Material remains in pocket operation when step over > 50%

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hans
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Re: Material remains in pocket operation when step over > 50%

Post by hans »

Hope not to get too much on your nerves with my pockets.
But lately I was milling wood and I was wondering if it is possible to optimize the trajectory.
I simplified the part to make it clear. The left hand pocket part is machined from inside (1) so outside what is good. But the right hand part is machined from outside (2) to inside (3). This leads to breaking of the last remaining piece of material in the middle.
Can that behaviour be improved by e.g. path rules or similar?
If not you may could have it mind while refactoring the pocketing algorithm..

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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

The spiral pocket does it's best to avoid doing a blind plunge into the work. It tries to start on edges so there is more room for the chips to clear.
Point 2 is an edge while point 3 is not. As far as breakout is concerned, starting at point 3 would potentially be worse. When it finishes cut 3 it will now be cutting a thin unsupported vertical wall which would be pretty likely to break off.

The next release will have a shiny new zigzag pocketing algorithm that is good for step overs up to 95%. I've been working on it flat out for the last week and it's now looking pretty good. I've been putting some time into trying to break it and so far every test drawing I've thrown at it has been filled with no missed areas at 95% step over. I'm aiming to get the release out in the next few days.
hans
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Re: Material remains in pocket operation when step over > 50%

Post by hans »

Les Newell wrote: Wed Dec 23, 2020 3:25 pm As far as breakout is concerned, starting at point 3 would potentially be worse. When it finishes cut 3 it will now be cutting a thin unsupported vertical wall which would be pretty likely to break off.
Yes you are right I didn't think about that.
But a solution would be to cut first 3 then 2 and then go to 1 and machine all remaining from there.
Les Newell wrote: Wed Dec 23, 2020 3:25 pm The next release will have a shiny new zigzag pocketing algorithm that is good for step overs up to 95%. I've been working on it flat out for the last week and it's now looking pretty good. I've been putting some time into trying to break it and so far every test drawing I've thrown at it has been filled with no missed areas at 95% step over. I'm aiming to get the release out in the next few days.
Very suitable to Christmas. Great!
Please tell me if you are just prior to release it. Then I will send you my current state of the german translation file
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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

hans wrote: Thu Dec 24, 2020 9:59 am But a solution would be to cut first 3 then 2 and then go to 1 and machine all remaining from there.
Yes that would work but it means two blind plunges, which the algorithm tries to avoid. In many cases this approach would also increase the number of rapid repositioning moves.
The zigzag pocket doesn't have this problem. You never end up with unsupported areas unless they are in your drawing. Even then it supports them as much as possible until the last cut pass.

Assuming the rest of my testing goes well I hope to release an update today or tomorrow.
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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

The new release has a new zigzag pocket operation 'Zigzag pocket 2' which uses the new algorithm. Give it a try and see what you think.
If it works out this will replace 'Zigzag pocket'.
hans
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Re: Material remains in pocket operation when step over > 50%

Post by hans »

Ah nice that went fast :).
It works generally but I don't like the forward and backward move and the end of each line. What was wrong with the finishing surrounding path like in the old zig zag pocket ?
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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

The zigzags have to go right up to the edge of the outline to guarantee clearance even when the zigzag is at a shallow angle to the outline. You could do away with those moves and have a final cleanup path but that path would be cutting air half of the time. These cleanup moves look ugly but spend less time cutting air.
If the surface finish is critical you can specify a separate cleanup pass but it wastes a bit of time time as that pass can't exceed 50% step over without potentially missing bits.
hans
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Re: Material remains in pocket operation when step over > 50%

Post by hans »

This example below would have the same time cutting air like zigzag pocket 2. But this avoid the forward and backward move.
Addionally you could add a checkbox "force same direction" where you have an even number of zig zags (like in this example) though it could be done with one pass less. But this only would make sense if you have a fixed step over. (height dived by passes in this example)
I hope you can follow me...
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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

Unfortunately your suggestion only works for rectangles where the height is an exact multiple of the step over. Rectangles are the easiest possible shape for a zigzag pocket. Whatever I do has to be able to handle any shape you throw at it.

Thinking about it, if you try that exact shape with the current algorithm, you'll find it spends less time cutting air and with fewer rapids. Rapids can be quite time consuming, especially if you are using a shallow ramp on the plunge.

Is the reversal causing problems on the machine?
hans
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Re: Material remains in pocket operation when step over > 50%

Post by hans »

Les Newell wrote: Sun Jan 03, 2021 3:24 pm Unfortunately your suggestion only works for rectangles where the height is an exact multiple of the step over.
Only if you take the step over value as a fixed value. Assume you have a rectangular pocket with a height of 35mm and a 10mm mill. So you need 3 passes with 10mm step over and one with 5. But you can divide it into equal steps of 8.33 mm. So you have the same thing.
Les Newell wrote: Sun Jan 03, 2021 3:24 pm Rectangles are the easiest possible shape for a zigzag pocket. Whatever I do has to be able to handle any shape you throw at it.
Yes but zig zag pocket makes only sense on rectangles and similar primitive shapes. Because on more complex shapes a spiral pocket with 50% step over takes almost the same time as zig zag 2 with 90% step over. So I think the zig zag pocket can be optimised for rectangular pockets.
Les Newell wrote: Sun Jan 03, 2021 3:24 pm Thinking about it, if you try that exact shape with the current algorithm, you'll find it spends less time cutting air and with fewer rapids. Rapids can be quite time consuming, especially if you are using a shallow ramp on the plunge.
Hmm the old zig zag pocket is much faster than zig zag 2 because it leaves much material on complex shapes. Bad to compare.
So zig zag 2 is much better.
Les Newell wrote: Sun Jan 03, 2021 3:24 pm Is the reversal causing problems on the machine?
Not really, but I usually want a smooth surface without going back and forward so I always have to add a finish pass what takes extra time.
But may it doesn't makes a big difference in machining time with a finishing pass. It has to be figured out in practice but unfortunately you only released the dev version for windows :-/

And how to you calculate the step over for the finishing pass? It seems to have 30% in my example. I think 50% would be enough. Maybe calculate it as half of the entered step over for the zig zag?
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

hans wrote: Thu Jan 07, 2021 12:50 pm Yes but zig zag pocket makes only sense on rectangles and similar primitive shapes. Because on more complex shapes a spiral pocket with 50% step over takes almost the same time as zig zag 2 with 90% step over.
Hmm, I never tested speeds. Hang on....
Using a C shaped pocket which is designed to be difficult for both spiral and zigzag
Due to the awkward shape I could not run more than 50% step over in spiral pocket without missing bits.
Spiral pocket 50% 53s
Zigzag2 50% with cleanup pass 68s
Zigzag2 50% without cleanup pass 60s
Zigzag2 90% with cleanup pass 48s
Zigzag2 90% without cleanup pass 41s

Using a circular pocket.
Spiral pocket 50% 46s
Spiral pocket 90% 27.7s
Zigzag2 50% with cleanup pass 53s
Zigzag2 50% without cleanup pass 49s
Zigzag2 90% with cleanup pass 34s
Zigzag2 90% without cleanup pass 30.5s

Using a square pocket. 79% was as high as I could go with spiral.
Spiral 79% 45.6s
Zigzag2 90% with cleanup 47.6s
Zigzag2 90% no cleanup 43.6s
Zigzag2 95% with cleanup pass 46s
Zigzag2 95% no cleanup 42s
Your proposal 95% step over 41.3s

This is simulation in SheetCam which admittedly does not do a very good job of simulating acceleration. I can't currently go out into the workshop to test on real machines. It looks like if you can get a decent step over with spiral it will beat zigzag but with most geometry zigzag is quicker simply because you can run a big step over. Zigzag is definitely not a good choice for small step overs. As expected the cleanup pass slows zigzag down significantly.

Your proposal was emulated by using a face operation with manually entered coordinates with the two cleanup passes done as an offset operation on two lines. It was slightly quicker than zigzag2 but of course it only works for rectangles.
Not really, but I usually want a smooth surface without going back and forward so I always have to add a finish pass what takes extra time.
But may it doesn't makes a big difference in machining time with a finishing pass. It has to be figured out in practice but unfortunately you only released the dev version for windows :-/
Yes, surface finish is it's biggest downfall. It depends a lot on your machine's rigidity. The cleanup pass adds a significant amount of time.
Are you running linux? If so you can run the Windows version using Wine. Install Wine using your package manager then download and install Dev just like you would on Windows. Wine has a few quirks but it works pretty well. The Linux version is Dev but it only gets updated occasionally, at points where I think Dev is pretty stable. The next update is due around mid February.
And how to you calculate the step over for the finishing pass? It seems to have 30% in my example. I think 50% would be enough. Maybe calculate it as half of the entered step over for the zig zag?
Yes you are right it's 30%. I wanted this algorithm to be bomb proof. 50% won't quite do if you have really sharp internal corners in your shape.
Jolbas
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Re: Material remains in pocket operation when step over > 50%

Post by Jolbas »

Would it be possible to reuse the "Overcut internal corners" for the spiral pocket? I noticed it is used on all passes on spiral pocket if it's activated. But it would help make it possible to increase overlap if it's always activated except on the outermost pass. And one thought I had earlier when you released it was that "Overcut internal corners" should have different length depending on angle so that the tool always tangents the corner.
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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

I remember looking into this some time back. It is not a complete solution but it should help in many situations. I can't remember why I didn't implement it at the time so I'll take another look into it.
hans
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Re: Material remains in pocket operation when step over > 50%

Post by hans »

Les Newell wrote: Thu Jan 07, 2021 3:18 pm Yes you are right it's 30%. I wanted this algorithm to be bomb proof. 50% won't quite do if you have really sharp internal corners in your shape.
Okay better so, than leave material remaining.

Just a pity that the simulation also stops where the limitation of the trial version ends. I thought only the output is limited. So maybe I have to test it installling in wine...
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Les Newell
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Re: Material remains in pocket operation when step over > 50%

Post by Les Newell »

Simulation is just a specialized post processor so demo mode will limit the amount of code sim generates. I can send you a 30 day license if you want.
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