calibration for the design and initial leveling

[RonVais]

Hey guys
I must say thanks to all the people here helping and sharing so much information!

Im currently designing moving gantry CNC mill, the design will be a poor mans version of this:


The Design :
The main use for the machine will be plywood/mdf, with some occasional aluminium milling .

The table will be made of 40*40 box section profile with 1.5mm wall, partialy welded and partialy bolted (so i could move it later)
For the frame - ontop of the table I plan to use 100*50 RHS steel profile with 3.2mm wall - (two beams under the linear rails) in between them i will be welding 40*40 box section supports for the spoil board. also the two beams with bolts to the table.

for the rails i plan to use 20mm HGR linear bearing

I tryed to use the calculator that"CNC router" made in the pined topic in this forum, as far i understand the results the tool deflection should be less then 2.5micrometers

http://www.mycncuk.com/threads/2023-...ign-principles

For the gantry i plan to use 300mm 50*100 RHS on witch the catridges are mounted and those pieces will be welded to the Y axis beam made of 2 beams length of 1500mm and 100*50 RHS

and here the deflection (bend and twist) should be less then 50 micrometer

so as far as i understand the calculations give 4 time the precision i try to achive


The questions:
1. To get the X axis flat and coplanar between the two beams i have seen lots of methods but as i sayed this is a poor mans build - i dont have access to precision grinding machines and using a dial - i dont have reference flat surface... so what other methods can i use?

2. The X Frame will be welded to get more stiffness - although the steel can get twisted - how can i plan my design to compencate for that later?

Edit:
i have added some screenshots:


the red arrows shows where the frame will be welded and the steel dimentions, i intend to use 2 types of profiles: 50*100mm with wall 3.2mm and 40*40 with wall 1.5mm