threading problems

[jocat54]

You should be able to reverse without any problem with chuck coming loose after you back out the cross feed. I use to do it all the time with a SB9A.
I would check for any problems with thread dial----have had the problem of not engaging the feed screw when pushed in and being too loose and disengage.

 

[bfd]

after the first pass return to the next pass but leave the tool bit back and start the next pass. when the tool would start cutting shut the lathe off and coast to a stop. then turn the cross slide in to see if the cut is in the right place. if not try to move the carriage back and forth to see if there is anything that skips, half nut or slop in the lead screw. too many things could be wrong tool bit loose or moved. do this a few times to see if it ever comes back into alignment if it does there is something wrong with your geartrain. bill

 

[cathead]

The "Process of Elimination" is a very useful tool in solving many kinds of problems. Once you determine all the
things it isn't, you end up with what it "is". I'm sure you are well on your way to figuring this out and I for one will
be watching this post to find what it is.

 

[Tozguy]

Yes Mike. Mine is set up the same way and I do disengage it when not threading. I consider your suggestion later this week when I get back on this. I do have the South Bent book on how to run a lathe.

When the second pass rips into the threads made by the first pass, is it ripping into the exact middle of the first pass?
How many teeth are on the thread dial gear? The problem almost certainly lies with the thread chaser dial gearing.

 

[stupoty]

might be worth checking another TPI or visually inspecting the gears , their might be a gear with a missing tooth some ware between the spindle and the lead screw.

Stuart

 

[Fixnair]

Wow! I'm overwelmed with the number of replies to my problem. I'm impressed with the interest you guys have shown. I will work on some of the suggestions this week & let you guys know what I find.

 

[neilking]

I'm having good luck on my 9b, no thread gage. Cross slide in - cross slide out, leaving the compound alone and leaving half nuts engaged.

Sent from my SM-G920P using Tapatalk

 

[Chuck K]

Sounds like the same problem as trying to cut metric threads with an imperial lead screw.....

 

[neilking]

A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.



I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.



Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544

 

[Fixnair]

Thanks for all you r input. I have finally made something that looks like a thread! 3/4 - 10, it is a little undersize (.015") and the nut fits snugly so I'm sure it is not the correct form. My single point threading tool I made myself and all I have to make such is a bench grinder. The root and the crest of the threads come to a point so my tool needs some work. I think I'll purchase a carbide threading tool. I'll post a picture below.

I think I'll work on the grind for my tool and try the 3/8"-20 thread again, the one I tried first and wouldn't work. Stay tuned & I'll let you how that comes out.