NEWLY-ACQUIRED JET 1236PS

[Steggy]

China is ready to take over Taiwan.

...and I'm ready to go on a date with Jeri Ryan. Doesn't mean it will happen.

[spro]

We were commenting about your lathe. We share that experience. If lefty, your chuck will spill out and score the bed.

[liveaboard]

Lefty Righty China Taiwan... getting into forbidden territory!

[Steggy]

Lefty Righty China Taiwan... getting into forbidden territory!

Sometimes spro blathers...

[Steggy]

I had one of those. The spindle nose thread was a bastard thread, something like 63 mm diameter x 8tpi. Check before you spend money on 2-1/4 x 8 tpi tooling.

I have one as well.

I believe it's 60mm x 8 tpi.

The lathe's documentation is correct. It is indeed a 2-1/4" × 8 TPI spindle. See below.

Dial Caliper Reading

Threads per Inch Reading

[GlennW]

That's a good thing!

[Steggy]

That's a good thing!

Yep! Beats trying to find things to fit an oddball spindle.

The vendor from which I got the collet chuck and backing plate was playing doubting Thomas when I said it appears the backing plate has a bad bore. I sent him the hi-res versions of the above photos, which should convince him to replace the backing plate.

[Harold_V]

I sent him the hi-res versions of the above photos, which should convince him to replace the backing plate.

Hmmmm. That just may backfire on you. The image seems to indicate that the lead is not correct. Being 8 pitch, each thread should intersect the 1/8" lines on your ruler without gaining or losing. Unless it's an optical illusion, it appears that's not the case, and would easily explain why a proper pitch doesn't fit all the way.

How loose are the fittings that go all the way? Do they start out loose, then get somewhat tighter as they advance? It's entirely possible that there has been compensation for a less than ideal lead. Crazy as it may sound, the thread indicates it may be 3mm pitch, not 8 pitch.

H

[Steggy]

I sent him the hi-res versions of the above photos, which should convince him to replace the backing plate.

Hmmmm. That just may backfire on you. The image seems to indicate that the lead is not correct. Being 8 pitch, each thread should intersect the 1/8" lines on your ruler without gaining or losing. Unless it's an optical illusion, it appears that's not the case, and would easily explain why a proper pitch doesn't fit all the way.

You are seeing the effects of the camera being set in "macro" mode in order to get the close-up—the lens was about two inches from the subject. Depth-of-field distortion, which is due to the relative focal length being longer near the edges of the image as compared to the center of the image, becomes pronounced at such a short distance.

How loose are the fittings that go all the way? Do they start out loose, then get somewhat tighter as they advance?

The backing plate in question runs on to the threads almost all the way and then abruptly stops. If it were a thread pitch mismatch I would expect the backing plate would gradually become tighter the further it was advanced on the spindle. I've got two other backing plates that were specified as having 2-1/4 × 8 TPI bores, both of which fit the spindle.

Here's another image of the thread measurement. It's a little washed-out, exposure-wise, but has a little less depth-of-field distortion.

Spindle Thread Pitch

[Harold_V]

So the optical illusion won the battle!
I'm not a fan of threaded spindles, and this is a good example of why. I'm also known to reverse my machine under adverse conditions. Not a problem with my Graziano, as it has electromagnetic clutches and a D type spindle. A real problem when one has a threaded spindle, but one simply works accordingly. No big deal, really.

Mean time, good luck with the machine and the replacement faceplate.

H

[liveaboard]

Since I went to a VFD, the chuck pretty much stays put when reversing; the vfd slows down and reverses much more gently than a paleolithic motor.

[Steggy]

So the optical illusion won the battle!

'Fraid so.

I'm not a fan of threaded spindles, and this is a good example of why. I'm also known to reverse my machine under adverse conditions. Not a problem with my Graziano, as it has electromagnetic clutches and a D type spindle. A real problem when one has a threaded spindle, but one simply works accordingly. No big deal, really.

I'm no fan of them as well. When I put a chuck, face plate or other attachment on a threaded spindle, I give it a good spin with my hand to make it seat hard against the spindle shoulder. Fortunately, I've never had anything unscrew itself from the spindle. That said, I'm cautious about reversing a lathe with a threaded spindle. I have no desire to study chuck ballistics.

Mean time, good luck with the machine and the replacement faceplate.

The vendor is taking their time about righting this problem. I bought it through their eBay store, which means I could get unpleasant about it if they don't soon respond to my request for an exchange. eBay vendors don't like it when they get neutral or negative reviews.

Since I went to a VFD, the chuck pretty much stays put when reversing; the vfd slows down and reverses much more gently than a paleolithic motor.

A VFD conversion is planned for this lathe. It will address the risks of snap-reversing (technically, "plugging" the motor), as well as the need to fiddle with V-belts to change spindle speeds.