BP Series I accuracy problems - Centroid controls

[turbostang]

I have a BP Series 1 that I just recently bought off of ebay and have finally got to start making chips with it. I have noticed that it is consistently off of the target dimension by .006-.007 in X and .004-.005 in Y. This comes with milling a circular pocket, rectangular frame, etc.. it doesn't matter what you are doing, it's always off close to the amount listed above.

I found that the spindle had some scoring inside of it near the top of the taper (NMTB30) so I polished it with a die grinder/flap wheel arrangement and it made the consistent chattering go away.. but didn't help the accuracy any to speak of. It even made it rattle the collet nut loose and drop the tool in mid-cut, but that seems to be gone too.

So, I figured there must be some sort of compensation tables in the centriod controls - and there is, but there is no description on how to adjust them and the numbers don't really have any rhyme or reason to their meaning. The programming manual just mentions calling Centroid for help.

I haven't looked real close at it, but are there any manual adjustments to the ball screws that can help take up the slack?

Thanks!

[jderou]

Sounds like it could be backlash, mine had almost that much before I replaced the screws.
Do you know how to check it?

Are pockets coming out small?

could also be deflection of the cutter if you are taking too big of a cut. Try several finish passes.

Joe

[turbostang]

Well.. I did some testing last night. With a test indicator touching the spindle it would lose .001 on the first move. Every move therafter was right on the money. I'd move it 1.000 at a time and it would return with in what appeared to be a couple of tenths at the most. I even ran it 7" away several times and returned to the test indicator and it was still less than .0005.

I did notice that the spindle has a bit of runout when touching the O.D. of the tool holder, although it may not have anything to do with the problems. I could put pressure on the spindle and get the indicator to move, but I really had to lean on it.

[TRANSATOOL]

Replace the belts before you spend the money to replace the ball screws

You may be surprised!!

[turbostang]

The belts are in fair shape, but they do seem to have a lot of oil on them. I did think about that, and just might do that.

[acerocket]

Wow, this sounds so familiar. I have a Bridgeport Series I with Centroid control. The guy I bought it from had done a complete rebuild a few years earlier and it was a sweet looking machine. But I could not for the life of me cut a square square or a round hole. I too played with the backlash comp numbers but couldn't get it much better. I also had a bit of spindle runout but not too much. Finally got fed up with it and had a repair man come out. The gibs were way to lose. Once they were tightened up, I was back in business and I was making nice square holes and round holes. Sometimes the simplest things we forget make the biggest difference.

[turbostang]

Wow, this sounds so familiar. I have a Bridgeport Series I with Centroid control. The guy I bought it from had done a complete rebuild a few years earlier and it was a sweet looking machine. But I could not for the life of me cut a square square or a round hole. I too played with the backlash comp numbers but couldn't get it much better. I also had a bit of spindle runout but not too much. Finally got fed up with it and had a repair man come out. The gibs were way to lose. Once they were tightened up, I was back in business and I was making nice square holes and round holes. Sometimes the simplest things we forget make the biggest difference.

You know, I went through everything I could think of. I re-trammed the head, I used different indicators, I checked the ball nuts. You name it. So, today, I was talking to my wife wile she was at work(she's a NC programmer) and she handed the phone over to one of the guys she works with - who just happens to be a maintenance guy at her work. We went through the normal stuff over the phone.. and he said "did you check the gibs?"

DOH!

So, tomorrow morning that is the first thing I am going to check. I also called Centroid just in case. When I was testing the machine with a test indicator, I noticed it would lose .001 the FIRST move you made - if you adjust the indicator it would never lose the .001 again. Change to the opposite axis and it lost that .001 again... The centroid guys theory was that since it was so consistent - it was probably a gib and not a setting in the compensation tables. He did send me a service bulletin on how to adjust it on my own though....So, I guess that is tomorrow's project.

[turbostang]

Ok, so I couldn't wait till tomorrow. I just got back inside from pulling the gibs, inspecting them, re-installing, and adjusting them. They looked fine, with no galding at all on them. The X axis gib was definately loose and Y seemed pretty good. I milled another circular pocket and it was much tighter than before, but I noticed that had small, very small bumps where each axis changed directions..... so that alone leads me to believe it's now a setting problem.

This part will have to wait till tomorrow for sure....