I’m having an issue with my Primo. If I cut a slot along the x-axis using two passes, the router shifts 1-2 mm in the -Y direction when the X direction reverses for the second pass. The gcode does not have any shift in the Y value. If there are multiple passes I think the shift only occurs on every other pass. If I cut several slots like this, the amount of shift is very similar for each slot. If I cut several single pass profiles on top of each other and only move the router in one direction, the slot is cut perfectly without any shifting.
The belts and pulleys are all tight. And this only seems to be a problem if the router reverses direction. Any ideas about what the cause might be?
Are you reversing directions on one side of the slot? If so you are changing from climb to conventional milling. This could be putting more stress on the Y axis,or the bit,however yoy want to look at it. Climb will always leave a nicer finish
Here is a picture of what I describe. These slots were cut with a 1/4" endmill, total depth of cut 0.4" in two passes (0.25" & 0.15"). The cuts are on the vector lines, with pass #1 from left to right and pass #2 from right to left. The bit does not lift after the first pass, but plunges down for the second pass. You can see a small ridge near the top of each slot because the second pass is slightly lower in the Y-direction. The slot width is larger than the 1/4" that the endmill cuts. I can minimize this effect by taking smaller depth of cut for each pass, slowing the feed rate, and slowing the plunge rate. But this does not eliminate it completely. If this is due to a problem with the core, I don’t know what to focus on. Everything seems pretty tight already. Any ideas would be appreciated.
Is that oak? looking at the pictures; you can see on the right side of the picture that when you switch direction and the bit drops it pulls the bit down (-y ?)and to the left as you look at the picture. As the bit cuts deeper it pulls the bit right and down more. when the bit is at full depth you can see the offset already.
The moment the bit travels left it pull even more down (-y) but now your cutting the full depth and it pulls more.
Bear with me for a moment. When you mill a slot in one direction one side is upcut and the other is conventional. There is a fixed amount of defection.
A nice straight line. At the end of the slot you plunge to your final depth. Going right to left. The forces on the bit now are pushing left and pulling -y. But this causes the full depth of the mill trying to cut as it is pulled into the work. I think you may have your belts a little lose. Both x and y. Or a little play in the bearing.
First thing I would try is to change the cut order. Try cutting .15 first pass and cut the .25 the second pass. See if it changes the offset.
Something I noticed about the picture. the left to right cut is very clean, and the right to left is not. When using oak I have found at times I needed to slow down going against the grain.
Thanks for your comments. I’ve tried tightening the belts and the core clamps. This has had no effect. If I lift on the core, there is no movement. If I lift the router, the only movement is the backlash (?) at the leadscrew nut.
This is oak, but I’ve tried a soft pine and have a similar (but smaller) effect. This is a Whiteside 1/4" Upcut bit. I am plunging 1/4" on the first pass because I was trying to use a compression bit with the upcut portion at the bottom of the bit slightly less than 1/4". I have tried a feedrate as slow as 10 inches/min, but this still shifts the bit a small amount (<1mm).
My design for this project is done in Vectric software and I am just selecting a Profile Toolpath On the vector. When cutting on the vector, the software does multiple passes left-to-right, then right-to-left, without lifting the bit. The error only occurs on the right-to-left passes, not on the left-to-right passes if there are more than 2 passes.
My machine is a Primo. I am using a 0.25 inch depth of cut with feedrates of anywhere from 10 inches/min to 80 inches/min. If I use a smaller depth of cut, I still have the problem of the bit shifting when it reverses.
I see this is hardwood and it’s less noticeable in soft wood.
I see you’re using a 1/4" upcut endmill. What are the details on it? How long is it? The longer it sticks out of the router, the worse I’d expect this to be.
I would try switching to an 1/8" single flute upcut endmill and see what happens. You’re trying to make a 1/4" slot with a 1/4" endmill. When you switch directions, the forces change. With an 1/8", you have less force and you can mess with stepover and finishing passes.
Thanks for the comments. I may have made some progress. Some of the bolts holding the truck bearings seem a little loose and tightening these seems to have reduced some of the shifting when the cut reverses. I still have to work on this more and I am not sure that this is the only problem.
There are other ways to do these slots without the problem. For example if I cut left-to-right, lift the bit, return to the start point, plunge and do another cut left-to-right, the shifting does not happen. But I think this error should not happen with the Primo, so I’d like to fix it.
I’m from the US, but I still stick with metric for CAD, 3D printing, and CNC.