CNC Machine Setup and Alignment Part 8: Backlash 

Many times with Fadal its the thrust washers at the end of the screw and the whole screw moves. Happy hunting and I'm glad it was helpful.

Thank you Wes, I will try that method when I replace the Z ball screw shortly. Never tried that method before.

Thanks

The three backlash values are for different areas of the screw. A lot of times the center will have more wear and thus more backlash. So the center is just that, the middle third of the screw. The pos and neg and the other 1/3 of each end. You should run the backlash measurements in each area and apply them as needed.

Hello, the translations are a bit rough there. But I think you said you get errors at fast feed rates but not slow feed rates? It might not be backlash at all. Typically when you get a feed rate dependent error check the servo drive gains, balancing, and matching.

​@@AtManUnlimitedMachining Hi, I have this exact problem. my backlash value is dependent to the feed, and it is also exacly proportional: the faster i go, the smaller my bl comp should be... everything started when i decided to level the machine (it was really hight on the back) and then i check the survey data, and it was completly wrong in the y (all zeros untill the midddle of the machine and then 10, 20, 30 ecc.). I think that the old owner changed the y axis card without changing the survey. I replaced the datas with the ones that i found, wrote by a fadal operator in the very first calibration in the factory. i also changed the gain in the Y survey from maximum to normal. Now my machine cuts at the exact length in the y (+/- 0,01 mm on 300mm test). then I noticed that my circles now have steps every 90 degrees, when the axis change direction (the problem there was't before, so I think it is not a mechanical problem). My backlash is ok at low feeds, but it should be reduced at hight feeds. I also tested the axis drives: the balance is ok, the signal gain is ok, the following error is correct in the test program. I can't adjust correctly the compensation pot, but i tried ajusting it, and my backlash on fast feed does't change, and the steps on the circles doen't change... I also tried to put back the gain in the Y from normal to maximum again, but nothing change. Any Idea of what is going on? thanks a lot, and sorry for the bad english.

Are you referring to using a touch probe to set work offsets and tooling length, diameter off sets?

Ah, ok, your talking about a Fadal command called "Learn Mode" or "LE". Yes I can show the use of that command.

Yes, LE command. As I have mentioned that I heard an operator without using probe by touching off with an indicator and use of FADAL LE command can reverse engineering a part. I am not sure if I heard it correctly but I think it make sense according to my understanding reading the FADAL user manual.

Let me see what I can come up with.

Hello, it could be a number of things, thrust bearings, ball screw, couplers, resolver or encoders..... More testing would be needed.

did you fixed that issue?

I personally use Mobiltemp Shc 32

Hello, if your referring to backlash, it will actually show up at the 90 degree points, IE 0,90,180,270 when the axis reverses direction. The controllers do a really good job at compensating for backlash when properly setup. Please refer to this video where we do a circular interpolation with a ball bar and plot the error around the full rotation. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-GhU7gTWo11s.html Errors at 45 degree points, IE 45, 135, 225, 315 are typically related to squareness or servo tuning.

Thank you very much for your support and boy to review your video

Thanks for the comments and for watching!

Yes, Fadal has 3 for X and Y, 1 for Z. But it depends on what the machine is doing. If you have two vises on the table then the wear will be at the 1/3 and 2/3.

Correct, there is a procedure to test and adjust the gains on each servo drive. They are located in the control cabinet on the right side above the card file. I would check that and see if there adjusted correctly and balanced.

Ok I'll check and let you know