Lathe Threading Problem

[Richard]

Hi people, I need some suggestions.
I am new to the machining hobby and recently purchased a used 6 inch Atlas lathe 18 inch bed. Works like a charm except threading....

When I engage the auto feed, the threaded rod that drives the threading dial (and the carriage) moves slightly towards the lathe bed. This movement is enough to disengage the gear on the dial, and it stops rotating. If I stop the auto feed, the dial begins turning again.

I don't think this rod threaded rod that drives the feed and the dial should be bending when engaged....any suggestions, help, or advice would be much appreciated!
Richard

 

[Tin Falcon]

Richard.

The part in question is called a lead screw.
sounds like it is bent someone may have used the lead screw to lift the lathe at some point.

You can try straightening it but may be better off replacing.

you may be able to get a new one from atlas or a used one.
another option is just buy a piece of stock acme thread of the right size and machine the ends .
On a older lathe you may need to repair replace the half nut as well.

Oh and please post an introduction tell us a bit about yourself your shop and your interest in model engine building.
Tin

 

[weez]

The threading dial should stop turning when the auto feed is engaged as the carriage is moving at the same rate as the leadscrew.

 

[Richard]

Tim, I don't believe the lead screw is bent as it runs true when the auto feed is not engaged. Also, I have checked at both ends and have the same issue. When I engage the feed lever, the clamping jaws move the lead screw sideways, pushing it out of the dial gear. It is like my lead screw clamping jaws are too far forward. I also thought my compound? needs to be adjusted closer to the operator, on the lathe bed?

 

[Richard]

Really Weez? Is this supposed to work this way? I thought the dial continued to turn throughtout the threading sequence?

 

[Tin Falcon]

It is like my lead screw clamping jaws are too far forward.

What you call clamping jaws is the half Nut. It is possible that the lathe was disaembeled and there are supposed to be gibs what you might call wear strips missing. hard to diagnose without seeing.
Tin

 

[aonemarine]

Yes the dial should stop when the feed is engaged....

 

[Richard]

Gibs are in place Tim, but it seems I don't have a problem afterall? Aonemarine and Weez both say the dial is supposed to stop turning.
Thanks for the help gentlemen!

 

[dman]

the dial turns while you have it disengaged so that you can find a start point that is a multiple of the thread pitch. but if you have any doubts you can back out the cutter and reverse the spindle without disengaging the half/split nut. the dial turning represents the inches of thread that are passing by the cutter. when its engaged the cariage moves and the wheel stops, it hasn't disengaged the leadscrew, it it that the caiage is moving as fast as the thread on the leadscrew. this way you can see that you engaged the halfnut at the targeted line as it passes by.

youtube "southbend how to run a lathe" it's an old instructional video based on the original southbend literature they sold with the machines. the southbend literature is clear and easy to understand. you don't need to be an engineer to decipher it.

 

[Richard]

Thanks dman

 

[Tin Falcon]

I gues me bad did not read carfully yse the dial stops turning when you engage the half nut.

to be safe pick a number and always engage in that spot. there are rules but always the same spot covers about everything.

 

[cheepo45]

I have done a lot of threading on my Atlas/Craftsman 6 x 18. Let me know if you need additional help.
cheepo45

 

[Richard]

Thanks everyone.
And Cheepo45, I just might be doing that!

 

[chrsbrbnk]

threading dials can have a couple other weird things going on. the first thing to do before starting to thread is to make sure your threading dial is fully engaged with the lead screw. its on a swing arm to enable you to disengage it from the screw when you not turning its kinda old school but it was standard pratice to prevent wear on the worm gear on the thread dial.
the next thing to check is where EXACTLY the half nut FULLY engages the lead screw the mark on the thread dial could be off, mine is by half a thread off. you could do this by lightly pressuring the half nut lever until you can feel the nut drop in to engage the thread on the lead screw then remember how far the lever moved to. just some cautionary thoughts

 

[Hopper]

If the mark on the chaser dial is off when the halfnut fully engages, this can be remedied by putting a washer or spacer on the chaser dial pivot bolt, between the dial body and the lathe carriage. This moves the dial along the lead screw and the position of the dial marks move accordingly. A bit of trial and error with different thickness washers/spacer and you should be able to get the dial mark dead nuts on when the half nut engages.

 

[robcas631]

Richard......exactly. I believe you need to check the apron/ carrige adjustment.

http://www.mini-lathe.com/Mini_lathe/Features/features.htm

 

[Richard]

Now can I bother you people to tell me how to run this lathe's chuck in reverse?
And is it a big issue engaging "back gears"?

 

[mu38&Bg#]

To reverse the chuck you must reverse the motor. Back gears offer additional reduction ratio between the motor and spindle.

Greg

 

[Tom Jamboretz]

The Southbend book is usually on E-bay or most of the used book sellers on the web. Great bookl and and a good reference source.