High Speed Cut Off Attachment for a Milling Machine

I’ve been using a Dremel MotorTool attached to the quill on my milling machine for some precision cutting of CZ-527 Magazines .

http://rvbprecision.com/shooting/cz-527-rifle-magazine-conversion.html

Although the Dremel is acceptable, it is very under powered and take too long to make the cuts I need. A more powerful motor is needed.

I went by Horrible Freight and picked up a Rotary Saw. Price was $24.95 and they gave me 20% off and a free pair of work gloves! I’m not sure how they can offer such price points and still make a profit.

This is the saw I purchased:

I had to cut the top handle off so it would fit on the adapter I welded up to mount it to the spindle on my milling machine.

When I got it home, I installed the 1/8″ collet and my cut-off wheel arbor to see how true it might spin. Once again, you get what you pay for! It was terrible. The arbor is about 1″ long and the run-out at the end was nearly an 1/8″!. Totally unacceptable.

Try as I might, I couldn’t get it to run true. I mounted the Rotary Saw in my milling machine vise and put an indicator into the bore of the collet chuck. It ran very true. About .001 TIR. This was good news. Upon inspection of the collet nut, I could see the hole was drilled off center by about 1/32″. This was the cause of the run-out. I attempted to true up this collet nut, but even the threads were off center. The only true area was the inside of the main shaft.

So, on my lathe I made a new mandrel that would register on the inside of the shaft. I made it a very tight fit and turned the end to fit into the bevel of the shaft.

I then took the collet retaining nut and turned the inside face to simply hold the new mandrel in place. It wouldn’t be indexing anything, just holding the mandrel into the main shaft.

Once mounted up I still had unacceptable run-out. So I turned the center section of the new mandrel so it wouldn’t touch the sides of the main shaft. I’m not sure why, but this worked great! Once installed TIR was .002…..plenty good enough!