Tool post grinder from Santa

[GailInNM]

On December 23 Santa showed up in the USPS truck with a new to me Tool Post Grinder. It is Dumore model 14 that was also known as the "Tom Thumb" back in the day when it was made. It's 40 or more years old, but that's OK because I have wanted one for about the same period of time. Other than the old fashioned rubber power cord that was cracked with age and a few places where some of the paint was a little thin, it was in excellent condition. After replacing the power cord and putting fresh oil in all the required places it was good to go. The newer models have permanently lubed bearings. Then a mount was made to fit my AXA QCTP so I would not have to remove the QCTP to use it.

While it will do external work, I wanted it to pre-finish small engine cylinders after boring and before lapping. This is mostly to save lapping time, but I also want to play with some hardened cylinders. For hardened cylinders I plan to harden them after boring but before lapping. This means more material being left before lapping.

The only problem is that for the depth of cylinders I want to grind, the smallest diameter that the nose will fit into is 1/2 inch with out excessive overhang on the mounted stone. So a few new spindle noses were machined up to allow me to get into 5/16 diameter cylinders. This should be fine as I don't plan to do anything smaller than 3/8 where I would need grinding.

I think Santa made a good choice as it will do what I want and Santa could not afford, or justify, a new one.

 

[ksouers]

Very nice, Gail.

I would think this would eliminate the lapping operation, no?

I've been thinking of maybe acquiring a tool post grinder (someday) but I worry about the weight cantilevered off the post. Have you noticed any issues with it?

 

[Maryak]

Gail,

Santa was kind to you. :bow:

I have been toying with the idea of making a holder for my Dremel to mount it on the tool post/compound slide. Any comment about this being a viable option. ???

Best Regards
Bob

 

[steamer]

Bob,

I tried that route, and it works to a degree.

The spindle is not very accurate, and more importantly, is not very rigid. I think you would be happier building a Quorn spindle and fitting it out with the proper tooling...or find a gem like Gail did

Nice grinder Gail!

I'll send you a PM....

Dave

 

[GailInNM]

Thanks guys,

Kevin,
The Model 14 is the smallest TPG that Dumore makes. I think the model number came from the fact that it is rated at 1/14 horsepower. So it is not very heavy. I would not try to mount any larger TPG on a QCTP. Standard practice is to remove the tool post and replace it with the TPG using packing to get it up to center height. Preliminary tests show that mounting it to the QCTP is satisfactory, but I have not yet used it in anger, only testing.

In my case it will not eliminate the lapping as a final step. I have been building small compression ignition engines (PMC-IMP and the Lobo's) and they have some special requirements. First the piston-cylinder fit has to be near perfect and the force of holding a cylinder in the collet may distort the cylinder a small amount so the finish ground may not be a perfect circle. Second, the cylinder needs to be tapered a very slight amount so the piston effectively jams in the cylinder as TDC is approached. This taper is only in the order of 0.0002 inch, and while easy to put in with a lap it would be very difficult to do with a TPG. There would probably be no problem with not lapping when building glow or spark ignition engines of greater than 1/2 inch bore or with a ringed piston. I would probably still lap them anyway, but just a small amount. I have been using a 5 micron diamond lapping compound for the final lapping and that gives a mirror finish.

Bob and Dave,
I have been down the Dremel style tool several times in the past and have never been very satisified. You can get a better finish than turning on short bores, but at the depth required for a cylinder it has not been adequate for me. My last effort used a Proxxon IB/E tool, and while it was much better than a Dremel I was still better off just forgetting it and lapping after boring. I did make several improvements to the Proxxon tool which helped a lot, but it just does not compare to a regular TPG. I will pull some photos out of the archive showing a couple of the things I did to the Proxon and post them here later today. But Dave's comments are very valid no matter what you do. There are reasons that a TPG costs at least 10 times what a high end Dremel type tool does.

Gail in NM

 

[steamer]

Thanks Gail

Bob....PM sent....

Dave

 

[GailInNM]

Bob,
I thought I had more photos of my Proxxon IB/E setup and trials and tribulations, but these were all I found. I think I got discouraged with it and gave up taking photos. I had tried using a Dremel tool before, but it was not very usable.

The Proxxon IB/E tool is their industrial hand tool. Ball bearing and rated for continuous service. A lot of people have used them for small home built CNC. Most notable feature is that they have a 20mm machined aluminum nose piece on them for clamping in a fixture. I made up a holder out of 1.5 X 3/4 6061 with a dovetail cut in it to match my QCTP. I have another holder that I used on my small mill that fits around the spindle housing that I used for small hole drilling. I have since gotten a small high speed drill press so that is no longer used.

I always knew that there was a little bit of runout in the Proxxon spindle, so when I tried using it for a TPG I checked the spindle taper where the collet seats and found that it was off by a couple of "tenths". After measuring the taper, I set the the tool up in the lathe set over by the measured taper and ground the taper using a 1/8 diameter mounded stone. See the first photo. The measured taper, if anyone is interested, is 1:4 or Arctan=0.25. Just a touch over 14 degrees per side, but easy to set up on the compound slide with a dial indicator. Ran the lathe spindle at top RPM (4000) with the stone and the Proxxon at 20K RPM. It cleaned up nicely and eliminated any measurable runout at the spindle end. Biggest problem is that 1/8 shank mounted points is the largest that can be chucked. To get to the bottom of a cylinder there was too much overhang for that small a shank.

I made some hollow shanks with a matching taper to fit the spindle. I had previously purchased so extra spindle nuts, so by sliding a nut on the spindle and Loctite-ing a mounted point in the new shank I was able to get a more rigid stone mount. Still I was limited to the opening in the spindle nut, but I really did not want to make new nuts.

Last photo shows dressing a wheel with a Diamond dresser in the lathe.

All this improved things, but it still was not rigid enough. And there was a little bit of vibration from the Proxxon tool and this did not help any. So I shelved the idea. I thought about other options until I found the small Dumore. Now having it, I can see no reason to return to the Proxxon, so it is now retired to it's original intention for hand work.
Gail in NM

 

[GWRdriver]

Hi Gail,
I also have a DuMore #14-011 which I've had for some time but have not yet used or even tested. This is partly because it was missing the bloody expensive little belt, but partly because during the years I had a mentor toolpost grinding was not a part of the course and I'm a bit timid about trying it out. Not too long ago I found a relatively inexpensive belts, and there are several bits on my current locomotive project which need OD grinding, so my excuses for not going ahead with it are dwindling. I am VERY concerned though about grinding dust migration as I only have one lathe to do the grinding on and while I can cover it easily enough my workshop is close quarters and everything else is in the open. I'm sure once I get the hang I'll wonder what all the fuss was about, but any pointers you can pass along would be appreciated.

Before my TPG arrived I also made a couple of attempts with TGP substitutes (a Dremel and a hand-held die grinder) with completely unsatisfactory results.
Harry

 

[Alan J. Richer]

Re: Grinding dust:

Just to toss out an idea here - what about a vacuum inlet next to (wrapping around, perhaps) the grinding stone? This way as little of the debris as possible would be allowed to fall to the ways, and airborne dust would be kept to a minimum.

I've made custom vacuum inlets before by heating and reshaping PVC pipe - the stuff is cheap and can be cut, formed and glued pretty easily. Thinking a bit of PVC pipe cut off at an angle, then a bit glued to the bottom, drilled and threaded for a mount behind the wheel could be made pretty easily. It won't get it all, but certainly could be configured to get a lot of it and keep the crud out of the air.

Alan

 

[GWRdriver]

Alan,
I do exactly the same thing when I turn cast iron, I just hand-hold the shop-vac nozzle near the cutting tool. I had thought maybe the same thing would work for grinding but hadn't tried it yet. It may be that a more effective collector than a hand-held shop-vac nozzle is needed, but maybe not. In either case it's worth a try. I do think it would be important that whatever collector/nozzle assembly I came up with not be mounted on the toolpost, or maybe not on the carriage either, as any external influence on the carriage travel might cause irregular grinds. This may be over-thinking things but this notion came from an old mentor and old machinist who told me to always take my hands off the lathe during a power-fed final pass so as not to affect the cut.

 

[GailInNM]

Hi Harry and Alan,
The biggest thing to remember is that grinding is a finishing operation for us. In industry there are creep feed techniques that are used for roughing, but that has no place in the home shop. I have never allowed more than 0.002 grinding allowance when machining, and most of the time much less. This means very little crud floating around. The only time there is much of a mess is when dressing the grinding wheels. I use a shop vac when doing that. The rest of the time I just cover things up. I generate much less debris than I do when grinding a lathe tool on the bench or tool grinder where we are shaping as well as sharpening. Still a mounted vacuum pickup as Alan suggested would be an advantage if I were doing a lot of grinding.

One side note. When covering things up, use paper towels. A light spray with WD40 will help trap fine particles and keep them from bouncing off. Most important -- throw the towels away as soon as you are finished. Don't wipe ANYTHING with them. Get a fresh towel for cleanup. They are cheap. Don't use rags. I have a thing about rags in the shop anyway for safety reasons, but beyond that if I have one I keep using it and just spread things around. Just too cheap to throw them away I guess.

Gail in NM

 

[GailInNM]

Harry,
I have an old "Bull of the shop" cartoon ( does any one else remember them?) that shows a lathe being carted off from the shop floor. The caption being two of the shop guys talking. "We had to retire the lathe. Joe retired and he was the only one who knew where to lean on it to make it cut accurately."
Gail in NM

Edit: I think it was "Bull of the Woods", not "Bull of the Shop". CRS syndrom.

 

[mu38&Bg#]

Nice tool. I don't think you can get away from lapping the final fit. Even Peter Burford laps pistons and liners after grinding. http://www.peterburford.com.au/finishing_fitting.php

 

[GWRdriver]

"Joe . . . was the only one who knew where to lean on it to make it cut accurately."

Bingo!

 

[deverett]

Bob

I too have been thinking about using a Dremel as a high speed drilling/milling unit but have been given to understand that the bearings are not 'precision' items to give accurate results.

There are various designs around that incorporate the Dremel or similar as a power unit. One of the better designs was in the Home Shop Machinist Sep/Oct and Nov/Dec 2008 by Jerry Pontius.

One day I'll get around to making it! As someone else wrote: 'So many projects, so little time'.

Dave
The Emerald Isle