Machining a Drawbar

ddickey

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I want to make a new drawbar for my Bridgeport clone.
I was thinking about buying a piece of 7/8" stock but that is a fair amount of stock removal. ~.380" over 18".
The other option is to buy 1/2" 2' long pressing/pinning the larger hex end.
Ideas?
 
the drawbar I made for the Rockwell vertical mill, I used a piece of 7/16”-20 B7 hardened all thread and made the nut for the top.
 
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Use good steel rod for the drawbar, perhaps something like 1144 stressproof, or even something partially pre-hardened, but not too hard, as the collets are also hardened. The rod needs to be straight. The threads of a drawbar take a load and are tightened and loosened many times over the life of the drawbar. Softer, gummier alloys are not a good idea. If the threads gall or deform you will be frustrated using it. I would not machine the drawbar in one piece, but rather thread or otherwise lock the hex nut to the rod. That could be pinning it, welding nut to rod at the top, using permanent Loctite on threads, or whatever works best for you.
 
I am just coming around to finishing my drawbar for my mill. I did it in 2 pieces because I had a lot of the small diameter & just a piece for the large nut. All that is left is to machine the mating surfaces. Is there a better way than an interference fit + a pin? Here they are, the 2 pieces waiting for final lathe work.

20170614_191356245.jpg

I sweated most over cutting the threads as my Grizzly lathe / mill combo is a challenge for precision work. Most happy with how the hex came out though! Really happy with the threads as well as they are spot on accurate.

My mill actually came with several drawbars - but the simple versions are not really for my mill as they are too long. This project fits my needs! So, I say, use what you have to make what you need!
 
Best is to thread both ends of the drawbar, thread a extra long nut on the top and pin it, either radially or axially, I have done both, and they work fine. I think using all thread is tacky, not good practice. Using stressproof or 4140 HT is best.
 
What about 01? It's locally available at Fastenal.
I don't have anything long enough otherwise. Would have to order.
I was thinking 1/2" should fit nicely into the spindle then turn down to 7/16 for the threading operation on the end.
The hex part needs hardening, you think the 7/16 threads do also?
 
What about 01? It's locally available at Fastenal.
I don't have anything long enough otherwise. Would have to order.
I was thinking 1/2" should fit nicely into the spindle then turn down to 7/16 for the threading operation on the end.
The hex part needs hardening, you think the 7/16 threads do also?
I would go with 1/2" threads at the top end; I see no need to harden the nut on top, although they do tend to mushroom over with hammering on the end to release the taper, I use an end wrench on it, so the mushroom makes no difference, but do cut a healthy chamfer on top of the nut.
O-1 steel would be better than 1018, but without heat treatment, it is not a lot harder.
 
I suppose a 1/8" spring pin would be to small?
 
It would be OK if used axially, should be larger, 5/32 or 3/16 if used radially.
 
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