Loosing Zero Reference on new CNC Mill

[robert4wd]

Hi All
I have just purchased a Chinese CNC Router 6040 ( http://www.ebay.com.au/itm/320774368487?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 ). I have set-up a PC with Windows XP installed a licensed version of MACH3 and set-up as per the instructions provided with the router.
I downloaded the Scorpion from the download section of this forum. It seemed to cut fine until just near the end when the cutting line seemed to suddenly shift. I put on a new piece of board this time I drilled a hole at the (0,0) position the board. I ran the Scorpion again. When I got back to (0,0) I drilled another hole. The holes had shifted by 5mm in Y and 3 mm in X. Repeating this process multiple times the (0,0) point always shifts between 0.5mm and 40mm. Never the same amount twice.
I have tried the following
•   Turned off the steping motor controller and turned the two lead screws through their entire lengths. No tight spots felt
•   Changed the frequency from Kernel Speed from the recommended 35,000Hz to 25,000Hz. No difference still losing zero.
•   Halved the Motor Tuning Velocity & Acceleration parameters from the recommended 1200 & 300 to 750 and 150. It made no difference.
•   Went through the Windows XP tuning guide on the MACH3 support site and made all setting suggested. No difference.
I am at a loss to know what else to try. Any suggestions? Thanks
Regards
Robert

[ger21]

Try reducing the acceleration to 75.

Looking at the specs, it seems to be somewhat underpowered. Make sure the screws and bearings are well lubricated, and make sure there's no binding anywhere. Disconnect the motors and make sure the screws turn easily with your fingers. The slightest amount of binding can cause problems.

[robert4wd]

Thanks Ger21,

what would you suggest to lubricate with? Grease or silicon or oil?

Regards,
Robert

[budman68]

Hi Robert, I may be wrong but I "think" I remember Gerry recommending this product from Mcmaster:

 p/n # 1378K32   High-Temperature Synthetic Grease with PTFE, 11-Ounce Aerosol, Nlgi #2

http://www.mcmaster.com/#1378k32/=etdbk6

Please wait for Gerry to confirm.
Dave

[ger21]

Wasn't me.

On my acme screws, I use pnumatic tool oil.

I'd just recommend any light oil or grease. Just be aware that if you don't have good dust collection, it'll be attracted to the lubricant.

[budman68]

Thanks for commenting, Gerry, could have bet it was you 

[robert4wd]

Thanks for all the advise and sorry to have taken so long to let you know how things turned out. The Mill was much better with an acceleration of 75. It would still loose zero sometimes but at least in general would reproduceably do multiple paths around a circle. I am looking now at upgrading the servo motors. Thanks again for all the help
Regards
Robert