2015 POTD Thread Archive

hman said:
I'd suggest not making a shoulder on the drawbar inside the chuck body. Instead, add a shoulder (see also below) to the far end of the drawbar, where it exits the spindle. If nothing else, you'll have a larger diameter for the needle bearing. You might even want to fabricate a drawbar centering collar to fit inside the far end of the spindle, with a nice large flange at its outer end for the needle bearing.

Finally, instead of machining the "shoulder" as part of the drawbar, you could fabricate it as a separate collar, which you can secure to the drawbar with a pin AFTER you have all the parts built and test-ssembled. That way, it can be located in an ideal place to allow tightening the collet.
Click to expand...

I had actually thought about the draw bar tightening against the rear of the spindle much the same as the 3C collet setup. After looking at it , I believe you are correct and that is the right way to go, But the hand wheel to tighten will have to thread on the .750" draw bar as the draw bar has to go through the spindle and the end of the draw bar in the chuck is 1" in diameter which is too large to go through the spindle.

Spindle bore = just over .750"
draw bar inside chuck to screw into collet = 1"
 
This is a revised drawing for a possible solution and still keep it simple. The angle on the draw bar functions the same way as the SB 3C draw bar. The angle creates a minimal contact surface when tightening and loosening to prevent "galling" or "drag". This is why the SB draw bar is tapered on the shoulder and I think the same idea may work here.
5C Collet concept drawing.jpg

I like your idea of tightening on the rear of the spindle but the front of the draw bar is too large too go through the spindle.
 
Mark, I made something for my SB 9a similar but threaded the end and used a nut similar to an ER40 adapter to push on the 5c collet rather than to use a drawbar. Works great for me and still lets you pass stock through the spindle as you would with a regular chuck.
 
Mark,
My overall comment is "Don't do it", but I know that won't deter a determined hobbyist. IMO, you'd be better off making an ER40 chuck for many reasons. ER type collets are much shorter so less overhang means a stiffer setup. ER40 goes up to 1" capacity (5C=1.125), close enough. ER collets have a much wider "grip" range for a given size than 5C. 24 ER40 collets will cover the full range from about 3mm to 26 mm. It would take about twice as many 5C collets to cover the same range. You won't need a draw bar with ER collets so can work with wrenches completely from the spindle nose. You can buy an ER40 nut (hardened, ground w/collet 'puller' lip). ER collets systems are often used as tool holders in mill spindles so your collet set could do double duty.

If you're set on 5C, use a 3/4-20 thread on the draw bar and make one adapter to 5C collets. Put the adapter in the collet, not on the draw bar, which will simplify everything. I presume that you know 5C collets are intended to be 'drawn' by the outer thread and the inner thread is intended for use with a 'stop'. I expect 'drawing' with the internal will be OK but you wont be able to use standard stops. Many 5C collets have no internal thread so needing an internal thread will limit your sources.

Either way, 5C or ER, design in maximum bearing area between the lathe spindle planar face and a shoulder in your chuck (to the resist bending moment).

Good luck.
 
I have a job to do tomorrow that requires chasing a 1"-20 TPI thread. It has to be done while the shaft is still in the machine. It's 1 hours work vs. 9 hours work. I have a 1'-20 Die but it's too big for my largest Die Stock. Adapter time. Now I'm ready for the job.

"Billy G"

102_1070 (800 x 531).jpg 102_1071 (800 x 531).jpg
 
Last edited by a moderator:
Mark-f,

I made one for a SB9 some time ago very similar to what you showed. It worked well but my tolerances were in need of improvement at the time.
But for what it was it worked well.
 
extropic said:
Mark,
My overall comment is "Don't do it", but I know that won't deter a determined hobbyist. IMO, you'd be better off making an ER40 chuck for many reasons. ER type collets are much shorter so less overhang means a stiffer setup. ER40 goes up to 1" capacity (5C=1.125), close enough. ER collets have a much wider "grip" range for a given size than 5C. 24 ER40 collets will cover the full range from about 3mm to 26 mm. It would take about twice as many 5C collets to cover the same range. You won't need a draw bar with ER collets so can work with wrenches completely from the spindle nose. You can buy an ER40 nut (hardened, ground w/collet 'puller' lip). ER collets systems are often used as tool holders in mill spindles so your collet set could do double duty.

If you're set on 5C, use a 3/4-20 thread on the draw bar and make one adapter to 5C collets. Put the adapter in the collet, not on the draw bar, which will simplify everything. I presume that you know 5C collets are intended to be 'drawn' by the outer thread and the inner thread is intended for use with a 'stop'. I expect 'drawing' with the internal will be OK but you wont be able to use standard stops. Many 5C collets have no internal thread so needing an internal thread will limit your sources.

Either way, 5C or ER, design in maximum bearing area between the lathe spindle planar face and a shoulder in your chuck (to the resist bending moment).

Good luck.
Click to expand...

I understand what you are saying but you missed the point. I don't want to invest in another set of collets and chucks and adapters. I have the 5C collets. My other equipment uses 5C collets. I am trying to stay with one system. That being said I believe this will work and I thank you all for your ideas. I think with everyone's comments , I now believe I have the information to make an accurate and useful addition to my tooling.
 
Whyemier said:
Mark-f,

I made one for a SB9 some time ago very similar to what you showed. It worked well but my tolerances were in need of improvement at the time.
But for what it was it worked well.
Click to expand...
I am not concerned about tolerance because I know I can keep it within a few tenths. So, I think I shall give this a try.
 
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