2007 Tri-Power not repeating

[jsmithwe]

I was a general machinist for several decades and have a sense of what I'm doing, but I am having trouble getting my Tri-powers to repeat. When I tighten up the gibs the servos just bog down, and when I loosen them up there is too much flex when changing direction in any axis. Even with tuned Mach III motor tunings and rigid setups my machines don't repeat. I bought these machines in 2008 and one has factory installed ball screws (ST108) and factory installed 4th axis servo (ST98S-4) I've been able to use them but I would like them to be more accurate. Any suggestions?

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[Goodlett]

What kind of accuracy are you looking for? Plus or minus .0002 or .002?

First, I'm no expert by any means, so take what I say with a grain of salt. Seems like lack of accuracy could be caused by several things;
1) Gibs out of adjustment. (Seems like you covered this)
2) Slop or inaccuracy in the screws or drivetrain. (I had a pulley loose that almost drove me crazy.)
3) Loosing steps in the motors for some reason. (Maybe trying to move too quickly)
4) Software not programmed correctly. (Maybe incorrect steps per # or backlash not calculated correctly)

There is probably more stuff that I have not thought of.

Do you have a DRO installed? Have you tested it for accuracy?

I am actually shocked at how accurately my machine moves. Generally the DRO matches the computer screen by plus or minus .0004. At least I think that is pretty accurate. It's all relative I guess.

[instructor37]

I was a general machinist for several decades and have a sense of what I'm doing, but I am having trouble getting my Tri-powers to repeat. When I tighten up the gibs the servos just bog down, and when I loosen them up there is too much flex when changing direction in any axis. Even with tuned Mach III motor tunings and rigid setups my machines don't repeat. I bought these machines in 2008 and one has factory installed ball screws (ST108) and factory installed 4th axis servo (ST98S-4) I've been able to use them but I would like them to be more accurate. Any suggestions?

From your description, I would first looked for warped gibs- that will make adjustment impossible- they will either be too loose and allow the table to move around, or so tight it can't move at all-
lots of other possibilities there, most of which you probably already thought of as a machinist, but loose pulleys, that slip back and forth can drive you crazy- be sure the set screws are not worn on the contact end, and are pressing against the flat of the shaft. Thrust bearings that are loose or worn can allow the lead screw to move back and forth in an inconsistent way, loose brackets holding the lead screw nut etc. and lots of possible mach 3 setting issues- mach3 has a good support forum.

[aballworth]

Check the thrust bearings for ball screws. Specifically the y axis. Mine were binding up causing the table to bounce instead of move freely.