LR2 - trouble with first pass when cutting parts

Hi guys…I built my LR2 last spring and with the help of this great forum I’ve been able to resolve every problem which has come up so far, but his one has me stumped:

When cutting out a part it seems to cut “inside the line” on the first pass, but only on the right side of the part. The remaining passes are right on the money and I’d have a perfect part if not for the unsightly rabbet on the top right edge. This hasn’t mattered for most of my projects to date, but the time has come to fix it.

A bit about my setup - LR2 on 4’ x 6’ table, mini rambo, Estlcam, the following example was cut with a 1/4" 2 flute endmill (though I’ve had the same issue with other bits), 8mm/s, 0.10" DOC. Now some pics:

good from afar


top and left sides - no problem.

front right corner

right side, notice defect goes away when cutting to the left

defect comes back for the rest of the right side

remainder of the right side

I would really appreciate any thoughts you have on what could be causing it. And for the record I double (and triple) checked the tightness of my grub screws.

Any suggestions on things I can try to figure this out?

I don’t have a Low Rider nor any particular idea about what is going on, but I suggest a few tests to collect some information. First for a test cut, I’d define the material thickness thicker than the actual material in the CAD program, say 1/4" thicker, and then I’d set the bit 1/4" above the stock when starting the cut. Another test might be to place a board under stock stock before you clamp it to see if the problem occurs at a different level. Both tests are to determine if the issue occurs at a specific height, or if the issue is caused by the forces of the bit first cutting the stock. If the problem happens at a specific height, then there is probably some sort of mechanical obstruction that is pushing the router. But if I had to guess, the problem sounds more like a deflection issue caused by something being too loose. So if the problem occurs at the top of the stock no matter what the height, then with the stepper engaged, pull your router different directions to see how much play there is.

Have you tried to power all your steppers and then grab the router and move it side to side and forward and back to see if there is any play anywhere? Looks like something shifted after your first cut because you seem to have the error on all the features on the same side?

I wonder if the wheels are wandering on the first pass.