Bridgeport drawbar - is there a washer?

When I got my Bridgeport 2J head, there were two crude washers between the drawbar and the top of the spindle. The hex part of the drawbar wobbles a little with this arrangement although the drawbar does not appear to be bent. Should there be a "washer" between the drawbar and the spindle and should that washer have a narrow part that goes inside the spindle to center the drawbar in the spindle? If so, what are the heights of the washer and the narrow part; I'll turn one on my lathe to replace what may be missing.

Yes there is a crude washer (at least one.) It does not have a centering lip. When I bought a new drawbar to replace the old one, it also came w/ a washer. But, since it was a little longer the threads would bottom out in some collets, so I stacked the washers. Now works like the old one. AFAIK, it doesn't matter that the hex part wobbles a little. The R8 collet is located via the inside of the spindle. The drawbar is only providing tension, no centering.

Not a BP, but my excello's draw bar uses a pin to hold the hex head on the shaft. The head is actually rather loose, but as was mentioned, it doesn't matter. I'm guessing the pin is intended as an over-torquing safety (weak link).

I was trying to determine why my head has a slight vibration and the slightly wobbly drawbar looked like a likely culprit. Mine has a pin holding the hex end onto the 7/16 bar too, but there's no wobble there. I reasembled my Vari-speed head last evening after doing a front bushing replacement and it still has the slight vibration without the drawbar being in place.

I think my BPT has the original drawbar and washer. The washer is precision, possibly ground, about 3/8" thick, flat, OD just smaller than the splines. Can't get at it right now though. Den

dennh said:

I think my BPT has the original drawbar and washer. The washer is precision, possibly ground, about 3/8" thick, flat, OD just smaller than the splines. Can't get at it right now though. Den

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Is it just a flat washer, or does it have a smaller diameter part that drops into the spindle to center the upper end of the drawbar?

I took a look at mine today, and found that the washer was missing.

For some time, it has bothered me that I have to spin the drawbar so many times to get the collet to be drawn into the taper. Without the washer, it takes 15 turns from the point where the 7/16"-20 thread starts engagement until it is snug. That's 3/4" of thread engagement, which seems a bit excessive.

dennh said:

I think my BPT has the original drawbar and washer. The washer is precision, possibly ground, about 3/8" thick, flat, OD just smaller than the splines. Can't get at it right now though. Den

Click to expand...

A 3/8" washer will reduce the thread engagement by about half, which seems right to me. I didn't have any washers handy that would fit, but I drilled out a couple of soft steel washers that had 7/8" OD with smaller ID. (I used a 29/64 bit.) The pair of steel washers combined thickness is less than 1/4". I like that they help make the length of thread engagement closer to ideal.

My other choice was to cut the tip of the threaded drawbar by about 3/8", but making washers seemed quicker and easier.

To get the washer(s) out, I use a magnetic tipped screwdriver.

That washer is called a thrush washer. They should have a turned down length that will center it up to the quill when installed and are hardened. Every machine that uses a draw bar must have one. If it doesn't, the top of the quill will begin to wear instead of the thrush washer and that is where you will see the draw bar lean off to one side. Regular washers are not the same. If the top of the quill is already worn it can be fixed relatively easily. Or you can run it as is, but it will only get worse. It's more of pain having the draw bar kick off to the side when using an air draw bar set-up.

Tom

just picked up a new drawbar for my bridgeport. first 5/8" or so under the hex section measures .495" in diameter so it will self center very nicely in the top of the spindle and it came with a machined washer of about .3" thickness.



dave

rlamparter
The Bridgeport drawbars are designed to have a washer between the spindle & the hex portion of the drawbar. This washer does not have to be hardened,there is a counterbore in the face of this washer to accomadate an "O" ring, the purpose of this "O" ring is to hold the washer onto the drawbar when the drawbar is removed from the spindle. There are several styles of drawbars available, some have longer hex heads for use when you are using a 90 degree head or a quilmaster, this is because when these attachments are in use,the quil is lowered to clamp these attachments on to the quil.

You can visit the ebay store, matacoinc.net, or talk to them direct @ 1-888-785-7810, they are very helpfull. Good luck with your machine.
Jeff

Jim Shaper said:

Not a BP, but my excello's draw bar uses a pin to hold the hex head on the shaft. The head is actually rather loose, but as was mentioned, it doesn't matter. I'm guessing the pin is intended as an over-torquing safety (weak link).

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My BP drawbar failed me - the threads at the end stripped out, possibly due to many over-tightenings. Luckily, I had a replacement on hand - possibly left over from a head rebuild. I decided to try to figure out the construction of the original drawbar.
The hex head at the top is a very hard press-fit with another very tight press-fitted perpendicular pin locking it in place. I broke a chisel trying to drive out the pin. Since the drawbar was trash anyway, I used a bandsaw to carefully cut it apart to see how it was made. The hex part has a .4375 inch hole that goes about half its length, and the bar is pressed in. Then a .125 inch hole goes through the hex and the bar in the sideways direction, and a very tight-fitting pin is pressed into the hole. The pin would not come out until I breached the side of the hole it was in using the lathe. Oh, and I did have a conical washer that went between the hex and the top of the drawbar tube. That will keep the bar centered. This was not a feature of the replacement drawbar. The replacement bar diameter is very slightly oversize, so the washer won't fit, but I've had no trouble with it.
I'm pretty sure the pin will *not* protect against over-tightening the drawbar.

We fitted an aftermarket power drawbar kit to a Jet-branded Bridgeport lone a couple of years ago. That mill also uses a washer, but the washer was in such crappy condition on both faces (like galled, grooved and positively squished) from bearing on the inner sleeve of the spindle and the hex head of the drawbar that I made a replacement from O1, hardened and tempered.
Part of the job of fitting the kit was to replicate the work wirecutter describes. The kit gives you an overlength threaded drawbar and the head, which you must turn/bore for a press fit and then pin.