[Japazo]

Hey everyone,

I have a couple of problems that are plaguing me right now. About a week ago I faced some large (30" long by 8" wide) aluminum bars in our mill to get the bottom of the part flat before machining the top. I ran my hand across the face after cutting and realized that the tram of the mill was off quite a bit. The face mill was running across the part in the Y axis direction, leaving vertical lines which had visibly noticeable steps. After throwing an indicator on the plate and running across the steps, they measured between .0006" and .0012". We determined that the head was tilted to the left at the nose. We decided that since the machine hadn't been rebuilt in a long time that it was time for a full recalibration. We ran through the entire gib/strap procedure for the tabel in X and Y and also the head. We were able to get the spindle to tram to within .0002" on a 10" circle with less than .001" total movement when pushing and pulling on the head (up and down). We were happy to have it calibrated so nicely, but then came another problem. The Z-Axis servo motor started overheating VERY quickly, within minutes of starting any type of program. We decided that the gibbs and straps must have been tightened too much so we loosened them each by the same amount, which naturally threw the tram out again. We are to the point where we can't get the tram right without overheating the motor and vice versa. The only thing we haven't done is mess with the middle leveling feet. Our machine is not currently bolted to the pad so we cant adjust the middle feet very much without throwing the level way off. Do we need to bolt the front and rear down and start messing with the feet so we can loosen the gibbs and straps enough to not overheat the motor? Any other ideas on what we might be doing wrong?

Problem number two, possibly related to problem number one. We are machining some large coil covers for a race motor and are doing a 3-axis stepover to create the fins (see below). You'll notice some large gouges in the bottom of the troughs that look like the mill dove down too far. The simulation for the program looks fine with no gouges. The problem seems to be the machine itself. Has anyone ever dealt with this before? If so, any ideas on how to eliminate this problem? On a side note, I tried machining in G64 mode (default) and in G09 Exact Stop Check. Both produced about the same result. The only thing that helped a little bit was slowing the end mill from ~140ipm to ~70ipm, but the gouges were still there, just not as deep. At 70ipm the machine is going much slower than should be required for this kind of work.

HAAAAALP!

EDIT: Machine is a 2008 Mag-Fadal VMC 4020 with a Fanuc 0i-MC controller...

EDIT #2: I tried G09, but it made the motion way too choppy and slow. G08 leaves a good finish but I can't get the feed rate over 60ipm, which is going to be about 8 hours of machine time JUST for the fins. G05.1 had the same result but at 90ipm, still too slow. Is there any reasonable way of increasing the feed rate in g08 or g05.1?

EDIT #3: I need to quit posting here before the day is over! I did some reading and found that the G5.1 has an attached R value which controls the speed vs accuracy curve of the AICC. Setting this to R1 got the speed back up where I needed it and still produces a good finish with no gouges. Problem solved!

Attachment 201474

[jeffn]

just a suggestion here. you still might want to open up the top of your spindle and take a look at the Belleville washers. if some of them are broken it would help both problems. before tearing it apart, though, I would use an M19 to lock the spindle and see if you can wiggle the toolholder in the spindle. if you can, you need to replace the washers. when they break, it might give you the impression that the Z axis is not lined up right, when it's actually that the toolholder is not held tightly in the spindle.

[carbidecraters]

Get someone in there that knows what he is doing. You may have put a warp in the base casting and you Z axis may be too tight. Without the machine being level you shouldn't be turning it on.

[Japazo]

jeffn,

I'll check that out tomorrow morning. We inspected the springs not all that long ago and I didn't notice anything wrong in there, but I wasn't looking at the washers specifically. My concern here is that we are able to measure the misalignment in the head and adjust it using the gibbs. A loose tool holder wouldn't show the misalignment that we are seeing when we measure off of the spindle itself. Am I wrong in this thinking?

carbidecraters,

How could we have warped the casting? The machine is sitting level currently with all of the feet on the floor. Level was never an issue. I was just saying that I've heard of people bolting them down and intentionally warping the casting, using the middle leveling feet, to get the z-axis straight. I'm not saying that we have done this, or intend to, without first checking to see if it is an option.