is 12 tpi an issue ??

R

rsmithsr

Well-known member
i have had no issues cutting 16.18.20.24 tpi, but have had 3 failures trying to cut
12!

every time i get a 180 out second thread
wtf
i engage at what i believe to be the same spot.
lathe has a large dot, and i engage as it hits the spot
actually using the same "number"
thanks
 
Try cutting it

rsmithsr said:
i have had no issues cutting 16.18.20.24 tpi, but have had 3 failures trying to cut
12!

every time i get a 180 out second thread
wtf
i engage at what i believe to be the same spot.
lathe has a large dot, and i engage as it hits the spot
actually using the same "number"
thanks
Click to expand...

Leaving the half nut engaged, advancing and retracting with the carriage under power. Peopled do this when doing metric threads on an imperial machine.

Pete
 
doing this upside down, cutting out(left to right) in reverse.
on return how do i do get back to START without crashing tool?

Pete Wass said:
Leaving the half nut engaged, advancing and retracting with the carriage under power. Peopled do this when doing metric threads on an imperial machine.

Pete
Click to expand...
 
Sounds like a machine-dependent thing...

rsmithsr said:
i have had no issues cutting 16.18.20.24 tpi, but have had 3 failures trying to cut
12!

every time i get a 180 out second thread
wtf
i engage at what i believe to be the same spot.
lathe has a large dot, and i engage as it hits the spot
actually using the same "number"
thanks
Click to expand...

Sounds like a machine-dependent thing, but I'll relate this in case it helps. Some years ago I was trying, in vain, to thread something with a very fine pitch (36ish, the details elude me) and could not for the life of me figure out why my threads were failing. To make it worse, my eyesight wasn't helping, so it wasn't immediately apparent that at some point the thread was being split... I don't recall the particulars (other than 2-3 unsuccessful attempts) before I (re)discovered that my lathe has a "fine" and "course" thread selector lever. Most of my threads (24 or more course) were "course", so I had long forgotten the purpose of this lever that I never touched... Upon rediscovering said "feature" all was well with the world, except my self-image as one who remembers things...

GsT
 
Here's how I do it

I also cut upside down and backwards. Once the tool completes its cut, stop the lathe, back the tool out and reverse the direction of the lead screw back to where you began. Reverse the direction of the lead screw or feed, advance the tool for the next cut. There are Youtubes on doing this that you can watch. it helps if you have a jog feature on your lathe. Joe Pi has a good one.

Pete
 
Gene,
the 16/18/22/24 tpi are all " fine" or "b" gear, the 12 is a coarse or "a" gear.
but
"a" is also used on 32 thru 56 tpi
GeneT said:
Sounds like a machine-dependent thing, but I'll relate this in case it helps. Some years ago I was trying, in vain, to thread something with a very fine pitch (36ish, the details elude me) and could not for the life of me figure out why my threads were failing. To make it worse, my eyesight wasn't helping, so it wasn't immediately apparent that at some point the thread was being split... I don't recall the particulars (other than 2-3 unsuccessful attempts) before I (re)discovered that my lathe has a "fine" and "course" thread selector lever. Most of my threads (24 or more course) were "course", so I had long forgotten the purpose of this lever that I never touched... Upon rediscovering said "feature" all was well with the world, except my self-image as one who remembers things...

GsT
Click to expand...
 
Threading 12 tpi

I generally thread upside down and away from the chuck with carbide around 240 rpm. A while back I was threading a Mauser the same way and the lathe wanted no part of that 12 tpi. I have no idea why, same setup as everything else, but it wanted to chatter to no end. Adjusted speed with same result. I changed threading tools to ground hss, re-aligned the thread, lowered rpm and cut towards the chuck...... Not chatter at all.

Sometimes things just don't work for whatever reason. I'm sure there are several solutions: heavier lathe, better inserts, vfd, etc. but i didn't want to experiment any longer than i already had.
 
lathe weighs 2000 pounds
3 phase 220
aloris tool holder/ tiN COATED carbide pre ground

as stated it does use a diff gear than the 16 and on.
 
I don’t think I have ever seen a lathe with an Imperial lead screw that would not catch a 12 tpi or any even number thread, on any number or any letter.
 
Mine is troublesome

I went to keeping the nut engaged because I sometimes was unable to engage the half nut when it needed to . I've had it apart a couple of times trying to see why it is problamatic but saw nothing wrong.

Pete
 
Last edited:
technically correct jackie.
4 numbers, 4 hash marks, the book says any of the 8 work.
real life did not work out that way.
as was pointed out my low thread counts are on a different gear than the common 16-24's.
i think that is the issue. it did cut 12 when left in gear, but cut 2 different 12's when re-engage was used.


jackie schmidt said:
I don’t think I have ever seen a lathe with an Imperial lead screw that would not catch a 12 tpi or any even number thread, on any number or any letter.
Click to expand...
 
ycl-1440 gh
birmingham
from cp tools

than and no replacement bulb for the halogen work lite are the first issues.
 
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