Circular interpolation problem on FanucOiMD

[yaji63]

I' am getting this funny problem of toolpath offsetting itself (or not running as per program) while running a circular interpolation program.

Eg. When i make a program for a bore of 10mm with a 6mm endmill, the dimension i get is 9.6mm. This value of 0.3mm is not consistent and varies depending upon the bore size. During trials we found that a 20mm bore made with a 10mm endmill had no problems and the dimension was perfect. There may be some issues with NC parameters which may be causing this as there is no problem with any linear interpolation programs.

Does anyone know the set of parameters which affect circular interpolation behavior on Fanuc OiMD controllers ?

Thanks a lot for the help

[fordav11]

There are many parameters that affect axis movement. Most of them are only understood by the engineer who designed the controller. You shouldn't mess with them.

I wouldn't worry about it. Adjust the diameter offset smaller by some amount and re-run the program again.

[texaspyro]

If you are using the cutter radius compensation commands (G42/G43) to do the offsetting, a lot of controllers don't like it when your tool diameter (6 mm) exceeds the radius of the circle that you are cutting (5 mm).

Try turning off the tool compensation and manually calculate the required tool path.

[dcoupar]

I' am getting this funny problem of toolpath offsetting itself (or not running as per program) while running a circular interpolation program.

Eg. When i make a program for a bore of 10mm with a 6mm endmill, the dimension i get is 9.6mm. This value of 0.3mm is not consistent and varies depending upon the bore size. During trials we found that a 20mm bore made with a 10mm endmill had no problems and the dimension was perfect. There may be some issues with NC parameters which may be causing this as there is no problem with any linear interpolation programs.

Does anyone know the set of parameters which affect circular interpolation behavior on Fanuc OiMD controllers ?

Thanks a lot for the help

Why not post that section of your program so we can see if it's something obvious?

[angelw]

I' am getting this funny problem of toolpath offsetting itself (or not running as per program) while running a circular interpolation program.

Eg. When i make a program for a bore of 10mm with a 6mm endmill, the dimension i get is 9.6mm. This value of 0.3mm is not consistent and varies depending upon the bore size. During trials we found that a 20mm bore made with a 10mm endmill had no problems and the dimension was perfect. There may be some issues with NC parameters which may be causing this as there is no problem with any linear interpolation programs.

Does anyone know the set of parameters which affect circular interpolation behavior on Fanuc OiMD controllers ?

Thanks a lot for the help

Dave's (aka dcoupar) suggestion is a good place to start. Also supply the cutting tool material and the length of the cutter protruding from the tool holder. Cutting tool deflection has a distinct relationship to the length and diameter of a cutter and the cutting tool material. If the the 6mm diameter cutter is HSS and a reasonable depth of cut is involved, a deflection of 0.20 on radius would well be possible.

If you are using the cutter radius compensation commands (G42/G43) to do the offsetting, a lot of controllers don't like it when your tool diameter (6 mm) exceeds the radius of the circle that you are cutting (5 mm).

Cutter radius compensation is initiated with G41/G42, G43 is used to apply the Tool Length Offset. I've never known the diameter of the cutter being greater than the radius of the circular path being an issue with any control, particularly a Fanuc control. A Fanuc control using a cutter radius offset equal to the radius being cut will raise an alarm, but a cutter radius offset just 0.001mm less than the radius of the circular path will work just fine. In this case the diameter of the cutter will be much greater than the radius being cut.

Regards,

Bill

[fordav11]

Cutter radius compensation is initiated with G41/G42. I've never known the diameter of the cutter being greater than the radius of the circular path being an issue with any control, particularly a Fanuc control. A Fanuc control using a cutter radius offset equal to the radius being cut will raise an alarm, but a cutter radius offset just 0.001mm less than the radius of the circular path will work just fine. In this case the diameter of the cutter will be much greater than the radius being cut.

actually it could be a problem on some machines where the MTB has modified things. On some of our machines (mostly 16 or 18 series) we put the radius of the tool into the diameter offset (the usual practice). on others (most 0-series) we have to put in the diameter of the tool. There is a parameter for that (diameter offset = radius of tool or diameter of tool). But yes, it is technically impossible to cut a radius smaller than the tool radius while in the G41/G42 tool compensation mode.

If the offset is too big and the tool is not far enough away from the circle being cut an 'overcutting' alarm will occur when G41/G42 is applied so that's not a problem in this case because the circle is machined.

it looks to me like if the machine is working 100% in all other aspects that the diameter offset is too big or the actual diameter of the tool is not 10mm (meaning the diameter offset is wrong). accurately measuring the tool will give the real diameter.

so do we stop production and think for days how to solve it or do we simply adjust the offset, re-run the part, get the job off the machine and the next job onto the machine. I know what I would do

[angelw]

so do we stop production and think for days how to solve it or do we simply adjust the offset, re-run the part, get the job off the machine and the next job onto the machine. I know what I would do

Not at all. But if I had a machine that was giving strange, unexplained errors, I would want to find out why. And if the problem could be worked around to allow production to continue whilst a resolve was sought, then I believe that would be the approach made by most.

The OP hasn't provided enough information as yet, not even if cutter radius compensation is being used. Accordingly, advice now can only be based on speculation.

Regards,

Bill

[texaspyro]

Cutter radius compensation is initiated with G41/G42, G43 is used to apply the Tool Length Offset. I've never known the diameter of the cutter being greater than the radius of the circular path being an issue with any control, particularly a Fanuc control.

Sorry... G43 was a typo... meant G41.

I've run into the cutter diameter vs the inside circle radius issue with tool compensation a couple of times. I don't remember which controls were messing up. I do remember that one would throw an alarm, and others would blindly cut a bogus circle.

Cutter radius compensation tends to be one of the more subtly buggy and/or poorly or improperly documented features of controls (despite taking up the most space in most manuals).

[yaji63]

I was stuck with the below mentioned problem and hence could not look in here.

I' am not using cutter compensation and i very rarely use it. These codes are centerline NC codes generated on a CAM system. These codes were cutting parts earlier with no issues and all of the sudden the issue cropped up. A day before the problem the machine was interfaced with a 4th axis table and seems like some digital servo parameters are changing while FSSB setting is being done. Both the installation guy and me are at our wits end to sort this out.

I went to the extent of putting back the MTB given backup parameters which solved the issue but no 4th axis working ! As soon as the FSSB setting is done, it modifies some parameters which makes circular interpolation programs to misbehave. There is no problem with Linear interpolation programs at all.

I' am still on the job and hopefully we should find a way out tomorrow. It still perplexes me as to what parameter could change the behaviour of circular interpolation and how can the controller change the preset parameters on its own when another axis is mounted onto it..

Should i repost this in the Fanuc specific section of the Forums ?...confused...

[fordav11]

first you should punch out the modified parameters and see exactly what has changed checking the parameter numbers in the manual.

the other controller has a circuit board in it and an on-board CPU & software program in ROM that can communicate with the main controller. If it changes things in the parameters then it is programmed to do that. you can only stop it by modifying the 4th axis control software. that'll probably require the services of the 4th axis control manufacturer.

[angelw]

yaji63,
If you download a complete copy of the parameters when the machine functions correctly without the 4th axis, and a similar parameter download when the 4th axis is installed and when you have the condition that gives the error, and then attach the two copies as files in a post, I have software that compares two parameter files for any changes. It will be a quick way of finding the parameters that are being changed and allow you to investigate what the respective parameters relate to.

Regards,

Bill

[fordav11]

actually anyone can compare text files using a free online tool
Free Online File Compare Utility

yaji63, punch out both original and modified parameters as I hinted
in post#10 and just use that online compare tool yourself.

here's one I just did myself.....