Scratches during fast moves

Sorry if this issue has been asked and addressed, but I couldn’t find the answer. . .

After my bit starts to carve it occasionally “skips” quickly to a random point on the other side of the piece, badly marring the piece with scratches. It seems to be random - it’s not going to certain points in the pattern (that I can tell).

It also does not seem to be going from the end of one tool path to the beginning of another. . .

I tried raising the height of the bit during fast moves, but this didn’t seem to do anything. Maybe I didn’t raise it enough? I can try raising it some more. But the question still remains of why the thing is jumping around in the first place. Sometimes it jumps from one section, carves for a few seconds in another point - often just a tiny mark - and then jumps back, scratching the piece the whole way.

I’m still playing around with scrap wood, but I’d like to solve the problem before I run out of excess maple stock and before I’m working on something I don’t want marred!

BTW, thank you, experienced guys, for reading these posts and trying to help. I’m sure some of our questions make you shake your head with wonder at our ignorance, but I think I can speak for all newbies when I say we truly appreciate your wisdom! Most of us are learning as fast as we can… lol.

Which CAM program are you having this problem with?

Possible to post a file pair?

This is a tough one to address without a little more information, so:

What machine?
What software are you using to generate the toolpath?

The machine matters since the machine-based possibilities differ from a Shapoko to a Nomad.

The software matters as, in my experience, it is the likely culprit.

Carbide Motion. Sorry - what’s a file pair?

Carbide Motion.
And I maty have been wrong - it may be going from the end of one tool path to the beginning of another. I’m carving very small letters around a 2" circle (like a coin) and in a few places the letters are carved out of order if one was going clockwise. Maybe it would help if I went from one to the next. But still, it also seems it’s “crashing” through the walls from one letter to the next in places.

Carbide motion is the tool to send the g-code program (probably a .nc file) to the machine. It doesn’t produce the G code.

Do you mean Carbide Create? Or did you get the g-code file from some other source? Or produce it using a tool such as MeshCam, or Fusion360, or tinkercad, or…?

Most software will produce toolpaths that sometimes do parts of the operation in a non-logical appearing sequence. Sometimes there is a reason, sometimes not. That in itself is not an issue. If the tool is not fully retracted before such a move, you get damage to the work or the tool.

Okay. After additional examination, I can see I was wrong - it’s definitely worse in those places where I’m asking the tool to go from the end of one tool path (letter “A”) to the beginning of another tool path (letter “B”) where letter B is located on the other side of the circle from “A”.

So that tells me I need to stop doing that! I should go clockwise from one tool path to the next. But still, I’m concerned whatever is happening will still happen (but will be less noticeable) even if the letters are next to one another… in other words, it’ll still “skip” to the next letter without raising up, thus crashing through the walls between the letters.

Again, are you using Carbide Create to produce the tooolpath?

Thanks. So maybe I simply need to retract the tool some more.

eni_public, yes. Carbide Create and then Carbide Motion.

I’ll try retracting the tool some more and see if that solves the problem.

Many thanks!

Yes, you need to be sure the retract height is above the stock surface. You also need to be sure to set the zero for the Z axis correctly. If the material surface isn’t dead flat, you might hit it in some places and not in others, so check several spots.

I would suggest 10mm or so for the retract height until you are more familiar. Then you can bring it down to gain speed.

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10-4. I’ll use 10mm. Thanks, again!