away with convex stones, then clearly, there is no point in paying someone a hundred bucks to grind them. Renzetti says it's extremely hard to create really flat stones without a grinder, and not all of us have one in the shop.
To make things more complicated, some stones come with a lip ground into them, along the long side. It allows you to put the stone up against a part and reach under it a little. I don't know how you would reproduce that lip without a grinder.
I kind of wonder what a local shop would charge to grind a couple of stones.
