Need Advice To Complete A Collet Drawbar

John C

John C

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I've nearly completed a drawbar for my SB H10. The last item to address is a way to retain the cone portion that bears against the spindle so that it won't fall off. I've considered short dowel pin(s) driven into the tube that would engage a slot in the cone section, with sufficient clearance for free movement. Or a ball detent in the cone piece to engage a groove in the tube. Not sure which method to use. Don't want to mess it up at this point. The tube is .125 wall thickness.

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The ones I've made I've put a groove where the cone section goes on the tube. Then I put an allen screw in the cone section (non cone area) that will lightly go in the groove you cut in the tube. Make the groove a little wider so the cone has some in/out play. Groove does not need to be too deep, just enough for the allen screw to keep the cone section from fallen off, yet still allow it to turn freely on the tube.

Put some red or blue locktite on the allen screw and you are good to go.


I've seen one that had a cut a groove on the tube in front of the cone and used a round wire clip (no ears) to keep the cone from falling off. I choose not to go that route because I did not have a wire clip large enough on hand.
 
Thanks Craig. That sounds like the most logical way to go. Do you think a groove about .050" deep in the tube is about right? More, less? Probably less I'd think. Think 10-24 set screw would be large enough, or go 1/4-20? Either way, I'll face off the cup and turn a small tenon on the end.

Thanks, John.
 
You could probably even use 6-32, it's only to keep the piece from falling off.
 
Yes, it does not need to be large...as Andre said, it is only there to keep that cone from falling off. Needs to be sloppy so that the cone will ride on the bearings and not bind from the allen screw. The screw could even be nylon so as not to need locktite.
 
Thanks. I tend to over build things by nature. The smaller set screw/hole won't throw the balance off much either.
 
Thanks again guys. Used an 8-32 set screw. Cut the groove .035" deep with plenty of clearance towards the bearing side. Works great. Will be parkerizing the components once I complete a spider I'm making. All made from 12L14 which is starting to rust only 1 week after I started.
 
John: Nice work! I especially like the wooden handwheel you made - very attractive. I have a question. I want to make a 5C drawbar for an older Harrison 10-AA lathe I have. I was planning to model it after the drawbar on my Hardinge mill - which does not utilize a thrust bearing or tapered cone as shown in your photographs. After looking at your drawbar, I think you have a better idea. What is the purpose of the thrust bearing? Would the drawbar work as well without it? Thanks for enlightening me. Bob
 
Bob, thanks. The cone bears against the outboard end of the spindle on a SB, which has matching 30deg angles. Once you take up the slack, the cone would need to turn while bearing against the spindle. The two piece design with the bearing in between reduces friction and allows you to draw up much tighter. Haven't epoxied the wooden wheel on yet, need to parkerize the pieces first. Hopefully the epoxy will stick to a parkerized finish. I made the wheel 5" dia. Thinking I probably should have gone a little bigger -- 5 1/2 -5 3/4"? We'll see..

(I took me a while to understand why they used bearings in the originals as well.)
 
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