Crazy Threads...

The only issue with reversing the motor trick, threading in front of that shoulder will be next to impossible without crashing... i may have to just abandon this particular project for now i guess.
 
Make sure your tool is not loose in the holder, or the holder to the tool post, or the compound loose. Wrestle them to make sure. Use the same spot on the threading dial for each pass. It does not matter if it is even with a line or number, just the same place each time until you get this sorted out. Make sure the threading dial gear that engages the lead screw is not slipping on its shaft, and that it engages the lead screw well, and without the fit changing as it revolves (bent shaft, bad bushing, damaged gear, etc.) Some lathes have shear pins on the lead screw or other means of failing soft in case of a crash. Make sure your lead screw is not slipping between it and the change gears. Slide the carriage left and right with the half nuts engaged to see how much wear they have. Also inspect them visually as best you can, after cleaning them up, and check for swarf filling the threads. Might there be a key missing or broken in one of the change gears, the lead screw, the spindle, or anywhere that might cause a slip?

Every good test is worth a hundred expert opinions, and perhaps a million hobby-machinist opinions... :cool:
 
Bob Korves said:
Make sure your tool is not loose in the holder, or the holder to the tool post, or the compound loose. Wrestle them to make sure. Use the same spot on the threading dial for each pass. It does not matter if it is even with a line or number, just the same place each time until you get this sorted out. Make sure the threading dial gear that engages the lead screw is not slipping on its shaft, and that it engages the lead screw well, and without the fit changing as it revolves (bent shaft, bad bushing, damaged gear, etc.) Some lathes have shear pins on the lead screw or other means of failing soft in case of a crash. Make sure your lead screw is not slipping between it and the change gears. Slide the carriage left and right with the half nuts engaged to see how much wear they have. Also inspect them visually as best you can, after cleaning them up, and check for swarf filling the threads. Might there be a key missing or broken in one of the change gears, the lead screw, the spindle, or anywhere that might cause a slip?

Every good test is worth a hundred expert opinions, and perhaps a million hobby-machinist opinions... :cool:
Click to expand...

tool post/holder/compound all tight, VERY little play if any at all. maybe a half thou. any tighter and i cant advance the compound. i strong armed it plenty when putting it all back together and tightening.
i dont think any shear pins or keyways are gone, very little play in the carriage, any slack goes away once its advancing. was some slack in the lead screw, but i tightened that out. however, there is about a half a revolution capable in the lead screw inside the gear box. not sure whats up there. but again, once the lathe is running, the slack is taken up and it runs true. (i may pull the gear box and investigate this to make sure somethings not broken. it wouldnt seem like a broken tooth, because the play is there no matter the position of the gears.)
but no matter how many times i start on the same number, it cuts in a different location.
again, the only place i did not pull apart was the gear box... that may have to come next.
 
In your photos, it looks to me like your compound is set at 60 deg instead of 29 deg. That may not be the cause of your threading problem, but it will give you a poor quality thread.

Ted
 
What about making a manual handle to fit in the at the rear of the headstock spindle and cut the threads by manually turning the handle.
I cut the 39x4mm threads for my back plate this way, slow but steady.
 
talvare said:
In your photos, it looks to me like your compound is set at 60 deg instead of 29 deg. That may not be the cause of your threading problem, but it will give you a poor quality thread.

Ted
Click to expand...
its set at 61 deg on the graduations. which makes the tool 29 deg to the work piece. i guess some compounds are labeled differently?
 
savarin said:
What about making a manual handle to fit in the at the rear of the headstock spindle and cut the threads by manually turning the handle.
I cut the 39x4mm threads for my back plate this way, slow but steady.
Click to expand...
i suppose that would help with preventing crashing the lathe on a shoulder cut?
 
What kind of lathe do you have ? Is it a imperial or metric lead screw? How far past the beginning of the thread lead are you coming to allow the lead screw to take up any backlash that may be present, and I cant be sure but I would bet there will be some. Is there a quick change gearbox or do you have change gears? Are they set for imperial ( TPI ) threading ? I ask this because that was my trouble when learning to thread , I would get the first scratch pass down and looked good. Returned the carriage to the start watched for the thread dial to come around and whamo it would cut right beside the first thread. Lots of unanswered questions here, lots of good advice but missing info to get to the root of your trouble.
 
Hukshawn said:
its set at 61 deg on the graduations. which makes the tool 29 deg to the work piece. i guess some compounds are labeled differently?
Click to expand...
The compound angle looks correct in the pic above. It is certainly not 30 degrees off of where it is supposed to be.
 
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