Electronic Lead Screw

GunsOfNavarone said:
@bcrosby you can input your lead screw value of 8 tpi into the setup and you would want 1:1 ratio since you are using the Clough ELS. A large stepper motor probably isn't a bad idea from my experience and whatever that stepper is, you can adjust it's steps in the stepper driver setup. I thik his setup is pretty versatile. I also think there is a Clough specific thread you may want to post on as this one is more for the OP's journey to his very different setup. Search for Clough42 and it should be one of the 1st hits.
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Guns, there are two threads titled Electronic Lead Screw. The one by greenail, started in Jan., 2019, was not Clough specific although the vast majority of Clough42 related postings are there. This thread was started by ttabbal in Sept., 2019 and is specific to the Clough42 ELS and the PM1127.
 
I've installed clough42 ELS on my PM-1127 and have had it running for the last couple of months. I just need to make the box to contain the electronics, but everything else is buttoned up. I've cut threads but mostly use it to quickly change feed rates to get better finishes. I've had no issues with the stepper handling the cuts the lathe is able to do. If you need any info or pics just ask and i'll post them.

Cheers
Michael
 
I'm happy to help with questions on integration with the PM1127. It sounds like the gear ratios might have changed, but that can be adjusted for in the code.
 
Thank you SO MUCH for your input over the past few hours! A gentle reminder why this is such a great forum!

Your feedback confirms the change in gearbox ratios. This simplifies calculations for the programming phase of the project. My thoughts at the moment are to take a couple of unique steps in my build.

The first is to actually replace the spindle gear with an M3 pulley and drive the encoder 1:1.

The second is to experiment with a direct connection between my stepper motor and the gearbox input shaft. My stepper motor is 8.0 Nm (1,133 oz-in). I might try driving it 1:1 through the gearbox, though more likely I'll try driving is 2:1. That would give me more torque as well as RPM. I can always retreat to a belt drive if that seems advisable.

I have everything mocked up on the bench at the moment and I'm very pleased with its performance. As usual, I welcome any input anyone might have to offer. I'll keep you informed as the project progresses.

Thanks again!
 
bcrosby said:
I know this is a very old thread, but I'm hoping to revive the conversation. I also have a PM1127-LB and am in the process of installing the Clough42 ELS. I took delivery on my lathe in March of 2020.

I have been researching gear ratios on my lathe and am finding a VERY DIFFERENT reality from some of you. My lead screw is 8 TPI. With the gearbox in position "A", my gear ratios for both the lead screw AND the drive shaft are 1:1. With the gearbox in position "B", my gear ratios for both the leadscrew AND the drive shaft are 1:2. And, with the gearbox in position "C", my gear ratios for both the lead screw AND the drive shaft are 2:1. Does anyone elses experience match mine?

I'm also curious what other's experiences are regarding the sizing of your stepper motor. Has anyone tried a larger stepper motor set up as a direct drive to the gear box input shaft? If so, what did you choose for sizing?

I'm not to the point where I can take pictures, but when I get there, I'll share my experience.

Thanks in advance for anything you can offer . . .
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Hi bcrosby,

I just finished the Clough42 ELS on my PM1127-VF-LB lathe and my lathe is the latest version with the updated pulley system same as yours, I thought the same thing as you about the gear ratios, mine are also 1:1 on both the lead screw and the feed screw.
But, here's the problem, the gearing in the carriage is not the same as the lead screw, if I set the ELS for a feed of .010", the carriage only moves .006" per revolution.
So, I used the "#define STEPPER_RESOLUTION_FEED STEPPER_RESOLUTION * 1.66" (as mentioned by ttabbal) and it solved that issue. Now it feeds at whatever rate I set it at (within a tenth or two).
BTW, the ratio for threading was spot on when I programmed it for an 8 TPI lead screw!

It's an easy fix but if you're not aware of the issue, it can cause you to scratch your head a few times! Lol :)

Best of luck!!

Joe
 
I'm in the process of installing and modifying the Clough42 ELS on my lathe. One enhancement I really want is a limit switch. I'm not a programmer - beyond VBA excel macros I write for my work, I get a little lost. I've done some other minor modifications to the code, but I'm stuck on how to handle GPIO with the TI board. I find the documentation difficult to digest. Can anyone point me in the right direction? Which GPIO inputs should I be looking at? Ideally I want a simple switch against a GPIO pin, so either ground or 3v, then be able to pick that up in the code to set enable to false. Am I on the right track?

Thanks.

edit: spending a little more time looking at the code (procrastinating instead of working) I'm beginning to understand the GPIO situation a little better. I'll be interfacing via the booster board and hook into one of the GPIO pins on that header. To be honest I'll probably end up re-using the stepper alarm pin, as I can't really see myself using a stepper alarm (especially with all the built-in security of the recent Clough42 updates).
 
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I tried a limit switch in my 602 using the enable function on the driver. It worked OK but I realized that if you disable the stepper, you lose any synchronization with the spindle, the same as you would if you disengaged a gear in a standard lead screw drive. This makes it unusable for threading. It would function for power feed though. One peculiarity that I noticed was that if the driver was disabled and then enabled, it would start up a random speed and direction unless the driver was shut off before enabling. I suspect that this is due to the timing sequence requirement of the enable, direction, and pulse.

As I recall, the ELS functions by counting total pulses from the encoder to determine the spindle orientation and uses that information to determine lead screw position and orientation. Theoretically, with a suitable homing reference, you should be able to set the ELS to set the feed to zero upon hitting a predetermined point. You wouldn't be able to disengage the half nuts though.

@greenail uses a different strategy for his ELS and I believe that his design is capable of moving to a limit. You might want to check his Electronic Lead Screw thread out. It is a lengthy thread and you might want to start around post 465.
 
Thanks, will check out that thread. I hadn't thought about losing sync on a thread using a limit switch.... I wonder if I could code my way around that. Tough problem.
 
Just a thought, the rotary encoder I'm using (and probably all/most rotary encoders) has an index pulse. If you modified the code to always start operations at the index pulse, would you always stay in sync, even with a limit switch disabling the stepper drive arbitrarily?
 
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