atlas tail stock

Interesting thread about what the tang is there for...so assuming that it was the original 'driver' for the rotating piece to be made, how do they (the manufacturers) make an MT arbor with no tang, but drawbar threads?

The reason I'm asking this question is that I recently ordered two MT-2 arbors with drawbar threads on Ebay, only to find that the drawbar threads were out of concentricity with the Morse Taper. In other words, if you mount the arbor on the drawbar and rotate it with your fingers (off the machine), the arbor wobbles enough to see in plain sight...almost like the drawbar threads were the last operation and the tap was not plumb.
No harm done other than aggravation, and I got a refund, but it's definitely poor manufacturing repeating itself.

Thanks in advance for comments.
 
Machinery has progressed over the years ..
In days of yore the drawbar threading would have been put in place before the taper was made then a live centre or free rotating /live tailstock chuck with a threaded bar in it be used to support the taper being turned/ground.
There must be numerous ways of doing it in truth for the above method is just straight out of my imagination .

Doing it on a fair quality CNC machine nowadays with a capstan head & multi directional capstan work piece holder as part of a the production event used when making the arbor would be just so easy to get it perfectly right .

Lousten,
What you said about the draw bar not being central ......... Does it really need to be such a precision alignment for the draw bar , for the male taper is drawn into the female , so it should fit well no matter if the screw is not true to the central axis .
Your thoughts please.
 
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The allowable eccentricity of the tapped hole is if nothing else limited by the actual diameter of the hole through the spindle for the draw bar. The hole will normally be a nominal 3/8". The tapped hole cannot be eccentric enough that you can't screw the drawbar fully into the arbor without use of a wrench.
 
Gentlemen;

I have sourced some MT-2 arbors with the 3/8" x 16 drawbar threads from Little Machine Shop. When I checked them with my rudimentary method and poor eyesight, they seemed to be properly fabricated and concentric with the rotating drawbar. My gut feel is that the previous items purchased were poorly made, and maybe 1 or 2 steps shy of a full CNC operation.

While I'm still not sure of the actual steps necessary to make the arbors with the drawbar, I' fairly sure that they are initially turned between centers, and the drawbar threads added as a final step. Whether or not it's really important for the threads to be concentric with the piece, I don't know...but when you order an item advertised as a 'precision MT-2 arbor', you certainly don't expect this kind of defect.

Lou O.
 
I agree. The drawbar threads should be concentric with the taper and with the hole for the milling cutter. Besides the potential difficulty in getting the drawbar to screw into them that I mentioned earlier, it doesn't help the dynamic balance of the machine any to have the drawbar spinning off center.
 
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