[MOTOXMAN]

I am new so please be nice. I have a Fadal 4020 FX with a fanuc control. My X axis has a backlash problem. If I am to the far left of the table the backlash is .0007. In the center it is .0002 and at X 4.0 (from machine home) I can not find any backlash. This machine is a 2007 (received Jan 2008) and I have had this problem since I got it. I have always ran parts all over the table to evenly distribute wear. I have had the machined leveled by several people and gibs have been adjusted and it has never went away. Any ideas?

Thanks, for any help

[ekim1956]

OK here we go. I have machines MUCH older than that and I don't have any type of backlash like that. I would imagine that you have some type of backlash compensation adjustment somewhere in your parameters page, (For God sake, a Proto-Trak has one.) which needs to be reset.

[MOTOXMAN]

I have asked the people that I purchased the machine from and they told me that I can not zone my backlash compensation. I have not found any info to back that up or not. I was under the impression that a Fanuc was a great control but.....

[machinetoolmad]

What control is it? Usually Params 1851 and 1852 are used for backlash compensation (Backlash feed and Backlash rapid respectively).

[MOTOXMAN]

The machine has a Fanuc Oi-MC control.

[MOTOXMAN]

OK, maybe I am jumping to conclusions. When I got the machine I did not have this problem. Could it be something else besides the screw or the pitch or the screw?

[machinetoolmad]

OK, maybe I am jumping to conclusions. When I got the machine I did not have this problem. Could it be something else besides the screw or the pitch or the screw?

Whenever there is backlash present, it can be one of a number of things! If you did not have this problem when you took delivery of the machine, its more than likely the backlash you are experiencing is due to wear on the slide OR the ballscrew itself. You can either make the adjustment through the backlash parameters or thru Pitch error comp. (Personally, I would just adjust it in the backlash parameter)

Parameter 1851 is for normal backlash on the machine or if Param 1800#4 RBK is set to 1, then 1851 is used for normal backlash (feed) and 1852 is used for rapid traverse. See FANUC Oi MC Parameter Manual page 116 for more info!

Hope that helps!

[oldedi]

I have asked the people that I purchased the machine from and they told me that I can not zone my backlash compensation. I have not found any info to back that up or not. I was under the impression that a Fanuc was a great control but.....

The Fanuc control only has one backlash setting for the entire axis being compensated, unlike the Fadal Legacy control which allows a setting for center, negative, positive independently.

Loose at one end and tight at the other could be a misaligned ballscrew, or improperly adjusted gibs/straps, or even weight on the table at one end like a rotary table or heavy workpiece.

[MOTOXMAN]

Can a ball screw come out of alignment? I did have the right side of the screw come loose. This is the good side of the machine. The bolts had loosened up to the point that I could move them with my fingers. The dealer told me to just tighten them up and all would be good. I noticed this problem about two months before I found the loose bolts. I do not think the screw is pretensioned though. I was told that they were when looking at the machine. GERRRRRRRRR. How do I check the screw alignment? Is this something I can do without special tools?

[oldedi]

Can a ball screw come out of alignment? I did have the right side of the screw come loose. This is the good side of the machine. The bolts had loosened up to the point that I could move them with my fingers. The dealer told me to just tighten them up and all would be good. I noticed this problem about two months before I found the loose bolts. I do not think the screw is pretensioned though. I was told that they were when looking at the machine. GERRRRRRRRR. How do I check the screw alignment? Is this something I can do without special tools?

If the bearing mount is not pinned, then the machine will line itself up. Sometimes this is the best way anyway. I have seen new machines with misaligned ballscrews that were pinned on both ends.

However, if your machine is indeed dowel pinned, you will first have to remove those pins. This might involve more disassembly than you perhaps want to attempt, you tell me. But basically to align with the machine you just loosen the end of the screw you want to align and then jog the ballnut as close to that end as you can and still tighten the screws. Tighten the screws.

Fadal ballscrews are not "pretensioned", or "stretched" between two thrust blocks. They have a thrust bearing set on the smaller machines, and the bigger ones have a support bearing opposite the thrust bearing. Sounds like your distributor is perhaps not informed or has another agenda that doesnt include happy customers for the long haul.

[MOTOXMAN]

oldedi

I will definitely check the ball screws. I hope that is it. You also mentioned gibs and straps. I had someone come out and adjust them but they did not move the table to check the slack in more than one place. Is that correct? The procedure seemed simple enough for the gibs. He said the straps should be fine and he did not touch or check them. I also wanted to mention that the biggest thing on the table has been a vise. I move them all over the table when I set up to keep wear even.

Thanks,

[oldedi]

oldedi

I will definitely check the ball screws. I hope that is it. You also mentioned gibs and straps. I had someone come out and adjust them but they did not move the table to check the slack in more than one place. Is that correct? The procedure seemed simple enough for the gibs. He said the straps should be fine and he did not touch or check them. I also wanted to mention that the biggest thing on the table has been a vise. I move them all over the table when I set up to keep wear even.

Thanks,

You do not have to change axis position to adjust gibs/straps, he should have set up an indicator on each axis and pried the axis one way then the other to set the proper clearance. Straps are done with shim stock. That said, I do not think your problem sounds like a gib/strap problem. Especially after you mentioned you found the loose bolts on the ballscrew.

[MOTOXMAN]

OK I checked the ball screw alignment and it was not even close. In fact on the end of the screw (with out the drive) I had to grind the holes out to get the screws in without a bind. After that I checked for backlash and found that it only got a little better about .0006. I then checked the backlash of the nut and found none. I found the nut to be flexing on the mount and the mount also flexing to the table. The combination of the two gave me .0007. This was when the nut was near the right of the screw. When I moved to the left of the screw I found no flexing. What is going on? I have ran the machine rotating the vises over the entire table to make for even wear. It has been like this since I got the machine. Could the machine be flawed?

[overflowmachine]

I was having similar trouble with my 4020 we replaced the resolvers on both axis motors and still had trouble. $300.00 bucks each I think or for both ? we eventually found the aluminum coupling was loose on the end of the ball screw. It was hard to tell until we removed the motor and rubber piece that goes between the motor and ball screw coupling. My machine is a 98 it is still not perfect. I have trouble circle milling within .002 and when machining in X Y simultaneously I get vertical lines in the material. (very slight but enough to bother me) This machine has put out a lot of parts and has run almost seven days a week for the last two years.