Help! My mill is cutting parts undersize, but only in one axis <resolved, bolts loose>

[rk9268vc]

I have a standard 3 axis mill
I have the same ballscrews, servos, revs/in, and steps/rev on all 3 axis

For some reason my parts are coming out undersize, but only in the Y axis

For example, I am machining a 1.75" Square out of aluminum and it measures 1.750 left side to right, but only 1.741 front to back.
It is cutting around 10 thou undersized, but only in the Y axis. It is clamped in the vice from front to back side

I originally thought it was just my endmill/part heating up, because I use the same endmill to rough in the previous OP, but that wouldnt explain it being undersized only in one direction

I am cutting all 4 sides of the square in the same OP, clockwise from the top, climb milling, and repeating finishing pass, 4 flute 1/2" HSS endmill, mist coolant (and lots of it)

Thoughts? I have to get some parts out for a customer and burned all day troubleshooting this. The same issue has happened 3 parts in a row, so it is repeatable at least.
Thanks

[cncsnw]

Is the amount of error, e.g. 0.009", the same no matter how large or small the feature you are cutting?

If so, that is sounding like uncompensated backlash.

What did you find when you measured backlash and set your backlash compensation?

[rk9268vc]

I already have my backlash compensation dialed in, it is under 1 thou in x and y

as far as what features, i dont remember having this issue in the past. I wont be able to try cutting anything else until tomorrow.
I have made accurate parts in the past though, with no changes to acorn settings

[centroidsupport]

Did you set your revs/in? Please supply a report from your system

[martyscncgarage]

I have a standard 3 axis mill
I have the same ballscrews, servos, revs/in, and steps/rev on all 3 axis

For some reason my parts are coming out undersize, but only in the Y axis

For example, I am machining a 1.75" Square out of aluminum and it measures 1.750 left side to right, but only 1.741 front to back.
It is cutting around 10 thou undersized, but only in the Y axis. It is clamped in the vice from front to back side

I originally thought it was just my endmill/part heating up, because I use the same endmill to rough in the previous OP, but that wouldnt explain it being undersized only in one direction

I am cutting all 4 sides of the square in the same OP, clockwise from the top, climb milling, and repeating finishing pass, 4 flute 1/2" HSS endmill, mist coolant (and lots of it)

Thoughts? I have to get some parts out for a customer and burned all day troubleshooting this. The same issue has happened 3 parts in a row, so it is repeatable at least.
Thanks

We don't really have enough information from you to give you good suggestions without guessing. PLEASE take the time to follow this post:
viewtopic.php?f=60&t=1043

ALWAYS Post a fresh report when asking for help. (F7 Utility, F7 Create Report)

[tblough]

If it's repeatable and you have to get the parts out, reprogram the feature to be 1.750"x1.759".

[rk9268vc]

Turns out the bolts in the bracket that holds the Y ball nut to the saddle stripped out partially. So the nut wasnt tight to the saddle. Had 10 thou backlash.
I retightened so i could run the job (ended up with 2 thou backlash) but ill need to get a new bracket

thanks for the help

[martyscncgarage]

Turns out the bolts in the bracket that holds the Y ball nut to the saddle stripped out partially. So the nut wasnt tight to the saddle. Had 10 thou backlash.
I retightened so i could run the job (ended up with 2 thou backlash) but ill need to get a new bracket

thanks for the help

Repair (Helicoil) or make the bracket?
Glad you got it sorted.
Marty