Bob,
I assume you bought a used Chinese Mill/Drill. They normally have at MT3 Quill taper or some of the newer ones have an R8 spindle.
I assume you have the MT3 variety. In Europe the tool for these machines use am M10 thread. In the US those tools use a 3/8-16 UNC
thread. The purpose of the drawbar is to prevent any helix in the cutter from pulling the tool holder out of the quill. I too had
to make a draw bar. It is no problem to do. I used a 3/8 rod. threaded one end and pinned a piece of 3/4 hex stock drilled for the
rod on the other end. Be sure to use two pins, not just one. Tighten lightly or you will shear the pins. It just needs to be snug.
those mill drills are incredibly handy. I wouldn't be without one, but like everything else from China, there are good ones and
bad ones.
Steve

"Bob La Londe" wrote in message ...
I need to make a draw bar for a garage sale piece of equipment I picked up cheap recently. Its got a drill chuck and a metric
draw bar, but it won't work for the collet holder I want to use instead of the chuck. The collet holder has the right taper, but
uses a 3/8 draw bar. There is only about 1/4 or maybe 5/16 passage through the spindle for the draw bar.

I figured to get a piece of rod, thread both ends with some standard threads, and make a theaded bushing to loctite onto one end
to go in the collet chuck. Then make a knob to go on the other end to make it easy to loosen if I ever want to take the collet
chuck out. Something easy to hit with a hammer instead of slipping of and smacking a pulley.

(The draw bar holding the drill chuck taper was similarly configured except metric and just had a nut.)

I can't think of any reason to get overly obsessive compulsive over it, but I thought I'ld ask you guys if there was any reason
I needed to go ape over balancing it or getting my bushing highly accurately concentric? This machine spindle is relatively low
speed. Top speed is 3840, but I don't see me using it at that speed very often. I just plan to use it for the occassional
manual milling operation that I can do faster by hand than to write a snip of code for one of the CNC machines, or for when I
have a project going on the machines, and have something else I want to try.

With it basically going through the axis of rotation it would take a pretty significant imbalance I am thinking to cause any
vibration. That and it doesn't have anything holding it EXACTLY centered at the top end anyway. I suppose I could make the knob
with a slight taper to do that if I wanted to, but I think I would rather have a flat washer in between to protect the surfaces.
Speaking of washers, Since the taper is actually holding the chuck. Any reason to need a spring washer under the knob?