Making semi-precision toolroom stones

Bob Korves said:
Look here, Cadillac:
https://www.hobby-machinist.com/threads/precision-ground-toolroom-stones.59776/page-3#post-531410
Start at post 83, then read to the end of the thread.
Click to expand...

Looks good. I’m gonna hold out to make the combs. They will be useful for many other materials, and I love making stuff. I have acouple diamond wheels. I had bought two like the ones you have. One OD and one face or cup wheel. Then I got two name brand ones from a auction lot so I should be with wheels.
Side note I saw you have the same mag chuck as mine. Have you felt the need for a fine pole? I picked up a compound sine mag chuck and it just seems a little more powerful but I haven’t used it on the grinder yet. I haven’t had any problems with mine just curious.
 
Cadillac said:
Have you felt the need for a fine pole?
Click to expand...
The conventional rule of thumb is small poles for small work, large poles for large work. But in reality it is not that simple. Small poles make small flux fields at closer spacing, large poles make large flux fields at larger spacing. It all depends on what you are doing. Not only is the the field larger or smaller, it is also shorter or taller. If you put a 6x12" x2" thick plate on both chucks, both will hold the work down just fine. If you are putting tiny work with big poles, it will hold it down if it is right over a pole, but not at all in between poles. Conversely, grinding a part 1x1" by 2" tall on a fine pole chuck, the flux will not reach very high into the part and could very possibly be thrown on a fine pole chuck if it is not blocked in. Of course, it is usually pretty easy to block it in. It is not so easy to add magnetism where there is none on a coarse pole chuck. I have a B&S adapter plate that fits my B&S mag chuck perfectly, and matches the big chuck pole spacing, but it transfers magnetism well or poorly to parts on top of the fine pole plate, depending on many things. I will take some pictures of it... Done.

The top photo shows the B&S coarse pole mag chuck. On it is the B&S adapter plate. Note that the adapter plate notches on the bottom need to straddle the chuck poles for best transfer of magnetism. On the adapter is a 6" ruler in the front, it is held down very well. The 1/8" thick bloc behind it with the two holes in it is also held down well. There is also another ruler on the mag chuck to the left of the adapter. It is held down marginally, I would not try grinding it like that. The dressing tool on the right rear of the adapter is held down "adequately" for dressing a grinding wheel. It has a 3/4" square cross section. When it is on the main chuck, it is rock solid. On the left rear side of the adapter, and on the chuck, are two short Rex 95 HSS 5/16" square lathe tools. The one on the adapter is held down just adequately, the one on the main chuck is barely held down at all.
SAM_1891.JPG
In the lower photo is a magnetic transfer block with a 3/4" diameter dowel pin in it. As shown, the transfer block is rigidly held to the chuck, the pin is held down, but it would slide if it was ground in that position and the pin would need to be blocked to prevent that. With the block turned 90 degrees, it is worthless. Mounted on the adapter, in any orientation, it is also worthless. I suppose (but do not know) if it would work a lot better on a fine pole chuck.
SAM_1892.JPG
So, it is a mixed bag. I got the 6x18" B&S mag chuck from a friend of a friend for $100, needed major cleanup and grinding the top and bottom in on the grinder. The handle works smoothly and easily. It is a good chuck. I would prefer a fine pole chuck for the work I mostly do, but this one is working out OK for me so far. The rule for chucks on surface grinders is "be creative, but don't be stupid." Now I need to go demag some tools...
 
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Hi Bob,

You mentioned "Demag" ! I'm curious as to what you use. I do have a home brew device that I use for things like drills and screwdrivers, and that works very well, but is quite limited.
 
Hi Bob,

Thank you for posting that picture, as they say "A thousand words". My demag is based on an old motor winding, the sort that you see in record players and washing machine pumps. Everything has been removed except the windings and laminations. Pull a drill or screwdriver through the middle and it removes any magnetism. I do wonder seeing that picture if adding a couple of steel plates on top of the laminations would make it more useful. If I get chance I'll take a picture t
 
Hi Bob,

As promised. Pictures of my demag device.
30-09-2018-001.JPG

30-09-2018-002.JPG
This is actually the coil from a Bosch washing machine water pump. On this machine the pump rotor and impeller are all inside a plastic moulding.
The plastic bits are held in place by a tag that fits into that slot in between the poles.
 
Before having the nice big L-W demagnetizer, all I had to use was my Weller soldering gun, could put smaller pieces like screwdrivers through the loop to the heating tip to demag them.

Control and demag units like the Electro-matic Neutrofier for electromagnet surface grinder chucks (http://www.em-chicago.com/chuck_controls.html) have programs that reverse the DC current while reducing the voltage in steps to zero over some seconds. You can watch the rat fur on the chuck flip back and forth, less and less, until it is just laying there, totally non magnetic. Those are very nice chuck controls. They also let you dial in the magnetism level you want, which can be important for delicate parts.

Another H-M member and I are currently working on a poor man's version of that, using a potentiometer to manually control the voltage and a drum switch to manually reverse the current. It works, but still has some glitches...
 
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