Can anyone tell what's happening here please?

@Swinly That’s odd about the Z gantry nut. Others will jump in here, I hope. In my case, the cap screw is not touching the nut when the gantry plate hits the motor mounting plate. I hope that’s clear. Even if it is, I realize that it does not help you much. Yours touches, mine does not. There, everything is fine now. :grinning:
WRT to the Y gantries, there was a discussion quite a while ago where one user hit the nut screw against the front foot hard enough to break the nut. I installed some delrin stops that the gantry plates hit before the nut screws hits the feet, just to avoid that problem.
A solution to all your issues is to replace the cap screws with the set screws that shipped with the Mill. Adjusting is not as convenient, but installing them eliminates any “collision” issues.

Back to the ridges. Were you able to see if they always occur at the same XY coordinates of the Mill?

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@Swinly In addition to my question about position, Lonnie, when the ridges appear, are you cutting along X or along Y?

I have a theory, but will hold off putting it out there, as my track record over the past couple of weeks is not good. :grinning: I’m not trying to be a jerk, but my theory really all depends on the answer to my two questions.

I am good for any and all theories

If I’m understanding what you’re asking correctly it is cutting along the X-axis. I got a smaller carve I’m going to try today. I’ll see if it does happen in the same spots or just around the same areas.

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@Swinly The only reason that I am holding back, Lonnie, is that my theory may well be all wet and it will only end up costing you time and aggravation to confirm that. :grinning: If, after your test, you find that the ridges are not always in the same location in the Mill’s x and y travel, then my current theory is dead wrong. I know that @paullarson @Bill and @kellyz are following this thread and they may well have some theories, too.


Sorry it took so long to get back to this. My Friday morning game of go fetch turned into an all day affair.

Yesterday I set up the CNC so I could do two carves in as close as the same spot as I could make it. I used pine 7.25"x13.75" x0.75" which is all I had. The pieces I did before were bigger so I tried to position them where I thought some of the groupings would be.

On the first carve, the ridges are not as proud as before but there is one that I made note of at 4.875" from the bottom

The second carve is not finished but I can see a ridge in the same spot. 4.875"

I’ll post some pics later.

There was some foul play with my first carve so no pic of it. My friend was visiting and picked it up off my sanding stack and started sanding while we had coffee this morning. Didn’t realize until now that it was my test piece . I have a third, carving now. Anyway here is a pic of the second carve. The ridge does not come out well in the pics but it is there. It seems to disappear at the surface of the “S” and reappear on the other side. Maybe it is slowly getting better…IDK?

Edit: Dang it they are kind of hard to see in these

@Swinly Well, Lonnie, I’m going out on a limb here, but here is my theory. Let me back up a bit, first. Here is what I understand. When you are carving, you are carving side to side, that is along the X axis. The carve goes well for some time, then leaves a ridge, then carves for a very short space, then another ridge, then it finishes fine. The ridges appear in the same physical location all the time.
To me, and I am very open to being proven wrong, this is a hardware issue, not a software issue. Further, I can’t see how it can be something like bottoming out the Z axis, or the bit shifting in the collet since the cut resumes after the ridges and cuts just fine.
So, to me, the X gantry is rising up very slightly at the same point in its travel along the Y rails.
If it were my Mill, I would be looking to see if the lower wheels on the X gantry plates are touching the middle feet holding the Y rails. If they are, that could be pushing the X gantry up each time the wheels pass that location. At all other locations, the cut is fine.
I realize that this is a long shot.


Han had more optimism on the day he was betrayed by his old friend Lando and frozen in carbonite than I have right now. :disappointed:

@Swinly Can I conclude that my theory was wrong? :cry:

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Guys - After watching the postings and seeing the pictures to me it seems to me that maybe something in the Z axis is slipping and somehow dropping back into place. Drive belt too loose or belt gear too loose causing belt to jump teeth. Or possibly teeth missing on the belt. Coupler not tight enough and jumping up or down, back and forth on lead screw. The anti-backlash nut not tight to the plate maybe moving up and down. Just throwing these out there since we all know there is a lot of torque with these motors when they change direction. Hope this might help. If not I tried.


@Heyward43 When I can go back in my shop without feeling disgusted I’ll check those areas. At this point, I might feel a little better if I knew there was some other beginner getting these kinds of results.

Thanks again for all the suggestions

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@Swinly , don’t get too discouraged, a little is fine.

Setup, Setup, and Setup. Wheels especially will get you off track, lots of subjective talk here, “Tight, but not too tight” you will discover and learn the happy place. Listen to the machine while it’s working, moaning, etc, you can audibly hear where the machine struggles. Listen, work the wheels on that axis, when the moaning is gone, your issues will be gone.

Determination is required, even the best design has that dial in requirement!


Well, I am back in the game.

Thanks to everyone here and at Sienci. Kelly, big thanks to you. Because of you and everyone else’s suggestion I now have a much better understanding of how the Longmilll works and sounds.

Now for the issue at hand . It was not mechanical or anything like that. No funky g-code or glitch in the matrix. No, it was my dumb*** self. I built my table kind of high so I can use my barstool to set up and run the CNC. (It’s easier on my knees) I got in the habit of moving my work table with the laptop beside me so all I had to do was turn to my left.

I started resting my arm right in front of the waste board causing a very slight flex in it. I can’t even see the flex but you can diffidently see the results of it in the carvings. This is why the first one only had a couple of lines and they progressively got worse from carving to carving. With each one, I started getting right on top of it more and more while it was running inspecting every little thing.

Now I have to call my ex-girlfriend and ask, “remember when you called me a bearded idiot? Not that you’ll be surprised but…”

Lol thanks again, everyone.

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@Swinly I’m really glad to read that you figured things out, Lonnie. I never would have thought of that. Going forward, you may want to look into additional bracing for the top of your table.

I’ll close this topic now that the issue is resolved. Have fun.

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