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View Full Version : Accuracy Issues with CNCRP PRO4896-Please Help



talonosi
08-28-2015, 11:39 AM
I just discovered accuracy issues with my router and am having a hard time thinking of what the error could be. If I cut 2 6" squares stacked on the Y axis there will be .060" of variation between two that are right next to each other (Starting at Y0, I haven't tested across the entire Y axis yet). I contacted CNCRP and they said that it may be caused by bowing in the Y axis rails, however I can't fathom how that could cause an issue unless it is so much resistance that it is causing the stepper motor to lose steps. Losing steps or a loose pulley on the stepper motor should both manifest themselves with other problems, but everything else is working fine. Its a very repeatable error, I could drill 1/8" holes 6" apart and they would be off by .060" inches each time in the Y0-12" range. But the machine stays properly zeroed and could drill the exact same holes again perfectly. (Something I wouldn't expect if I was losing steps). Any suggestions? My only thought is that it must be related to an inaccurate rack (which I intend to measure later today) or that somehow it could be an error in Mach 3 if it is treating the low side of the Y axis differently because of soft limits and how it may be effecting velocity/acceleration (I don't know enough about Mach 3 to know if this is even possible, but I can test it by removing soft limits). So, Any thoughts?

Thanks

jueston
08-28-2015, 04:32 PM
i'm not sure i'm 100% clear on where the inaccuracy is manifesting.

when you cut two squares, one of them is longer on the y axis then the other one? meaning in one area its cutting correctly and in the second area its too big or to small?

i would be interested in seeing the results of testing the rest of the Y axis.

also how long has this machine been assembled and running? was it working and then this started to happen, or has this been happening since it was assembled and your just noticing it now?

ahren
08-29-2015, 10:00 AM
Talonosi,

Give us a call on Monday and we can delve into this with you in more detail. If your top rail is not straight (if there is a localized dip in the rail), this can cause the z axis to "swing" as it is traveling along the gantry. We can help you sort this out when we're back in the office.

Ahren
CNCRouterParts (http://www.cncrouterparts.com)