difference in scale between the stl file & print

[Polygonhell]

If it's off in ALL dimensions, i.e. X/Y and Z you want to change the steps per mm, not the arm length.
But I'd make absolutely sure that the error scales with the print before messing with either, the steps per mm is derived from the tooth spacing on the belt and I would assume in general that ought to be pretty accurate.

[Polygonhell]

I don't think so, but it would be worth a sanity check - I think the way the math works out, the diagonal length is only supposed to affect the scaling in X and Y.

The value has to reflect the actual pivot to pivot size of the arms, the value not only affects X/Y scaling but unfortunately introduces doming in the effector motion, the doming is a different curve that that introduced by delta radius and attempting to dial that out one using the other will then leave you with a saddle shaped motion at the outside of the build plate.

[iad]

Hmmm... Well, when I print the little 25mm hollow cube, it comes out 24.75mm on a side (every side), so it's definitely X/Y/Z scaling, and I've noticed the same scaling factor on a variety of other parts I've designed. It's very consistent... Granted, it's less than 1% off, but when I'm design press-fit parts that attach to off-the-shelf components, it definitely comes into play.

Ah, maybe I'll just leave well enough alone, and keep scaling things in Repetier Host.

-Luke

[geneb]

Wouldn't that 1% account for the shrinkage of the plastic?

g.