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Narrow space, inside/outside cut-order issue

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Simko
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Narrow space, inside/outside cut-order issue

Postby Simko » Tue Dec 19, 2017 2:35 pm

I am not sure what to call this issue, but lets say that I am cutting only the lowercase 'a' in the script font shown below. If I make the letter too small, the space at the top of the lowercase 'a' is too small for SheetCAM to travel in/out of, so it creates an inside and outside cut rather than a continuous cut.

The biggest problem, other than SheetCAM not telling me about this issue, is that this automatically generated inside cut is being done AFTER the perimeter is cut. All of my 'planned' inside cuts are done first as expected, but not this automatically generated inside cut. It is done at the very end.

Any ideas of how I can get it to tell me that the gap is too small and allow me to fix it, or at least make these cuts before the perimeter is cut.

Thanks!

text.png

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Re: Narrow space, inside/outside cut-order issue

Postby tcaudle » Tue Dec 19, 2017 3:31 pm

Either take control of the cutting process by putting inside and outside cuts on separate layers (and turn off the auto stuff) or make the clearance wider.
By using layers and separate operation sou can make it cut in any sequence and any type of offset you want.

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Re: Narrow space, inside/outside cut-order issue

Postby Simko » Tue Dec 19, 2017 4:22 pm

tcaudle wrote:Either take control of the cutting process by putting inside and outside cuts on separate layers (and turn off the auto stuff) or make the clearance wider.
By using layers and separate operation sou can make it cut in any sequence and any type of offset you want.


When I create the drawing, I would assume that it would be a continuous cut so I wouldn't even think it would need to go onto a separate layer. Then SheetCAM doesn't tell me that the gap is too small and instead just creates a separate cut that I don't know about. Then to top it all off, it cuts it in the wrong order after the perimeter of the part has been cut and released from the rest of the sheet.

I could be wrong, but there has to be a better way than what you are proposing. The letter 'a' example above is is a simple example, but what if I had a large art piece. How am I supposed to know where all of the places are where SheetCAM decides to make this decision and then cut out that detail after the part is cut from the sheet? Why not just give an error that there is a gap that is too small for the kerf in/out of the detail?
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Re: Narrow space, inside/outside cut-order issue

Postby Les Newell » Tue Dec 19, 2017 4:36 pm

I see the problem. I should be able to make it give a warning. Getting it to change the cut order is more tricky.

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Re: Narrow space, inside/outside cut-order issue

Postby SeanP » Tue Dec 19, 2017 5:27 pm

I would have thought the problem starts at the drawing stage, you need to be measuring gaps when adding tabs to stop centres dropping or as in that case what material is left with font design and widen gaps to suit material.
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Re: Narrow space, inside/outside cut-order issue

Postby Simko » Tue Dec 19, 2017 5:57 pm

SeanP wrote:I would have thought the problem starts at the drawing stage, you need to be measuring gaps when adding tabs to stop centres dropping or as in that case what material is left with font design and widen gaps to suit material.


I agree Sean and I do that the best that I can, but I had this happen to me twice over the weekend on two different cuts. Once on a font and once on a silhouettte.

I am not blaming SheetCAM for my designs that are not cut-ready. Only asking for a warning that my drawing sucks and I put two lines too close together rather than the software just deciding to cut an inside cut after the perimeter is cut away from the sheet. Not a big deal for an art piece, but when you are cutting something where the dimensions are somewhat important, it would be nice if this didn't happen.

8-)
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Re: Narrow space, inside/outside cut-order issue

Postby motoguy » Thu Dec 21, 2017 2:22 am

I used to have this exact same issue in Sheetcam. It would come back at the very end of a file, after my perimeter/interior detail was cut, and start cutting another interior detail. It did not show as a numbered pierce point in the toolpath, or anything. Just had to notice a pierce with no #, or lead in/ lead out if I was using those. @#[email protected]#%*!!!

In order to avoid this issue (among others), I've adopted the following process: Once I'm happy with general layout, and I need to start "fine tuning", I'll set my line width at (a minimum of) 1.5x my kerf size. By doing this, at any point where the lines are just kissing, I SHOULD have 1.5x my kerf width between the centerlines of the path. On my machine, that should be enough to prevent a blowout. So, if any spot in my drawing has 2 lines touching, I know it might be an issue. I adjust the spacing until the lines are not touching. Then, I should be able to avoid burn-through, as well as making sure the kerf can make it through any gaps (such as your a, above).

Take this lower case v:

kerf test 1.JPG


Looks good, right? Let's change our line width to .07:

kerf test 2.JPG


Whoops! We're going to have a problem here. See how the lines overlap? This is potential burn through/inability of the kerf to get through the opening. In this case, it could cause exactly the issue you're having with your "a".

Let's use the node tool to spread the lines, until there is a slight gap between them:

kerf test 3.JPG


Since we have a slight gap there, we should be good. It may be close, but we shouldn't have burn through. You'll have to test with your machine to see exactly how close you can get. If you want to make SURE there's not a problem, open the lines up even further (or set your line width thicker...say, .09 vs .07).

kerf test 4.JPG


Now we can go back to thin/hairline/no-width, which I use for drawing. We should be good to go! I do this to my ENTIRE drawing before cutting. It's a quick, effective way to look for kerf-width/cutting/path issues, without having to scrap any material.

kerf test 5.JPG

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Last edited by motoguy on Thu Dec 21, 2017 2:34 am, edited 3 times in total.
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Re: Narrow space, inside/outside cut-order issue

Postby motoguy » Thu Dec 21, 2017 2:28 am

Les Newell wrote:I see the problem. I should be able to make it give a warning. Getting it to change the cut order is more tricky.


The ability to show us where those "red stopsign warnings" are occuring would be AWESOME, Les.
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Re: Narrow space, inside/outside cut-order issue

Postby Les Newell » Thu Dec 21, 2017 4:34 am

I'll see what I can do.

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Re: Narrow space, inside/outside cut-order issue

Postby Simko » Thu Dec 21, 2017 7:22 am

Motoguy... Thanks for the great response! That is a great way to quickly highlight possible issues. I will definitely be giving this a shot on the parts that I am cutting tonight.

Les... Thanks for taking the time to respond and look into this. 8-)
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Re: Narrow space, inside/outside cut-order issue

Postby tnbndr » Thu Dec 21, 2017 5:58 pm

Following.!!!
Great suggestion motoguy. And yes, if SheetCam would highlight where the red warnings are would be nice.
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Re: Narrow space, inside/outside cut-order issue

Postby acourtjester » Fri Dec 22, 2017 8:01 am

Thanks for the trick Motoguy, This site is great many minds looking at a problem and someone comes up with a solution.
I read earlier about finishing up a drawing with as thin of a line width for finer detail of the cut path. Now start with fatter line to check for lines from bumping/cutting one another. It just shows more prep-work less problems ;) :D
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