050826-1313 EST USA
We have a surface finish problem on a VF-3, 1998. This shows up worse at 7500 rpm.
Rather than have HAAS replace one component at a time to find the cause I want to find a means thru measurements on the machine to try to pin point the bad component.
So far we have spent about $1000 on HAAS service and talked to the factory without any clear direction.
What we observe ---
The surface finish problem is visual and is probably in the range of 10 to 100 millionths of an inch ( in the micron range ) in surface variation.
This is somewhat erratic but appears to have some component on the order of 5 revolutions of the spindle. In other words a visual pitch of .02" at 30 inch/minute feed and 7500 rpm gives us, 7500 rpm = 125 rps or 125 Hz for the once per revolution frequency, 30 in/min is 0.5 in/sec and .02" corresponds to about 25 Hz.
If we double the feed rate to 60 in/min then the .02" pitch becomes about .04". This implies that the problem is spindle related rather than X or Y axis. At 60 in/min ( 1 in/sec ) I can see an .008 to .010 pitch also. This is a frequency of 100 to 125 Hz or on the order of once per revolution. In other words we see a once per revolution component, and another at 4 to 5 revolutions.
Both end and side milling shows a surface finish problem. Changing cutters from two to three flute, or changing cutter length does not eliminate the problem. Can not say at this time whether the surface finish changed. Running the same cutters, material (6061), and program on a different HAAS ( VF2 of 1993 or VF0 of 2000 ) produces roughly a mirror surface on the side milling.
The side milling surface is identical whether X or Y axis is viewed.
HAAS tests on drawbar force were just slightly under low limit. Their ballbar test was better than some new machines (well below spec limits). Their spectrum analysis from accelerometer measuring perpendicular to bearing housing produced nothing that stood out. And their testing for end play did not indicate anything. Note, the surface finish problem is under very light load conditions.
We are clearly looking at a variation that results from once per revolution and lower. Thus frequencies below 125 Hz.
The spindle speed on the problem VF3 appears to be very stable.
The VF3 with a problem has a HAAS vector drive. The VF-2 and other VF3 are variable frequency and the VF0 is a HAAS vector drive.
Runout (TIR) on all the machines is on the order of 0.000,5". Also from my tests I am fairly sure there is at least one ball bearing cage velocity of about 1/2.3 of the spindle velocity (rpm). HAAS has been unwilling to tell me what cage velocities I might expect. My 2.3 comes from runout frequency analysis. Also this correlates approximately with an open ball bearing (arbitrary) that I measure about 2 1/3 for this value.
I have now run many tests on vibration (perpendicular on spindle housing), power input to the vector drive, and runout on the different machines. In fact the cage runout component on the VF2 is worse than on the VF3 but the VF2 produces better surface finish.
My next test is force vs displacement on the spindles.
Runout by itself does not appear to be the problem.
The problem VF3 spindle feels very free when rotated by hand.
I am not looking for an individual ball problem because this would produce a higher frequency than once per revolution.
We believe the problem may have developed over a year or two period.
I am following the instrumentation path because it is useful to have a way to pinpoint a cause rather than simply use substitution.
Is there anyone else that has had this problem and what was the cause?
.