Should I increase microstep setting

[George]

Using Mach3
I'm running my gantry at 1500 velocity Maximum I can obtain is 1867
Accel is set to 250 mm/s max I can obtain is 468
and I have 800 steps per rev set.

My steppers are KL23HM276-30-8B(kelling) 2NM 3A/Phase
I havw M880 drives set to 10 microsteps Full current
Supply = 48v
Current limit set to 4.9A

Can I improve on any of these settings without going to larger steppers?

[BobF]

What kind of improvement are you looking for?

What screws or drive system are you using?

Kelling steppers are 200 full steps/rev. With 10 microsteps that would be 2000 steps per rev. If you had 4tpi screws you would need 8000 steps per inch.
It looks like you are working in metric so the calculations would be a little different, but I don't think your steps/rev are correct.

[George]

Thanks BobF, Please assume all measurements in Millimetres.

My screws are 1.2Mtrs long and 16x2.5mm (single start)
Using Mach3 I have set 800 into the 'steps per' box. I have two screws driving the Gantry, A is slaved to X and both settings are identical.

I'm getting 1800mm/minute thats just over 70 inches/minute, reading around the message area's I reckon I should be able to get around 150 inch/minute.
So maybe I have a setting wrong somewhere!
My drives are set to 10 microsteps which as you say should give 2000 styeps per revolution.
The drives should not be working too hard as they can go to 80volts at 8amps. I have them current limited to just under 5 Amps. Perhaps my steppers are just not up to it. They are rated at 2Nm by Kelling and I'm running them at 48Volts which was suggested by Cr as the max that these steppers should handle.

Any suggestions ?
Thanks
George (Manchester UK)

[ger21]

The problem is your screws, with 2.5mm lead. You'll get much more speed with screws with a lead of 10-15mm, or even more. Steppers lose torque as rpm increases, and with those screws, you have to spin them way too fast, where they run out of torque.

[BobF]

OK.
With 2.5mm lead your steppers must turn 720 rpm to get 1800mm/minute
200 steps/rev * 10 microsteps = 2000 steps/rev
2000 steps/rev * 720 rpm = 1440000 steps/min
1440000 steps/min / 60secons = 24000 This is about the top kernel speed in Mach at the default settings.

I think you need to change the "steps per" box to 2000. This so the DROs will read correctly in Mach, and your code will work.
Try this:
Zero the X axis DRO, go to the MDI screen in Mach, type in G0X50 (those are zeros not letter O) and measure how far the axis travels. Change your steps per setting if needed to get 50mm travel.

Once you get this correct, you can see if Mach can go to higher kernel speed on your computer. Look at the settings screen.

Steppers don't like high RPMs. You may be able to run yours at 1000rpm or so. Thats probably about max. You may get screw whip at that speed especially on your longer screws.

So what else can you do?
Higher lead screws will allow more speed for the same RPM at a reduction of force. You probably have enough torque from your steppers to operate screws with 5mm -8mm lead.
Larger steppers like higher rpm even less than the ones you have, so larger steppers won't help with the same screws.
You could reduce the microstepping and get more speed from the same kernel speed in Mach.

Get the steps per setting correct first so you get the correct travel for your setup.
Now you have a starting point and a known steps per formula for your screws.
If your drives have a reduced microstepping setting try that. Don't forget to change the steps per setting to match. If you can turn the steppers at 1000 rpm, and the screws don't whip too bad, you could get 2500mm per min.
Higher lead screws would be the way to go if speed is your goal.

[Andre' B]

Originally Posted by BobF I think you need to change the "steps per" box to 2000. This so the DROs will read correctly in Mach, and your code will work.

I have never used Mach so do not know for sure what it is looking for in the "steps per" box but I suspect it is more interested in the number of steps per UNIT be it inches or mm.

2000 steps per rev. / 2.5 mm per rev. = 800 steps per mm

[BobF]

Andre' B may be correct, I have never setup a machine for metric. Thats why I suggested the little test to make sure travel is correct.

[BobF]

Try setting microstep to 5 and set steps per to half of what you determine is correct before the change.

[George]

Thanks guys,

With the 'steps per' box set to 800 and the drive set to'10 microseps' when I tell the gantry to move 500mm, it moves 500mm bang on. It is repeatable. the DRO says 500. So the acuracy of movement on the gantry is spot on and agrees with that in the DRO. I find that I have to reduce the speed to around 1000mm/min (which is not exactly rocket fast) much faster than that then I have found that one of the steppers stalls and the gantry then racks. That's not good!

Point is at 1000mm/minute (40"/min) I can achieve the acuaracy but not the speed. Does this make my machine unusable as a hobby cnc router?

I think that I have learned an expensive lesson. I chose 2.5mm screws thinking that these would give me good acuracy but I didnt research the speed issue before buying.

Thanks

George

[BobF]

George,
Set your driver for 5 microsteps. I think I read it can do that.
If you can set 5, change steps per to 400, or half what you had with 10 microsteps.
This should allow you reach about double the speed.

Look in Mach at the diagnostics screen, it should tell you the cpu speed of your computer near the center of the screen. Write this down so you can post it later. Now look under the "ports and pins" menu item. You should see kernel speed listed. It is probably set to 25000. You can run at 45000 or more on a fast computer. The screen will tell you you have to reboot to change this.

I would try the 5 microsteps first. That should double your speed. If your screw whip is OK at that speed, you could try setting the kernel speed higher and see how fast it will go then.

at 1000mm/min your motor is only turning 400 rpm. What you have may hit is midband resonance, and that is why you get stalling. try some of the above and see if it helps.

40 in/min is not rocket fast, but certainly you can use the machine at that speed.

[ger21]

Originally Posted by BobF George, If you can set 5, change steps per to 400, or half what you had with 10 microsteps. This should allow you reach about double the speed.

No, it probably won't. At 1m/min, Mach3 is only sending 13,000 steps per second. It should be capable of almost double that the way it's set up now. It could be a resonance issue, but i think that usually occurs at lower rpm's??

[BobF]

Originally Posted by ger21 No, it probably won't. At 1m/min, Mach3 is only sending 13,000 steps per second. It should be capable of almost double that the way it's set up now. It could be a resonance issue, but i think that usually occurs at lower rpm's??

You are correct. The original post said 1800mm and thats what i used to do the math to get Mach at its limit.
"I'm getting 1800mm/minute thats just over 70 inches/minute, reading around the message area's I reckon I should be able to get around 150 inch/minute.
"