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JET 1240PD
- Thread starter WiscoF100
- Start date
Depends on a few things like who you listen to, what material you're threading, depth of cut, the tool you're using and the power and rigidity of the lathe. If I'm threading 12L14. 1215 or 360 free machining brass on my bigger (3 hp) lathe it doesn't matter. Threading 4140 or tough mystery metal, 29.5° is better. On my little lathe (11x26, 1 hp) I have re-cut existing threads going straight in but it's happier with the compound set at 29.5°. Also, threading small diameter stock works best at 29.5° as it reduces the pressure on the stock.
An additional benefit of adjusting with the compound is that you don't mess with its position when you retract the tool with the cross slide. Just set the cross slide to 0 and after you back out and go back to the starting place, go back to 0 every time. Advance the tool with the compound slide.
An additional benefit of adjusting with the compound is that you don't mess with its position when you retract the tool with the cross slide. Just set the cross slide to 0 and after you back out and go back to the starting place, go back to 0 every time. Advance the tool with the compound slide.
- Joined
- Mar 30, 2024
- Messages
- 23
@David2011 what are your thoughts regarding the initial scratch pass inaccuracy? Tried another one just a bit ago, checked with the gauge and after the 4th tooth it goes astray. Maybe a mechanical issue causing an in-synchronous travel?
I verified the change gears to be correct for inch threads. Other than (lack of) lots of practice or tribal knowledge, I seem pretty confident in the base setup.
Out of material for tonight. Will stock up tomorrow. Not going to waste any more grade 8 bolts
I verified the change gears to be correct for inch threads. Other than (lack of) lots of practice or tribal knowledge, I seem pretty confident in the base setup.
Out of material for tonight. Will stock up tomorrow. Not going to waste any more grade 8 bolts
- Joined
- Mar 30, 2024
- Messages
- 23
That was one of my going to sleep thoughts, Thanks! Didn’t know if it was a silly idea or not. I’ve got a bunch of leftovers I could use.
- Joined
- Dec 3, 2017
- Messages
- 2,158
First time I used threading inserts on steel, I busted 2 out of three tips in about 10 minutes. Then my trainer took over because of course that was our last insert tool. I think it took him about two minutes to finish my threaded part. Argh!
Not sure I have a good answer to the question but I'll ramble about with some thoughts. First, I would try a HSS threading tool whether you have to buy or make it. At least you won't be trashing carbide every time something goes wrong. At best it will just plow through a mistake and at worst it will need to be resharpened. The closeup of the cut threads look a lot like what I did before I understood how to cut metric threads on an Imperial machine.
Don't be offended; do you fully understand the thread engagement chart? Just making sure. My chart is just like yours in that it lists 1-8 but has numbers 1-4.5.
The PVC is a good idea. I see that you're cutting 10 tpi. At this point diameter isn't important. I had to cut 10 tpi on a 3" diameter thread recently. It's no different at 3/4'-10 tpi or 3"-10 tpi. Color it with a marker for good contrast and tell us the results.
Consider cutting a thread that is divisible by 8; either 8 or 16 tpi. 8 tpi will make it the easiest to see inaccuracies. You can (should be able to) engage on any line with threads divisible by 8. If that doesn't result in the tool following in the same path, start on 1 every time just for the sake of troubleshooting.
Could you explain "4th tooth"? Do you mean 4th pass or something else? It's just not clicking in my head.
I just noticed something else. In the very close shot of the scratch pass it looks like you're using a general purpose threading insert. Where you show the boogered threads it looks like you're using a thread pitch specific insert. If the insert is for a different pitch that what you're cutting, that could be a problem. Just by eyeballing, and I know that's sketchy in photographs, it looks like the thread pitch specific insert is for something coarser than 10 tpi. That insert is designed to cut the root and crest profiles when it's at full depth.
- Joined
- Mar 30, 2024
- Messages
- 23
No offense taken from anyone. I’m pretty easy going and I understand details or confusion that may occur in a forum setting. All good
Some vids talk about divisible by 4 and based around the common 8tpi lead screw which I have. Tpi and fractional all have their own tricks and whether or not number matters or half points etc. I won’t give up on this but threading is def above my head for now. I’ll stick to boring, surfacing and facing (which is the other 95% of why this machine is essential to me) My off-road trucks get all proper grip length bolts. Some shoulders off the shelf work for common mounting widths etc but sometimes I like to stick a random LH thread because of the accessibility and force required to install or remove, forces acted upon the fastener or thinking about extraction in the event that even 3/4 and 7/8 bolts get bent during a race.
(Also for giggles I tried 2-4, 4-2, 1-3, 3-1 etc etc. Admittedly for repeat passes, I failed to zero out or adhere to any repeatable infeed procedures. After the failed scratch pass I was only farting around after that)
So here’s a quick and dirty pvc test
10tpi engaged on 1. 105 rpm for all 3 tests
8tpi engaged on 2
8tpi engaged on 1.
***For compound infeed only*** perhaps my 29.5* should be 60*-60.5*???
Some vids talk about divisible by 4 and based around the common 8tpi lead screw which I have. Tpi and fractional all have their own tricks and whether or not number matters or half points etc. I won’t give up on this but threading is def above my head for now. I’ll stick to boring, surfacing and facing (which is the other 95% of why this machine is essential to me) My off-road trucks get all proper grip length bolts. Some shoulders off the shelf work for common mounting widths etc but sometimes I like to stick a random LH thread because of the accessibility and force required to install or remove, forces acted upon the fastener or thinking about extraction in the event that even 3/4 and 7/8 bolts get bent during a race.
(Also for giggles I tried 2-4, 4-2, 1-3, 3-1 etc etc. Admittedly for repeat passes, I failed to zero out or adhere to any repeatable infeed procedures. After the failed scratch pass I was only farting around after that)
So here’s a quick and dirty pvc test
10tpi engaged on 1. 105 rpm for all 3 tests
8tpi engaged on 2
8tpi engaged on 1.
***For compound infeed only*** perhaps my 29.5* should be 60*-60.5*???
Yes! The compound angles on many Asian lathes are reversed compares to US and European lathes. That is not what's causing the pitches to not match, though. It really looks like there is an incorrect gear in the change gear train causing the pitch to be shorter than what is selected.
BTW, I'm envious of your pitch selection. I can't go below 8 tpi on my 13x40.
Don't give up on threading. In our gunsmithing classes the introduction to the lathe included making a mandrel that had a 1.10" x 12 tpi thread; first time most people had touched a lathe. It might be worth pizza and beer or something to get a seasoned manual lathe machinist to take a look.
BTW, I'm envious of your pitch selection. I can't go below 8 tpi on my 13x40.
Don't give up on threading. In our gunsmithing classes the introduction to the lathe included making a mandrel that had a 1.10" x 12 tpi thread; first time most people had touched a lathe. It might be worth pizza and beer or something to get a seasoned manual lathe machinist to take a look.
- Joined
- Mar 30, 2024
- Messages
- 23
Agreed. I counted my change gear teeth but maybe I’m overlooking or do t understand something else. I’ll try to find a local machinist but otherwise I’ve got a cnc proprietor in Utah (he learned on leather belt driven machines in his basement before his cnc shop) and my brother in law is a handy machinist but he lives in Manitoba.
Thanks for everyone’s input.
Thanks for everyone’s input.