From the very beginning I noticed there was a problem with the X rail alingment, now I need to cut some squares so I spent some time disengaging the pulleys from the belts and making the necessary adjustments to trace close to perfect squares.
Are you using an X-Controller(or similar) to run both y-motors individually or are they tied together as setup in the stock configuration? Have you checked wiring and possibly adjusted the voltage to the motors?
On the physical side, Did you check the diagonals of the assembly to check for squareness? Another test you could do is to use two equal blocks and space the gantry from the front and then run a test and then double check with the blocks to see if it torqued during the carve.
Are you saying that without belts you are square? If so, one thing you can try is to turn power off and pull the gantry forward until it stops at a uniform place on each side. I used end stops I made using the post assembly limit switch stops to do this. While holding the gantry against the stops, turn power on to energize the motors. This should ensure that the gantry is square when you start. Try cutting your squares again and see if it’s now correct.
This is a technique that I read about in a ShopBot manual for their PRS Alpha, which looks like a big brother to the XC.
Use the hard stop method until you have $287.96, go to openbuilds and buy 2 1000mm c-beam actuators, the better choice for a gantry machine. You can easily install these and mate them up to you current machine.
Yours seems to be tthe only suggestion that makes sense, I am tired of trying to do something the machine is not capable of doing, do you know if there is any info on the web on how to install the acuators?
The end plates that are at either end of your axis that is perpendicular to the axis with dual belts(can be X or Y) has end plates that use rollers to interface the extrusions on each end. Remove the rollers and motors, save the rollers for future projects, use the motors on the new c-beam actuators (make sure the shaft size is the same size as supplied coupling, and Motors are nema23, if not buy correct coupling size for your motors, $5.00-$8.00 on Amazon) before you assemble the c-beam take the plates and align them with the plates from the X carve(I would remove the plates from X carve so all 4 plates can be stacked together and aligned so both sides are the same) and drill four holes, equally spaced in a square pattern, through all the plates, you will bolt the c-beam plates to the X carve plate during the assembly, this needs to be done in a sequence unless you plan on tapping the c-beam plates. Now you will have no misaligned axis once you get them square. I would recommend getting the no backlash acme nuts from openbuilds with your c- beams, this pre-load will help keep your axis aligned even more in a motor off situation.