Advice on improving speed

[Jon.N.CNC]

Hi there, I'm looking to increase the speed of my 8x4 router,
It runs ballscrews on nema 34 in x so increasing pitch of screw will be the solution there, where I'm a little lost for mathematics and a cost effective solution is in the y. Y gantry weight is around 220kg. Current stall rate is 5.5m/min, run Rapids at 4.5m/min

The y runs 2 slaved nema23 3.1nm with 40:1 planatary gearboxes (43nm) on mod 1 rack then geared back up with a 40 tooth pinion.

Ideally the motor mounts are nema 23 and alteration would be pretty tricky, so a upgrade in motor to possibly servo with same flange would be the easier option than going larger.

Servo? .. All I have looked at in this size are significantly less Nm @2nm max but good rpm at 6000. With a gearbox or same gearbox could I gain any speed before stall?

Fitting a 4nm nema 23 instead of 3.1?(4nm is the highest I've seen, do they go more?) would there be much of a gain, I'm not sure.

reducing pinion size is a possibility, not so much in favour of increased pinion wear doing so and I can likely only loose a few teeth before I again would need to alter motor mounts.

Larger pitch rack.. Possible accuracy drop?

Appreciate any and all advice on the matter.

Cheers

Jon.

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[OlfCNC]

What about using higher voltage drives and power supply?
With that you could push the torque/speed graph and get the motors stall on higher RPM.

[ger21]

Y gantry weight is around 220kg.......
The y runs 2 slaved nema23.........

I would say that you are way under powered if that weight is correct.

However, your 40:1 gearboxes are not helping.

Most rack and pinion machines you see here are geared so that 1 motor revolution gives about 1" (25mm) of travel. Typically with a 3:1 reduction and a roughly 25mm pinion.
If my math is right, 40 revolutions of your steppers will give about 125mm of travel. Divide by 5, and you have 8 motor revolutions for 25mm of travel.
So, for a given speed, your motors are spinning 8x faster than the average rack and pinion machine.
Steppers lose torque as rpm's increase. What's happening is that your steppers are running out of torque.

reducing pinion size is a possibility,

I believe that this would make it slower, as the motor would need to spin even faster. I think a larger pinion would increase your speed, but probably not by much.

Servos would definitely help, as they retain their full torque all the way up to their full rpm rating. But, they typically are not the same size as stepper motors (physically), so a bolt on replacement is unlikely.

Back to my original statement. I really think that your motors are about 1/4-1/3 the size that you really need.

[louieatienza]

Teknic makes servos that can retrofit on stepper mounts, I believe.

I agree with Gerry that the gearboxes may be a bit much. The solution is not a smaller pinion but a larger one. On the CNCRP, they use a smaller pinion because the belt reduction is 3:1 for the NEMA23 mount, and the pinion is 1" diameter, which is roughly 1:1 final drive ratio. So on your machine, doubling the pinion diameter can potentially double the speed. And potentially lead to smoother operation with less backlash, because now you have more tooth engagement.

Or, find 7:1 gearheads...

[Jon.N.CNC]

Thanks for your replies, yes the motors and boxes were fitted on some bad advice.

The motor drivers are all already running at their max voltages, a larger pinion sounds like a good plan of attack with plenty of + adjustment on motor mount it's easily do able.

If I can get 10m/min Rapids I'll be happy but it very may well lead to taking the lovely waterjet cut dual gantry plates off and sending them to the furnace which will be real shame, then getting some more made up with 34 mounts.

Quick question, servo + r&p, require gearbox or ok without?

Cheers

Jon

[ger21]

Quick question, servo + r&p, require gearbox or ok without?

Yes, unless you have rally big servos.
Servos of similar physical size to steppers will have far less torque. They make up for that with rpm. A 2:1 reduction doubles the torque. 40:1 gives you 40x the torque of direct drive. Ideally, you want to run your servos at about 80% of their rated rpm at your maximum rapid speed.

[louieatienza]

Thanks for your replies, yes the motors and boxes were fitted on some bad advice.

The motor drivers are all already running at their max voltages, a larger pinion sounds like a good plan of attack with plenty of + adjustment on motor mount it's easily do able.

If I can get 10m/min Rapids I'll be happy but it very may well lead to taking the lovely waterjet cut dual gantry plates off and sending them to the furnace which will be real shame, then getting some more made up with 34 mounts.

Quick question, servo + r&p, require gearbox or ok without?

Cheers

Jon

There are such beasts as direct-drive servos, but they're expensive.

Depending on the maker of your gearheads, you may be able to find the proper input adapter. Or you may be able to make an adapter plate, and reducer bushing for the NEMA34 motor shaft which is likely bigger.