Parts too small in XY dimension

I was wondering if anybody else is experiencing parts that are way off in XY (~2-3% too small) while Z is spot on?

I played around with the rod length in the config.g file, but it doesn't appear to have any effect on the parts. I still end up a few mm too short in my 100x50 mm test print.

Any ideas what might cause this and how to adjust the geometry?

In case it matters, I'm doing 7 point bed probing before each print.

Edited 1 time(s). Last edit at 09/23/2015 02:31PM by floppah.

It's probably caused by a combination of shrinkage as the print cools after extrusion, and the effector tilting as it translates in the XY plane. You can scale the part up in the XY plane if your slicing program supports that, or reduce the rod length in the M665 command in config.g.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].