Backlash

[davesnd]

Does any one here have any idea what would cause my lathe to cut smaller and smaller diameters from one part to the next ? Like every time my x axis changes direction it gets closer to center by .001 I recently changed my handwheel to work off of electronic gearing - would this be related at all? I am a little fuzzy on what the registers are and if they need to be reset when turning off gearing. I think my x axis ballsrew might not be the greatest - I could have some backlash. I have tried to use the camsoft backlash compensation but it doesn't seem to have the effect i'm looking for - I can use it to make my problem worse but not better. Help

[Karl_T]

I had a drift issue once, pulled my hair out over it. But, I had a +/- spec of .0005" that would be out every 50 parts. You're drifting orders of magnitude faster. I'd first triple check your mechanical enoder connection, then I'd run an old .cbk from well before you had the issue.

I use native galil commands electronic gearing to rigid tap. This screws up the Camsoft position register and I have to MACHZER0 at the end of the routine. If you're doing this with a handwheel, I'd certainly try running your machine without this code present to see the effect.

I don't see how mechanic backlash could cuase your issue. If you read your manual you'll see a lot about encoder rounding errors. For my above problem I went to a 10,000 cout per inch encoder - never have a partial count move. But, the solution was a differential encoder and new cable; machine noise during tool chage was causing lost encoder pulses.

karl

[davesnd]

I checked it out and it is partly a mechanical backlash issue with the ballscrew - It is a little springy. My encoder is running with a timing belt off of the ball nut and the backlash comes from the nut (and therefore encoder)turning a little bit before it starts to pull the screw one way or the other. I don't know how to use the camsoft backlash compensation. I have followed the instructions in their manuals and that gets me nowhere. You can set the backlash compensation for whatever you want and it doesn't compensate at all. The book mentions it compensating after your homing routine - I have no home switches on my machine and I never home it - could this be the problem? The way I think it should work is every time the axis changes directions it ignores a user specified number of counts before beginning to count for the move. What am I missing?

[Karl_T]

Can't help you with backlash comp. When I've found backlash, I work on the machine and fix it. A camsoft control is worth $10K+, doesn't it deserve good equipment? But, again, this can't be your drift issue. The control should return that ballnut to the exact same spot over time.

Home the machine just gives a repeatable MACHZERO. Without it, your lathe has a different zero position after every power off. I can't imagine running a lathe without homing, all your tool offsets would need to be redone. If you can't install home switches, it is possible to home off a limit switch. I have a mill routine that does this.

Karl