Surprising Edit Start Point behavior

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TomWS
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Joined: Thu Dec 26, 2019 11:15 pm

Surprising Edit Start Point behavior

Post by TomWS » Sun Jun 14, 2020 1:46 pm

While working on a Plasma project that required indexing a design that spanned multiple table sizes, I discovered a surprising behavior with Edit Start Points. I'm posting here to see if anyone else had noticed this, I didn't see it reported anywhere.

Since my design (Created in Inkscape) spans multiple table sizes I had to break up the design into multiple open paths, each sets of paths for a given section are on a unique layer (with a unique color). Loading the drawing into SheetCam I then created Operations for each layer, separated by an M06 so I could reposition the workpiece after cutting each section. Each operation had Offset Open paths and Leadins on Open paths checked. I also had Reverse cut direction checked since it is a plasma cut - this turned out to be the key. SheetCam very capably created the sets of cuts, all of them nicely ordered in the proper cut directions.

However, I realized that it would help align each indexed section if I could begin the first cut in the next section at the end of a cut in the last cut section. So... easy, I tried to force the start point at one of those junctions, bearing in mind the correct cut direction, and found that the 'Sn' point jumped to the other end of the segment, rather than the point I was trying to select. Well, without going into all the silly experiments I tried, I've concluded that, IF Reverse Cut Direction is checked, then Edit Start Points REALLY edits End points and if I truly want to start at a specific spot, go to the end of that segment and place the start point there...

So... is this a known behavior or just something wacky with my setup? If known, is it documented somewhere? If not documented, should I post in Tips and Tricks?

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Les Newell
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Re: Surprising Edit Start Point behavior

Post by Les Newell » Mon Jun 15, 2020 4:46 pm

Could you post a job file (File->save job) with the job set up. Ideally if you could set it up so there is just the troublesome outline active that would help me figure out what is going on.

TomWS
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Re: Surprising Edit Start Point behavior

Post by TomWS » Mon Jun 15, 2020 9:12 pm

Yes, I can post it, but I won't be able to do it until Tuesday morning East Coast US time. Just the Job file?

I think I can create a very simple design that will demonstrate the behavior, but I'll post something tomorrow for sure.

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Les Newell
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Re: Surprising Edit Start Point behavior

Post by Les Newell » Tue Jun 16, 2020 10:50 am

I should just need the job file.

TomWS
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Re: Surprising Edit Start Point behavior

Post by TomWS » Tue Jun 16, 2020 1:17 pm

I've attached a simple job file and the svg source just in case.

When you open the job file you'll see two cutting operations, the first is the lower section with its 'start', S1, indicated on the left, implying that the cut is anti-clockwise. The second cutting operation has its 'start' indicated on the right. However, looking at the cut direction, it is correctly clockwise for an outside cut, but only after I changed the 'start' points. But I had to pick the end of each segment to get the correct start point.

For these cuts I chose a perpendicular lead in, no lead out because I'm hoping that will help me line up the second cut to the end of the first (I only need to align in the Y direction as the table has a fence for referencing the X axis).
Attachments
sectionedOval.zip
(5.01 KiB) Downloaded 20 times

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Les Newell
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Re: Surprising Edit Start Point behavior

Post by Les Newell » Tue Jun 16, 2020 3:06 pm

Ah, I see what you mean. Yes, this is expected behaviour even if it isn't very intuitive. Open contours have no inside or outside so SheetCam doesn't really know which side you want to cut. Instead it always cuts to the right of the start point. If you imagine you are stood on the start point looking down the line the cut will always be to your right. Now if you reverse the cut direction the only way to keep on the right is to start at the other end.
The alternative to this behaviour would be for reverse cut direction to also reverse the cut side but I decided it would be too easy to accidentally ruin your job if you change the cut direction in your operation and don't notice it has swapped sides on open contours.

TomWS
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Re: Surprising Edit Start Point behavior

Post by TomWS » Tue Jun 16, 2020 3:12 pm

I agree with your conclusion and can deal with the behavior (now that I know it's 'normal'), but I wonder if this specific behavior should be documented somehow (Tips and Tricks?) to help others who might find it as 'surprising' as I did.

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Les Newell
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Re: Surprising Edit Start Point behavior

Post by Les Newell » Tue Jun 16, 2020 3:49 pm

I could move this thread to the tips and tricks section.

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