Thread Problems Part Failure

Latheman

Latheman

Registered
Registered
Joined
Sep 23, 2015
Messages
31
By part failure when closing in on final cuts, I wind up bending the part. I use a 60 deg on compound a fish tale gauge to square up. But when I get close to final few thousandths I bend the part. I center the tool on my tail stock center and I just can't seem to figure why I am bending the part. I am trying to thread 1/4-20 on 1018 crs and have just enough stick out of the chuck to get the job done. But the tool just bends the part when .005-.008 away from final depth. I would love to hear what you guys think. Please ask any question that could help me solve the problem. Also tried on a 7/16-16 and same problem.
 
Hi, are you taking full-width cuts with the cross slide, or advancing at 29-1/2 degrees with the topslide? a straight-in cut puts much more force into the cut as it's closing on final diameter as the full width of the thread is being cut, plus there's much less space for the swarf to curl and get out of the thread over the top of the cutting tool. If you're cutting straight in, try setting the topslide to 29-1'2 degrees (assuming a 60 degree thread) so that it only cuts on the advancing edge - this also helps keep a consistent threading feed, as the unidirectional force between work and tool keeps the leadscrew and nut engaged.

If you're unsure of the angle, for a right-hand thread cutting towards the headstock turn the topslide ANTIclockwise through almost 30 degrees, so that increasing depth of cut pushes the leading edge of the tool into the work, the trailing edge just shaves and cleans up the other flank of the thread.
 
Besides British Steel’s questions, I will also ask what depth of cut are you taking on the pass that bends the work piece? What is the initial diameter of the work piece before you make the first threading pass? What thread depth are you cutting to? Does your compound or cross slide scale (whichever you are using) show the actual depth of cut or does it show the reduction in diameter of the work piece?

Tom
 
On small threads I prefer to use a die. Any thread over a 1/2" dia I would try to cut a thread. Unless you have a small lathe a die is easier.
 
Exactly how much is just enough to do the job? What is the tool position along the thread when the bend happens?

"Billy G"
 
That's pretty small for single pointing. Good advice above. Definitely need the compound on the angle to lesson the tool pressure. RPM plays a part as well. Slow speed will grab.
 
I am threading in back gears. So slow rpm

Sent from my SM-G360P using Tapatalk
 
British, i feed with top slide. At 29 1/2. I am feeding at a rate of .005 a cut.

Sent from my SM-G360P using Tapatalk
 
Tool position: about half an inch from the farthest point away from the chuck.

Sent from my SM-G360P using Tapatalk
 
.2484 was that last 1/4 20 attempt

Sent from my SM-G360P using Tapatalk
 
You must log in or register to reply here.
Back
Top