Dual Stepper Y axis ?

[jkarpy]

I am building a laser with a 24.5" X 48.5" cutting area. My X axis gantry will use Makerslide and my Y will use a more heavy duty slide. My concern is that since my X axis is so long (24" on each side of the stepper), my Y axis shaft could twist. I was considering using two steppers for the Y and eliminating the shaft. Since this is my first CNC machine I am not sure how to implement that. I am using one of the DSP controllers from light Object.

James

[Techgraphix]

I wouldn't eliminate the shaft. Even when you want to use 2 steppers, you should have to couple them. If one stepper misses one or more steps and the other doesn't, your X and Y are not square anymore..
Even with normal portal-routers with much more heavier gantrys, you see that the two axis-steppers are coupled, most of the time,
I wouldn't worry about twisting the shaft, not if you use a stailess-steel rod with 8mm or more in diameter.. Your belt will lose its teeth before serious twisting takes place.
What kind of torque you had in mind for those Y-axis steppers??? 24nm?

Kees

[twehr]

I am building a laser with a 24.5" X 48.5" cutting area. My X axis gantry will use Makerslide and my Y will use a more heavy duty slide. My concern is that since my X axis is so long (24" on each side of the stepper), my Y axis shaft could twist. I was considering using two steppers for the Y and eliminating the shaft. Since this is my first CNC machine I am not sure how to implement that. I am using one of the DSP controllers from light Object.

James

I believe the DSP is capable of driving 2 drives per axis, so add a 2nd Y drive and motor.

Like the previous post, however, you will likely want to tied the together to prevent uneven lost steps. The second motor, in this case, is just giving you a power boost.

[jkarpy]

Thanks Guys. I will change my shaft to 8mm and keep it. I am not sure what my torque requirement will be yet. I have not gotten that far into the design yet. So I am not positive of my gantry weight.

James

Millennium R/C

[iGull]

Hi James

If it puts your mind at ease, my table is 1200x600mm (48"x24" in USD ) I use a dual shaft NEMA23 stepper - 1.24nM holding and 75n at 20mm radial. Drive shaft is 8mm steel rod (not stainless) - turned to 6mm at one end to suit the pulleys - now with solid shaft couplers I was lazy and had some lying around, otherwise I would use large bore (12 to 20mm) alloy tube with steel ferrules on each end. The alloy tube keeps the mass down and reduces whipping and compliance.
I now don't have any great measureable backlash (about 0.075 to 0.11mm in both axes).

I've used dual stepper/servo systems in the past on CNC routers - I've never connected them with a shaft (no room) - ensuring both steppers and drivers are equal and driven in parallel by separately controlled step/dir signals certainly works.
Both sides of the Y axis need to have independent home sensors to ensure that the system stays orthogonal - you really need to ensure that the axis is not overloaded and well within the acceleration profiles or you may lose steps on one side and cause the axis to rack.

Good luck with your build!

[Techgraphix]

Both sides of the Y axis need to have independent home sensors to ensure that the system stays orthogonal !

Which ( DSP-)controller/software supports this feature???? I haven't found it in Mach3 nor in USBCNC, Lightobject-or Thunderlaser lasercontrollers..

I have coupled two Nema24 3nm steppers with a 8mm hardened silversteel rod for Y-axis accelerations of 50.000mm/s^2 (5G!), start 100mm/s, max speed 2000mm/s.. Reduced it a bit, because the whole machine started to travel through the room when the bridge (total of 2.7kg) "bangs" back and forward.. Probably there is no need for such speeds and accelerations on the Y-axis.. But i can ..

Kees

[iGull]

Hi Kees

This was on a largish cnc router, I only have the lightobject controller for my laser, I don't know if it is capable of this yet.

The cnc router was controlled using Supercam from Super-tech a number of years ago (although it may have been emc with the supercam controller, I had a few setups back then). Check Super-Techs website, I'm sure you'll find the info there. I now use DeskCNC for my smallish cnc router. Supercam was (probably still is) an excellent bit of software - mine was in DOS - back when men were men
It was a simple sequence of checking both home sensors for the first touch, halting that axis then driving the other until second touch - not exactly rocket science - I'm sure a few external logic gates (or a wee pic micro) attached to a couple of switches could ensure the correct sequence without the software knowing.

OK on your speeds - you certainly don't want to be banging your stage off the endstops after you have achieved laser alignment

Cheers

Neil

[Greolt]

Both sides of the Y axis need to have independent home sensors to ensure that the system stays orthogonal !

Which ( DSP-)controller/software supports this feature???? I haven't found it in Mach3 nor in USBCNC, Lightobject-or Thunderlaser lasercontrollers..

This is a very common way to set up a dual driven axis. At least on routers and plasmas. Mach3 handles this very well.

I doubt you will find a similar feature on a dedicated laser controller.

Flying optic laser gantries are typically much lighter construction and are well served by one motor driving both sides via a cross shaft.

I don't agree with hard coupling two stepper motors, but it is not something I will argue about.

Greolt