Ball Bar Testing

[heeler]

Does anyone out there perform ball bar testing on their nc machines? Pro's/Con's.

 

Does anyone know the parameter on a Fanuc 18M to allow it to move in G1 G2 G3 without haveing the spindle on.

 

Thanks

[Greg Williams]

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ball bar testing

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Do you mean lead screw?

 

As for performing a G03/G02 funtion all Fanuc controlers that I have used can do this by simply removing the M03 command.

 

[mark l]

You can move in a feedrate mode if you program in G94(inches per minute), but not if you program in G95(inches per rev.), been there done that, racked my brains for hours trying to figure out why the machine would not move when I removed the M03.

[heeler]

Renishaw has a ballbar system that will check the accuracy of your machine. It is being done all around the Boeing company and now they are going to implement it here. I have to get the programs to run our machines. I'll try the G94, but I thought that our machine defaulted to that already. I already tried it without the M3. No go. I really think that there is a parameter to change. When I try to run the program I get an alarm No. 2113 using a feed mode with the spindle off.

[MichaelJ]

I have a I80M that I tested last fall and it worked with gust the G3 and F15. with the arc. move

[Guest CNC Apps Guy 1]

Our Mori Seikis move with the spindle being off. Must be a machine parameter.

 

Ball Bar testing is a very good idea to do periodically (after moving the machine, after earthquakes, after severe crashes or once a year depending on the kind of work you do).

 

JM2C

[Joel Schreiner]

We got our own 2 years ago, because we were having troubles with our old machine. We since got a new machine and we run it 3 times a year as it sets in. tells you alot about your machine.

If you need anything let me know.

joel

[iowajim62]

Hi,

We have the Renishaw system as well and it is an invaluable tool for our Maintenance Dept. We would like to run it every 3 months but sometimes work gets in the way. As far as spindle goes our Mazaks run with spindle off no problem. Must be a parameter on the machine control is my first guess.

HTH

[McRae]

In addition to this question of Ball Bar Circular Interpolation Pitch Error calculations, At what frequency do other plant or operations Laser calibrate the full machine volume. We have been asked to determine a frequency for this sort of a test and it looks as though quarterly is the current guess... Any others?

[heeler]

Good news, there is a M84 to allow for cutting with spindle off, and M85 to not allow for cutting with spindle off. It is an M code for DAEWOO machining centers. Hope comments keep coming for the Pros/Cons.

 

Thanks

 

Glenn

[chris m]

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We have been asked to determine a frequency for this sort of a test and it looks as though quarterly is the current guess... Any others?

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I guess I need to ask why the machines are being tested. If there are no accuracy problems, part quality issues, etc I don't really understand why you would want to run these kinds of tests on the machines. We had two new Okuma machining centers done with the ballbar when we bought them and I really never quite figured out what the testing really told us. Laser and ballbar testing I feel have limited value as they don't put a load on the machine and therefore will not pick up things like loose gibs, way wear, spindle wear, etc in many cases as the machine isn't "pushing" against something. I also think that pitch error problems, backlash, etc can be more simply and economically tested [on smaller machines, anyway] with tools you already have in your shop.

 

I guess that my view is (as James pretty much said) that if the machine has been thumped or dropped on the floor or is exhibiting characteristics of ballscrew problems or something it would be worth the testing; otherwise skip it.

 

quote:

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there is a M84 to allow for cutting with spindle off, and M85 to not allow for cutting with spindle off. It is an M code for DAEWOO machining centers

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That is pretty odd (at least in my experience) I'll definitely remember that one.

 

C

 

[ 12-03-2002, 04:57 PM: Message edited by: chris m ]

[Guest CNC Apps Guy 1]

What Ball Bar Testing does is to ensure that the machine is both accurate and will cut round circles within a specified tolerance.

 

Laser Calibration helps with doing volumetric calculations to comp for probing errors, and telling weather your machine is square and paralell, if it repeats, etc.... I know that if you are a Boeing Supplier, using your machine as a CMM (Probing) and Boeing is buying parts off based on the results (report) then they REQUIRE regular Volumetric Error tesing done on your machine at prescribed intervals.

 

True the machine is not under load when laser testing is done but it will exhibit certain symptoms if the conditions mentioned above are present

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... therefore will not pick up things like loose gibs, way wear, spindle wear, etc ...

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. There are other tests that can be done with indicators to determine if loose gibs, way wear, and spindle wear are present.

 

But with that said, if your machine has not been crashed, has not been through an earthquake, has 5,000 hours or less, does not have problems holding tolerance all day every day and your customers do not require it, it's probably not necessary. But if you plan on going after high precision work ( ±.001 or less IMHO) then I'd suggest it just for piece of mind.

 

On the same note, as a AE I encountered many situations where the machine was blamed for problems with the way the machine was set up. For instance, if you are having problems holding flatness, you may want to check tram on the machine (perpendicularity between the head and the table). Contrary to popular belief, how level the machine is or is not is completely and totally irrelavent. What matters is that when you put a level (.0001 per 18") pointed in X and in Y (on a VMC) is that as you move over the travel of the machine that the bubble does not move. That's where MANY errors hide. As a general rule a brand new machine should reasonably be able to hold flatness to .0001 or better over the entire travel but if the machine is old and has worn ways than obviously this will be effected. As your machine ages, it's important to keep check of these things. Though if your machine only has 4 leveling points then you'll have an awful hard time getting rid of sag in the center of travel.

 

HTH and sorry for the novel.

 

[ 12-03-2002, 08:03 PM: Message edited by: James Meyette ]

[Trevor Bailey]

I had a tech from Fadal out today to look over our machine and check everything out. He kept insisting on the ballbar test that would only cost $200.00. Basically, I could not see doing this. After all was said and put back together, he did the test anyway. He said that he wanted to "see for himself". I said hey great, go for it. After the test was done, he said my machine was out of balance by a thousandth(sp) - .001.... I looked at him and said, "You wanted me to pay $200.00 to find out my machine was not balanced within .001!!!" Then there came this big long explaination about what the numbers REALLY meant. Not to make this any longer, I do not suggest doing this kind of test unless you are cutting extremely close tolerances on a regular basis and have crashed the machine. Do not get me wrong, the guy was really nice and gave us a great price break on everything, but he also wanted to throw in a few grand worth of work that is/was non-essential. Don't get "suckered" in by having work done that you do not need.

[Guest CNC Apps Guy 1]

... and to add to Trevor's post, MOST issues ca be dealt with by adjusting machine parameters (on Fanuc Controls at least) and making sure everything is square and parallel.

[Hugh.Venables]

Thanks for that James. I was a bit surprised that the guy who moved our Mazak VQC20/40A from its previous site to our workshop didn't want to run it to get it level. I presumed he knew what he was doing. I'm off to borrow the good level.

Hugh Venables.

[chris m]

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There are other tests that can be done with indicators to determine if loose gibs, way wear, and spindle wear are present.

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Yes sir; thats what I was driving at with

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can be more simply and economically tested [on smaller machines, anyway] with tools you already have in your shop

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For my $ if the machine makes good, repeatable, parts then its good whether the laser (ballbar, whatever) says so or not

 

C

 

[ 12-04-2002, 10:16 AM: Message edited by: chris m ]

[McRae]

James,

 

You are exactly right, the probing is why we do the Laser Calibration. What is the frequency as dictated by Boeing?

[Guest CNC Apps Guy 1]

Andrew, I'm not really sure but I think that at least 1x per year woudl be a safe assumption. When I worked at Cummins Engine Company, Ford mandated we laser calibrate our machines every 12 months.

 

HTH

[Joel Schreiner]

When we got our new cincinnati the tech leveled it to what he said was .0005. The machine had not been hooked up yet so he said he would be back, he never did relevel it once the machine was up and running.The funny thing is what he said was a .0005 per ft level was only a standard run of the mill .005 per ft level that most shops have. So I told my boss and we leveled the machine. After we were done we ran a ballbar test what a diferance from .00077 down to .00018 on circularity.

We use the ballbar to set max feedrates and still retain accuracy. helps alot. The accurracy will drop a bit at higher feed rates. So depending on the tolerance we may have to slow it down for finishing. I think it has helped lot in optimising tool pathes.

joel

[Guest CNC Apps Guy 1]

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T...he machine had not been hooked up yet so he said he would be back...

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Like I said before, leveling the machine makes no difference, but machines cannot even be correctly leveled without being powered up and able to move.

 

JM2C