new DIY woodworking cnc questions

[endgrainguy]

I just finished wiring my woodworking CNC router, and I'm having lots of problems with electronics. Often getting stuck in E-Stop mode. Z axis delivers only much slower speed than I expected and want, and z stepper grumbles even when not moving. All I"ve done so far is tune motors and jog them around a bit.
I did a sloppy job wiring my controller box. Could this be part or all of the problem? I used these steppers and drivers http://cgi.ebay.com/Stepper-motor-64...742.m153.l1262
with power supplies from same vendor, and this breakout board http://cgi.ebay.com/CNC-Emergency-St...742.m153.l1262.
Machine uses high quality mostly used components - THK rails and ball screws mostly, sturdy 80/20 frame.
Z axis weighs about 20 pounds, largely because of a mounting sysyem that allows me to run spindle horizontally or vertically or anything imbetween.Z axis uses a fine pitch 2mm lead THK ball screw. Can I only expect about 20 inches/minute from this with a 640 oz/inch stepper? Since I want to use this mostly with spindle horizontally to cut dovetails and the like, a faster speed would be really nice on the z --maybe 40 ipm. The x and Y have no problem zooming around at 300 inches/minute. Its a fixed gantry, moving table set up.
And what are the likely causes of my getting stuck in e-stop mode?
I posted this under electronics last night, but thought maybe here is more appropriate. Plesase let me know if this duplicate losting is unacceptable! Thanks, Al

[Gir]

The e-stop mode sounds like faulty wiring. Make sure no bare cable is exposed, and ensure the button isn't "jumping" due to vibrations. Vibrations may be enough to cause the switch to very quickly connect, on the order of nanoseconds. As for the Z giving you trouble, make sure everything is aligned well and runs smoothly. You can test this by disconnecting the stepper and moving it up and down. If you encounter any resistance to motion (other than gravity), you've got a problem.

Also, those links to the ebay pages don't work.

The machine looks nice, though, good job!

[johnmac]

Al,

I agree with Gir on the E-stop wiring. The Z may have a loose connection also. I think I had the same problem at one time, But I can't remember for sure.

Nice looking machine, so why not tidy up the wiring to match? If you used crimp type connectors, they may be your problem, not griping the wire good. Can't beat a good solder joint.

The slow Z speed may not be as much of a problem when in real use. Set the "safe Z height", or whatever your software calls it, to just clear the work surface. That way time is not wasted waiting for the Z to raise and lower more than needed.

You may try running the Z with full steps, rather than half. That may speed it up some.

John

[mcyr]

What are you using to control the BoB? I have some experience with Mach3 and might be able to help.

Besides vibration issues as already discussed, electrical noise in your wiring may be triggering the e-stop. Does it occur sporadically as the z-axis moves up and down or does it stop in the same spot all the time?

Mike

[endgrainguy]

Figured out my electronics woes. Barrel connector for 5 volt supply was unreliable, causing e-stop problem, and then vendor gave me bum instructions for wiring BOB, which I figured out through trial and error -lots of error.
I still only get about 17 inches/minute for my Z axis. Since I"m doing much of my work up and down, with spindle horizontal for dovetailing, this is a drag, and much of the blame goes to what was probably a bad choice of z ball screw - a THK 2 mm lead -tight and accurate, but slow. I'm using a 640 Oz/inch Kelling stepper. If I go to double that, (1180, nearly double) can I expect nearly twice the speed? Otherwise its alot of work changing out the ball screw. Thanks for all your help!

[johnmac]

Al,
A bigger stepper won't run any faster. In fact, it may run a bit slower. My first machine has the same problem. I used 1/4x20 threaded rod, and only get about 10 inches per minute.

Maybe you could use a pair of timing pulleys and a short belt and "gear it up", say 2:1? Also, have you tried running in full step mode? It helped for me.

John

[ger21]

Yeah, the bigger stepper will almost certainly be slower. If you want the motor to spin faster, smaller is better. But it takes the right combination of motor, drive, and power supply, as well as the proper screw. The best screw for you would probably be with a 10-15mm lead. But I have a feeling part of the issue may be your drives. Can you give us some more info?

As was mentioned, the Ebay links don't work that you posted, so we don't know what you're working with

[endgrainguy]

http://cgi.ebay.com/Stepper-motor-64...742.m153.l1262

Does this work as Ebay link to driver, stepper combo?

Here's the info:Brand New NEMA 34 640 oz-in stepper motor Includes documentation And a high end Bipolar Microstepping Driver

Motor Specifications:

NEMA 34

Suitable for dirving mill tables with 5/8" to 3/4" drive screws

Dual Shaft Front shaft=1/2" x 1-3/16" with Flat. Back shaft= 1/2" x 1-3/16" with flat

200 steps per revolution

1.8 degrees per step

No. of wires=8

Bipolar series Volts=.54, Amps=3.2, Ohms=1.42, Holding torque=4.5Nm. 0r 640 oz-in

Bipolar parallel Volts=2.30, Amps=6.4, Ohms=0.36 Holding torque= 4.5 Nm. or 640 oz-in

Unipolar Volts=3.2, Amps= 4.5, Ohms=0.71, Holding torque= 3.2 Nm or 455 oz-in

Body length= 80 mm or 3.0"

Body Diameter= 88 mm or 3.45"

Bipolar Driver Specifications:

Supply voltage up to +50VDC, current output up to 3.0 ampspeak
* Optically isolated input signals,

* Automatic idle-current reduction
* 7 selectable Microstep resolutions.

* Suitable for 4,6,8 lead motors
* DIP Jumper current setting with 12 different values
* Built in motor test switch feature, (very handy on setup)

* +5 vdc output available on board for limit switch input power.

It's Hubbard CNC's 159$ combo -the stepper's have Kelling label on them.

How much extra speed am I likely to get from gearing up? Could I double speed? Or would another drive make a big difference? This z speed is a huge disappointment -manual machine I've been using would certainly cut faster. I'll change the screw if I have to. Could one expect speed increase in direct proportion to lead change? So if I went to about a 12MM lead I'd get 100inches/minute? That would be nice. I thought the 2 mm lead would have been fast enough, but thought I could get 750 RPM out off the motor. Thought avoiding any freewheeling would be a nice thing, but not worth this slow speed.Thanks!

[ger21]

What voltage are you running them at, and how are they wired? Bipolar series?

[endgrainguy]

I have to confess to knowing very little about electronics and wiring. My steppers are wired Bipolar series. According to the spec sheet Voltage current/phase (V DC) = 4.5 wired in series. I have no idea what this means, or if it answers the question of what voltage I"m running my steppers at. . I followed the diagram for bipolar series and I"m using a 38 V power supply.
Here is the actual stepper
http://www.kelinginc.net/NEMA34Motor.html
This one: KL34H280-45-8A (1/2" Single Shaft) Specification Price: $89

Might an error or bad choice in drive wiring result in this slow speed? Or is this speed not unexpected, giving gravity, 20 pound axis, and 2 mm lead screw? The z azis stepper does sort of grumble all the time, even when it's not doing any actual work, while the other two are silent. I haven't powered up my 12 amp router yet, but there are home and limit wires (unshielded) running near the Z axis cable.DO I really need to use shielded wire for the home and limit switches? This stuff >?
http://cgi.ebay.com/Cable-22-AWG-PVC...QQcmdZViewItem

Thanks!

[ger21]

I'd guess that it's a combination of wrong choices. Wrong choice of motor for that drive, wrong choice of screw.

When wired bipolar series, high speed performance is much lower than bipolar parallel. Couple that with a larger motor that will already spin slower, and you get a combination that won't spin very fast. Couple that to a screw that needs to spin fast, and you're out of luck.

I'd guess that a 280oz motor for $39 will give you more speed than your getting.

As for the roughness, it may be resonance. You can try using different microstep settings on the drive to see if it helps to run smoother.

If you're stuck with that motor, you could try getting a Gecko Drive and running it bipoolar parallel at 6.4 amps. That would possibly double your speed.

But with 640 oz, you could probably gear it up 4:1 or so and get 4 times more speed, maybe even more.