Single point threading problem

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No-ladder

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Using 9x20 import lathe. Trying to cut 1/4 x20 threads to a shoulder. Feeding using compound at 29 deg. Catching the threading dial every pass. Back out crosslide at end of each pass, back to 0 for next pass, run compound in 3 thou. Repeat. Running 120 rpm so I can catch it.
So all of this is on .5 drill rod, with the last .75 turned down to .248. 6 or 8 passes into the threading, just getting about 50% of the threading done, and the tool digs in...snap breaks the end off the rod!
Now what I do notice is that after the first 3 or 4 passes, I get a pass where the tool does not touch the work after advancing the compound. Takes a pass or two advancing each time then the tool starts cutting again, go a couple of passes, but then all the sudden the tool seems to gain all the passes that did not cut.
Been careful to take up all the slack on compound and crossfeed at the begining.
Doing everything just like Tubal Cain videos.

Any Ideas? Tried several times, same results.

And all this after knocking over my poorly made grinder/vise stand, destroyed my panavise and grinder when they hit the floor

Charlie
 
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Man you were having a bad day!

Were you backing out a full turn or only enough to clear the cut, on each and every pass? What I am thinking is that you were not advancing enough to remove the backlash in the cross feed screw. Or possibly the gibs are just a little loose and one of the slides or both are backing up a bit just on inertia as you spin the handles? Can either one move easily with a light touch?
Just thinking out loud.
Pierre
 
You might be onto something, the compound does turn really easy.
Using the exact same setup, I am parting off successfully, something that is not normally very easy to do on this lathe.
I am taking all slop on the crossfeed each time, clearance and then some. All dials zeroed, once slack has been taken up and ready for first pass, and return to zero for next pass.
 
Also make sure your tool bit is EXACTLY on center height especially on small diameters. Make sure your bit is sharp and dress it with a hand stone. If you are taking care of the slop in your cross slide each time I suspect that your bit is not cutting until you "force" it in to the work because of wrong height or dull edge.... clearance angles can also create similar problem.
 
lotechman said:
Also make sure your tool bit is EXACTLY on center height especially on small diameters. Make sure your bit is sharp and dress it with a hand stone. If you are taking care of the slop in your cross slide each time I suspect that your bit is not cutting until you "force" it in to the work because of wrong height or dull edge.... clearance angles can also create similar problem.
Click to expand...
excellent advise!
mike:))
 
good info here i have had this problem after reading this i dont think ill have a problem again ill check all
these items each time, i have one thought i have noticed the carbide tipped tools seem to be less robust
for this than hss tools
 
I ahhh think you should be using the tailstock on something that small, once it starts to flex, thats the
end of that. Or Im reading this wrong, but I always use a center when treading no matter how big
or small threading it longer then cut to size. Looks like your getting a good bite then all hell breaks loose.
And then there is the metal/material law. Two (look the same stock) one turns or threads perfect the
other piece of crap.?? I still find it amazing people not using a thread stop? That takes all the guess
work out, In fact it stays on all our lathes.
 
First off, drill rod is awful to thread! Try and get a few passes done and then finish with a die - still get crappy looking threads but...

Also, how far is the work piece sticking out of the chuck, anything over 1 1/2 - 2" and you need to get the tailstock up there to support it.
 
I agree with all advice above, all good. You didn't say if you were using a carbide or HSS cutter. If carbide, your speed is pretty slow and the threads wont look so good when done. Also, I think a lot of people think carbide is always sharp, it's not. Carbide needs touched up just like any other material. Hone a HSS cutter and try that, you will see a huge improvment in thread quality. It also sounds as if your work is flexing, you have gib play, tool bit is off center, or try turning from centers if you aren't. When cutter all of a sudden digs in and takes a huge cut, work is flexing back toward cutter instead of away from it.
Check everything that everyone has mentioned and make sure you apply sulphur oil to the cut often.
Keep trying you'll get it, it's all a learning experience.:))
 
GK1918 said:
I ahhh think you should be using the tailstock on something that small, once it starts to flex, thats the
end of that. Or Im reading this wrong, but I always use a center when treading no matter how big
or small threading it longer then cut to size. Looks like your getting a good bite then all hell breaks loose.
And then there is the metal/material law. Two (look the same stock) one turns or threads perfect the
other piece of crap.?? I still find it amazing people not using a thread stop? That takes all the guess
work out, In fact it stays on all our lathes.
Click to expand...


I think this is right on from what you are describing.
 
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