Problem Z axis off .009 over 12 inches


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Thread: Z axis off .009 over 12 inches

  1. #1

    Question Z axis off .009 over 12 inches

    I ran into an interesting problem on my 1994 Fadal 4020. I was machining blocks to a height of 6.000 . When I check it with a height gauge it was small by almost .005 I thought it may be a faulty reading on the height gauge, but the height gauge is correct. X and Y axis check out, so this is unique to Z axis only. I thought it may be a backlash problem, but that is correct also. I checked the axis card for calibration and it appears to be set right as well. Would a bad resolver cause this? The machine doesn't give me an error.

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  2. #2
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    Default Re: Z axis off .009 over 12 inches

    I had a similar problem when machining identical parts that were located on the left end,middle and right end of the table. Turns out the table had bowed up in the middle by .008". Had to fly cut the whole table to get it flat again. I mentioned this to a retired tech I know who worked only on Fadals. He said was common for the tables to do this over time. Not sure that is your problem but I would tram the table just in case. Check your thrust bearings if that's not it. Good luck and let us know what you find.



  3. #3

    Default Re: Z axis off .009 over 12 inches

    When I checked the Z axis and how much it was changing, it was on a single point on the table. The error is proportional to the distance. About .00075 per inch which leads me to think it is some kind of scaling problem, and maybe a card error.

    I originally had slop that wasn't adjustable with backlash. I thought the cause was the thrust bearings, and a possible reason for the error. However, as I started disassembling it, I discovered a loose set screw in the coupler that was the cause. I tightened it and was able to adjust the backlash (which ended up being 9) within .0001.

    I checked my 6030 and found an error of .002 over 18 inches. This is something I've never thought to check before until I had this problem.



  4. #4
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    Default Re: Z axis off .009 over 12 inches

    hey you need to just get your Z laser calibrated. the laser calibration uses an interferometer to update the ballscrew comp table. it will make that offset go away at all positions, and will get rid of the backlash too.

    problem is u need a laser interferometer, such as the hp 5528, or newer renisahw systems. new sys. costs about 15k or so, so just have a local machine maint. shop come out and comp your ballscrews.

    fadal did NOT comp the Z screws from the factory.

    my x was out 5 thou for example, now its perfect. you just need to have this done either one time, or maybe every year or whatever u can afford.

    also, you will want to check and adjust all the gibs/straps prior to laser comp. just get used to the idea that you actually do need to maintenance your gear, and immediately you can give up on the 'it wont happen to me' attitude. you'll be big time dollars ahead if you learn how to do all the maint. yourself.


    about the table being sloped or whatever issue, just use a surface plate, or if you have the guts you just mill the table flat. trouble with that is that its likely a turcite issue, and eventually you will have to pull the table off and replace the turcite. thats the 'right' way to do it. then ud mill the table flat anyhow after all that.



  5. #5

    Default Re: Z axis off .009 over 12 inches

    Or you could just go the quick route (after checking your gibs and straps on the Z axis, and even relevel the machine) if you know approximately the error per inch just go into the SV (survey) command and type in the error per inch starting closest to the table. It will defiantly improve your results.

    Tip you can only have a difference of 9 (.0009) per inch Which if you did 9, 19, 27, 36,45 in five inches you would have a comp of 45 or(.0045) screw compensation. When your done imputing all the compensation . One othe options will be to write the survey to the card. And then exit and you will have to do a CS. Done



  6. #6

    Default Re: Z axis off .009 over 12 inches

    Here's what I found out. The machine has comp tables for all 5 axis. Using the SV commands, I found the Z table was corrupt. FADAL sends comp sheets with the machine, but only for the X and Y axis. I'm guessing at some point the axis card was changed but the chip wasn't moved to the new board? I had a local gauge inspection company come out to laser it and he adjusted the comp table. Works great now! I haven't got the bill yet, but it took 2.5 hours.

    Thanks for all the Help!



  7. #7

    Default Re: Z axis off .009 over 12 inches

    Glad you got it fixed. Fadal never comped the Z axis at the factory. One thing you could have done or checked was the screw alignment. To do that after adjusting the Gibs, you loosen the Three bolts at the mount top of the Column. And jog Z axis up close to the mount and re tighten the Bolts. You may have done that or the repair guy did. Anyways glad its all good now



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Z axis off .009 over 12 inches

Z axis off .009 over 12 inches