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Author Topic: Why is it running off at random?  (Read 10371 times)

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Re: Why is it running off at random?
« Reply #20 on: June 01, 2010, 11:00:13 PM »
I have 1/2-10 Acme screws and Xylotex 269 motors. (I made a mistake on the 425's)
I am not sure how fast I was going but the max speed is set to 60 ipm

Neil

Offline Zaae

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Re: Why is it running off at random?
« Reply #21 on: June 02, 2010, 12:07:53 PM »
I've been thinking about this, and I'm betting it is stalling, but it may or may not be for mechanical reasons. I will say though, 60ipm with 10tpi screws is going to be turning those motors at the upper end of their torque curve, and slowing down may be your only option. That aside, I do have a couple observations.

If Y is vertical, and X is horizontal;
The little bump at the top would be where X stopped moving, and Y attempted to continue moving out to the edge of the circle. The lower mark would be where X started moving again, attempting to finish the right side of the circle. You can see that X was *trying* to move, as it does angle a bit to the right. Once it reaches the lower mark, the motor started moving again.

I know how frustrating this can be. It can seem like everything is sailing along smoothly, and out of the blue, stalling happens. I'd like to refer you to my stalling post from months ago, there may be some things in there for you to try, and there were lots of helpful posts from folks trying to help me. If you want to see what worked for me, check page 4, but don't skip what was said on the previous pages.

http://www.machsupport.com/forum/index.php/topic,9943.0.html

Good luck!

« Last Edit: June 02, 2010, 12:13:21 PM by Zaaephod »

Offline docltf

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Re: Why is it running off at random?
« Reply #22 on: June 02, 2010, 01:52:26 PM »
that looks like one axis just quits for a while then starts back.you might want to check your wires from the motors back to the drivers.
everything might be ok except for one motor is not getting the signal all the time.

bill

Offline Zaae

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Re: Why is it running off at random?
« Reply #23 on: June 02, 2010, 02:05:25 PM »
that looks like one axis just quits for a while then starts back.you might want to check your wires from the motors back to the drivers.
everything might be ok except for one motor is not getting the signal all the time.

Good call, Bill. Especially considering the stopped axis looks like it might have been trying to move a little bit. I'd bet a short could do just that.

Offline ger21

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Re: Why is it running off at random?
« Reply #24 on: June 02, 2010, 10:33:40 PM »
I have 1/2-10 Acme screws and Xylotex 269 motors. (I made a mistake on the 425's)
I am not sure how fast I was going but the max speed is set to 60 ipm

Neil

60ipm is probably borderline for that system. In motor tuning, try a velocity of 45 and an accel of 5, and see if it still does it. I think you're just pushing it a bit too hard.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Why is it running off at random?
« Reply #25 on: June 03, 2010, 01:21:07 PM »
I cleaned and lubricated the lead screw with Boeshield t-9 this morning. I cleaned the screw by spraying Blade & Bit cleaner while traversing the X axis. At full speed I could stall the motor with the rag with only moderate pressure. After lubrication the screw wouldn't stall unless I applied a fair bit of pressure so that helped some.

Last night I made one of the captive slug type dampers. It is crude because I cut it out on the router and the holes aren't perfectly round. My Harbor Freight 7x10 mini lathe is horribly sloppy but I did eventually get a flange that is round.

Installing the damper on the Y axis did little or nothing. The Y runs quiet and smooth all the time. Putting it on the X axis however reduced the noise by at least 50%. It will now rapid at upwards of 90 IPM without stalling. That isn't cutting anything though. It only stalled right in the middle of the travel. The rod is 1/2" x 10 and is nearly 5 ft long. I fear that the high speed whipping may have bent it slightly.

I am going to try running it at 50 IPM for a while and see if there is any problems.

I have a question about the numbers on my motor tuning but I will post that separately.


Neil

Offline Zaae

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Re: Why is it running off at random?
« Reply #26 on: June 03, 2010, 01:44:36 PM »
I have struggled with the *exact* same problems  :-\

1/2" screws at 5' are really hard to get straight. Even with a "straight" screw, by nature they will begin to whip at high speeds. Over the 5' span, gravity alone causes the little 1/2" screw to sag a little. I switched to 8tpi 1/2" screws on one machine, and it's better since they don't have to turn as fast, but I still think I'd have been better off with 5/8" 6tpi. The problem with that is, that requires all new bearings and motor couplers. I was also concerned that the motors may have a hard time dealing with the extra mass on fast, tiny movements. Maybe someone else has experience with this.

I also made some of those dampers, and aside from making a LOT of noise, they did little, if anything to help. I took them off after a few hours of messing with them. They may help for other problems like resonance, but not for my problems.

On the machine that I'm talking about, I'm using those plastic anti-backlash nuts, and those things can be finicky. I could feel some small bumps / burrs on the acme screw, so I took some fine sandpaper and ran the screws back and forth with the sandpaper wrapped around it until things felt a bit smoother. After that I cleaned everything up really well, lubricated it again, and it's been better. I still run it slower than I'd like though. I decided I'd rather have my projects come out decent rather than wrecking every other thing I cut. Steppers have a lot of torque when they turn slower, but it quickly fades as they increase in RPM.


Offline RICH

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Re: Why is it running off at random?
« Reply #27 on: June 03, 2010, 02:55:06 PM »
Neil,
Consider the following:
I would guess that the screw is not even straight within 1/16" ( .062") in 5 feet. So chances are that you will bind unless there is enough
 motor torque to deflect the screw and  keep it turning unless there is additional slop.  I would adjust the screw position at each end
and see what happens in the middle.You may need to comprimise some.

Then do some rapids away from the ends, and end to end, and see what the max velocity you can get till it skips. Then cut the velocity in half.
Get a piece a scrap material ( worst case stuff you will be using) and now do some cuts at the ends and also the middle of the travel.
The depth should be the deepest you will cut. You will quickly come to some velocity and acceleration value where you can have confidence
with your machine.

Speed is nice, but is not worth crap, unless in the end the part can be machined. You have what you have and don't compare to something else
which is different.

Now if you are not satisfied with the results then change the machine to suite the desired operating conditions. 

So consider experimenting to see what works for you.

FWIW....

RICH

Offline ger21

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Re: Why is it running off at random?
« Reply #28 on: June 03, 2010, 07:00:13 PM »
I have a Xylotex with 250 oz motors. My X and Y axis use 1/2-8 2 start. I can get 180ipm on the 40" Y screw, but the two 60" X screws are limited to about 150 ipm, due to severe whipping.

My Z axis, however, has 1/2-10 acme, and it's only good for 55ipm with an accel of 5. On 2D parts, I can up the accel to 7 or 8, but it'll stall on 3D carving.

And I've found that a light oil is a much better lubricant than the dry lubricant sprays. I use pneumatic tool oil, and it works great.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Why is it running off at random?
« Reply #29 on: June 03, 2010, 08:09:27 PM »
I am considering replacing the X axis leadscrew. I have seen 1/2 - 10 2 start and 5 start. These would'nt require any sort of bearing or coupler change.

I have also considered going up to a 5/8 - 8 2 start. This would help with the whipping problem.

What are the pros and cons of these options?

As I understand it, multi-start will reduce the precision but this is a wood router so 1/32" is more than enough.

Neil