# Coarse threads on a 9 x 20 lathe

• posted

I've got a Grizzly 9 x 20 lathe and need to cut some threads at 4 tpi. Any thread charts for this lathe I've got only go down to 6 tpi. Question is, can I cut 4 tpi on this lathe? And what gears do I use? Has anyone done this? FWIW, when cutting coarse threads I use a hand crank to turn the spindle. TIA, Paul

• posted

"Paul" fired this volley in news:kS4dl.26289\$ snipped-for-privacy@en-nntp-01.dc.easynews.com:

So, what's the prob. with using the backgears, and turning under power?

Sure, you can turn that, if you have the gears to make the ratio.

You know the pitch of your leadscrew. You know the number of teeth on your spindle gear. You can do the rest of the math yourself.

Just make sure everything is lubed well, and the gears aren't too tight on clearance, since your lead screw will be turning faster than your spindle.

Also, you'll probably have to custom-grind a single-point tool to make up for the geometric changes when that high a slope in the screw is called for. Remember, a level tool cuts narrower than its width in a sloped cut.

You'll either have to adjust the attack angle or side-rake on the tool to cut approximately square in the thread, or adjust the included angle of the point wider. I haven't done the trig for you, but expect the included angle on the point ought to be more like 70 degrees than

1. The side-rake solution is cleaner, because then you can control the back rake more easily.

LLoyd

• posted

One way to do it is to get a set of gears that will give you a 1:2 ratio and put them into the geartrain for the feed. Run the thread pitch setting on the lathe at 8 tpi. I don't know what gears you have to work with but you could also decrease the diameter of a driven gear by 2 or increase the diameter of a driving gear by 2 and get the same result.

John

• posted

Well, Jeese, you guys made me have to actually think. There's a concept. I'm so used to just looking at the threading chart then slapping this gear here and that gear there, I forgot what was actually going on. Thanks for the headslap to bring me to my senses. Got it figured out. I'm happy Paul

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• posted

I would be surprised if Grizzly 9x20 has backgears. Their lowest speed is usually in excess of 100 rpm.

• posted

"Michael Koblic" fired this volley in news:gl3b5p\$k5\$ snipped-for-privacy@news.motzarella.org:

Whew! I hope that's not the case. But, if it is, then that's the genesis of "yet another project". A lathe with threading capability has GOT to have back gears! Got to! (damn! I'll MAKE the backshaft!)

LLoyd

• posted

My daily driver lathe doesnt have any backgears at all. Just a two speed motor.

And the reeves drive variable speed.

Course it is a Hardinge HLV-H......

Biggest problem I found with it is that it wont thread bigger than 11 tpi. No way to do it either.

Course on the other end...IRRC..it does thread down to 120 tpi.... And Metric.....

Shrug

Gunner

Whenever a Liberal utters the term "Common Sense approach"....grab your wallet, your ass, and your guns because the sombitch is about to do something damned nasty to all three of them.

• posted

Yup. No back gears. Slowest speed is 130 rpm

• posted

Maybe this will help some for the next time: