faster feed rates out of motors, what are my options?

[dougie329]

I would like faster rapids and feeds out of current setup and for future builds on a cnc router which has nema 23 stepper motors (425oz, 3Nm) (2 sync`d on y axis), 48v power supply and gecko G540 driver. I have 5mm pitch 16mm dia ballscews on all axis at moment. I want to keep these sizes and components if possible.

Do I:

1) gear it up using pulleys?

2) Get some larger pitch ballscrews ie 10 or 16mm pitch ones?

what would be the advantages of each method and potential problems?

Thankyou

[margni74]

Originally Posted by dougie329 I would like faster rapids and feeds out of current setup and for future builds on a cnc router which has nema 23 stepper motors (425oz, 3Nm) (2 sync`d on y axis), 48v power supply and gecko G540 driver. I have 5mm pitch 16mm dia ballscews on all axis at moment. I want to keep these sizes and components if possible. Do I: 1) gear it up using pulleys? 2) Get some larger pitch ballscrews ie 10 or 16mm pitch ones? what would be the advantages of each method and potential problems? Thankyou

I like the pulley idea you can mix and match until you find a good combination and wont have to spend $$$ on new screws/end blocks, etc.

Either way I think you're going to knock down your resolution

[jsheerin]

Any method you use to move faster with the same motors will reduce resolution.

If you put gearing between the motor and the screws, that will make the screws turn faster which could cause the limit of your speed to be screw whipping (depending on the length).

If you use higher lead screws of the same diameter, then the screws will turn slower for the same speed which will allow you to reach a higher overall speed assuming your motors have the torque.

I attached an Excel sheet that calculates some useful figures for these decisions. It lets you input the motor's torque curve and details on the screw (or R&P) drive, gearing, weight to move, number of motors and desired acceleration. Then it calculates the force available for cutting at various speeds. There are some examples, probably using the same 425oz*in motor you have as that's what I have as well. I'm working on the same issue currently with my router. The still unaswered question is what the cutting forces are. I'm trying to think of an easy way to measure that.

[ger21]

You should still have plenty of resolution, as a lot of people are using 2 turn/inch screws with no problems. The benefit of higher lead screws is that they spin slower, so you have less chance of whipping.

[rowbare]

You might get more speed by using smaller stepper motors that are better matched to the G540's output.

If you are using the Keling 425s they need about 85 Volts (32 * sqrt(6.8)) for optimal performance. Something like the KL23H2100-35-4B with a 2.8 mH inductance (54V) takes full advantage of the G540s 3.5A output and your 48V power supply.

It is probably cheaper (and less time-consuming) to replace the motors than to mess around with pulleys and the like.

This post is quite informative:
http://www.cnczone.com/forums/showth...xta#post530370

[pminmo]

Originally Posted by dougie329 I would like faster rapids and feeds out of current setup and for future builds on a cnc router which has nema 23 stepper motors (425oz, 3Nm) (2 sync`d on y axis), 48v power supply and gecko G540 driver. I have 5mm pitch 16mm dia ballscews on all axis at moment. I want to keep these sizes and components if possible. Do I: 1) gear it up using pulleys? 2) Get some larger pitch ballscrews ie 10 or 16mm pitch ones? what would be the advantages of each method and potential problems? Thankyou

What rates are you getting, how long is the axis, what is the motor coil characteristics (voltage, current and inductance) and what is the symptom of your at your maximum (steppers miss steps, software is at max, leadscrews whip, etc)?

Motor rpm's are affected by motor coil voltage and coil inductance. A lot of time the larger nema23's have a high coil inductance which is problematic to higher rpms.

[dougie329]

Some excellent information guys thankyou, the motor spec is below, wired as bipolar parallel:

The SY60STH86-3008BF is a High Torque three stack Nema 23, 1.8 degree hybrid stepper motor with a holding torque of 3Nm (425 Oz-in)


Specifications:

Voltage 2.73v
current (phase) 4.2
Inductance (phase) 3.2
Holding torque 3Nm
Rotor Inertia 840 g.cm2
Step Angle 1.8 Deg
Step Angle Accuracy 5% (full step, no load)
Resistance Accuracy 10%
Inductance Accuracy 20%
Temperature Rise 80OCMax.(rated current,2 phase on)
Ambient Temperature -20OC~+50OC
Insulation Resistance 100M Min. ,500VDC
Dielectric Strength 500VAC for one minute
Shaft Radial Play 0.02Max. (450 g-load) Shaft
Axial Play 0.08Max. (450 g-load) Max.

The longest axis on the machine is 1100mm, I can get about 3-4m/min rapids-much more and the steppers start to miss steps especially the 2 syncd y axis motors.

[pminmo]

The sync'd motors on a shared axis is problematic as you go up in motor rpm's...
With those motors your simplest option might be to ditch the G540 and goto G203's. With no other changes you can run the motors at full current, thus upping your motor power, plus the G203 will give you more mechanical power at higher rpm's than the G540 at the same current rating anyway.