Ballbar Testing???

[zrwhat]

We just started to conduct Ballbar tests in-house as part of our Equipment Qualifications. We will be running these on a quarterly basis or after any major crash. We will be conducting the tests on all equipment, but I decided to start with our HAAS Mills. We have seven VF-3SS's that are pretty much our work horses for 5-Axis machining. I have the basics of the ballbar test and software down. I am trying to set some machine tolerances, basically an acceptable range that we can run in and anything greater we would need to get maintenance/service involved to troubleshoot the machine.

I did start with my HFO Service Coordinator, but haven't come up with any data yet. I would think HAAS and any OEM would have an acceptable range for say circularity?

For reference one of our brand new VF-3SS's that was tested had a circularity of 0.000457in and another VF-3SS that is almost a year old tested at 0.001087in. That’s quite a difference in my mind, but may still be acceptable?

[underthetire]

1st, remember a ballbar will show stuff that you may not see in a cut. Now it depends on what is actually out. If it's squareness, than can be easy or hard to adjust. Backlash, usually pretty easy; scale missmatch, servo tunning; cyclic error, mechanical adjustment. .001 on what size diameter? You left a lot open. Maybe post your charts ? Normally, at .001 in our shop on the generic machines, I will try simple adjustments to get it better. If the simple stuff won't get it, we let them run the way they are. If they become worse the next time, then we dive in to it.

[zrwhat]

Here are the charts for the two machines I listed.

1 Year Old VF-3SS



Brand new VF-3SS

[underthetire]

You need to get the tram checked. Adjust X comp by .0001, then I think you will be good, IMO. Guess the Haas's aren't that square, that one would be tough to fix.

[Bryan33]

Haas machines should hold .0005 tir on your circularity

[Bryan33]

haas machines hold a .0005 TIR on circularity

[Bryan33]

The spec on a haas VF machine is .0005 circularity

[underthetire]

On what size circle? Full travel?

[Caprirs]

The ballbar test will reveal a lot. However, the test is performed without the load of a cutter pushing/pulling the head, table, and saddle. Thus, the ballbar test is great, but the machine must ultimately be tweaked to the parts that are being run. For most users, the goal is to get the machine to cut perfectly round using circular interpolation. My experience with the Renishaw ballbar tester is it suggests backlash and reversal spike compensation values that are too high and have to be backed off when actual cuts are performed. These values will vary depending on cutter load, diameter, and feedrate. Cutting a 1" diameter bore in steel with a 1/4" end mill at 20ipm needs different values than cutting a 4" bore in aluminum at 100ipm.

When I worked for a machine tool builder, we would guarantee .001" TIR for circular interpolation. Doing better can be done but takes more meticulous everything; tooling, programming, fixturing, machine calibration, leveling, tramming, climate control, etc.

[Bryan33]

Its a 6in cir

[underthetire]

I know his test was a 6" circle, but if your saying all Haas machines should be .0005, what do you base this on? A 30" Y axis machine is pretty useless if it's .0005 on 6" circle.

[hank123]

I am new to this so if I am posting in the wrong place I apoligize.
I just ran a ballbar test on my VF-3 and can't figure this one out. i will put in pics of the test to see if someone has an idea of where to go from here. i just leveled the machine and it actually got worse. the pics are after i levelled the machine. before it was out .0018