[Zeppelin1007]

Im actually pleased to say its not flex in the machine, I've narrowed it down to the board, or, possibly Mach3 itself. Ive tried different accel/velocity/pulse widths.. CV mode on and off..for some reason i can't figure out, when cutting arcs/circles, the motor gets about half way through the arc, then slows down, then just like completely loses its direction/speed, you'll see the shaft spin erratically back and fourth!

Never fails. 37.5IPM as a feed rate triggers it like clock work. Its the worst here. I found that cutting around 50+IPM solved the issue, or so i thought. Apparently its been there all along, just at higher federates its not as noticeable on the end result, and at lower federates (15-19) its gone completely. around 20-25 it starts, depending on the direction of the arc.

Guys, this will do it with NO machine attached to motors. Exists if i swap motors, chips. Ive reflowed the board, hell, i took it to a technician and had him reflow the board on a Weller station. Ive tried different versions of mach3, I've changed computers. Changed parallel port cables. I just spent the most of the evening cutting and my arcs i had to go ridiculously slow..and I'm sick of it!

Tried Sherline mode. That seemed to make it run a bit..smoother..the chatter is still there, just smoother. I mean, it up and reverses direction! how?? Microstepping = same result. Ive had it! and it frustrating since i bought it second hand, i can't get into the support group.

Im not sure what other things to play with in mach3, so I'm going to try LinuxCNC just for the heck of it, but, yeah. i can't have this problem! Does it with Gcode from any source or the built in wizards. its something to do with slowing down/speeding up the motors in a circle/arc.

I will say if I'm cutting a part with not too much for curves/arcs, and i do the flip...its perfect! I use 0,0 in my "top left" corner for both sides. Have preset jigs on my table, that are simply bowel lines, predrilled screw holes, etc etc. I can easily come out every day. Fire up the machine, load an offset preset, load the machine and go. Minus this arc problem. With the holidays coming up, the incredibly slow rates for cutting projects is NOT an option! But thank you guys for assistance on the flipping issue. That works fantastically.

BanduraMaker, I've wondered about 4 sided machining. Any useful links/advice?

[alan_3301]

can you set your post processor for line segments instead of arcs?
I think it will slow the feed down because of the many many short line segments, but you could see if your problem still exists without g2/g3 commands.

[ger21]

Guys, this will do it with NO machine attached to motors.

What you're most likely seeing is resonance causing the motors to stall. Resonance is even more likely when the motors aren't attached to anything.
If you have dual shaft steppers, add some dampers to them. Even a hockey puck pressed onto the rear shaft can make a big difference.

[louieatienza]

It is possible that with fine leadscrews (10tpi for example) that you enter mid-band resonance zone before you get to a useful cutting speed with these less expensive driver boards and larger steppers. THis had happened to a lot of Xylotex owners who got the 425in-oz steppers and attached them to their Sherline/Taig mills. Gerry makes reference to using dampers; and there is a thread on how to make "rattler" style dampers. The person did eventually upgrade to a G540 which eliminated the need for dampers.

As to arcs... a lot will depend on your CAM as well as CAD. If you're cutting a 2.5D part, where X and Y are continuous and Z is indexed, many CAM software will translate the "arc" moves as G2/G3 commands. If however the machine moves in simultaneous 3-axis, most CAM will translate arc moves as line segments (unless you have a very high-end CAM system.) Some CAM will only do 3D arc moves with Z waterline or Z level finish strategies.

If you already hae CV tured on in Mach3, another thing to try is to change the LookAhead number in the GeneralConfig screen. I found this helped smooth machine movement when movement consisted of many line segments. It seems to be default at a measly 20 lines, but you may try experimenting with maybe 150-200 to see if it helps smooth movement.

My best guess without seeing your machine is, you probably would benefit by just switching your driver to a GeckoDrive G540, which has electronic resonance damping.

[Zeppelin1007]

Hey guys

Im using Solidcam thanks to my school. So I'm sure i can. just using the Fanuc output. But, like i said, the built in mach3 wizards will do it too.

Tried hockey pucks. No luck. :-( Just made me realize the skating rink near me is open and i should go lol.

what does work, is pulling the motor off the machine, laying it down, and pressing as hard as i can on it with the palm of my hands. For some reason, it acts fine then through the ugly parts. as soon as i release pressure, the problem comes back.

What the heck?

these are 425 oz-in keling motors but since its the hobbyCNC board, its at 305oz-in.

[BanduraMaker]

BanduraMaker, I've wondered about 4 sided machining. Any useful links/advice?

Here's a link to a thread I started on this topic: http://www.cnczone.com/forums/diy-cn...p_success.html

[Zeppelin1007]

Ger21 you were correct. I added something alittle heavier and things got better.

Can anybody guess what these are??


Training wheels! lol. Wrapped some electricians tape around the back of the axel, wedged these on...now i can still tell theres some there, but nothing like it was. Guess my hockeypucks werent heavy enough? then again they werent regulation ...the only regulation one i had was a souvenir from the now defunct Cleveland Lumberjacks.

So i think to start and finish the weekend here, im going to mill some "penny" dampers i saw on youtube out of some 3/4" scrap stock i have lying around. I do however have about 200lbs of tire weights we use for weight in the back of my brothers car in the winter, so im thinking of CNC'ing a nice little lead mold for a set of dampers.

Heck even the machine sounds better.

id like to know more/understand about the resonance, if anyone can break it down in laypersons terms.

Bandua, AWESOME neck. i was wondering about necks specifically actually. though not like that, i want to try it.

thanks guys.