Hi Guys,

Sorry about this super long post, but I tried to send this to Gary at Fadal and it bounced back as he is likely not there anymore. Rather than retyping I thought I'd paste it in here and see if anyone can give me some hints.

Cheers,

Andy

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Hi Gary,

I am not sure you are still around at Fadal, but let’s see!

A while back I bought a new AMP-0021 for the Z axis on my 4020HT. You coached me along with the tuning and it has been working.

However fairly soon I started to get motor overload alarms on rapid moves which I never had before while running the Z from the A axis amp which is an after market amp for smaller motors. Anyway I just dropped the rapids to 50% and had no further problems. Gradually I noticed the head getting “floppier” meaning vibrating at direction changes and making thumping sounds when jogging with the mpg in the fast setting. Also very noticeable during peck drilling.

A few weeks ago I started setting up a job which required to drill a very precise 0,82 mm diameter orifice exactly centered in a tapped hole and I started worrying about getting the orifice elongated in the Y direction due to the flex in the head. I ordered some .001” shim stock and tried to follow the directions for adjusting the head gibs and gib/strap assemblies. At first I couldn’t measure any sideways play in the X direction despite using a serious pry bar. Also I wasn’t too sure about where to place it on the top of the head to adjust the top gib. I thought I would just leave it and check the gib/strap assys as I had noticed most play in the Y direction. The manual talks abut loosening all four adjustment screws and then sliding in the shim stock. This was not possible anywhere, so I loosened them all the way until the threads bottomed out. Only by putting my whole body weight on the head could I slide in the shims between the column ways and the head. After this I followed the manual, tightened both top screws until I could not pull out the shims, reversed until I could pull them out and tightened a full turn each CCW. For the bottom there was no way to slide the shims in so I had to pull the gibs completely out. I cleaned the gibs and one of the trucite laminations fell off. Still it didn’t look bad so I just figured it would stay in place due to the rough grinding pattern on the steel. After sliding the shim stock in first I could wiggle the gibs back in and followed the same procedure as for the top gibs. I noticed that it was very difficult to find a definite point where the shims was pinched. Maybe the trucite pads are a bit soft and more worn on the short ends so the pinching point comes gradually as more surface compress the shim. Anyway I followed the manual, but after the final one turn CCW I noticed the gibs was still so loose I could wiggle them side ways with my fingers.

After this I ran the head up and down a few times but didn’t really see a big improvement in rigidity. I tried a tool change and now I got over load alarms halfway through the down stroke when the head rapids down to pick the new tool. I reset and tried a few more times and always the same. I tried a few rapid moves up and down with MDI to get a consistent rapid feed rate and there was no way I could use 100% speed. I tried 50% and this worked, but on every downward move I saw the following error double from the nominal for a second or so just in the beginning of the move. On the upwards move it is much more smooth and starts with a split second lower following error which quickly goes up to the nominal. So this looks like a stick slip problem. I tried to adjust the two top and bottom gibs which controls slop in the X direction. The only way I could get the indicator to show some movement was with one guy pushing the pry bar using he doorway for leverage and pushing as hard as he could while I looked at the indicator. This way we could just about create a .0002 - .0005 play but it varied a lot.

So I tightened a bit until we had it between nothing and .0003. Again lots of variation between trials. The top was nearly impossible to get an indicator movement on, but I think this is because it is much more difficult to get sufficient leverage with the pry bar. Eventually we had to place the bar between the column way and the spindle motor chassi as the head has too much cooling lines and wiring.

Sorry about this long story, but should it really bee this hard to get the head to deflect? As this adjustment did noting to solve the problem I tried to alternate between loosening the top and loosening the bottom gibs just to see it it made any difference and it did not.

I had a quick look at the back lash and it is the worst I have ever seen! It is 0.0066, which means it cant even be compensated. The highest BL comp seems to be 0.0063 but if I use that I get an over load alarm just by moving the MPG one pulse. I think this is because the resolver see the position deviation. I tried to increase the over load setting in the parameter to 4 instead of the default 2. I also dropped the rapid from 500 IPM to 400 IPM and with this I no longer got the alarm, but moving the Z in the minus direction only one pulse makes the head drop half an inch and swing back up. Moving in the plus direction works like normal though.

I should ad that I had a brand new Z ball screw and ball nut installed when I bought the machine and it doesn’t have more than around 300 hrs use. I have checked a few forums and most suggest the weakest part is usually the thrust bearings. Are those the same as ball nuts? Apparently they can go bad quickly if the seals are bad and the dow frost leaks out on them.

Is it normal that a healthy Fadal makes these thumping sound on quick rapid moves like when peck drilling? I have an old Hitachi Seiki here with a bad ball nut in the X and it also makes a thumping sound after a rapid direction change. The z is smooth and makes no sound at all when peck drilling.

I tried to just move the head down to around 10” from the table and used a big pry bar between the table and head. The indicator showed a 20 micron lift when I pushed as hard as I could. Is this bad or normal? Maybe this is just the defection of the head chassi or the whole column?

With the over load parameter set to 3 I can now do the tool change with out alarm but each time the head changes direction from up to down it seems to over shoot about half and inch. It decelerates and completes the tool change but I worry about peck drilling my orifice as each peck is only 0,8 mm.

If I put some MDI rapid moves in the MDI I can use 100% rapid (400 IPM) without overload. It works fine in the plus direction but on the minus travel it starts out at full speed and the following error shoots up over 2500. after a second it drops the rapid move to 50% speed and completes it with out alarm.

Any ideas what to do?

All the best,

Andy