# Dremel 'Tool Post Grinder' Mount



## JRaut (Jun 10, 2020)

The crankshaft for my Edwards Radial 5 requires a snap ring groove to be machined into a hardened dowel pin. Such machine work is ideally sorted out by grinding, of course. Though it could potentially be ‘hard turned’ if you had the right tooling? Not sure.

Anyway, I decided to grind it.

I don’t have a tool post grinder, so I figured I’d make my own makeshift version using a Dremel. Designs of such an attachment are peppered all over the internet, but I figured I’d toss my design out there as well.



The sketchiest part was chucking up the plate in my ‘3 jaw chuck’  to cut the 3/4-12 thread to match the nose of my Dremel. I just made sure I took light enough passes and didn’t spin the part too fast.



There was one small hiccup with cutting the internal thread on the lathe: I have two carbide insert boring bars for internal threading. The smaller is a 3/8” boring bar and uses “11 IR A60” inserts, and the larger is a 3/4” boring bar and uses “16 IR AG60” inserts. The “A60” style insert can cut threads no coarser than 16TPI, which wasn’t coarse enough for the thread I needed to cut. The “AG60” style insert can cut coarse enough threads, but the boring bar it was mounted to was too large for the thread I was cutting.

I’m unaware of any ‘in between’ options using those inserts that would have worked, so I went and picked up this Micro 100 IT-320750 internal threading tool off eBay for about half the retail price. It was (1) small enough to get into the bore I needed, and (2) could cut coarse enough threads. Annoying that I had to buy it, but I figure I’ll use it again in the future at some point. (Yeah, yeah. I suppose I could have ground one from HSS.)




Once threaded, I took it over to the mill to machine in the part that clamps in the QCTP holder. I took 0.200" cuts using an end mill with a corner radius of about 1/16" at about 3 in./min. The version I made is about 1/2” tall and fits in my AXA knock-off.




One thing I wish I had done before removing the Dremel mount from the chuck, is check where the Dremel ‘clocks in’ when it’s screwed into the mount. I got as unlucky as one can get with mine. The on/off switch is completely obscured by the QCTP, so in order for me to turn the Dremel on for use, I need to unscrew it a quarter turn, flip it on, then screw it back in tight. It’s annoying and screws with repeatability. I probably won’t do anything about it though, as I can’t imagine using this tool more than about once a year. Who knows.

(Reversing the setup, or simply machining down the thickness won't work because there's a short shoulder on the nose of the Dremel. Doing either of those would make it so the shoulder no longer has any place to fit. So the solution would be to both (1) machine down the thickness and (2) increase the depth of the recess for the shoulder.)

Anyway, here are some photos of the completed design. The Dremel is not all the way screwed down in the few photos with the on/off button facing up. Once I had the right threading tool, it was a quick and easy job.


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## Reddinr (Jun 10, 2020)

Nice.  How did the pin come out?


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## JRaut (Jun 10, 2020)

Reddinr said:


> Nice.  How did the pin come out?


Absolutely perfect on the first attempt.

More on that in a future installment in my Edwards build log...


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## Reddinr (Jun 10, 2020)

I have an old dremel.  Wlll have to book-mark this in my head for when the time comes I need to do something similar.


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## ThinWoodsman (Jun 10, 2020)

The usual approach is to slit the tab on the end and run a bolt-and-nut through it, so that the dremel is clamped rather than threaded in (for reasons you've discovered).

For owners of the Foredom rotary tool, the straight-handle version fits perfectly in a 1" QCTP boring bar holder.


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## Buffalo21 (Jun 10, 2020)

I see you had the proper lathe bibbig in place during the operation, about 99% of the time my lathe is covered, when not being used, the airborne grime in the shop can be incredible at times.


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## JRaut (Jun 10, 2020)

Buffalo21 said:


> I see you had the proper lathe bibbig in place during the operation, about 99% of the time my lathe is covered, when not being used, the airborne grime in the shop can be incredible at times.


I recently finished making up some way covers for my Bridgeport using an old treadmill belt. I've got some leftover material, so the plan will be to make some covers for my lathe too. Just haven't gotten around to it yet.


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## C-Bag (Jun 10, 2020)

JRaut said:


> I recently finished making up some way covers for my Bridgeport using an old treadmill belt. I've got some leftover material, so the plan will be to make some covers for my lathe too. Just haven't gotten around to it yet.


What good idea! I have a whole treadmill belt my junkyard dog self couldn’t toss still waiting for a use.


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## hman (Jun 11, 2020)

JRaut -
Nice dogbone mount!  I've built several aluminum Dremel nose mounts (when I was building Rose engines).  Even bought a ¾-12 tap to do them with.  Here's a suggestion regarding the "clocking" of the Dremel ... don't raise the bridge, lower the river.  In other words, you can probably make a spacer washer to go between the Dremel and the mount, to get it clocked correctly.  If it's ½ turn off, that's 1/24", or 0.417".  If you can find some .040" sheet metal, that will probably get you close enough.


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## JRaut (Jun 11, 2020)

hman said:


> Here's a suggestion regarding the "clocking" of the Dremel ... don't raise the bridge, lower the river.  In other words, you can probably make a spacer washer to go between the Dremel and the mount, to get it clocked correctly.


Ha, funny how sometimes we miss the most obvious solutions to problems. Thanks for thinking outside the box for me!



hman said:


> I've built several aluminum Dremel nose mounts (when I was building Rose engines).


Way cool. I've always been interested in clock/watchmaking, and Rose (and straight line) engines are near the top of my fascination list. Would love to see some photos.


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## Forty Niner (Jun 11, 2020)

I bought a Dremel holder on eBay at a reasonable price.   There are several listed.
Example item numbers:  113612709777 ,   114255671079 ,  283905213781


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## silverhawk (Jun 11, 2020)

What if you flipped the holder that you threaded? Would that change, or did the thread come out at exactly the same point as where it went in?

joe


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## ericc (Jun 11, 2020)

I don't use a thread in mine.  It is just a sled with a couple of bored holes.  It is pretty rigid.


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## westerner (Jun 11, 2020)

hman said:


> don't raise the bridge, lower the river.


Beautiful anology. Mohammed and his mountain, ya? I really believe that a significant part of my mental health revolves around this exact exercise. 
Sleep on it, and allow your brain to calmly examine ALL the alternatives.....


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