Genuinely beautiful Stel.
Just curious, did you notice any difference in the swarf as you traversed the length of the screw from right to left - not initially, but as you finished up?
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Cross-Slide Leadscrew & Nut
- Thread starter thestelster
- Start date
Genuinely beautiful Stel.
Just curious, did you notice any difference in the swarf as you traversed the length of the screw from right to left - not initially, but as you finished up?
Ok, the acme threads are done.
Pitch diameter is 0.646" and consistant throughout the whole length of the thread by less than a thou'.
I had to readjust the jaws of the follow rest because I was measuring a greater dimension in the center vs the ends. I guess the bronze jaws were wearing slightly.
I cleaned up the OD with 400grit sandpaper backed on a 2" wide sharpening stone.
And I just saw that I need to chamfer the corners of the thread, 0.0945p @45° which comes to 0.019" so I'll do that after lunch.
Pitch diameter is 0.646" and consistant throughout the whole length of the thread by less than a thou'.
I had to readjust the jaws of the follow rest because I was measuring a greater dimension in the center vs the ends. I guess the bronze jaws were wearing slightly.
I cleaned up the OD with 400grit sandpaper backed on a 2" wide sharpening stone.
And I just saw that I need to chamfer the corners of the thread, 0.0945p @45° which comes to 0.019" so I'll do that after lunch.
Attachments
Thank you.
It's funny. When I started the threading, going in at 14.5°, the resulting thread looked pretty ragged, and I had to knock off the leading edge burr every pass so that the jaws of the follow rest wouldn't affect the cutting process by pushing the screw towards the cutter and downwards, and so the burr wouldn't cut into the bronze jaws. On that last part I've read where the thread can cut deep enough into the jaws that when you disengage the half-nuts, the carriage wants to continue. That's why I decided to stop the lathe at the end of a pass, then disengage the half-nuts, and back out the cutter. With the braking resistor, and cutting at the lowest high gear, but turning the VFD down to 15hz, it stopped instantly.
But as soon as I rotated the compound to parallel, it cut like a dream.
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Awesome Tell!
Your comment about adjusting the follow rest answered my question. You actually measured it and I was just wanting to infer that by looking at the swarf.
Rigidity or angle of attack or both?
Nice work!
Your comment about adjusting the follow rest answered my question. You actually measured it and I was just wanting to infer that by looking at the swarf.
Rigidity or angle of attack or both?
Nice work!
Going in at 14.5° you're cutting at the nose, which is pretty wide, and the flank. While at parallel, you're only cutting at the flank. Maybe if I ground the nose of the cutter to a greater clearance angle, it might have helped?
Unless it was high and rubbing, I doubt it. And knowing you the wee bit that I do, it wasn't rubbing.
Thinking a bit more about it, I'd bet on both. When you are cutting on the nose, there is pressure against the follow rest which wasn't solid - rigidity and angle of attack both working against you. When you are at parallel you are only cutting toward the chuck which is pretty solid and follow rest isnt really needed - rigidity and angle of attack both helping you.
Since you had to cut sideways anyway, it might have been interesting to see what happened if you had used a narrower nose.
Well, toward the tailstock (left hand thread), and the threaded section is almost 11" long, and I had to have several more inches sticking out past the chuck to allow clearance for the follow rest. 3/4" bar, so thats a 17:1 L/D ratio.
Yes, that's why I ground the hss tool to around a 7tpi instead of 5tpi, to provide less load on everything.
Ah yes, I forgot the LH thread.
But wouldn't that be less important when you are only going parallel to the work toward the tailstock? And besides, that is only worst case.
And besides that, the only reason I discussed this was to try to answer your comment
I think it's just the fact that the follow rest isn't really needed when you are not plunging at all
I was thinking of something really small like a 16 tpi tip.
How did that job make your priority list? NM. I'll guess it has SWMBO origins.
Again, looks real good. What make is your threading insert/shank?
Another tool to consider for thread relief & other grooving jobs is parting tool shanks where you can mount various insert nose profiles. They can be rectangular like what you have, or you can also get full round to avoid sharp inside corners or O-ring grooves etc. Or they make leading angle one way or another so the part 'finishes' on one side or another. The ones I have are AliExpress. I believe the inserts/shanks come in metric blade increments like 1.0 1.5.. mm.
The tool is Sandvik. The 18tpi is full-form topping Sandvik, and the 20tpi is..can't remember.
Usually I use my partingtool to do reliefs, but its 1/8" wide. Fine for coarse pitches and larger diameters and longer thread sections, but seems disproportionate for small diameters and fine threads.
I've been meaning to get some grooving tools but never seem to remember to order them.
I just use HSS parting blades. They come in a variety of widths and work great for making thread reliefs. You can even use a thin one to make a wider relief. I know it's sacrilege but if it works, it works.
I use them too, but they don't have their dedicated tool holder, so I would have to get spacers to go underneath, and then adjust tool height, and, blah, blah, blah.
Let me rephrase that.
Hmmmmm..... Sounds like a damn good excuse to spend some money and go buy one! I'd suggest making one but I wouldn't know how to tackle that.
Might be up your alley to make a dozen of them.......
Na, just buy a half dozen. I'd only make one if they didn't already have what I want.
Yes, it does feel good. Of course after spending almost an eternity making it, I've come to the realization that I could never be a real machinist. Or at least not a profitable one!