[mikeklon]

I have a home built 2'x4' machine I did on the very cheap. Machine works for my purposes (for now), but I would like the machine to cut faster. At the moment, I'm only cutting mostly PVC boards and some MDF.

I built the machine using Chinese motors from Wantai, model 57BYGH603 (Hybrid Stepping Motor 57BYGH:Hybrid Stepping Motor 57BYGH wholesaler) and their Chinese 6550 Driver board. I installed a 1/2" - 12 TPI, single start screw and nut I got at Home Depot to drive the X and Y axes. If I remember correctly, the motors are rated at 187 oz inch. When I calibrated Mach 3 to drive the board/motors, it seems I started losing steps if I pushed past the 6 inches per minute calibration (20K steps).

I'm wondering if I upgrade the screw drive for X and Y to a 2 or 4 TPI (which I assume will produce faster X-Y movement), will my existing motors support that.

Any help and/or guidance would be appreciated.

Thanks,
Mike K.

p.s. I'm considering a new build or kit, but I'm still looking for a cheap, fast upgrade to the existing machine.

[widgitmaster]

Yes, if you were to purchase 3-start acme screws & nuts from McMaster-Carr, your machine should get 300 IPM rapids!

A 1/2-10 3-start has a speed ratio of 5:1, moving 1/2" per revolution.
Widgit

[mikeklon]

Widgitmaster: Thank you for the fast reply.

I understand your explanation of the 3-start screw. Thank you for that. I'm curious how you determined that going to a 3 start screw would give me 300 ipm. You said the ratio was 5:1. Currently I'm calibrated to go 6 ipm. If I follow your ratio, wouldn't I get 30 imp after the upgrade? Or did I just blow it with my existing calibration (that's not out of the realm of possibilities - lol).

I was really curious though if the existing motors support that screw and/or will there be a loss of torque, and/or would I need to get different motors/drivers to support the extra starts. I assume the extra starts would create more drag!

Thanks again everyone.

Mike K.

[LeeWay]

I think you are currently using 1/2" 13 all thread, right? Standard threaded rod?

Acme is a step up in precision and less friction as well, especially when coupled with an anti-backlash nut made from something like Delrin.
You will get faster speeds at lower friction and would probably be a lot more precise.

[widgitmaster]

Widgitmaster: Thank you for the fast reply.

I understand your explanation of the 3-start screw. Thank you for that. I'm curious how you determined that going to a 3 start screw would give me 300 ipm. You said the ratio was 5:1. Currently I'm calibrated to go 6 ipm. If I follow your ratio, wouldn't I get 30 imp after the upgrade? Or did I just blow it with my existing calibration (that's not out of the realm of possibilities - lol).

I was really curious though if the existing motors support that screw and/or will there be a loss of torque, and/or would I need to get different motors/drivers to support the extra starts. I assume the extra starts would create more drag!

Thanks again everyone.

Mike K.

The 5:1 ratio is not 5 times your current speed, here is a better idea of how it works

The starts are also referred to as "Speed Ratio" by suppliers.
A two start rod would move the axis twice as fast as a single start rod when turning at the same rpm, so it is designated as having a speed ratio of 2:1.

Widgit

[doorknob]

I know that you only asked about the drive screw and not the electronics, but you may be able to get some improvement by simply rewiring your motor.

It looks like your motor has 6 wires and has a relatively high winding inductance at 18 mH. That motor is poorly matched to the capabilities of your stepper motor driver (and the driver itself is not particularly capable, but that's a story for another time).

Your driver is designed to handle four-wire motors, while your motor has 6 wires. So you must currently have it wired up by using four of the six wires, and taping off the other two wires. There are two ways to do that - either by using a "full-coil" hookup or a "half-coil" hookup. If you are currently using the "full-coil" hookup, then I would expect that you would see a noticeable speed increase by simply changing to a half-coil hookup (but don't expect to see 300 ipm).

There's a good explanation here: UniPolar vs BiPolar wiring schemes for 2-phase Stepper Motors (make sure that the power is turned off before disconnecting or connecting motor wires to your driver).

[mikeklon]

The 5:1 ratio is not 5 times your current speed, here is a better idea of how it works

The starts are also referred to as "Speed Ratio" by suppliers.
A two start rod would move the axis twice as fast as a single start rod when turning at the same rpm, so it is designated as having a speed ratio of 2:1.

Widgit

Thank you for the reply Widgitmaster. Well then maybe I don't understand your explanation of the 3-start rod. If a 2 start rod has a 2:1 ratio, why does a 3 start rod have a 5:1 ratio?

[mikeklon]

I know that you only asked about the drive screw and not the electronics, but you may be able to get some improvement by simply rewiring your motor.

It looks like your motor has 6 wires and has a relatively high winding inductance at 18 mH. That motor is poorly matched to the capabilities of your stepper motor driver (and the driver itself is not particularly capable, but that's a story for another time).

Your driver is designed to handle four-wire motors, while your motor has 6 wires. So you must currently have it wired up by using four of the six wires, and taping off the other two wires. There are two ways to do that - either by using a "full-coil" hookup or a "half-coil" hookup. If you are currently using the "full-coil" hookup, then I would expect that you would see a noticeable speed increase by simply changing to a half-coil hookup (but don't expect to see 300 ipm).

There's a good explanation here: UniPolar vs BiPolar wiring schemes for 2-phase Stepper Motors (make sure that the power is turned off before disconnecting or connecting motor wires to your driver).

Doorknob - Thank you for the suggestion. You are correct - four wires connected to the drivers and two taped off. I don't remember off hand how I wired the motors (half vs. full). I do remember that I could only get the motors to turn using one but not the other. I will check on the configuration this afternoon and report back.

Are you hinting that a driver only upgrade might improve speed and/or performance? (The driver board actually came in a kit with the motors, power supply, and printer port cable.)

[doorknob]

Are you hinting that a driver only upgrade might improve speed and/or performance? (The driver board actually came in a kit with the motors, power supply, and printer port cable.)

Many times I have seen that the combination kits of motors, power supply, and drivers offered by Chinese sellers are poorly matched.

In order to get a significant performance boost, you would want to both upgrade the drivers and use a higher power supply voltage.

The specifications that they list for the motor are not as detailed as I'd like to see, but the very high 18 mH winding inductance rating would seem to indicate that a power supply voltage of over 100 volts would be required to get the best performance from that motor (while the TB6560 driver board is usually paired with a 24-volt power supply, and can burn out with voltages much over about 30 volts).

The torque vs. speed curve that they publish for that motor shows a really severe drop-off in performance as the speed is increased (when running with a 30-volt driver):

[JEST]

Using a TB6550 and a 24V supply, my gantry would begin losing steps @ 50IPM
Changing to a Gecko 540 and a 48V supply became 300IPM before any loss of steps.
Any questions?

[mikeklon]

Doorknob - You are correct - four wires connected to the drivers and two taped off. I don't remember off hand how I wired the motors (half vs. full). I do remember that I could only get the motors to turn using one but not the other. I will check on the configuration this afternoon and report back.)

This is how the motors are wired to the the 6550: White & Yellow are open. Black XB-, Green XB+, Blue XA+, Red XA-. I don't know if this is a full or half coil hookup. I followed the diagram provided by the manufacturer. I remember experimenting with a couple of other configurations to no avail, so I left it as it is now.

Off hand with my limited experience and sketchy documentation, I wouldn't know what to change to get into the half coil orientation if it is indeed in full coil now. What is the difference between UniPolar and BiPolar and how does that relate to the full and half coil configuration? The article you referenced also mentioned a series configuration (which if I read the chart correctly, that's what I've wired in my configuration). By the chart, I surmise I can only connect these motors in series?

[mikeklon]

Using a TB6550 and a 24V supply, my gantry would begin losing steps @ 50IPM
Changing to a Gecko 540 and a 48V supply became 300IPM before any loss of steps.
Any questions?

Jest - thank you for the info. What kind of rod/nut are you using? I presume those IPM measurements are rapids? Do you remember your wire configuration with the TB6550?

[JEST]

Yes those are rapid speeds.
Depending on what I am cutting, 25IPM to 150IPM feed rate.
Diameter:20mm Pitch:5mm Ballscrew (Ebay/Chinese import)

[doorknob]

This is how the motors are wired to the the 6550: White & Yellow are open. Black XB-, Green XB+, Blue XA+, Red XA-. I don't know if this is a full or half coil hookup. I followed the diagram provided by the manufacturer. I remember experimenting with a couple of other configurations to no avail, so I left it as it is now.

Off hand with my limited experience and sketchy documentation, I wouldn't know what to change to get into the half coil orientation if it is indeed in full coil now. What is the difference between UniPolar and BiPolar and how does that relate to the full and half coil configuration?

According to the datasheet at Hybrid Stepping Motor 57BYGH:Hybrid Stepping Motor 57BYGH wholesaler you are using a full-coil hookup.

To change it to a half-coil hookup you could replace the green wire with the yellow wire, and replace the blue wire with the white wire.

The TB6560 is a bipolar driver. The full-coil hookup is analogous to a "bipolar series" hookup, while the half-coil hookup is analogous to a "bipolar parallel" hookup.

[widgitmaster]

Thank you for the reply Widgitmaster. Well then maybe I don't understand your explanation of the 3-start rod. If a 2 start rod has a 2:1 ratio, why does a 3 start rod have a 5:1 ratio?

Personally, I don't think the ratio is very important! The MOST important factor is the distance the nut moves in one revolution of the screw! Thus a 1/2" diam 10-TPI 3-Start acme screw will advance 1/2" per revolution. So you get more motion with a smaller amount of RPM. The torque requirement also increases slightly as the motor has to work a little harder to rotate the screw. For optimal performance of a 1/2-10 3-Start acme screw, I would suggest a 200+ oz/in 4-wire stepper. This combination will give you 300 IPM rapids, and handle any of the cutting capabilities of the rest of your machine.

[mikeklon]

According to the datasheet at Hybrid Stepping Motor 57BYGH:Hybrid Stepping Motor 57BYGH wholesaler you are using a full-coil hookup.

To change it to a half-coil hookup you could replace the green wire with the yellow wire, and replace the blue wire with the white wire.

The TB6560 is a bipolar driver. The full-coil hookup is analogous to a "bipolar series" hookup, while the half-coil hookup is analogous to a "bipolar parallel" hookup.

Doorknob - Thank you for the clarification. I will try the half-coil configuration you suggested and report back.

Thank you also for the clarification on the series vs parallel hookup. Is there somewhere I could read up on how to make that distinction on my own?

[mikeklon]

Personally, I don't think the ratio is very important! The MOST important factor is the distance the nut moves in one revolution of the screw! Thus a 1/2" diam 10-TPI 3-Start acme screw will advance 1/2" per revolution. So you get more motion with a smaller amount of RPM. The torque requirement also increases slightly as the motor has to work a little harder to rotate the screw. For optimal performance of a 1/2-10 3-Start acme screw, I would suggest a 200+ oz/in 4-wire stepper. This combination will give you 300 IPM rapids, and handle any of the cutting capabilities of the rest of your machine.

Widgitmaster - thank you for your feedback. Most helpful and I do see how the 3-start, 10-TPI 1/2" diameter screw would move 1/2" per rev. And, you've now actually answered my question about if the screw is upgraded, would I need a bigger/heavier/larger torque motor to handle the load.

[mikeklon]

Yes those are rapid speeds.
Depending on what I am cutting, 25IPM to 150IPM feed rate.
Diameter:20mm Pitch:5mm Ballscrew (Ebay/Chinese import)

Jest -- Thank you so much for your response. I guess I should have asked what size motors for X and Y and how many starts on that Ballscrew you're using. Thanks again.

[Mike 1948]

I'm confused now, wouldn't a 10TPI screw have to have a 5 lead start to move 1/2" in one revolution??

Mike

[mikeklon]

I'm confused now, wouldn't a 10TPI screw have to have a 5 lead start to move 1/2" in one revolution??

Mike

OK -- yeah -- me too.