QCTP too tall

[WobblyHand]

I'm learning about small lathes by reading this thread. It never occurred to me that they would lack that reversing feature. I've made left hand threads by accident by selecting the wrong gear lever. Did that when I was first learning to thread. As has been suggested, get some cheap material to practice on. I've got a variety of tooling and for many things I still prefer HSS. my tool holders accept 5/8/ 16mm tooling and 3/4 /19mm with XL holders. But I don't use the biggest HSS I can get into them because it takes too much grinding compared to 3/8". Easy to make any shape I want. Easy to sharpen, cheap!
My first experience with an unknown stainless was a disaster. I didn't go after it aggressively enough and work hardened it.

I learned about the reversing issues from reading on this website. I solved the problem by making an ELS. My first thread on the ELS was a left hand thread, since I had a 50/50 chance at getting the rotation direction correct. Flipped the rotation sense, and all was good.

 

[Larry$]

I solved the problem by making an ELS.

That seems like a neat idea. Are there any limitations on thread pitch? I.E. can you do barrel riffling? Multiple start, very long pitch. I know nothing about either.

 

[WobblyHand]

That seems like a neat idea. Are there any limitations on thread pitch? I.E. can you do barrel riffling? Multiple start, very long pitch.

Thread pitch is not limited by the ELS per sue. It's more limited by spindle speed and torque. I didn't design my ELS for barrel rifling. I'm sure there's some significant tradeoffs, but I've not reviewed them as my application was different. For any pitch, there's a ratio between the spindle angle and the lead screw angle. Need a different pitch, it's just a different ratio. Or at least that is how I implemented it in my software. My code is independent of spindle speed, but obviously one needs to take into account the limitations of one's platform, be it your spindle drive, or the encoders you chose.

It's very possible to do multi start. In full disclosure, it's on my to-do list, but I haven't made much headway on it, due to dealing with life's distractions. I have nearly all the information necessary to implement it since my ELS is connected to my DROs as well as a spindle encoder.

A multi start simply means an advancement of the spindle angle relative to the previous spindle angle at the start of the cut (with the same pitch ratio). It can be implemented several ways, but I have yet to figure out which one will be easier to implement without tearing up all my previous work.

Pitches like a barrel correspond to a very high amount of lead screw movement as compared to spindle movement. On my lathe I don't have a back gear, my minimum spindle speed is 100 RPM. The carriage speed would be frighteningly fast. I'd want to put it both hardware and software safety stops to avoid high speed crashes. Or I'd do that and modify the spindle drive to run at 1 RPM! I'd also need to review my stepper characteristics to see if it could deliver the required torque at that step rate.

So theoretically possible, but it probably requires a whole different set of requirements on the whole system as compared to simple feeding and threading. I can tell you from experience that 4TPI is awfully fast and scary at 100 RPM near a hard stop, like your chuck. Really have to be on your game that day!

 

[chris.epp]

You should be aware that unless your lathe has a reversing banjo, you can't cut left hand threads. The G0602 doesn't have that feature nor does the King 10x22. I built one for my lathe and have since added an electronic lead screw which has a reversing drive for the lead screw. However, both of these solutions require skills beyond a beginner level and access to a milling machine.

Ya so just learned that.. there is a reverse but that is just motor reverse. What's the purpose of having that itself? Can't imagine you want to cut backwards flipping a bit. Just to back out the carriage under power? ELS looks like a big project. I guess I'll have to work out a reverse. There is someone selling ready made ones on ebay. It's what looks like a simple one that uses existing gears but you habe to install and change, not like the nice ones you switch with a lever. I do have mill access as well but I am trying to find more info on this other type. Expensive shipping though.

 

[Larry$]

So theoretically possible, but it probably requires a whole different set of requirements on the whole system as compared to simple feeding and threading. I can tell you from experience that 4TPI is awfully fast and scary at 100 RPM near a hard stop, like your chuck. Really have to be on your game that day!

I can see the problem with the rifling idea and spindle speed! My lathe's slowest is 40 rpm and I have cut 4 tpi but always away from the chuck.
Grinding an Acme tool turned out to take more tries than it should have. I have yet to try an internal Acme thread.

 

[Ischgl99]

Ya so just learned that.. there is a reverse but that is just motor reverse. What's the purpose of having that itself? Can't imagine you want to cut backwards flipping a bit. Just to back out the carriage under power? ELS looks like a big project. I guess I'll have to work out a reverse. There is someone selling ready made ones on ebay. It's what looks like a simple one that uses existing gears but you habe to install and change, not like the nice ones you switch with a lever. I do have mill access as well but I am trying to find more info on this other type. Expensive shipping though.

Metric threads. You need to keep the threading half nuts engaged during the entire process, so you need to reverse the spindle direction to get back to your starting point for your next threading pass.

 

[chris.epp]

Metric threads. You need to keep the threading half nuts engaged during the entire process, so you need to reverse the spindle direction to get back to your starting point for your next threading pass.

I was wondering if there are metric thread indicators like the imperial one so that wasn't necessary. I think the reverse function would be more a priority. Blondihacks had what looks like a cool suggestion for cutting threads backwards, from left to right so your timing is not as crucial for stopping potentially, would be nice to have both directions to turn it seems like. (Coming from no experience of course but in my head it seems handy. So the nicer lever change would be ideal instead of the easier option I posted above which I think takes some effort to switch back and forth.

 

[Larry$]

Joe Pie also has a good video on cutting threads. Straight in and away from the chuck. Makes prefect sense.

 

[WobblyHand]

I was wondering if there are metric thread indicators like the imperial one so that wasn't necessary. I think the reverse function would be more a priority. Blondihacks had what looks like a cool suggestion for cutting threads backwards, from left to right so your timing is not as crucial for stopping potentially, would be nice to have both directions to turn it seems like. (Coming from no experience of course but in my head it seems handy. So the nicer lever change would be ideal instead of the easier option I posted above which I think takes some effort to switch back and forth.

If you have a metric lead screw it is possible, but to do all the threads you need additional gearing or wheels. These extras are usually quite hard to find.

If you have an imperial lead screw, basically it won't work. Technically it could be made to work, with all sorts of sensors, math and computation up the yingyang, but that's the work of a pretty good ELS system. At the moment, even with my own ELS, cutting metric threads requires me to leave the lead screw engaged at all times. I have an imperial lead screw. I haven't solved the math problem yet. It's tantalizingly close, I can feel the answer, but still haven't worked it out. At least for me, handling the modulo stuff, the ratios, various angles, and sensors has been difficult to grasp the total necessary and sufficient conditions. I really need to spend a few days on just this - to work out the details. Bet it isn't quite as hard as I'm making it out to be.

 

[WobblyHand]

I can see the problem with the rifling idea and spindle speed! My lathe's slowest is 40 rpm and I have cut 4 tpi but always away from the chuck.
Grinding an Acme tool turned out to take more tries than it should have. I have yet to try an internal Acme thread.

At the time I cut the 4 TPI threads, I hadn't learned about threading away from the chuck. Even so, at 4 TPI, the carriage moves a quarter inch in one revolution. That's quite fast. Now consider carriage travel of 10 inches, or 30 inches in one revolution. Unless you have physical hard limit switches to protect you, you'd have to reduce your spindle RPM to very low values to avoid crashing in either direction.

60 RPM is 1 rev/second. At 30" twist, the carriage would move 30" in one second. 30 IPS on essentially a manual lathe, umm, no thanks. So at least for me, the RPM would need to be under 10. At 10 RPM and 30" twist, that's still 5 IPS and quite fast, at least for me. Of course, if you have lightning reflexes, have at it!