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Author Topic: Motors jerking and loosing zero on low speeds  (Read 2308 times)

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Motors jerking and loosing zero on low speeds
« on: February 27, 2013, 05:28:14 PM »
Hi all. Im new to CNC so my apologies now for any noob mistakes but this one has me stumped now.

Ive recently purchased a converted Denford (believed) micro mill, it was allegedly working fine when used by the last owner but I'm doubtful!

Ive rewired it all and neatened up the snakes nest of a wiring loom it had to isolate the issue but it is exactly the same as before so it would appear that was not the issue.

I have an after market control board (which I'm currently waiting for details on) rated at 12-36v
24v power supply
PK266 E2.0A motors (standard from the original machine)
running MACH3 (allegedly licensed but will only run 500 lines of code)

I'm reasonably tech savvy but cannot fix this issue so am finding out if anyone can even suggest an avenue for me to investigate please.

When using the jog function as full speed I now have the motors / axis running smoothly, no jerkiness or sticking. BUT when running a program as the axis move at much reduced speeds it appears to be loosing its 0 positions.

If i reduce the jog rate to 5 or 10% and then index along them there is an audible "jog" in the normal smooth running of the motor and the carriage stalls for a fraction of a second loosing position.

Ive tested this by doing three things.

1: Zeroing the machine to a point and then jogging it round for ages at full speed, when told to return to zero it instantly goes back to the exact point it is supposed to. Success!

2: doing the same at 5% or 10% jog speed which results in it returning close but definitely not perfectly to the position it should be going to. each time its results are different

3: running a program and then running it again, this results in the second cut being slightly off from the first and if I do it again the result is a third set of cuts differing from the first two.

All axis seem to be loosing settings at slow speeds but especially the vertical z axis which usually gets shallower and shallower the longer a program runs.

Any comments are very much appreciated but please excuse my ignorance of terminology right this moment I'm learning as fast as I can :-)
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Offline RICH

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Re: Motors jerking and loosing zero on low speeds
« Reply #1 on: February 27, 2013, 07:20:12 PM »
Mach demo is limited to 500 lines so appears that you do not have a license.

I would highly recommend that you have a look at the Mach Manual.

Please post info on your controller board you are using.

You need to make sure that the steps per unit are correct and that you have the motor tuning done propperly ie; velocity, accel setting for your machine.

Re: Motors jerking and loosing zero on low speeds
« Reply #2 on: February 27, 2013, 08:07:49 PM »
It reads registered on the about page and I have a mac1lic.dat file which was un named  .dat but once Ive renamed it it will now open past 500 but then suddenly stops?

Offline Hood

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Re: Motors jerking and loosing zero on low speeds
« Reply #3 on: February 28, 2013, 03:48:26 AM »
Attach your xml please and I will take a look.
Re: Motors jerking and loosing zero on low speeds
« Reply #4 on: February 28, 2013, 04:00:06 AM »
Fixed in the early hours of today :-)

Id renamed the file .dat when it already had the extension I just couldn't see it because of XPs silly settings!

I think ive remidied the jerky motors but am not 100% sure, todays testing will tell.

Ive rewired with sheilded cable and earthed the shielding but also now switched to 1/16 stepping which seems much happier at slow speeds.

Its been suggested to install 20 to 50Uh chokes on the motor leads too which is next if I see issues still.