2006 vm3 poor finish on interpolation

npolanosky · Apr 29, 2019

I just noticed an odd issue on my VM.
I am getting faceting on g2/g3 arcs, but seemingly only in specific places.
It seems to happen only in the upper left quadrant of the part. I am digging in further to see if it happens in both directions and at different feedrates.

It happens only on arcs, straight lines on the diagonal seem ok.

I already eliminated it as a programming issue (I am getting arcs, not lines, and it happens regardless of g187 setting), this is either something weird in the control or more likely a mechanical issue.

Is this indicative of bad thrust bearings? Bad encoder? Something else? It's just odd to me, everything seems to work perfect and hold dimensions except for this.
I have no measurable backlash. Everything is nice and rigid as far as I can tell.

I cut a small test part, you can see the difference from corner to corner. I will run further tests today at varying feedrates with different tools.

greggv · Apr 29, 2019

have you had a ball bar test done on your machine lately? Usually, poor finish at quadrants of an arc can be "dialed out" with a good ball bar operator. At least on our VM3

npolanosky · Apr 29, 2019

I have not. Is that something I need to call HAAS about, or are there third-party companies who do that?

Delw · Apr 29, 2019

npolanosky said:
I just noticed an odd issue on my VM.
I am getting faceting on g2/g3 arcs, but seemingly only in specific places.
It seems to happen only in the upper left quadrant of the part. I am digging in further to see if it happens in both directions and at different feedrates.

It happens only on arcs, straight lines on the diagonal seem ok.

I already eliminated it as a programming issue (I am getting arcs, not lines, and it happens regardless of g187 setting), this is either something weird in the control or more likely a mechanical issue.

Is this indicative of bad thrust bearings? Bad encoder? Something else? It's just odd to me, everything seems to work perfect and hold dimensions except for this.
I have no measurable backlash. Everything is nice and rigid as far as I can tell.

I cut a small test part, you can see the difference from corner to corner. I will run further tests today at varying feedrates with different tools.

Did you use a fresh tool? also what size and how much stock did you remove on the finish pass.

Reason I ask is the corners/fillets look like there broke down

rough the part out leaving .010-.015 stk then take 2 finish pass's at size.

this will tell you a few things. if your spindle is on the fritz. (ie cant handle tool pressure) encoders bad or back lash.

I can see the segments but they look awful large for a encoder issue. what happens if you cut feed in half?

Delw · Apr 29, 2019

one other thing you can do
put a parallel at 45º then pop a indicator in the spindle and run 45º program and see if its smooth on the indicator or jumpy

npolanosky · Apr 29, 2019

I'll run some more tests today with a fresh tool and take some pictures with my DSLR in decent lighting instead of my cell phone in the shop lighting. The tool is well used, but still doing OK. It's a 3fl 3/8" .005 radius variable flute ZrN tool from Lakeshore carbide, but it probably has a few hundred cutting hours on it and is getting a little streaky.

npolanosky · May 2, 2019

No pics handy, but I have been running parts. All different tools, holders, part geometry, stock size. Still noticeable with all combinations of the above.

It seems to only happen at a particular spot along the Y travel, and there is an accompanying change in sound. Very subtle, but I can hear it on light cuts or when handle jogging. Of course, it's right around where the fixed jaw of my vises tends to be, so it's tough to avoid.

Is it possible some crud got onto the rails or ballscrew and is causing this? If so, is it as simple as cleaning things or is it easy to permanently damage the screw with the slightest hint of FOD? That is, should I get out my wallet and order a new Y screw now or is there hope?

I'll pop the way cover open this weekend and have a look.

I'll bolt something to a different spot on the table and make sure it'll do a clean circle elsewhere to confirm my suspicion.

Chris59 · May 2, 2019

On the third picture it looks like my parts do when I have splines in the model. Long shot but something to look at maybe. When the program gets to the splines the sound changes too since the machine is making many tiny moves.

npolanosky · May 2, 2019

Chris59 said:
On the third picture it looks like my parts do when I have splines in the model. Long shot but something to look at maybe. When the program gets to the splines the sound changes too since the machine is making many tiny moves.

That is the first thing I checked, but I am 100% sure it is only doing arc moves.

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