I first noticed this when the front door is open (on this pre-release it is really stiff to open) the front edge of the lid would rub slightly on the left. Close the door and lid clearance was restored.
Since I had originally placed the machine, the left edge of the lid glass top had been about 1/8" raised from fully closed. I just placed a little weight on it.
Recently while troubleshooting the ventilation problem I was having, I moved the glowforge across the room to my steel welding table. I immediately noticed the lid was rubbing. I cleaned out the fan grill in back and moved the machine back to that slide out shelf it lives on. I re-positioned it maybe an inch from where it had been before, and not only was the lid not rubbing - but the lid shut completely.
The glowforge case is nice and rigid, but because of its size and weight a slight deviation in the supporting surface can telegraph into the form, and therefore the fit of the lid.
If the lid on your glowforge exhibits one side of the lid not seated completely, I would suggest you explore and see if moving it slightly or shimming a corner fixes that.
(BTW, the aluminum from a coke can makes excellent shim material. Scissors cut it like paper and you can stack it to achieve the required thickness.)
During furniture installation for customers, I would put a new dinning chair down on the floor and it would rock slightly. The customer would immediately assume the chair was defective. I would re position it and it wouldn’t rock, demonstrating that the floor was not glass-flat.
Point of that is your cart or table may telegraph a deviation of the floor its sitting on to the top your glowforge sits on.
Edit; Not a problem with the machine, a problem with gravity. Welcome to earth.
Good advice. @palmercr has talked about the importance of this quite a bit as well. Of course, if the lid is moving around enough to cause it to stick when the feet aren’t all coplanar, it’s going to be taking the camera along with it, and a small amount of camera movement will, presumably, translate into a greater amount of alignment error. Having the homing location somewhere other than the center of a hinged door would have been a wise move.
Is there any reason to think the feet of the case are coplanar? I only have a basic knowledge of plastic injection molding, but I believe that plastic builds internal stresses during the injection process, and once the part is ejected from the mold those stresses cause the plastic to warp while it cools. Unless the feet of the case are machined to be coplanar after molding, I suspect they have little chance of being coplanar when the Glowforge is being assembled. Hopefully the Flex workbenches are flat and level when the machines are being assembled and especially when they’re being calibrated, because finding a household surface that is truly flat and level is difficult enough, finding one that matches some unknown surface at Flex would be next-to-impossible.
This problem would exist, to some degree, even if the Glowforge wasn’t made of plastic. Every material will deflect by some amount and many machine tools have provisions to compensate for this fact.
Oh man, the machinist shop in the Navy had one that was a 5’x5’ table, surface about 2’ thick and legs that were part of the same piece of rock. ‘Microflat’ was the name on the tag. Smoothest, flattest surface I ever touched.
For some reason I think my grandfather had two of those sitting in the backyard for the brick barbecue stove? Yeah…gonna call it a stove top. We’d sit on/in it like a big brick throne…and then someone’d have to go and build a fire on the chair, drop a big steel grate over it, and it was now a grill. Ah. Backwoods living. Kinda miss those times.