Crazy Threads...

[Hukshawn]

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.

the lathe is an Enterprise 10. made in india. cant find a whole lot of info on it.
no idea what the lead screw is, how would i find that out?
i had been going about 1/4" past the work piece and letting it travel back to take up the slack.
yes, quick change gear box.
set to what you see in the photos. i really hope its just an error in operation... cause i was really hoping this lathe would be a keeper...

edit. let me elaborate a bit more... i had initially been trying to cut at 18tpi. i set it to 10 to do a few tests once i posted here. figured a wide thread would show the issues better.

 

[Hukshawn]

The compound angle looks correct in the pic above. It is certainly not 30 degrees off of where it is supposed to be.

no, i made that mistake at the very beginning. oddly enough, it gave a similar thread to what im getting now actually. how the cuts are stepped deeper running away from the initial cut... but its definetly 29 degrees from the work piece.

 

[Jason Annen]

It looks like your half nut is catching on top of the lead screw. I had this happen last week and got the exact same result. I was in a hurry and engaged the nut a bit early, and away it went.

Jason

 

[Hukshawn]

It looks like your half nut is catching on top of the lead screw. I had this happen last week and got the exact same result. I was in a hurry and engaged the nut a bit early, and away it went.

Jason

it seems to not want to engage where i want it to sometimes. the line on the dial would come around and id push the half nut lever and it would hit the top of the thread then drop in too far past the line. id pull back reset and wait for the line to come around again. i WAS trying to make sure i hit the exact same spot each time...

 

[Jason Annen]

Sounds like your problem may be in the half nut. You'll probably have to drop the apron in order to get to it.

Jason

 

[Hukshawn]

Sounds like your problem may be in the half nut. You'll probably have to drop the apron in order to get to it.

Jason

what do you think the issue is? i had the apron off when i got the lathe home to clean everything out and oil/etc. it all went back together fine.

 

[Jason Annen]

It's possible the half nut is worn and the threads are no longer square. There could be sharp edges or burrs causing it to grab. The half nut is more than likely brass and would wear faster than the steel lead screw.

There's not a whole lot in there with regards to the half nut and lever.

Jason

 

[Hukshawn]

ill take it apart again this week. it was less than a month ago that i got this lathe. when i had the apron off to clean and inspect, i didnt see any significant wear on the gears or half nut.
when i engage the half nut, there is no play or slack in the carriage. and the half nut does have a reasonable solid catch when it engages. its not sloppy, i mean. i had said it seems to ride the top of the thread when i try to engage, i was thinking it was maybe the thread dial indicator was out of alignment or something... when i try to engage on a number or line, sometimes id hit the top of the threads and then it would seat just past the line. i unscrewed the allen screw on the face of the dial and moved it so the line sits inline to where the half nut fully seats on the screw. so it was easier to hit, i suppose. tried to thread a few more times, only using the number 4 for each pass. the half nut seated comfortably inline perfectly with the number, but still, threads over top of the threads, and just beside... a mess.. (refer to the picture of the 5/8" stock bar i did the tests runs on.)

 

[Bob Korves]

it seems to not want to engage where i want it to sometimes. the line on the dial would come around and id push the half nut lever and it would hit the top of the thread then drop in too far past the line. id pull back reset and wait for the line to come around again. i WAS trying to make sure i hit the exact same spot each time...

To get your job done, move the tool farther to the right before engaging the half nuts. That will give you more time to assess if it feels correctly seated in the half nuts and in the right place. If not, disengage, back up, and try again, nothing lost but a second or two of your time. Longer term, fix it and make it correct.

 

[rick9345]

Hmmmmm! Last thing worked on,Apron? Trouble engaging half-nut consistently! Would recheck apron/half nut assembly/adjustments. Also with correct setup one can thread away from the shoulder , left to right. Requires lathe with reverse and a chuck or setup that won't unscrew. Good luck.(threading tool upside down)