Messages

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General Mach Discussion / Re: inconsistent steps, unsure if Mach3 problem

« on: March 21, 2013, 04:15:07 PM »

Thanks Ray, that's a great explanation. I'll give that a try as soon as I can!

My gib strips are far from perfect, I had to make them very tight to get rid of side to side play in the table/saddle. Long story, but it's a pretty old RF-40 table/saddle/base. I have a new RF-45 table on the way to go with my spare RF-45 saddle and base, which I'll take the time to match as well as I can. I'll have to make a new tapered gib and most likely scrape it to fit. Depending on how well that goes, I might scrape the saddle and table too, but I'm really not looking forward to doing that

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General Mach Discussion / Re: inconsistent steps, unsure if Mach3 problem

« on: March 20, 2013, 05:13:42 PM »

Thanks for the replies, guys. Yup, backlash is definitely evil.. Preloaded double ballnuts are on the to-do list, but it will likely be a few months before I get around to that. In the meantime, I'll play around with disabling backlash completely to see how that'll work. I don't believe the machine in it's current incarnation will be accurate to much more than a couple of thou anyway, so it's possible that disabling backlash comp won't introduce that much error, but will provide some other benefits.

Hood, that is a great point about being within the error limit of the drives. I have tightened up the gibs significantly to get around a generally poorly manufactured machine. The following error on the drives is 127 steps, which means at 30480 steps per inch, it's a little over 0.004". I'm sure the drive tries to stay as close as possible to the correct position, but like you say, it's very possible that it gives up if it's close enough.

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General Mach Discussion / Re: inconsistent steps, unsure if Mach3 problem

« on: March 19, 2013, 10:23:29 PM »

I knew I had forgotten some little detail this was measured with a test indicator.. To be fair, if half a thou was all the error I got with the machine, I'd be doing great! Just trying to sort out whatever I can..

I have also noticed that backlash compensation works a bit randomly - lets say I move in X+ until my indicator reads 0. I had 0.003" backlash, set comp to that, etc. if I step in the X- direction, the indicator will sometimes not move on the first step, then move 0.002" on the second step.  This is measured on the indicator, but not reflected in the DROs..

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General Mach Discussion / inconsistent steps, unsure if Mach3 problem

« on: March 19, 2013, 05:50:53 PM »

Howdy Going through the late stages of converting my RF45 clone to CNC. I'm using DMM Technologies servo drives and 400W motors, 3:1 belt driven, with the typical 5mm lead ballscrews.

I have noticed while tramming and measuring backlash, etc, that while jogging the machine in 0.001" step increments, the axis' don't always move a full thou.. The servos have 500ppr encoders, with quadrature, which turns out to be 30480 steps per inch. Even ignoring the quadrature, it should give me step accuracy of 0.0001" or thereabouts, but I'm not seeing that. It definitely averages itself out, if I move 0.020", it'll end up fairly close, but some steps will move it 0.0015, some are right on at 0.001 and some 0.0005.

Any ideas? It could just be horrendous ballscrew accuracy, but I thought I'd check if anyone has seen a similar issue. Any thoughts appreciated

Thanks!

edit: figured I should mention that I'm also using an ethernet SmoothStepper!