Southbend 5C Drawbar slop

[JustaTOOL]

I have SB Heavy 10 w/the 2-1/4 - 8 threaded spindle nose. I'm trying to use my collet chucks as opposed to my 3-jaw, for no particular reason.

I'm trying to turn 7/8" cold drawn 12L14 having OD at 0.874" to 0.875" as measured with a good micrometer that's been calibrated.

For 7/8", I have 2 sets of 5C collets. An older SB 5C collet that may have some slight wear and a new Chinese 5C collet that's never been used. Both collets have different lengths of external thread, but both bottom out when not in the lathe. The steel rod slides into the collets; no problem. And both 5C collets seat fully into the collet sleeve when not in the machine.

The problem happens when I assemble everything into the spindle. I have the handwheel type, and after getting it tight, the collet sleeve sticks out a bit from the thread protector. As soon as I take a cut, it becomes evident that the assembly isn't fully seated. I can usually move it with a decent whack from an open palm. This happens with both collets. Something seems to be too long.

I was under the impression that drawbar length came in 2 different sizes. One for the handwheel and the other for the collet closer. But, a recent review of a SB spec sheet lists different part numbers for the different models (10", 13", 14.5", and 16"+).

I'm guessing that there's a difference in length, and I need the shortest one. As there doesn't seem to be a part number on the drawbar, is there a length I should be looking for to ensure I can find the correct length drawbar to be able to use my collets??

Thanks in advance,

JustaTOOL

 

[MrWhoopee]

Put a spacer under the handwheel.

 

[BDRetz]

I have the same set up and my hand wheel draw tube is 11 9/16” from the start of the cone centering piece to the end of the tube. I think I read somewhere that the draw tube for the heavy 10 with a cam lock spindle was longer but I don’t know if that is true or not.

Completely agree with the recommendation above to put a spacer in place. It should tell you quickly if the threads are bottoming out before the collet taper fully seats.

I would also verify you have the correct collet spindle adapter. The south bend spindle taper is an oversized #3MT. A standard #5MT to 5C adapter will physically fit in the spindle but will not seat properly or be repeatable.

Hope this helps.

Ben

 

[SLK001]

I have the same set up and my hand wheel draw tube is 11 9/16” from the start of the cone centering piece to the end of the tube.

Not quite sure what you are measuring here. The length of the tube on the South Bend hand wheel closer for the 2-1/4" x 8 TPI spindle is 15.125"

 

[MrWhoopee]

I would also verify you have the correct collet spindle adapter. The south bend spindle taper is an oversized #3MT. A standard #5MT to 5C adapter will physically fit in the spindle but will not seat properly or be repeatable.

Ben

Correction, the spindle nose taper is MT 4.5

 

[SLK001]

Correction, the spindle nose taper is MT 4.5

Not on the 10L. The taper for it is 0.602 per foot, or an oversized MT#3.

 

[MrWhoopee]

Not on the 10L. The taper for it is 0.602 per foot, or an oversized MT#3.

I have a 10L. The large diameter of an MT3 is .938, a 5c collet is about 1.25 diameter. An MT3 will pass through the 5c adapter. Morse Taper Dimensions | uWoodcraft.com

 

[SLK001]

I have a 10L. The large diameter of an MT3 is .938, a 5c collet is about 1.25 diameter. An MT3 will pass through the 5c adapter.

Correct - thus it being called an "oversized MT#3". It has the same taper as an MT#3 - it's not an MT#3 though. Probably a poor choice of words. It's a proprietary SB taper which just happens to have the same taper as an MT#3.

 

[MrWhoopee]

Not on the 10L. The taper for it is 0.602 per foot, or an oversized MT#3.

I can see that we've been talking past each other. The taper is the same as an MT3, but the physical size is the same as MT4.5. Not sure if SB created this proprietary taper before the official MT4.5 was added or not, but I suspect they did. Both were created to accommodate 5c collets. Why none of them are .625/ft., which is what Morse was shooting for, is beyond me. Good old Samuel Morse continues to screw us up 150 years after his death.

 

[SLK001]

Good old Samuel Morse continues to screw us up 150 years after his death.

Not Samual Morse (he was the telegraph guy), but Stephen Morse.

There supposedly was a reason that Morse didn't use consistent tapers for all his tapers. His goal wasn't to hit 0.625 in per foot. Even in the 1860's that was a dimension that could easily be accomplished with the available tooling. He thought that smaller taper numbers would require a shallower taper angle to properly hold. I don't know what tests he conducted, but his actual taper numbers were what he wanted. A Jarno taper does have a consistent taper (0.600 per foot) over the entire range of available sizes.

 

[jim rozen]

..., is there a length I should be looking for to ensure I can find the correct length drawbar to be able to use my collets??

Yes. You want the collet to not bottom on the threads in the drawbar. Mark the collet threads with a sharpie and be sure there's at least a few threads left marked when it all goes together.

If the drawbar is too long (collet bottoms) then your stock will not lock up in the collet. If it does lock up, but things are still loose enough to shift radially then there's a good chance you have a collet adapter that has either the wrong taper or for some other reason not seating properly in the spindle. Sharpie again, mark the OD of the adapter and seat it in the spindle to be sure it's in full contact.