Can't Understand What A Tool Post Grinder Is Good For?

mohamer said:
If you want to try the Dremel on a tool post mount, the Flex Drive that I have fits my 1/2 inch Boring Bar Tool Post Adapter very well.
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Is there a trick to getting the rubber outer cover off of the flex tool? I took the two screws and front cap off but it won't come apart. What do you do for the spindle lock button?

Edit: got it apart but you must have left the tool intact and just peeled off the outer rubber cover?? Is that a Dremel flex tool?
 
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The flex tool shown is the older model that did not have a rubber outer cover. It is used as is.
And, the spindle lock is a hole that you have to insert a 1/8'' pin in to hold the spindle. The hole is visible in the knurling adjacent to the chuck.
 
That makes sense, thought I was missing something. Newer model is quite different.
 
I made one for just one use; making a custom sized drill bit with a 1/8" shank. Worked great. Spent more time cleaning up afterwards than grinding.
 
My understanding is that a toolpost grinder has light duty but extremely accurate bearings to allow it to achieve the tolerances that are desired. A dremel or home brew tool with cheap bearings will work but maybe not as accurately.

I think the limitation of the toolpost grinder on a lathe over a true cylindrical ID/OD grinder is that you are still cutting with the machine's inherent inaccuracies (like bed twist and taper). A purpose built cylindrical ID/OD grinder will produce more accurate parts more easily as it is built to a higher class of precision than a lathe.

All that being said, if I found a reasonably priced unit, I'd jump on it.
 
I bought a used Themac tool post grinder on EBay for $400 back when EBay had good stuff to buy. I bought it to recondition/sharpen punch and die sets which I also bought on EBay. The punch and die listing said it was about 400 lbs total - I ended up getting over 2000 lbs of assorted punches and dies (Pexto/Whitney/DiAcro style). The seller kept apologizing over and over that the shipping was going to be a little more expensive because of the added weight. I had no complaints - I kept 280 punch/die sets for myself and sold on EBay about 100 more. I made all my money back plus another $3000.

The Themac tool post grinder had a masking tape note on it when I got it. It said "Not for sale June 1960". It disintegrated when I touched it. The tool post grinder works great! I've used it a lot. Besides the punches I used it to resurface the brake rotors on my wife's car. They got pretty badly scored which I first tried to clean up on my lathe with standard carbide cutters.

Has anyone tried that? Maybe my machine is just not robust enough, but I couldn't cut into the brake rotor with HSS or carbide. All it did was skim along the surface and squeal a lot. Brake rotors are hard! I was a little reluctant to "dig in" with a lot of force since I worried about an 8 lb rotor working itself out the lathe chuck and bouncing around the garage.

My tool post grinder came to the rescue.. It ground the rotors down without any problems.

The other thing I noticed about the Themac tool post grinder is that the design hasn't changed since 1960. It looks identical to new ones being offered today (for a lot more money). Well, except for the guard - mine didn't come with a guard so I had to make one. It seems incredible to me that even in 1960 they didn't see the need for a device that can spin up to 40000 RPM.

Lynn
 
chips&more said:
Wow, what an interesting thread. So many opinions. I would like to input a few. A tool post grinder is just that, it grinds. A big difference when comparing it to the cutting action of a tool bit. Hard materials, interrupted cuts, surface finish, tolerance control to name a few are jobs for a grinder. A 1/8hp motor should be able to handle 2” diameter stones. Aluminum can be ground, but I would not do it all day, the stone will eventually load up. Frequent stone dressings (coarse) would be a top priority. IMHO a Dremel is not in the caliber of any tool post grinder, and one that is properly homemade. AND the most important of all, protect your lathe from the grinding grit/swarf. I would wrap the lathe with an easily tearable material, like newspaper. And when you are done, just to make sure, give your lathe a good cleaning. If you have or can find a tool post grinder for your shop, I would say definitely get it. When you need it, there is no substituting…Good Luck, Dave.
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Chips,

I totally agree. I see people guarding their ways with cloth. This scares me. If the cloth gets caught up in the spinning work it could be a disaster. But newspaper (or other thin paper) has never worked for me. If you're doing a lot of grinding the swarf builds up and starts the paper on fire. Then I'm left with the decision to finish the pass, or start fire fighting.

I've always found old beer carton cardboard works better. It doesn't catch fire as easily. I always seem to have a lot of it around anyway ;-).

Lynn
 
I used a Dumore grinding setup to grind bearing journals on all C-5 nose landing gear.
 
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