No consistency in cutting, its shrinking

Hi guys, here I am having an issue, not sure why is this happening, but on one side when the cust begins its fine, but when the second pass goes deeper its life if the size of the shape it’s shrinking on one side and leaves this trace as if they were rows of bleachers in a stadium.

I thought it might be some kind of things going wrong like with the gcode and used BASIC CNC VIEWER to check the file, and it did look good, then tried cutting an oval shape, but it does happen the same, as deep as it goes it’s like if the code it’s shrinking.

Here is the gcode for it, maybe I can get some ideas of what is going on here, and by the way I am cutting MDF and I have tried with two kinds of bits I use in my other machine (tool 46202-k & 46016-k from Amana tool) both are 1/4 bits and the deep of cut I am using is 4 mm and the speed is 15xy by 4z mm



[attachment file=“IMG_20190813_160717.jpg”]

oval.gcode (10.1 KB)

I saw a similar phenomenon when I ran at 15mm/s (although I was cutting 5mm with a 1/8 bit). I assumed it was skipping steps so I slowed it to 10mm/s and it fixed it right up.

I don’t know for sure it scored a step because I never saw or heard it happen, I just know it consistently had those steps before I slowed it down. have you tried slowing down?

Subscribing to see if anyone more knowledgeable has better insight.

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Hooo, I see, maybe that should the issue, maybe I’m still a bit too fast, even thou I thought I could be fine because the first bit I did use has 3 flutes, and running at arround 20,000rpm…

Despite that, should be normal that there’s vibration when cutting?

It looks like you are skipping steps. 1/4" bits need to go slower and shallower than 1/8" bits. I would start by just slowing down a lot and if things are fine then it’s an issue with your feeds amd speeds with that material and those bits.

Ryan recommends the 1/8" single flute bit (he sells them, but recommended them before he sold them) and I think it’s great for this machine. If you’re cutting the piece out, then having a thinner bit just goes faster and you’re not wasting time making a wider kerf.


more flutes = more spindle HP required + you must feed faster to maintain same chip load.


I was going to comment on this last night to say your feed rates seem really aggressive but at the last minute I realized this is for lowrider and I don’t have a lowrider so I don’t know how hard they can cut.

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I see, well the reason I was doing that speed is because since looked like the fastest that could go securely without missing steps I thought that I could cut through faster, and I’m cutting a 3/4 inch material so with 1/8 bit it might take way longer

Why? The width of the bit doesn’t affect the depth (much). I have cut 3/4" in three passes with a 1/8" bit. But you can push a 1/8" bit through the material faster, because it’s not removing as much. If you’re doing a pocket, then yeah, the 1/4" will be faster, but cutting the outline of a part, the 1/8" will be faster.


Well I’m quite new to the lowrider, so I’m doing my testing now, I so far use a rather more aggressive parameters on my carve like feedrate 50inch in XY and use arround the 20,000rpm for the spindle speed, but I cut deeper like 6.5mm so I cut a 1/2 MDF in two steps

Xcarve? If so yeah you should expect that. It’s more expensive and more rigid and smaller than your lowrider.

Mmmmm, I see, then I think I should give a try using a 1/8 bit single flute, I think I have one laying around, the thing is because I came from grbl and the parameter I used on that machine was like 50inch speed, so I am more used to go faster and using a 1/4 bits since I do not require much detail, just doing the outline, (I have total like 12 bits of 1/4)


Well I have just done a try, was still done using a 1/4 and speed 12mmXY and 4mm Z and its like still showing as each tie it should go deeper creating a new step (goes shrinking) and there was a moment it went in a rampage and cut the 3/4 at once and looks like the steppers still moves properly, but as if there not well oriented

Yeah the 500mm a small one, you’re right about that, but still, I thought I wouldn’t be much different at least regarding the spindle feeds I mean, the load should be no problem on the bit because of the speed it should go flawless

Can you share with me the parameters that you used to cut, and by the way I am not sure if the MDF I am using has to do, its a brownish color of MDF nothe usual white/yellowish