ELS Conversion on Weiss 1127

Nice threads!

Your tables for N and D will have to be regenerated or modified. Your screw pushes the carriage faster than mine. My lathe has a 12 TPI lead screw, yours is 8 TPI. So we need to turn your screw slower than I would turn mine.

For a 20 TPI thread, I need to step the motor 15 ticks, for every 128 encoder pulses.
On your lathe to get 20 TPI, the motor must be stepped 10 ticks for every 128 encoder pulses, or basically N needs to be 1.5 times smaller.

Of course N needs to be an integer, but the ratio N/D needs to be 0.66666 (1/1.5 or 2/3) the ratio that runs on my lathe.

Due to the differing lead screws (with the current tables) you will not cut the same threads as I would at 1:1 final stepper ratio. That is the explanation.

That's fixable! I can generate a custom build, but I really should have the sw calculate it for you. Modifying the table by hand is error prone, especially when there's 4 tables and everyone may have a different lead screw. Currently I calculate this offline using a python script. Need to convert that to C. For the moment, I can do a hack, but there have to be a lot of tests and checks in the real code to make sure 1) the ratios are correct and 2) that N and D remain integers.
 
The quick fix is to put in a couple of booleans LS_TPI8, and LS_TPI12. If (LS_TPI8) then multiply N by 2, and D by 3. I can try that. I also can create a command to enter this mode for test.

Longer term, I need to do something better.
 
I've not looked through the sourcecode to see how they do it but both the clough42 and the nanoels projects have a definition for the lead screw for the particular lathe you have. I would guess that would compile these tables for your specific lathe automatically given your parameters. Maybe this type of thing is an option for longer term?

I hope this thread and conversation is beneficial to others looking to add an ELS to their lathe. So far it appears that it's a conversation between the two of us but i hope others chime in should they have any questions or comments.
 
I did write a script to do this in python, which calculated all this. It works for all encoders, microsteps, lead screws (imperial or metric) and can account for one's encoder bandwidth. You can't run faster than your encoder bandwidth - which limits your top speed you can run at. The python code was trickier than I expected, with some weird cases, which seemed hard to test for. I need to port this code to C. Initially my ELS was just for myself and I could get away with an offline generated table. Can't get away with that for a broader audience. So I know what I will be working on...

Yeah, its pretty quiet here. Hope someone besides us gets something out of this...
 
@WobblyHand modified the software for my lathe for an 8TPI lead screw and i was able to test some threading on PVC - 24 TPI and then 13 TPI with a few clicks on the screen. This is sweet!

PXL_20230130_221659133.jpg
 
RE: the weak stepper motor - I have a plan to test the amp draw for the stepper motor but between work being busy and this arctic blast i've had no time in the shed to get readings.
 
Ok - @WobblyHand and i spent some time troubleshooting this tonight. Thank you for your help @WobblyHand. The next step is for me to chuck up a piece of steel and verify i can cut some threads without issues. I think i may have been chasing a red herring and as WobblyHand pointed out to me - if it cuts threads and feeds fine then what's the problem? :)

On my lathe there's a dedicated shaft for power feeding which goes through a gearbox that has very cold gear oil in it. The stepper motor labors less with the lead screw than the power feed shaft.
 
ivel03 said:
Ok - @WobblyHand and i spent some time troubleshooting this tonight. Thank you for your help @WobblyHand. The next step is for me to chuck up a piece of steel and verify i can cut some threads without issues. I think i may have been chasing a red herring and as WobblyHand pointed out to me - if it cuts threads and feeds fine then what's the problem? :)

On my lathe there's a dedicated shaft for power feeding which goes through a gearbox that has very cold gear oil in it. The stepper motor labors less with the lead screw than the power feed shaft.
Click to expand...
You might consider some heater tape on your gearbox, keep the gear oil a little warmer? Operation at sub freezing temperatures does put a higher load on the motor as does your gearbox and cross feed. (I have no idea if there's a winter weight gear oil?) Or put in an additional gear reduction when running through the gear box? There's no free lunch, since the stepper has to go faster, but it may help some. We just need to know the ratio, and apply the factor.

But yeah, if works as is, why not use it? So make the lathe work a little harder and report the results here. If it works, well you are done. If not, we will make it better. Try it out! Have some fun cutting 8 TPI in steel, or take moderate cuts in steel during feeding. Increase the load slowly and see when or if it has trouble. Basically try to characterize the ELS performance with steel.
 
It was much warmer out today and i let the lathe warm up about 15 minutes or so running the ELS at 24 TPI (i think) - i wanted to have the gear box spinning at a medium rate and have the power feed gearbox shaft spin at a medium rate as well. I guess that really doesn't matter when using the lead screw anyhow! :)

It was about 45* out today and while not that warm in the shed it was warmer than when i was testing previously. The lathe performed awesome - i grabbed a scrap of 3/4" rod and threaded a 8 TPI thread on it. I might be able to pull off a 4 but i don't trust myself with the carriage moving that fast. Was 3/4" a large enough piece to test with? I ran the lathe at about 70 -80 RPM as it seemed to go a bit better than the slowest speed of 55 or so. FWIW the manual for my lathe says that it's capable of cutting 8 - 56 TPI threads and .2 - 3.5mm metric threads.

I know the thread form is not perfect but hey, the little lathe did it!

PXL_20230208_215006764.jpg

The ELS works great - so my concerns about the stepper motor power is unwarranted at this time. Even if it is not as strong as the gear set the convenience outweighs the loss of power and also it has a huge advantage - the controller will fault before you break some expensive parts!
 
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Very nice to see, indeed. Hope that makes you feel a lot better about the stepper. I didn't think you would have a problem, but it is good to see, nonetheless. Eventually you may run into the limits - it happens as we get bolder with more experience. For very large diameter pieces with coarse threads, there might be a problem. Most of us don't do that kind of work, or very often. If you find there is an issue doing the big stuff (relative to your lathe capability), you could upgrade the stepper motor, or even go to a servo. For now, since it is working, hope we can call that good. for now.

Yes, 3/4 is fine for 8 TPI, at least for testing. Probably get deflection as you go to full depth. I used 1" diameter for cutting 4 TPI and that was a BIG mistake since the root of the screw wasn't large enough and I was getting major deflection of the work piece well before full depth. I needed a significantly larger diameter for a bigger thread. 1" - 8 is a standard thread, so 1" stock is more appropriate. For 4 TPI, I found you had to go to 2.5"! That's a big screw!

You will get a bigger load if you try your hand at an acme screw, but I have yet to try that.

So for now, you can celebrate a bit and do the happy dance! Congratulations.

4 TPI is fast at 100 RPM, you have to be on your game, since everything is happening quickly. This is why it would be great to implement a DRO based stop. The only issue is it would be good essential to have an alternate backup to stopping. I'd hate to crash at any speed, but a lot of stuff would break if there was a runaway situation with 4 TPI. The DRO stopping is easy in theory, and using imperial threads makes it a piece of cake. Not so with metric, since we have to also store the spindle angle. This is done, but some of the other bits need work. First thing is to come up with a proximity switch that can be the emergency stop. This switch needs to be very repeatable to within a few thousandths. I think there are some that will do this, but I don't know if they are small enough for our sized lathes. The ones I have seen are fairly long.
 
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