threading problems.....

[Bob Kelly III]

(I looked for a threading thread but didn't see any so I figured it was Ok to put it here <GRIN>)

Today I did a little practice on the Logan 922 lathe.
but it didn't turn out worth a darn ...I wiped out the threads because of hitting the half nut too late I think....
but regardless of the results i am not sure if I can cure the mistake... as I was extremely careful to engage the half nut on the same line every time
and i'm not sure why it wiped out my threads !!!!! it shouldn't have ! for all I know I did everything right ....obviously I didn't or the threads would be good ! LOL....
the thing is.... that threading dial is small and the enguagement of the half nut seams to take some time it's not like it is instantaneous !... and I think that is my problem
I have read where you need "Cat like reflexes" in order to thread on some machines..... is that true ? is the Logan 922 one of these things ?
.... I don't have a reverse switch hooked up yet on the lathe but I will get to that soon I hope. if I did I could just leave the half nut engaged and stop back out the threading tool and reverse the motor and then do another pass.... this may well be my last option because that thread dial is far from accurate...or so it seams !
......
do you guys engage just before the line? or right on it ?
I could slow the lathe down alot more, and probably should to some degree.... as my results were so poor !
do you have any suggestions ?
I was trying to cut 1/2" x 12 TPI threads on fairly soft 1/2" steel Rod.
it should be easy... I don't understand why I keep wiping out the threads about half way through the thread depth !
thanks....
Bob........

 

[brino]

do you have any suggestions ?

I could slow the lathe down alot more

Yup, that ^^^.

I would check carefully the threading dial gear engagement with the lead screw.
If you have any slip/skip that's your problem.

You could also run some practice on a piece of plastic pipe, or even with a sharpie marker, rather than a real tool.

Good Luck!, and please keep us posted.
-brino

 

[RJSakowski]

Check to see that your thread dial is exactly on the mark when the half nuts are engaged. There are multiple intermediate positions between the marks. If the dial is slightly off, you may be engaging a half tooth before on one pass and a half tooth after on the next. The thread dial can be adjusted be loosening the screw and rotating the dial to correct alignment.

Re: engaging the half nuts. As the mark on the thread dial approaches the index mark, you start to engage the half nuts so they fully engage as the dial mark passes the index mark. Once the half nuts are engaged the dial no longer moves. If the dial isn't lined up exactly with the index mark, disengage the half nuts and move the carriage back and give it another go.

You also didn't say what thread you were cutting. You can't use a thread dial to cut metric threads on an imperial lathe and vice versa.

 

[eugene13]

You could also run some practice on a piece of plastic pipe, or even with a sharpie marker, rather than a real tool.

Using a sharpie marker is probably the best way to practice threading, also, if your machine is new the half nut may be tight or filled with shipping grease and need "working in" until you get the "feel" of engagement. Keep practicing and you'll get it.

 

[Bob Kelly III]

Check to see that your thread dial is exactly on the mark when the half nuts are engaged. There are multiple intermediate positions between the marks. If the dial is slightly off, you may be engaging a half tooth before on one pass and a half tooth after on the next. The thread dial can be adjusted be loosening the screw and rotating the dial to correct alignment.

Re: engaging the half nuts. As the mark on the thread dial approaches the index mark, you start to engage the half nuts so they fully engage as the dial mark passes the index mark. Once the half nuts are engaged the dial no longer moves. If the dial isn't lined up exactly with the index mark, disengage the half nuts and move the carriage back and give it another go.

You also didn't say what thread you were cutting. You can't use a thread dial to cut metric threads on an imperial lathe and vice versa.

I am Sure that is the case... but I thought that was normal so yah I will fix that imediately ! thank you !!!!!!!
and I thought I did say ...it was 1/2"x12 TPI ....

 

[Joeman77]

Hate to be the elephant in the room, but are you sure you're set at 59-1/2 degrees and not 29-1/2? I've had trouble with that if it was a machine I wasn't too familiar with in the past. Some of the newer lathes aren't marked in a "user friendly" manner, the older ones were consistently marked, not so these days.

 

[MontanaLon]

The cutter matters too. HSS is the way to go for cutting threads at low RPM. It will cut much better than carbide when it is turning at a speed where catlike reflexes aren't required. Carbide will work fine when you get practiced with threading and can run the higher speeds, but at low speeds I have found it will tear up the threads instead of cutting them sharp.

 

[MontanaLon]

And for practicing start with a piece of stock, cut a thread into it and then turn the threads off and do it again. You can cut threads 6-8 times on a piece of stock before it is all chips and a tiny bolt. Rarely is it a good idea to try to cut threads into something that matters for the first time.

 

[higgite]

Hate to be the elephant in the room, but are you sure you're set at 59-1/2 degrees and not 29-1/2? I've had trouble with that if it was a machine I wasn't too familiar with in the past. Some of the newer lathes aren't marked in a "user friendly" manner, the older ones were consistently marked, not so these days.

I think you mean 60-1/2 degrees from spindle axis. That would be 29-1/2 degrees from perpendicular to spindle axis.

Tom

 

[Bob Kelly III]

Hate to be the elephant in the room, but are you sure you're set at 59-1/2 degrees and not 29-1/2? I've had trouble with that if it was a machine I wasn't too familiar with in the past. Some of the newer lathes aren't marked in a "user friendly" manner, the older ones were consistently marked, not so these days.

the compound does have degree markings on the back side and I have it set at 29.5deg.... are you saying it should be 59.5 deg ????
never heard that before !
.........
Um.... I am set at 29.5 degrees on the compound..... but it hasn't moved in 3 days ( blush !) i forgot and just used the cross slide ! DUH !!!!! would that contribute to taking out the threads ? because I just finished another practice run and although the threads are there they are the worst looking threads I've ever seen ! hunks of metal hanging off them even after I made a few passes with the file....
I guess for the last 3 days I've been teaching myself bad habits ! LOL.....
" no more cross feed BOB !!!!!..... just in and out and reset to zero and advance the compound ! geez Bob ! what a dummy !!!!"
.... I guess sense I've neglected to advance the compound and not the cross feed I should have no complaints ! LOL
oh well live and learn !
thank you for pointing that out !
...Bob.........