Ball Screw Conversion

[grimmindustries]

Hi Guys,
I have removed my pulleys and rigged ball screws onto my Rostock Max.
I've got the hardware done and now I need to make changes to the software.
Anyone know what I need to change in the firmware?

Thanks,
Ron

[Jimustanguitar]

I think you'll have to change your steps per mm. What pitch threads are they? 200 step motors x whatever rotation equals 1mm of movement would be the right answer.

So I'm curious. Did you switch to ACME screws for torque reasons, resolution reasons, or something else? I'll be curious how fast you can make it move without maxing out the stock electronics.

[Polygonhell]

The only thing you should have to change is steps per mm. Assuming those screws are 5mm pitch and you have an RAMBO with 16x uStepping the correct answer would be
16X200/5 =640 steps per mm

You might have issues with the standard electronics not being able to send steps fast enough, if you set uStepping to 2 you'd be close to the standard belt driven settings, your only other option is to step up to better electronics, smoothie would probably be sufficient.

[grimmindustries]

Thanks guys, I'll try those modifications and let you know how it goes.
I made the changes because I was having issues with the pulleys and I'd like to increase my printing speed and accuracy. It was this or I throw the printer out my window.

I was worried that the motors might have issues keeping up but you both think the electronics will be the issue, I guess I'll find out.

Thanks again.

[bot]

Defenestration is never the answer.

[grimmindustries]

Sometimes its the quickest way to reach a destination.

[JFettig]

You're going to have some serious acceleration issues with those large screws, huge rotational mass compared to before. You will end up with lower printing speed because it'll take much faster motor revs to print at the same speed with those screws. Torque rapidly drops off as speed increases with stepper motors.

[grimmindustries]

I realized that the size of the screws might be an issue after I received them.

[Nylocke]

http://www.mooreinternational.co.uk/cat ... T9-20.html something like this might work better? Smaller diameter and much more aggressive pitch.

[grimmindustries]

I changed the steps per mm, now it seems like the motors don't have enough torque. I had no problem homing it before the change but I couldn't set the new height because it would be in negative numbers before I reached the build plate.

I've been busy since I first posted but hope to get back to this modification this week.

[Jimustanguitar]

Check what speed you're telling it to move at. It's possible that the steps are going so fast that it's skipping instead of moving.

[JFettig]

You'll have to decrease your top speed and accel significantly. I'm guessing you'll be around 80mm/s top speed with ball screws.

[Polygonhell]

Acceleration is going to be the one you have to reduce the most, the issue with ball screws is they have significant angular momentum which has to be overcome.
My mill will happily run at 200mm/s with ball screws (though admittedly much bigger steppers and drivers), but the acceleration is incredibly low by comparison to any printer.

In the end the printer will likely be significantly slower because acceleration becomes the dominant factor really fast.
I'm interested in if you get any artifacts from the low acceleration, the plastic extrusion has significant hysteresis in it and you generally get the best results if everything is run at the same speed, because you don't have to accommodate the extrusion rate changes. The firmware does have some compensation for this in it, it'll be interesting to see how it fairs.

[626Pilot]

Wow, this is a hell of a mod!!! What are you trying to correct?