Tool offsets

[mark911]

1994 Bridgeport Romi

From what I understand, when setting tool offsets the control uses the "current" position of the tool relative to the machine coordinate system and inputs the "difference" as the offset into the offset screen. This should result in typical offsets of X-12.xxxx and Z-30.xxxx. However, when I perform the facing and turing process for setting offsets and input 0 for Z and the exact Dia for X (as stated in the manual), those same values are set in the offset screen. I didn't expect this. I'm using the ABS input mode.

My manual even states that the values entered will NOT be the same as those recorded in the offset screen. I'm confused . . . . . .

Also, the maual says to use the same part Z face to determine 0 Z for all additional tools used for that job. That doesn't sound like a very accurate way to set the following Z postions as without an actual cut all you can depend on is a visual or feel "touch off". I guess I could face an additional few mils, measure the exact delta cut and input that small value for Z

Another issue, but those with hands on experience, how accurate is the jog "step" function. I seem to get erratic moves, some right on, some long and some short moving in the same direction (Z is .0005 per step is spec). Mine can be off +/- half that. Could this be a servo amp POT adjustment or just a function of the static friction and small move?

Anyway, the Bridgeport manual sucks so any help would be appreciated.

[bret4]

Originally Posted by mark911 1994 Bridgeport Romi From what I understand, when setting tool offsets the control uses the "current" position of the tool relative to the machine coordinate system and inputs the "difference" as the offset into the offset screen. This should result in typical offsets of X-12.xxxx and Z-30.xxxx. However, when I perform the facing and turing process for setting offsets and input 0 for Z and the exact Dia for X (as stated in the manual), those same values are set in the offset screen. I didn't expect this. I'm using the ABS input mode. My manual even states that the values entered will NOT be the same as those recorded in the offset screen. I'm confused . . . . . . Also, the maual says to use the same part Z face to determine 0 Z for all additional tools used for that job. That doesn't sound like a very accurate way to set the following Z postions as without an actual cut all you can depend on is a visual or feel "touch off". I guess I could face an additional few mils, measure the exact delta cut and input that small value for Z Another issue, but those with hands on experience, how accurate is the jog "step" function. I seem to get erratic moves, some right on, some long and some short moving in the same direction (Z is .0005 per step is spec). Mine can be off +/- half that. Could this be a servo amp POT adjustment or just a function of the static friction and small move? Anyway, the Bridgeport manual sucks so any help would be appreciated.

On my machine, EZ Path SD. When I set Z zero at the face of the part close to the chuck I get a number over 30 inches in the offset screen. In the X I get a large number too. Not the same number entered. Everything comes from the home position. I wonder if your machine has some kind of problem with homing? Wonder what version of the machine you have? How old is it?

You have to touch off every tool to the part you are working on to set the offset for it. Most of the time this is not a problem because you are going to cut the part that you are touching off on. If it is a problem you can use a small strip of paper between the face of a part and the tool so you do not damage the part. Just remember to add the thickness of the paper to the z offset. Something around .002 should get you close enough for most work.

Its just the nature of the machine that you end up setting offsets on all your tools a lot if you make a lot of different parts all the time. Remember, this is not a production machine like a full blown CNC lathe. It's a manual machine that has a CNC control on it. If you look at the Romi lathe site you will see that these are manual lathes converted to CNC. Take the good with the bad. They blow away any manual lathe for day to day toolmaking. That is what they are really great at.

I never use joging in steps. One thing I do know is that the machine can not move in small amounts in the do event mode. I think anything under .001 thou of an inch and it will not move. That could be why it doesn't move the distance you think it should when moving at .0005. Anything over say .0013 and it should move just fine. When programed it holds repeatability right on the money.