TimmyZ wrote:

So just to be clear… Am I manually setting that for the 4 arm Z settings when

I introduce a workpiece? So subtract or add whatever thickness measured from

the sheet of wood or as long as the work piece is 3/4 inch thick the

calibration presets already accounts for the work piece?

in a perfect world yes.

in practice, the flatter the belts, the less it matters. Again, we don’t have

good testing of this (I think a lot in terms of theoretical problems, so not

everything I spot is a big problem in the real world, and it depends on what you

are doing. Are you doing theater sceanary? or small parts that must slot

together exactly?)

To put some numbers together here to see how much error is being introduced:

if you are near a corner, you have ~2’ of belt extended, let’s say 600mm to have

a nice round number.

If the real Z offset is 100mm, then the actual x/y distance to the anchor is

591.6mm

if the real Z offset is 120mm (~3/4" difference), then the actual x/y distance

is 587.9mm

3.7mm of difference when you add the height

now let’s do a lower arm

If the real Z offset is 38mm, then the x/y distance is 598.8mm

if the real Z offset is 58mm (again adding a 3/4" piece) then the x/y distance

is 197.2mm

1.6mm of difference

if you set things up so the anchor is level with the arm, the x/y distance is

600mm

add the same 20mm and the x/y distance is 599.7mm, a 0.3mm difference

now let’s say you are 4’ from a corner (1200mm)

Z offset, distance

38, 1199.4mm

58, 1198.6mm .8mm difference

100, 1195.8mm

120, 1194.0mm 1.8mm difference

20mm, 1199.8mm .2mm difference from flat

at 8’ (2400mm) from a corner 100mm z is 2397.9, 120mm z is 2397.0, a .9mm

difference

But keep in mind, if you add height to make the belts flat, but your anchors

have 3mm of flex in them under full load, you have added more error than you

eliminate. Flex is a bigger problem in most cases than the angle.

This is actually worse in the corners than I expected for the upper arms, and

this sort of error really causes grief if it happens during calibration, so it

may be that we need to mention setting the Z offset values and being sure the

router is all the way down before doing the calibration @bar, @anna

David Lang