Bridgeport ezetrack

[shmoo]

Are there any technicians out there who can help me resolve an
issue with a bridgeport ezetrack cnc? the machine runs fine when
running all the other canned cycles except for circle milling, it does
not make very round holes anymore. Is there a way to tune the
servos to resolve this issue, or would we be better off bringing in
somebody who knows how to work on this machine?

[NC Cams]

Circle milling is clearly a canned program that depends on 2 things for accuaracy:

1. good code

2. good mechanical integrity (low hysterisis) in the machine.

Chances are, the code is good.

Your problem is probably a combination of servo tuning and machine wear/adjustment issues.

We went thru a MAJOR amount of tuning and repairs to get our machine to A, mill round circles and B mill them WITHOUT having flats at the 4 direction change points. The problems are inter-related and BOTH need to be addressed as they affect other areas of operation - you just haven't run into them yet.

First thing to do is to check your gibs for adjustiment. Too loose is as bad as too tight. I played with mine for nearly 3 days before I finally figured out the "secret" to getting it just right, namely to move 1:1 as in table moves 0.0005 for every 0.0005 asked for by 'Trak and or on handle. If the gibbs are unevenley warn, this can cause grief in this area that only lapping/scraping can fix.

ONce you get gibs right, then you need to check X and Y backlash. Ball screw clearance and ball screw bearing slop/lack of rigidity will DEFINITELY NOT allow you to machine round circles. Combine this with ball screw/bearing wear/lack of stiffness will generate backlash and problems in this area.

This is where we found that our ball screws needed a "tune up" (we had a local outfit install O/S balls which helped ours immenselly). Even so, we still had problems.

So then we scored some trick ball screw bearings (long story) that replaced the factory bearings and made a HUGE difference in ball screw bearing rigidity. Fact is, the factory bearings (11060203)are garbage (compred to the proposed replacments), even when new - you can play with shimming them (did that too) but don't waste your time.

The fix: install real high $$$ ball screw support bearings, or medium $ angular contacts or rework less expensive angular contacts (no such thing as cheap bearings for machine tools). Sticking in new factory bearings, will help but will NOT fix the issue.

The high $ bearings are NSK 20TAC47BDFC10PN7A,
The less costtly ones are 7204CTYDUHP4 or PA7
The least costly are 7204BYG's modified to DF with at 150lbs preload by KAF Mfg in Stamford CT.

If the bearings are not grease lubed when you get them, pack them full of "moly fortified" Valvoline wheel bearing grease that meets Ford*Lincoln*Mercury specs.

You may have to come up with a small spacer to take up the space (the oem bearings are goofy non-standard width - ours were goofy) but this is pretty easy to do - we used Smalley 6204 OD preloading wave washers.

The replacment of the ball screw bearings alone took out the "flats" at 12, 3, 6 and 9 o'clock which was also an incidental problems. Even with days of gib work and an ungodly expense spent on redoing the screws and ball screw bearings, we still had out of roundness problems.

At that point, we called in a pro. Ultimately, the machien HAD to be treated to a well done servo tuning. Brian at BPT Machines in Carol Stream Il did ours (630-784-9942)

With the tune and the mechanical tune-up, we can now mill circles within a few tenths of roundness and we can machine masters for our cam grinder as well. The machine is DEADLY accurate and a dream to use. It goes where you tell it to go and does so repeatably.

You don't need to hire anybody (except perhaps Brian) as the problems you have are fixable with the right amount of servo tuning and mechanical parts service, replacement and/or adjustment.

Been there, done that, know better now....