Y axis negative direction drift. Help!

I'd also go along with Andy's points as we have previously discussed , being a mechanical issue and or overloading the cutter with feed rate too high

give use some details on the machine you have
what spindle are you using? , what type of machine is it etc , cutter used ? , lets see if we can narrow the mechanics down ,
is the spindle bearings ok etc or is the spindle moving in it's axial bearings etc .

I am simply cutting air at 30ipm. The machine is a Zenbot 24x24 and the router is a Hitachi. The machine uses belts.
Like I said, I can run other programs successfully.

With this one, when it finishes, it has drifted about a tool width

Have you tried running the program cutting air at say 10ipm?
According to the posted program it is calling for a cut speed of F60 and a plunge speed of F10.
If you run it twice is it then 2 tool width off?

Do any of your programs use tool compensation?
It is canceled with G40 .

You may also want to look here at G64
linuxcnc.org/docs/html/gcode/gcode.html#sec:G61-G61.1-G64
Your code calls for G64

G64 - without P means to keep the best speed possible, no matter how far away from the programmed point you end up.

You might try setting the tolerance with G64 Pnnn, I usually set mine at G64 P.001

Rick G

try this dxf attached and see if it cuts any better lowering the feed rate .

what you are describing in that it follows the correct path in air but not when cutting material , is either down to mechanical movement , steppers not able to hold position or to high a feed rate for the milling cutter to handle and shift the swarf correctly
and the cutter becomes blocked etc .

i'd try slowing down the feed rate to F30 on arc's and or increase spindle speed if you can ..

Arc's will show up the worse case on a machine mechanics , rather than straight linear cuts , due to side loading of the cutters amongst others , what type of milling cutter or engraving cutter are you using ?

also what is the material you are milling ?

in your attached dxf :
in that arc you have a lot of small moves which does not help matters , and depending on how cambam interprets arc's etc , you could get different results

If I read it right I thought he stated the problem occurs with air cuts.

At any rate as you stated he really needs to try running at a slower speed to see if the problem goes away.

Acceleration could also still be a problem.

Rick G

yes Rick , I agree .
just trying to cover most aspects mentioned

cncbasher,

Good point, and looking back this thread has some good information for any one who may follows it later.

Rick G

I am about to give up.

I programmed the attached DXF file to cut at 30IPM with G64 P.001
I simply cut air.

When the cutter returned to home position, it was off about three cutter widths.
I can run simpler shapes with no problem. I guess my machine can not handle long arcs.

Now I need to revisit a sign I was doing and figure out what the problem was there, I had drifting issues, but didnt start the debug process.

Like I said, I can run some old programs that have much smaller arcs with no problems.

Thanks.

cncbasher wrote:

try this dxf attached and see if it cuts any better lowering the feed rate .

what you are describing in that it follows the correct path in air but not when cutting material , is either down to mechanical movement , steppers not able to hold position or to high a feed rate for the milling cutter to handle and shift the swarf correctly
and the cutter becomes blocked etc .

i'd try slowing down the feed rate to F30 on arc's and or increase spindle speed if you can ..

Arc's will show up the worse case on a machine mechanics , rather than straight linear cuts , due to side loading of the cutters amongst others , what type of milling cutter or engraving cutter are you using ?

also what is the material you are milling ?

in your attached dxf :
in that arc you have a lot of small moves which does not help matters , and depending on how cambam interprets arc's etc , you could get different results

their should be no difference in cutting any size circles arc's or whatever , or works ok at one size but not at another etc ...
simply put if the cutter is moving off target path there is a reason for it , either feed rates too high or pushing the cutter through the material rather than allow the cutter to do it's work first .
or stepper is missing steps for whatever reason ...

as you are cutting in air and not material , that only leaves , mechanical issues , belts and stepper setup.

remember on arc's you have all axis moving at once and therefore drawing current from the psu at a greater rate , than if you were moving one axis at a time , so check your current settings on the stepper driver they may well be too low
or the psu cannot supply the amperage needed for all the motors at once , for example .