View Full Version : Atlas Lathe Threading Help

10-22-2011, 09:16 PM
I have been trying to learn to thread on the Craftsman/Atlas lathe (Model 101.27440) that I inherited. Having broken a couple of Arthur Warner threading tools mounted in an Aloris AXA without generating a usable thread, I am hoping someone may be able to help.

I seem to be able to get 8-9 passes into the piece with the beginning of nicely formed 5/8 -11 threads before the tool seems to end up digging into the thread. This happens mid-way through the thread (not at the beginning of the cut as if the half-nut was engaged at the wrong timing). It seems as though the tool digs in deeper than the .003" cut I was trying to take.

I notice a few things - there is a tendency for the backgears to disengage when the machine is idling (while moving the cutter back to start position for the next thread cutting pass). Also, there is some play between the back gear (PN 10-242) and the headstock pulley (PN 10-79). Finally, I can get the compound to advance if I use push it back/forth against the free play.

I am new to any machine work and appreciate any help anyone could offer.

10-22-2011, 09:49 PM
The play in the headstock is fine. Doesn't matter if it pops out of back gear either. The gearing for the leadscrew is meshed with the spindle, backgear just takes the power from the belt pulleys and reduces the ratio to the spindle/chuck/leadscrew gearing.

I have had what you talk about happen to me. My problem was the compound wasn't tighten down good and it would turn a bit in the middle of the cut and throw everything off. This could also happen with a loose tool post or holder as well. Make sure everything is good and tight.

Jim Hubbell
10-22-2011, 09:52 PM
There might be a clue in that you said the thread you started was 5/8 11tpi. As I recall the half-nuts must be engaged at the same position on the thread dial for each pass. There are even numbered threads where this is not necessary. Also make sure the back-gears stay engaged at all times during the entire thread.

edit: vpt is right on the back-gears.

10-22-2011, 10:02 PM
How much 'stickout' do you have from the chuck, what is the material, and are you supporting with a tailstock center? If you are plunging .003 straight into the Vee the piece might be climbing the tool. Try increasing depth of cut with the compound only, and with the compound set to 30 deg. (Some will insist on 29 1/2 deg).

You treat the compound backlash like any other, always 'taking up the slack' for each cut so there is no 'back and forth' play while cutting.

If you're threading steel you need plenty of good cutting oil too.

Don Young
10-22-2011, 10:24 PM
It sounds like the compound and/or cross slide gibs might be loose and letting the tool pull into the work. You need to lock everything not moving and snug up anything that has to move. This is especially important if your feeds have a lot of backlash.

10-28-2011, 06:51 PM
I have been away from my computer for a week - thanks for the responses - sounds like I don't need to waste time worrying about the back gears or the play in the them

I will focus on making sure the compound and cross feed are staying put. Seems like a saw a thread somewhere that showed someone adding some set screws to lock things in place that shouldn't be moving. Anyone recognize that? Should it be necessary?

thanks again

10-28-2011, 07:53 PM
I think your chuck jaws may be worn ..

as you cut deeper into the thread there is more contact area and forward pressure ..enough to push the bar back into the chuck...if the jaws are worn ..they wont hold the bar tight enough.

you must also use a tailstock centre .

if you put too much pressure on the tailstock centre against your work ..this will also push the bar into the chuck even if only slightly worn ..

if non of the above ..go through the whole lathe adjusting gibs on the slides and the gib at the back and underneath of the saddle.

also ...i say this a lot ..if your following books or diagrams on the net ..that show you how to profile your tools ..most of them are for old style tool posts, where the tool points up at the work.

all the best.markj

10-28-2011, 09:31 PM
I just got the same basic lathe, called Atlas & they e-mailed a manual & answered a question the back gears for me. If you don't have a manual PM your E-mail & I'll forward it. The guy that helped me has the same lathe also. I'm having a ball with mine! Eric:D

10-28-2011, 11:18 PM
I have an Atlas 10" also, had it for 40 years. I've cut zillions of threads from 4 TPI square down to the smallest.. so the lathe WILL do the work. The several pieces of advice given are all on the mark. Ensure that there is no looseness in your set-up. be sure to feed with the compound at 29 degrees, don't try plunge cutting. How long is the piece you are trying to thread relative to it's diameter? Too long and slender and you could be wipping near the center even if you are supported with the tail stock causing the stock to roll and climb up on your tool ( a follower reest would be called for)
Joe B

10-29-2011, 01:39 PM
I was having some similar issues and the same check the tightness of Gibbs, tool post, etc. was suggested. Turned out the immediate problem was the Screw in the tool holder was breaking. I also had a continuing problem keeping the slack out of the compound Gibbs. Something you might consider is making a block to replace your compound. This is the one I constructed and it has made a significant improvement in rigidity.

This negates using a 29 in feed but that is another discussion that will never be resolved.

I start with a .005 depth of cut for the first couple of passes then go to .0025. Finish with .001 and some spring passes when looking for a class 3 fit.