3D Elk cutting (video) #13 - Hagerman, New Mexico

[Gerald D]

Glad to hear you have a handle on it. I would still believe that a good trajectory planner in Mach should be able to join tangential line segments at a smooth speed, but unfortunately it doesn't.

[Greg J]

Here's my lastest dust foot pic and model. It's fabricated from PVC.

MM Dust Foot Photo.jpg

MM Dust Foot Model.jpg

[smreish]

Nice Greg.
Maybe I will get to actually hooking up all my dust collection next week after moving the machine. This should be a fun week for sure!

[sailfl]

Greg,

Very nice. I hope that I can worry about dust collection soon.

[Greg J]

Gerald or Mike or whomever,

I’m experiencing some random “missed” steps on the X-axis. The part is the 3D leaf that is a standard cut file in Vectric’s Cut3D. I was cutting a part in Ash when the X-axis missed a step in the middle of the part on the finish cut. The next missed step was right at the start on a piece of Walnut, also on the X-axis. Walnut and Ash are expensive test subjects, so I started doing “dry” runs and everything ran great. I next ran the same program on cheap pine and the parts came out great. Since the pine parts came out fine, I decided to lower my feed rates from 160 ipm to 100 ipm and try a part in Walnut.

Right at the start of the program, the X-axis missed / jumped. . I heard a strange motor/gear/whatever noise, but stopped the cut file in time to save the Walnut. I re-winded the cut file and started again. This time the Walnut part came out perfect. Nice finish, etc.

I’ve noticed that all 3 times, the missed step is in the positive X direction. So maybe on the first reversal of X direction, the motor cannot catch up. The X-axis is off by about ½ to 1 inch in travel.

I’ve checked all mechanical parts (loose pinion, motor, swing bracket) and everything is good. I’ve looked at the speed-torque characteristics (PK296A1A-SG7.2 / 35 tooth pinion) and calculate 62.8 lbs of force per motor (more than enough). My acceleration setting in Mach is set at 25.

Can either of you two suggest area’s I should be looking at? Mechanical? … electrical? …. Software?

[Gerald D]

Without any work on the table, you can hold a gantry (or car) back by hand to feel how much force it could generate. Try this for a simple rectangle cutting program, or get Karen to push the cursor keys while you hold it. You should detect a dud motor, dud drive, or bad motor tuning with this test. No harm in holding a car/gantry until the motor/s loose steps.

Could you "rotate" the part 90 degrees so that the y-axis does the work that the x-axis was doing before - ie. see if the problem transfers to the y-motor, drive, accel setting etc.?

[Greg J]

Thanks Gerald,

I have tried holding the Gantry while dry cutting. Those two X axis motors have allot more force than I can stop.

I'll try transferring the work to the Y axis. Simple in Cut3D.

[Richards]

Greg,

Also, check your acceleration. Stepper motors are picky about a lot of things. Too slow acceleration is just as bad as too fast acceleration. The motors have a "harmonic" region where they have trouble. If acceleration is set improperly, that "harmonic" region can cause missed steps.

One of the problems with stepper motors on a CNC machine is that one axis might be required to move very slowly when the the other axes are moving more rapidly. Slow movement can translate into speeds in the "harmonic" region. Sometimes reprogramming the part to run faster or slower can help.

Most stepper motors are used to position an axis without requiring other axes to be synchronized, in other words, a command is given to move two or more axes to end up at point X, Y, Z, A, B. Each axis moves independent of the other axes. As long as the final destination is reached, the move is successful.

On a CNC machine, it is expected that all axes are co-ordinated. That can cause one or more axis to run in its "harmonic" zone and problems can be caused.

Experiment a little to see if faster speeds or slower speeds help.

For example, a move such as G01 X96 Y1 F450, might cause problems with the Y-Axis, since it is only moving 1/96th as fast as the X axis.

[Gerald D]

I see that Mike is also suspicious of your accel settings . . . . from this thread, you should have an accel setting of 20 to 25 inch/sec/sec.

If you aircut that particular tough file, can you induce the glitch by holding the problem axis back?

[Greg J]

Thanks Guys,

I made a video and have posted on Youtube. The video is poor quality, but I think the sound is more important. I was jogging the X axis at 300 ipm. My accel is currently set for 25 inch/sec/sec.

http://www.youtube.com/watch?v=JrXoq0mA8A4

[Greg J]

Gerald / Mike,

I've lowered the accel. from 25 to 20 in/sec/sec and it seems to have made a difference. With accel set at 20 in/sec/sec, I haven't been able to reproduce the bad performance.

Always something to learn. Now, back to work.

[Greg J]

Here's a video cutting Walnut after reducing the accel. from 25 to 20 in/sec/sec. Cut quality is great and working fine.

The video quality is very poor (using digital camera) so unless you don't have anything better to do on a Friday night (my wife says I need to get a life ) view at your own risk of wasting time. I'll get a real digital camera for Christmas.

http://www.youtube.com/watch?v=BcZu9Ti4sXM

[Gerald D]

Glad to hear (not actually - don't have sound on my PC) that your problem is solved for now. Let's leave it for a few days before copying this to the troubleshooting thread.

[Greg J]

Shouldn't we start getting "ahead of the curve" (the learning curve) by incorporating sight (the written text) with sight and sound (video) for the troubleshooting part of the manual.

[domino11]

Greg,
Hey, what is better on a friday night than watching a MM Video? Your life is what you make it.

[gmessler]

Cool video Greg!!

[Gerald D]

Greg, at that point where the gantry has to reverse direction, is there a z-axis movement together with the x-axis movement? (That would make it MUCH more difficult for your PC and Mach3 to reverse those step/dir pulses smoothly)

[Greg J]

Gerald,

Yes, the G code has the Z and X axis's moving simultaneous when the X axis moves from a positive to negative direction (and negative to positive direction). Everything seems to be operating fine since I lowered the accel. I'm cutting another part out of Walnut as I write. If I don't have any more "screaming" motor incidents by tomorrow, maybe we can add the video to the troubleshooting thread. It'll show what too much accel. sounds like.


Greg / Heath

Watching a MM video is cool, but actually designing and fabricating something is the best. Having too much fun

[Greg J]

Gerald,

Lowering the Accel. from 25 to 20 (in/s/s) has made all the difference. The blue beast has not skipped a step since.

Having too much fun making stuff.

Once I get caught up, I'll post Mach settings, update trouble shooting thread and the "bits, speeds, and feedrates" thread. Oh yea, post some pictures also.

[Gerald D]

Glad to hear you have something reliable and predictable now. I vaguely remember that your motors/wiring/ ps voltage are from the early days when we didn't clearly know what we wanted for the MM . . . . . could you give us those numbers again please?
Motor type number:
Wired series/parallel/half-coil?:
No. teeth on pinion:
Power supply voltage?:

[Greg J]

Originally Posted by Gerald D

Glad to hear you have something reliable and predictable now. I vaguely remember that your motors/wiring/ ps voltage are from the early days when we didn't clearly know what we wanted for the MM . . . . . could you give us those numbers again please?
Motor type number:
Wired series/parallel/half-coil?:
No. teeth on pinion:
Power supply voltage?:

Motor Type: PK296A1A-SG7.2
Pinion: 35 tooth
Wired: half-coil (need verification)
Power Supply Voltage: Will Check.

Sorry, one last check before bed. All documentation is in the shop. Will verify and post tomorrow.

[Gerald D]

Okay, found your post: "I'm using the AnTek 70 V power supply with the PK296A1A-SG7.2 motors (wired unipolar, 1/2 coil) and G203 drives" All clear now. Suspect those 35 tooth pinions are a bit too big.

Did you ever check the resistors on your G203V's with a meter? They should be 18Kohm in your case

[Greg J]

Originally Posted by Gerald D

Did you ever check the resistors on your G203V's with a meter? They should be 18Kohm in your case

. Not yet. Those 3 minute jobs are the hardest to get done. You should see how many jobs Karen is waiting on.

I did meter during initial installation, but, I'll double check tonight.

[Gerald D]

Ja, I am officially on "holiday" myself, but painting the inside of the house because we are going to have visitors in Feb for son's wedding. (Daughter's boyfriend also nervously requested our permission for marriage recently - I am putting on two coats of paint!)

[hennie]

Gerald, how many herd of cattle did the future son in law pay you for labolla.

[Gerald D]

Labola for Detroit

[Greg J]

Karen will be glad to know that I am one hell'uva good negotiator . . . on second thought, maybe she will never know.

We still laugh today about what I paid for her wedding ring. "I have a "friend" in the diamond business."

I measured the resistance this evening. 12.5Kohm.

[Greg J]

Here's a sample of current project. Walnut, Curly Maple, Ash, and Clear Pine.

Leaf Pic for MM.jpg

[lunaj76]

Greg,
Those look very nice! Are they business cards as well as tree ornaments?

[Greg J]

Justin,

The size is 11.5" long x 6.5" wide.

I'm calling them jewelry dishes. The ladies put their jewelry on them at night before they go to bed. My wife is giving them to her friends for Christmas.

I added an engraving on the back to personalize them.