How do I square my x and y axis?

How do I square my x and y axis?

I have a gantry and table that needs to be made square. It is a
large sized table

with an x axis of 3meters and a y axis of 2meters.

I have tried to square it using the triangle, ie 300, 400 in a right
angle, then

the angle distance should equal 500. If the distance does not equal
the 500, you

would adjust the gantry so that it does.

The problem for me is that as soon as I readjust the gantry to meet
the 500

measurement the whole show will go out of whack!. This is because
the pivot point

for the y axis( the gantry ), where it bolts to the x axis is not
right in the

corner. So this would make the corner point move when I go to
adjust for the 500

distance on the diagonal.

I have also used the largest sized triangle possible. I have a
sheet of mdf

laying down that is 1200x2400(4'x8'). And I have a pen in the z
axis, drawing a

triangle. The triangle is 1200mmx1600mm and then the diagonal
should be 2000mm.

Problem with that is if my steps per unit are out and the machine
travels say

1201mm instead of the 1200mm the triangle idea will not work.

Anyway, that is what I have done so far.

There is another way using a square and setting up the dial
indicator. You set up

one axis, say the long one (x axis). Make sure that the indicator
stays on 0 the

length of the square. Then set it up for the y axis and adjust
until it is

square. Thing is though, what am I going to use to run the dial
indicator on as

a square. A normal square is to small and also the edge is to thin
to run a dial

indicator along.

I mean even if I weld up a 90 degree bend out of two bits of box, it
is never

going to be square enough for my dial indicator. It goes down
to .01 of a mm.

The box steel will warp with the heat from welding. I would have
to get it

milled square. But even then it would have to be pretty big to get
the best

accuracy possible. Not to mention it would cost a fortune to mill.

I am now thinking of using the sheet of mdf to square the machine
with. If I was

to lower the z axis to say 10mm above zero. Then push the mdf up to
the z axis I

could then rapid the x axis down the edge of the mdf sheet and then
push the sheet

up to the z axis there as well. I would continue to do this until
the long edge

of the mdf is parrallel with the x axis.

Once that is done I would just have to repeat with the y axis along
the shorter

edge of the mdf.

Would this idea work?

All and any ideas will be greatfull.

Peter
Australia