threading problems.....

thank you for the detailed depth of cut ! that helps alot ! I think I have been cutting way too much and tearing up the thread !
......
well the idler gears on this lathe are twins on a shifting lever for forward and reverse, so you might call them the forward/reverse tumbler set
but when it is in reverse ( cutting toward the chuck) it is the 2nd gear from the spindle gear....(counting the spindle gear as ONE).when it is in Forward, the gear just spins with the other one and serves no purpose (other than to make some noise ! )
the Bad gear drives the other idler gear and then that goes into the gear reduction chain for the lead screw , it is an ingenious setup I must admit !
...if it doesn't matter about the gear size I can simply replace the gear that is bad with a 36 tooth instead of the 34 tooth !
and that is a real good gear hardly any wear on it at all . .... all I would have to do Is mill or file a elongated hole in the bracket that swaps the 2 gears in and out.....
I even have the bracket they came on but it will not fit this lathe .
if you're sure it won't matter my problems are cured ! I'll just put in the 36 tooth gear !
.....
Bob......
 
Bob Kelly III said:
thank you for the detailed depth of cut ! that helps alot ! I think I have been cutting way too much and tearing up the thread !
......
well the idler gears on this lathe are twins on a shifting lever for forward and reverse, so you might call them the forward/reverse tumbler set
but when it is in reverse ( cutting toward the chuck) it is the 2nd gear from the spindle gear....(counting the spindle gear as ONE).when it is in Forward, the gear just spins with the other one and serves no purpose (other than to make some noise ! )
the Bad gear drives the other idler gear and then that goes into the gear reduction chain for the lead screw , it is an ingenious setup I must admit !
...if it doesn't matter about the gear size I can simply replace the gear that is bad with a 36 tooth instead of the 34 tooth !
and that is a real good gear hardly any wear on it at all . .... all I would have to do Is mill or file a elongated hole in the bracket that swaps the 2 gears in and out.....
I even have the bracket they came on but it will not fit this lathe .
if you're sure it won't matter my problems are cured ! I'll just put in the 36 tooth gear !
.....
Bob......
Click to expand...
While changing the size of an idler gear won't affect to final gear ratio, it will affect the position of the forward/neutral/reverse detents. It may also create interference issues. Check everything carefully before making any modifications that can't be undone.
 
OH yah ! your right ! so , not so simple a fix.....
that definitely will effect at least one indent....maybe 2

I gott'a go and think on this a bit, might just be easier to braze the old gear and re cut it !
thanks again for all your help !!!!!!
Bob....
 
Hey Bob,

Some may call me a stickler (or worse) but I'd like to get a few things cleared up for anyone learning threading from this thread......

1) in terms of the out-of-sync (wiping out the threads during the next pass) it does NOT matter if you advance the cut by either the cross-slide or the top-slide. Both are fixed to the carriage and the carriage is driven by the lead-screw. It must be a problem "upstream" of this.....the same list Bob (@RJSakowski) mentioned (half-nut, sheared pin, gears, etc.)

2) the big difference between advancing the cut with the cross-slide vs. the top-slide is the how the tool is presented to the cut on successive cuts.

When feeding with the cross-slide, the 60 degree tool tries to cut equal chips on both sides of the tool.

When feeding with the top slide (set to the proper angle) the tool cuts mainly on its' left edge, and just barely scrapes on the right side.

On some small, less rigid lathes cutting on both sides of the tool at the same time can cause chatter.
I typically feed with the top-slide for that reason......less forces on the tool, post, carriage, etc.

Keep going, I know you'll get there!

-brino
 
yes indeed !
Well I went out to the shop this afternoon and "thought about it" while ripping apart an old bed frame for the scrap steel.
and I got to thinking that if it was that gear causing most of my problems ( granted Far from all!) then cutting threads on the other gear...( going in the other direction) should go alot better.... so I put the lathe in back gears and ran it at about 50 RPM and gave it another try....
it seamed odd at first but that soon disappeared ... as the threads grew using the cross slide to bring it in and out only and the compound for the thread depth.... they started looking quite substantial and good threads ! then I blew it, and hit the half nut too late ..but unlocked the half nut before it moved more than 1/16" ... backed up the carriage and tried it again.... on every half nut locking in, I was dead on the money except 2 times in over 30 to 45 minutes of cutting this left handed thread ! and the threads were forming very nicely I was taking .005" cuts and then they started looking a bit ragged..... so I dropped it back to .002" in cut depth increases..... but once the damage was done there is no going back right....! the old saying " it's too late when you've gone too far comes to mind ! So Bob's wisdom in his cutting method is very apparent to me !!!!!
threading this slow makes it allot easier on the nerves and is much easier to stop the cutter fast if you screw up and miss your mark !
I continued on for a while but didn't like the way the threads were looking as they had a big slope on one side and a little slope on the other...
so I stopped and tried adjusting the piece of file I ground into a 60 degree point and moved it slightly.... Wrong move ! the next pass took out the threads completely.... but it was kind'a expected, I was just farting around at that point because it already told me what I needed to know
I also cut a different thread this time a 10 TPI instead of 12 TPI .... figured I'ed see if that made any difference at the same time.....
so apparently what has been happening is the bad idler gear can skip a tooth on occasion when it comes around just right and I hit the half nut and put a load on it, it can skip.... threading in the other direction didn't do that ... it was me that screwed up 2 times... so it's something I will really have to watch when threading ! ......( there is about 1/16" window on that thread dial !!! I think I will make a larger dial so I can see it better ! it is about the size of a quarter ! I think I will make a 2" dial and just make a off set bracket for the thread dial ! having a 3/16" to 1/4" window would be so much easier for me to do ! LOL......)
......
Now I know why this old tony always makes such large gutters for his threading videos ...... ! LOL
.... I think a big part of it is just getting to know the machine..... I've never had a REAL lathe before just a 3 in 1 from Harbor freight and it has no threading ability at all.... but I am a Mechanical appratious lover ! the more bells and whistles on it the more I like it !
I've been a motorcycle mechanic 90% of my life and there were times when I would have given my left leg for a lathe like this.... it is as old as I am
it was manufactured in 1952.... the same year I was born ! how is that for irony ? HAHAHAHHA
.....
I am leaning toward brazing the old gear rather than using the other gears that are slightly larger... I don't want to modify this Old iron....its too good for that ! although I am not real happy with the Metal-flake green paint job..... eventually I think I will paint it grey
a good grey will hide the oil and mess.... as I oil that thing every time I use it ! and it's starting to drip everywhere ! LOL.......
that reminds me I'm getting quite a pile of shavings behind the lathe now I should clean it up !
LOL !
......so... braze the gear and make a larger threading dial ..... easy peezy !
later all !
Bob.........
 
Just a check, you do use a fishtail gauge to ensure the tool bit is exactly at 90' to the work?

Center gauge - Wikipedia

en.wikipedia.org en.wikipedia.org
And I have had threads that tear when cutting when the steel rod was a bit suspect ie, reo bar or similar.
 
I probably missed some things so I will relate some of my threading problems that I "missed" here. The first is my Armstrong tool holder being tightened in the lantern tool post so it cannot turn horizontally as the cut gets deeper. Second is the regular cutting engagement lever interfering with the engagement of the half nuts? Third in your first thread you said you were going to cut a 1/2" x 12 TPI thread then later you said the nut would not start; correct me if I am wrong but I believe the TPI for 1/2" National course threads is 13. YOU HAVE LISTED EVERY PROBLEM I've had in threading and I have done what the guys here have suggested to improve my threads; use the back gears, keep the spindle speed slow. a really sharp 60` cutting tool set at the center of the work. and shallow cuts
Have a good day
Ray
 
Howdy guys !
Savarin...... well no i don't use a fish tail gauge.....don't have one !
and I ground the cutter by guess and by golly but I am sure it is very close( famous last words right ?)

Ray....... HAHAHAHA well you know....that may well be why the nut don't fit on the thread I made !!!!!!
I'll try it again with 13 TPI thanks ! ( very tactfully stated I must say .... I'm thinking..... hay stupid your trying to put the wrong nut on there that's why it don't fit ! HAHAHAHHAHA

My Machinery's hand book burned up in the Ranch fire darn it... and I have not had the funds to buy a new one yet.... i can't check those things very easily..... it would make a dandy locking nut on that rod ! for a one time use ! LOL......thanks Ray !

later guys !
Bob......
 
Once thread cutting is started do not take the lathe out of gear, remount the work, or make any changes to the cutting tool. You will lose synchronization.

If you do have to make a change, it is possible to resync the lathe. To do so, I engage the half nut and run to the previous cut with the cutter backed away. Stop the lathe and move the cutter into the groove using the compound and the cross slide to position it. When you are satisfied with the fit, make a trial pass with the cutting tool just touching the work to verify the fit. Reset your cross feed and compound dials and continue to cut the thread.

I had noticed the 12 tpi but there actually is a 1/2-12tpi BSW (British Whitworth) thread. I cut some very nice 3/8-18 threads in stainless instead of the required 3/8-16 tpi one time (I attributed it to my momentary loss of sanity :rolleyes: ).

If you peruse eBay, you will find perfectly usable used Machinery's Handbook's for less than $20.00.
 
LOL Yah I learned that real quick..... if you take the part out of the lathe you'ed best call it done !!!!!
I discovered that the steel I was practicing on was very very soft almost pot metal ...and it's ripping out the threads ...so I need a different practice hunk of steel....
the plastic PVC pipe idea works good for 3 or 4 passes.... but when you get close to crowning the thread it seams **** happens ! dunno what's up with that...... I think I was only using the cross feed on that and that may well be why..... I have stopped doing that and use the compound to advance the thread depth.
I turned out some fairly decent looking threads last night ( left handed threads) ..... the secret I think is going extremely SLOW ! at least for this old man anyway !
.....
yah I'll get a machinery's handbook soon I hope.... but keeping warm is more important right now ! being poor sux !
later !
Bob......
 
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