Bridgeport/Romi EzTrak lathe servo

============= Ancient wisdom says "if it works *DON'T* f*** with it.

Updated version is "the better is the enemy of the good."

Uncle George

Indeed.

Im a machine tool tech by trade. And I make money on machines that had someone with a screwdriver and far too much time on their hands.

Unless you know Exactly what you are doing...as George said so eloquently..dont f*ck with it. If you got it running without a rumble. (probably loop gain)...count your blessings and dont go for the gold.

Though..I could sure use the work.

Gunner

The aim of untold millions is to be free to do exactly as they choose and for someone else to pay when things go wrong.

In the past few decades, a peculiar and distinctive psychology has emerged in England. Gone are the civility, sturdy independence, and admirable stoicism that carried the English through the war years . It has been replaced by a constant whine of excuses, complaints, and special pleading. The collapse of the British character has been as swift and complete as the collapse of British power.

Theodore Dalrymple,

On an old Acroloc, we had a rumble in "Y". Solved it by cleaning the tachometer brushes. They were at the rear of the drive motor. Ten years ago. Memory fades...

Beege

Well, I've never been inside an SEM motor, so I don't know what sort of tach brushes they use in there. I'm pretty sure it is a traditional DC brush tach. The silver wire brushes usually don't need any attention until the completely wear in two, and then cleaning won't be much use. Cleaning them before that point would require nothing harder than a stream of alcohol, as the wires are hair thin.

This one definitely sounds like a servo loop problem, and the Bridgeport guy has been out several times at $500 a pop to do the same thing.

Jon

Well, since I designed and built my own PWM velocity servo amps, I do have some familiarity with the conventional velocity servo. (My amps have NINE adjustable pots on them, which makes them a bit of a nightmare. Three sounds a lot better.) We definitely feel it is better, and he will probably not be bothered by surface finish issues until the damn vibration comes back in a few months. I was hoping to get some experience from other users of the same machine, as it seems to be a fairly popular model. If we have to retension the toothed belt, or even replace it every year, that won't be a problem. But, I'd like to know if there is a stated procedure for that. (I don't have a good feel for how much radial load the SEM motors are comfortable with.) Obviously, if this keeps needing adjusting in the same direction, we are compensating for SOME change in the system, probably mechanical. Maybe it is the wearing-in of the Z ballscrew, as the preload decreases, the friction, and therefore the damping, decreases, and the loop tends toward less stability.

Well, I think the travel time would be a problem. You're in California, IIRC. We're in St. Louis, MO. Also, if you don't know this machine, the manual information supplied by Bridgeport is a joke. There is a wiring diagram. That's IT! It was enough for me to figure out which servo amp was the Z axis, that's all I was able to get from it.

Jon