losing Z axis position but i think i resolved it

[eelnad]

i have been using my 96x60 PRSalpha for a couple years with a few minor issues until last weekend when i started losing my Z position. i have the home Z position set for 4.000 above the table. i ran a basic cutout for a project that involved some circles and when the routine was complete, the bot returned to the home position but the Z axis physically measured 4.200 above the table even though the shopbot software indicated it was at 4.000. so i read up on the forum about comm issues and grounding problems and pc issues. since i am an IT guy i went ahead and reimaged my laptop with the win7 client and reloaded the shopbot software and still got the same issue of losing the z axis.

anyway, i decided to trace my steps as to when this whole issue began (what changed which could have caused this). i did change bits at some point and i did notice that when i put my trusty centurian compression bit back in, i didn't have the bit in as deep into the collet as i normally do. so after doing alot of unnecessary troubleshooting i believe that the problem of losing my z access had to do with the fact that the bit was not inserted deep enough into the collet before i tightened it. i ran a few more small cutting files last night and the z access is spot on when the routine completes. so my question is: does this seem logical and has anyone else made this mistake before?

[feinddj]

Do you zzero after every bit change? Make it a habit. Unless you are using machine collets which register the bit, your distance will change on every change.

[jerry_stanek]

Could the bit have slipped up in the collet

[beacon14]

If the bit was inserted to the full depth of the collet and tightened properly it should not have slipped, but collets do wear out and need to be replaced periodically. How much cutting have you done with that collet?

[joe]

David,


Thanks for posting about collets. You may have put a finger on the problem. I have a different depth on clean-up cuts. For example: Once I've done the area clear around the letters and background, my next step is to use a 1/8” bit around the letters. That pass is always deeper. "Always". It could be worn out collets. That's such a simple solution I didn't think of it. I'll be doing some test and post the results.

At one time I purchased a few range collets. It seemed like a good way to save a few bucks. I never trusted them. Even if there ok, it was always been difficul tightening them up. Now there doomed for the trash can.


Thanks,


Joe Crumley