Compensating for non-perpendicular axis

[lsteele]

Hello,

I've built myself a wood-constructed (MDF) router, loosely based on designs at buildyourcnc.com, but with quite a lot of reinforcement in the form of right angled bracing of the gantry and a much sturdier table. Much to my surprise it works quite well, and I've had some success cutting pine, mdf and even some aluminium. However I have one major problem which is that the y axis, which has an effective working area of ~290mm, is not entirely perpendicular to the x-axis. Between 0mm and 290mm on the y axis there's a deflection of around 1.25mm.

I want to redesign the gantry and y-axis anyway to solve other problems with rigidity, and the obviously would like to construct the parts on the router. But I don't want the accuracy to be undermined by this problem. Is there a way I can correct this problem in software - i.e. have the software operate the machine to compensate for the non-perpendicular axis? I'm using mach3 and solidworks. I have cambam, and have access to solidcam, though this is somewhat inconvenient as it involves travelling to a friend's place.

Any suggestions/input are gratefully received. If my description of the problem doesn't make sense please let me know and I'll try to better describe it!

Thanks,

Luke Steele

[ger21]

Try this. In Mach3, go to the Function Cfg menu, and choose formulas. Check the box to enable formulas, and change the f(x)= to x+y*(1.25/290)

As the Y axis moves towards 290mm, the X should adjust by 1.25 when Y gets to 290. I did a quick test in my Demo install with no machine, and when I typed G1 Y50 in MDI, the X axis moved along with the Y axis.

Do a lot of testing to make sure it works correctly, as I can't confirm that it will work for all situations, but it's worth a try.

[ger21]

Be aware that if you try this that the X axis DRO will display the actual value plus the compensated amount. So if you're Y axis is at 290, and you do a G1 X0, the X DRO will display 1.25, not 0.

[lsteele]

Thanks for this, it seems to be working great. My parts are visibly squarer than before! Now to build a router that doesn't require this sort of fix...

Luke