I semi-recently partially assembled a LowRider V3 with an SKR Pro 1.2 using a kit from the shop. I’ve had a chance to revisit this build and have been performing some calibration tests on the mounted unit. For reference, my LR3 is mounted to a 4x8’ frame.
I’ve run into an issue with my LR3, though, when I attempt to cut things along the Y-axis. I’m noticing significant Z-height drop as the gantry moves down the Y-axis. As an example, if I zero my bit above a piece, drop the bit 1mm into the piece, and drive 600mm down the Y-axis, the bit will “exit” the material around the 500-550mm mark. How this physically looks is pictured below:
The calibration tests seem to come out correctly (squaring and Z-levelling on the X-axis).
Things I’ve checked:
I don’t believe this z-height issue is due to an uneven piece. For reference, I’m cutting 1/4" MDF board that measures consistently. I’ve also checked and ensured that the board is secured to the spoil board.
My cutting surface doesn’t seem to exhibit a large y-direction warp. Placing a level on one end and pushing down does not reveal a large gap at the other end (y-direction-wise).
I’ve made marks on my bit and I don’t believe it’s shifting up in the collet during operation.
I’ve heard that levelling your spoil board is a possibility but my Z-height discrepancy seems fairly significant for this fix? I estimate that I would need to take about 3-4mm off of my spoil board to fix this issue.
I’m at a bit of a loss here since this is my first crack at a CNC-related hobby, so apologies if I’ve missed something obvious! Thanks in advance to anyone that has suggestions.
A 1mm difference in table height is not uncommon at all. Some tables will have 2-3mm of variation, depending on the materials and construction method.
This isn’t a huge issue if you are doing through cuts - just set the job to cut a few mm deeper than the material thickness (it will cut into the spoil board in places, but that is what it is there for.
Before surfacing the spoil board, consider surfacing or otherwise leveling the table surface under the spoil board. Some people have used shims under the table surface to try to decrease the low spots.
You could z-probe in several places over your table to put some numbers on it (write down the trigger heights). I found my tabletop was out by 3 mm. So rather than take it off the spoil board, I actually planed the tabletop, then I surface my spoil board, but I only need 1 pass with minimal material removal.
If you see that the gantry is dropping on the z-screws, it could be an adjustment is needed to maintain its position, but it could be a lot of other things too.
I z-probed the table and noted a slight slant that culminates in a 2.5mm discrepancy at the x/y extremities.
Glad to hear this is something a bit more common than I first thought. I’m going to take both of your advice and plane my table and surface the spoil board for a correction.
