New (to me) 1993 VMC40 Fadal with 88HS, circle interpolates ovals

Greetings everyone.
I'm going to start with a short intro. I've been machining for 18 years. I ran mills, lathes, wire EDMs. I have experience with Bridgeports, a Millport converted with Anilam Crusader II, Southwest Prototraks, Seimens 2400 controller on an H.H. Roberts mill, and lately Hurco VMCs all on a professional level.
I've been dying to find a VMC of my own but they've all been too expensive, too clapped out, or too far away.

In March I found a shop that was closing with a very cheap CNC Bridgeport listed on FB, but was sold in 5 minutes. I started chatting with the gentleman who listed it anyway. He was the foreman and close family friend of the owner. The owner passed, the kids weren't interested, and they were downsizing the shop. He offered a Fadal. I had experience with a ton of machines but never a Fadal previously. I went to check it out. It was a 1993 VMC40 with 88HS control. Cat40 tooling. It looked incredibly dirty but you could still see the scrapes on the table. It had 19k hours on time, but only 5k run time. (That's barely 2 years at 40 hours a week) of actual use. The machine was purchased new and had records of annual maintenance. I took a day to go up there. Did a few tool changes, brought a tenth indicator and ran over the table on X, Y. Mag base on the table to check Z. The ways were shiny except where it sat, parked, had discolored from coolant and age. With my indicator in the spindle, it had about .0003 across the length of x and .0001 over Y. (22" x 16")
Spindle run out was about .0002 (when I pushed up on the tool), and about .0006 when there was no load on a tool seated by hand. The X is a little loud on full rapid but I've read it's common for the thrust bearing to go.

It came with a Renishaw optical probe camera and box, but I'm missing one critical piece and I'm not sure what it is. It also had a cog driven belt, which I guess was an upgrade. 10k rigid tapping spindle with a Baldor motor.

I bought it and he threw in a rotary A axis and 4 tool holders with collets. I hired riggers and they delivered it. I used a digital level on the table to level the machine on 8" concrete in an old industrial building I'm renting. I have my own 220 3 ph supply and it appears clean but that's only measured with a Rat Shack ohm meter.

I've been making small parts. One part I make is a special washer with a sortof tight tolerance. .5512-.5520 diameter
I bolted down a sheet, drilled the ID, bolted down, milled the .5512-.5520 shoulder, milled the outside profile. No magic there. They all came out great. I was able to hold that dimension over 250 parts.

Now I'm working on a giant cast iron casting. The thing is probably 60 pounds. It has a 5" thru hole for clearance and a 6.000 +.003/-.000 bore for a pilot. I circle interpolated (minus .010 on the walls) to hog out material and ended up with a diameter that was 5.988 across X and 5.979 across the Y.

.002 on X? That's can be dismissed as tool wear. What I think I'm seeing is some progressive error where. It's undetectable on a micro level (like the washers), but on a macro level it's exacerbated (like a 6" bore).
I bought a Criterion boring head because I knew the pilot needed to be perfect (and I nailed 6.002), but losing .008-.010 over a 6" diameter concerns me. I don't have a mic'ing bar I can double check the machine against. Admittedly I never "tuned" any voltage frequencies either, which leads me here, and now. I just discovered this last night, the 28th. I missed the long holiday weekend where I could've flipped through the book to see but I thought I'd post up here anyway to get a second opinion.
Otherwise it's been a fantastic machine for the time I've owned it and I'm hoping to get many more years out of it.

Paraquat,

Without seeing and being there to do some checks and testing, it is hard to say what is causing the problem. I would do some of the usual maintenance tasks such as pulling out your gibs and make sure they are clean, not overly worn and adjusted properly. If you haven't already, level the machine again and check the square. Just because the machine is level does not mean the machine is square. I can tell you how to do this if you don't already know. Tune the amplifiers and make sure your backlash is compensated properly in all three spots on the table, both X and Y and check the Z. Adjust as necessary to get the BL within a couple of tenths. Don't use the handwheel. You must write a program that rapids away from a step block set to zero with a dial indicator, stops and feeds back to zero then comes back out .0001" and see how much the DI moves. Do this procedure for X and Y, then do the same with Z. Compensate with the BL command. If I were there, I would do all the above then Ballbar the machine and see how it looks. Then adjust the machine as necessary to get a nice, circular trace on the print-out.

Email me and let me know how it all works out. [email protected]. We can always send a technician out if things with your machine gets to that point.

FadalCNC Tech Support

Funny aside I didn't mention. When I got the machine to my shop the extra spindle air filter was never accounted for. The riggers had to remove it before getting it in the bay door. Whether they did something removing it, or I did something installing it, it blew the ENC0004 on top. Took me a while to track down why it would just stop half way through a cycle.
I actually ordered it from you guys, so if you remember one going to New Britain, CT that was me.

I also didn't mention I put the machine on 4x 4" by 4" by 1/2" steel plates.

Aside from putting the digital level on the machine in X and in Y and leveling it out again I'm not sure how to check square so I would really appreciate it if you would share that with me. I'm also not sure how to tune the amplifiers.

I'm just a hobbyist trying to make some pocket change, not start my own business. If these last 8 months have been any indication I can't afford to quit my day job. I barely make an extra 100 bucks a month after rent and electric and after the amount of time I spend there I'd be better served working OT at the daily grind.
Where I'm going with that sob story is that any advice would be greatly appreciated, but I'm not sure I can afford a technician yet. Then again, if I'm making out of spec parts, can I afford not to?

I'll send you an email.
Thank you.

It's easy to tell if your backlash adjustment is off, when interpolating a circle if there's a step at a the point when the X or Y axis leadscrew changes direction then the backlash comp is not correct.

Definitely check the backlash, then tune the axis amps, its amazing how just backlash and tuning the amps can dial them in. Obviously there are many other factors that can contribute, but as far as starters, its almost as easy as setting backlash.

https://www.fadalcnc.com/media/pdf/B..._Procedure.pdf

https://itscnc.com/images/tech%20doc...20-%20V1.5.pdf