electronic lead screw

[RJSakowski]

Watch Part 2 for how he works out the numbers. I'm facing the same issue, made more fun by the additional reduction inside my QCGB.

The correct ratio could be set by changing the lead screw pitch. Since I am driving at 1:1 (same lathe) and James is driving at 3:1, my lead screw will turn at 3x his. If I set the lead screw pitch at 36 tpi, , it will advance 1/3rd as far for each revolution and all should be good. However, this seems a kludgy way to do it.

I know that James ran 1:1 when he ran the stepper and he talked about possibly running other ratios to optimize so I suspect he has a variable for that ratio.

 

[ttabbal]

I haven't looked at the latest code version, but the one I looked at had a steps per rev value. I think that's what you use to adjust for the ratio.

I haven't gotten the stepper mounted yet, so I could be off there.

 

[GreatOldOne]

USB socket added to the control box for easy firmware upgrades. Servo / Hybrid stepper mounted, Control box hung on the back of the lathe, change gear cover modified to fit over the encoder and servo. Oh, and wired in so it all turns on when the lathe is switched on.

What I have encountered whilst testing is I can quite easily get the driver alarm to trigger... depending on spindle speed and thread pitch / feed selected. My lathe has a top speed of 2000rpm, and with the pulley ratio of 3:1 and then whatever the multiplier is for feed - you can quite easily top out the max RPM of the servo. I've just made a chart of max possible spindle speed for a given feed. For the most part, the feeds are fine. it's the thread pitches that can make it go down... but I very much doubt I'd ever need to do any single point threading above a couple of hundred RPM anyway. And the convenience of not having to bugger about with change gears far outweighs the possible need to do a 5 TPI thread at over 1000RPM

 

[GreatOldOne]

I have one question for the group. I have elected to go with a 1:1 drive for the stepper and will need to change the 3:1 ratio. I am having trouble locating where the stepper pulley ratio is defined in the source code. If anyone can direct me, I would appreciate it.

Watch Part 2 for how he works out the numbers. I'm facing the same issue, made more fun by the additional reduction inside my QCGB.

The correct ratio could be set by changing the lead screw pitch. Since I am driving at 1:1 (same lathe) and James is driving at 3:1, my lead screw will turn at 3x his. If I set the lead screw pitch at 36 tpi, , it will advance 1/3rd as far for each revolution and all should be good. However, this seems a kludgy way to do it.

I know that James ran 1:1 when he ran the stepper and he talked about possibly running other ratios to optimize so I suspect he has a variable for that ratio.

I haven't looked at the latest code version, but the one I looked at had a steps per rev value. I think that's what you use to adjust for the ratio.

I haven't gotten the stepper mounted yet, so I could be off there.

Guys - the ratio of stepper to leadscrew pulleys is handled by the micro step value in the config file. It took me a while to work this out and find the video where he explains it again... but if you’re using a hybrid stepper / servo you’re supposed to set this to 1, as they don’t micro step. But he sets his to 3 micro steps as this takes care of the 3:1 ratio he has - as it essentially triples the number of steps sent to the motor.

When I first flashed the firmware to the board and started testing I couldn’t work out why it was turning so slowly... until I realised that it was set to 1:1 rather than 3:1 as I have the same pulley ratio as James. After changing that it seems to be dead on now. Test cuts will show if thats true.

 

[kb58]

Another issue is whether the lathe's gearbox reverses rotation of the lead screw. If so, the servo driver box may have a way to correct that. If not, it means modifying the ELS software.

 

[RJSakowski]

Guys - the ratio of stepper to leadscrew pulleys is handled by the micro step value in the config file. It took me a while to work this out and find the video where he explains it again... but if you’re using a hybrid stepper / servo you’re supposed to set this to 1, as they don’t micro step. But he sets his to 3 micro steps as this takes care of the 3:1 ratio he has - as it essentially triples the number of steps sent to the motor.

When I first flashed the firmware to the board and started testing I couldn’t work out why it was turning so slowly... until I realised that it was set to 1:1 rather than 3:1 as I have the same pulley ratio as James. After changing that it seems to be dead on now. Test cuts will show if thats true.

Great Old One, thanks for that insight. I am using a 1:1 ratio with a hybrid stepper so it sounds like I don't need to make a change.

 

[GreatOldOne]

Another issue is whether the lathe's gearbox reverses rotation of the lead screw. If so, the servo driver box may have a way to correct that. If not, it means modifying the ELS software.

My servo driver has dip switch settings to set the initial rotation direction. I thought I might have to mess with it as the spindle on my lathe is fed by the shaft the encoder is on via a 1:1 spur gear setup deeper in the head stock - so it spins in the opposite direction to the encoder. Seems I lucked out though.

 

[GreatOldOne]

i completed my install with a 3d printed bracket which holds the ELS controls under my DRO display. I designed it to be offset so the cable wouldn’t interfere with the DRO mount, and to pick up the existing mounting holes in the DRO case.

Maybe I can get back to using my lathe now rather than modifying it!

 

[ttabbal]

Nice job! I might have to think about mounting the controls to the DRO display as well. I hadn't considered that.

 

[kb58]

i completed my install with a 3d printed bracket which holds the ELS controls under my DRO display. I designed it to be offset so the cable wouldn’t interfere with the DRO mount, and to pick up the existing mounting holes in the DRO case.

View attachment 306642

Maybe I can get back to using my lathe now rather than modifying it!

Curious how you power the ELS. Is there a separate power switch, or is it on whenever the lathe is powered up? I'm thinking of having both, basically a switch downstream of the lathe breaker dedicated to the ELS.

Edit - which reminds me, I found that the "power" button on the ELS doesn't do anything. I'm guessing that it'll flip an output bit intended to drive a relay. I'd be happy if it just disabled driving the servo, because there's no point in running it if not needed. Easy enough to modify it myself I guess...