[Chalkbot]

Hi,

Just finished building my first machine:Probotix 3-Axis sidestep driver kit
Steppers are Chinese from ebay, rated at 263oz 2.8amp
I have a 24v 16A power supply.
I used the basic design from buildyourcnc, because I only have hand tools.
My PC is 1.8Ghz 512Mb RAM, Windows XP SP3
I'm using Mach3. Full stepping.

So now the problem; While manually moving the motors around in Mach 3 motor tuning, they frequently stop movement and make a loud buzzing sound. Especially my X axis, it almost has no movement at all. I'm using 30 ipm for testing, pretty slow, nothing changes if I adjust it down. Moving the Y axis back and forth I noticed that it happens pretty consistently in one location on the rail, leading me to believe that the motors are really struggling to move the machine and there is just more resistance there. Is it possible that these motors are too weak? Before I mounted the motors I was able to turn the leadscrew by hand but they are sort of stiff I guess.

This has been driving me nuts for 2 days, nothing I try seems to make any difference. Any help would be much appreciated.

[crane550]

Not sure the design on your table, but it sounds like you are getting binding there at that one spot. Something is out of alignment at that spot. Find out what and correct the issue. The steppers are on the small side, but should be plenty to get you going. Some pictures might also help, or perhaps a video?

[ger21]

What kind of screws are you using?

Try setting the drives to 1/8 step. It's possible that part of the problem is resonance. 1/8 step should help, if it's resonance. You might also want to look into making some dampers.
http://www.cnczone.com/forums/steppe...tml#post256639

[kmacht]

I just went through a similar issue with my jgro build. I have 253 oz/in motors powered by the probotix 24v bi-polar drivers and 1/2-10 acme rod. No matter what I did I couldn't get past about 30ipm. Above 30ipm the motor would start to accelerate and then suddenly stop and make this high pitched buzzing noise. After reading on the forums here and doing some experimenting I found that it is a problem with mid-band resonance. I put some dampers on the motors and they are now running at 75ipm and I think I can still go faster with better dampers.

The motors vibrate when running. That is just the nature of a stepper since it moves in very small stop and go increments very fast. When that vibration hits a certain point it will actually cause the motor to stall out (the high pitch noise). What you need to do is move the frequency that it is vibrating at either higher or lower. You do that with a damper. The simple but not most effective way is to just put a counter weight on the shaft on the other side of your motor. Cut out a 3" disk of 3/4" mdf. Drill a hole in it slightly smaller than the shaft of your motor and then press the disk onto the shaft. Try to run the machine and see if it helps. If it does, then it is a resonance issue. Once the machine is up and running you can build a better damper. Do a serarch on this side for "rattler damper" and you will find a thread about 19 pages long detailing it all. There are even some dxf files in there to make a simple damper. Unless your machine is binding to the point where it is hard to turn even by hand, your motors should be plenty strong enough. Playing with a damper is a very inexpensive way to test to see if you have a resonance problem.

Keith

[Chalkbot]

Thank you for all the helpful replies. It's so nice to have a community like this at hand.

I know there is a good possibility that my table does have more resistance in spots than others. This wasn't exactly a product of precision. I was hoping to get this thing working well enough to start cutting the parts for a better machine.

As far as the resonance goes, is there anything I can do if my motors don't have a shaft extending from the opposite side? I can probably see if 1/8th stepping will help any. I was just reluctant to do that since the Probotix driver manual says not to use more than 2.5A in anything but full step mode and my motors are rated for 2.8. My initial suspicions were that the motors lacked the strength, so I was trying to give them all the power I could.

Oh, and my leadscrews are 1/2"-10 5 Start ACME rod.

[ger21]

Just set the drives to 2.5amps (or even slightly less) when using 1/8 step. Shouldn't make much difference, as the torque doesn't appear to be the problem.

If you're motors don't have dual shafts, then maybe you can mount a damper at the other end of the screws? Or, between the motor and the screw?

[neurofen]

hey, sorry you're having problems, i'm just building my first machine as well and just spent about 10 hours tuning my motors quite happily i might add though.

As the other guys said you may well have binding (if without your motors attached your having a tough time winding the axis by hand)or resonance problems, but what you could definately check is the motor tuning tab in mach3, sorry if this is the first thing you did, but you hadnt mentioned.

What frequency have you choosen to be your mach3 kernel speed? try dropping it down to the lowest 25000, which should be more then enough to send th ecorrect pusles to your motors for their max rpm.

are the units per inch(or units per mm) correct

have you added acceleration to your motors, remember they're pushing a mass and will need time to react to this. setting no acceleration can cause them to stall.

i read through the entire mach3 setup guide last night, its full of really good info on the matter of motors and their tuning.. its online and free here

http://www.machsupport.com/docs/Mach...all_Config.pdf

starts about page 73, though i'd reccom readin through a lot of the other stuff in there.

[kmacht]

If you don't have duel shafts on the motor it is still possible to put a damper on. You just have to put it on the leadscrew. Hopefully you left some leadscrew sticking out the other side. One other thing to check is to make sure you have it set to inches and not mm in mach3. I had mine set to mm by default and it was causing the same problem to start with. Turn the motor speed way down to something like 5 ipm. Jog the motor 1" using the dro on mach3 and see if your motor moved anywhere near 1".

Keith

[Flateric]

Quick question have you tried adjusting your Step number not just you speed? You could have one so out of whack that it's pulsing beyond your motor capabilities regardless of having the IPM at only 30.

Just a wild shot in the dark for ya.

[Chalkbot]

Yeah, I've moved the axes in fixed distance increments as well, so I know that's all sorted. Good thought though.

I went out in the garage to try some of these suggestions the other day and discovered that my water heater was flooding the garage, so I had to take care of that instead.

I will get back to this on Friday though and report back here. Don't forget about me!


Edit:
Well, I had a little time to look at it last night. I changed my driver to 1/8 step mode and while that sounded cooler, it didn't really help with the problem. Right now I'm kind of checking the alignment of the parts as I suspect there's a lot more resistance than there should be. After taking off the motors I was able to feel a significant difference in the amount of effort it took to wind the X axis as compared to the Y. After I get that issue sorted I'll try the dampening disk as well. More updates to come.

[Chalkbot]

Well, I disassembled my Y axis. There seemed to be a slight misalignment of the threaded rod and the aluminum rail so that at one end of travel the distance between them grew further apart and the motor wasn't strong enough to drag it all the way.

I drilled out the hole a little larger for the rod bearing, aligned them up the best I could and filled the void up. That seemed to fix the Y axis.

The X axis was very stiff, and I couldn't really see any misalignment. I oiled the rod a bit and then hooked it up to my cordless drill and ran it back and forth several times. It was a LOT easier to turn after that. Perhaps the delrin nut I had on there just needed some breaking in. I'm still experiencing a little drag on either end of the axis, but I have enough workable area that I can use the machine and build something better than what I have now.

I'm going to cut out some of those dampening disks now. I need something to test out anyways, haha.

I spent most of my day yesterday deliberating over which CAM software to get. I tried probably half a dozen demos, but I really only liked the Vectric brand stuff, and also MeshCAM, but that only has support for 3D from what I could tell. My only reservation was the price, but I grabbed Cut2D and it's a great piece of software. I know that I'm going to need VCarve Pro and Cut3D in the future though :\

Anyways, thanks for all the help and suggestions guys. I actually learned a lot from all this, haha.