[mflux_gamblej]

I got a VMC20 this year and have been running it for a few months now. I've been very busy, so I didn't have time to precision level that machine. I just checked it quickly with a digital level, and it was pretty close so I left the task of precision leveling for later. I've been making parts using a vise and softjaws on that machine, the parts come out without issue.

Right now I have a job to run that needs to go on a fixture plate, not in a vise. It's the first not-in-a-vise job I need to run on this machine. I got the fixture plate installed and went to mill a scribe line in the fixture to know where to put the stock material, and found trouble. The fixture is 10"x 10" or so and 5/8" thick. The scribe line is a xy axis like a plot so I can roughly align the stock material on the fixture for the first op. The lines in x and y are 8". The scribe was 0.006" deep cut with a 45 deg chamfer tool. In Y the scribe started too deep, and as the machine moved the y axis to cut that 8" line, you could see the scribe getting shallower until it finally wasn't cutting anymore. So there's a big slope in my fixture. That is strange because I know the fixture is reasonably flat (i made it on another mill without issue, it is a piece of aluminum plate, it is not face milled). I put a mag base and indicator on the spindle and put the needle down on the table and took a reading (on the table, not on the fixture) and i found the same damned slope. its bad, like over a 4" move in Y the indicator deflects 0.016"

So I went about leveling the machine to see if that would help. It didn't. I tried purposely tilting the machine fwd and back +/- 2° which is about all you can get out of the leveling feet. I read pretty much that same slope the whole time / no change no matter what leveling configuration I tried.

So its a bit confusing about where the error is coming from. It is not a spindle tram problem - that is a 'local' issue. It seems more like either a column tram problem or maybe there actually is some kind of nasty slope on my table. It might also be the y-axis ways. If there was a table slope, you could level the machine one way to compensate, but if it were the ways you would have to go the other direction. You can imagine the table riding the ways like a wave - which would read the same error on the indicator for opposite slopes in terms of a table slope vs a y-axis ways slope. I measure the same slope whether the table is near the front of the y-axis or near the rear of the y-axis.

at any rate, this is a millwright type of problem. I was not able to solve it via leveling. I am going to put the machine back level this morning and think about what to do. it seems like a very bad problem. if it were like 0.001" that'd be ok i guess, but its way more than 0.016" (more like 0.064" total) across the span of the y-axis. wtf!

[ifixcnc]

The spindle cartridges are shimmed to get tram on an Fadal. If one replaces the spindle, and miss places the shims, they get your problem.

[mflux_gamblej]

The spindle cartridges are shimmed to get tram on an Fadal. If one replaces the spindle, and miss places the shims, they get your problem.

no, you don't understand the problem yet. I could remove the spindle entirely from the machine and still measure this problem. it has nothing to do with the spindle, or with cutting. spindle tram would leave a low spot when you run a fly cutter for example.

this is some kind of column tram or table slope problem.

[ifixcnc]

Another common Fadal problem is the Turcite glue letting go and causing geometry problems. Sorry, I did not read all of your original post.

[mflux_gamblej]

I precision leveled the machine with a starrett 12" level on the ways. the error actually improved slightly, but it is still completely screwed. its about 0.016" / 5.04"; about 0.18 degrees, tilted such that the rear of the table is higher than the front of the table.

I suspect the turcite too now. I pulled back the y-way cover and cleaned everything very nicely. the ways look in good shape - no ruts, and an even film of oil front to back on both sides. it just looks pretty darn good for an old machine. so, it is disappointing if the turcite has worn into a slope.

I'm not the original owner of this machine, who knows what bad habits the previous guys had.


so now i need to band-aide this to get thru my job here. as mentioned before the parts made in soft-jaws coming out of that machine are fine. I have a 4.5" flat round plastic disk part as an example, made in the vise in soft-jaws on that machine. it is edge to edge in any combination flat to within 0.001". that doesn't add up. it should be wrong by a lot! almost 0.01" but it isn't, its flat.

I wonder if putting a surface plate on and milling it flat would fix it? I have seen this come up many times on other forums, but i'd like to revisit it and make sure to fully document whether or not that will work and why. the experience evidence says that my softjaws work fine - they're the same thing as milling a surface plate flat.

[mflux_gamblej]

I prepared several illustrations.

1.) normal configuration where the table and ways are flat.
2.) the table top is sloped

in that situation it is obvious that you could just mill the table top flat and be done with it. that being said I do not believe that my table came out of the factory with a 0.18° slope on it i.e. 0.05" higher on one side than the other.

3.) the turcite has worn itself into a slope. the pictures have an exaggerated slope angle.

i believe the pictures show that if you put on a surface plate and mill it flat, that you'll have a flat surface again. you cannot move the surface plate of course.. so you'd want to pin it or something for taking it on and off the machine.

[mflux_gamblej]

I can confirm that a milled flat surface plate works to solve this problem - at least as a band-aide (that may well last years)

the real way to fix it is to redo the turcite.