Lathe is turning a taper

[jwmelvin]

Seems like it would be pretty quick to investigate the runout by swapping to the 4-jaw and measuring parallelism (you know your piece has a consistent diameter but not that it is straight). If that is substantially different from the 3-jaw, then clean and reinstall the 3-jaw. If it does not hold work parallel to the spindle the. It would seem to require grinding the jaws.

 

[woodchucker]

so I don't think the goal should be to level the bed, I think the goal should be to twist the bed to get 0.000 taper.
sometimes a twist is necessary to get the bed in alignment.

I know many will disagree.. but if you want 0 taper from the chuck alone (with 0 tir at the end first) than you need to get the bed to support that.
if the bed is level and not giving you 0.000 taper, than twist the bed to get it to zero taper.

I've repeated myself twice... I don't think I need a third time do I...
flame shields on.

 

[Janderso]

so I don't think the goal should be to level the bed, I think the goal should be to twist the bed to get 0.000 taper.
sometimes a twist is necessary to get the bed in alignment.

In the manual that came with my 1970's Clausing Colchester, there is a procedure on leveling the bed (twist) and the head adjustment.
Why do we twist the bed to conform vs. moving the head if the bed is in fact straight? (not twisted)
I agree with the others. Take off the 3 jaw and use a collet chuck or 4 jaw??

 

[Janderso]

if the bed is level and not giving you 0.000 taper, than twist the bed to get it to zero taper.

Does your lathe have alignment screws like the tail stock to adjust/align the head? Mine does, I assumed all lathes did??

 

[tjb]

In the manual that came with my 1970's Clausing Colchester, there is a procedure on leveling the bed (twist) and the head adjustment.
Why do we twist the bed to conform vs. moving the head if the bed is in fact straight? (not twisted)
I agree with the others. Take off the 3 jaw and use a collet chuck or 4 jaw??

Yep. Using the 4-jaw is going to be my first course of action. I have a very nice Pratt-Burnerd 'New-Open Box' that I got on ebay. I've used it a few times and I know it's accurate. It'll be interesting to see the results. This is new territory to me, but I'm visualizing head alignment may be the culprit.

Regards

 

[tjb]

Does your lathe have alignment screws like the tail stock to adjust/align the head? Mine does, I assumed all lathes did??

Not sure, but I bet it does. It's 2019 Eissen Taiwanese machine - virtually identical to the high P-M's other than spindle diameter and some small tweaks.

 

[Al 1]

Terry, Dismantle the chuck and clean. There may be a chip stuck in it. Al

 

[benmychree]

Indicating a wobbling piece of steel tells you nothing about the taper problem. What sort of level are you using, what is its sensitivity?

Just saw this post, John. That's exactly what I'm thinking makes sense as the first order of operations. How do I know if there is a need to re-grind the jaws? Again, as in my latest post, that would surprise me given how lightly used the chuck is.

Regards

The wobble you see shows a likely need to regrind the jaws, if in fact the O-1 drill rod is really straight. The condition of the jaws might be bell mouthing, if you chuck it lightly, can you detect and shake out on the end of the bar? A two collar test will show if the alignment is off, the gold standard of alignment tests. Also, again, what is the sensitivity of your level?

 

[tjb]

Indicating a wobbling piece of steel tells you nothing about the taper problem. What sort of level are you using, what is its sensitivity?

The wobble you see shows a likely need to regrind the jaws, if in fact the O-1 drill rod is really straight. The condition of the jaws might be bell mouthing, if you chuck it lightly, can you detect and shake out on the end of the bar? A two collar test will show if the alignment is off, the gold standard of alignment tests. Also, again, what is the sensitivity of your level?

This is a link to the level I used (0.02mm per meter). I bought it new last year to level this lathe. Kept in its original case in a tool chest:

Kinex 8" Precision Inspection Machinist Spirit Level, Accurate to 0.02mm/meter 700667467139 | eBay

Find many great new & used options and get the best deals for Kinex 8" Precision Inspection Machinist Spirit Level, Accurate to 0.02mm/meter at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I've not checked to make sure the O1 is 'straight', but it's definitely 'uniform'. I mic'd it in several places, and in every instance it's exactly 1.2500.

I bought the chuck new - probably four years ago. Never had any issues with it until (possibly) now. The real mystery to me is 'why' is this happening? Some of my friends tell me when they die they want to come back as one of my pieces of equipment. I do everything I can to not abuse my machines, so I can't imagine it's the consequence of over-use or abuse.

I'll be out of town for the next two days, so I won't really dig into this until Thursday.

To be continued...

 

[benmychree]

what would that be in inches per foot? (I'm too lazy to do the math)