Arcs for only convex 'inner' corners and orieneted correctly.. HELP!!! fabrication process

Hello,

I am fairly new to grasshopper, but I have been looking at threads all day so my definition isn't compltely dumb.

I am going through a very large cnc fabrication process and am trying to automate some cut sheets, but not to optmize material, rather define some cut lines. Everything that I am cutting is made of planar wood elements, but there are very specific geometries (mostly straight lines) and I have to put tolerances and radiasas at the corners in order to cut on the cnc mill. Spending time to figure out how to automate is necessary, but I am stuck!

One thing the definition is doing is taking my brep modeled components in rhino and makking them into 2d close curves and laying them side by side. It works...not ideal as its not layed out in a sheet, but that is not the most important part.

Another particular problem is that you will see some notches in the curves, which other pieces will slip into, so different slots need different specific offsets (making them larger) as a toelrance to allow for material play. This I don't even know how to set up so maybe it will just have to wait.

THE MAIN QUESTION, and super important would be, LIFESAVER:

At all 'inward' corners...which I think will always mean concave corners (most are 90 degrees, but are within to sides, instead of a corner sticking out). I'm sure its obviousy, but the reason being the outward corners a circular dril bit can cut, but inward ones need an arc profile extended beyond where the corner of the other piece will fit into. The drill bit i am using is 6mm, so 6mm diamters arcs is what i'm working with.

I have managed to put such an arc at every vertices of each cut piece. The problem being some stick outward isntead of cutting into the piece. So each one needs to be orieneted correctly. Ideally they would also only draw into inward corners, but I can always delete them out. I think maybe I am missing a more logical mathematical way of defining?

For these geometries it is not very important which side the half circle arc in on in the inward corners, but I also have some geometries that I will have to control where the circles face according to the rest of the cut piece.

The cutouts in the middle of the pieces that are curves do not need such corners obviously.

The picture is an example drawn

I hope this isn't too specific and long. in general though automating fabrication, and controling pracitcal math and orientation problems like this is itnersting to me!

THANKS

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Replies to This Discussion

Permalink Reply by Pieter Segeren on July 21, 2011 at 5:40pm

hi Elliot, I made something that I think you decribed yesterday, meaning it does't look like the 1 copy.jpg you posted.

And @ Taz: thanks for the inspiration. I almost forgot to say:)

Attachments:

CornersOfClosedPlanarPolylinesTest_Convex-Concave_PSG.ghx, 179 KB

Permalink Reply by taz on July 21, 2011 at 7:13pm

;)

Permalink Reply by Elliot Mistur on July 22, 2011 at 9:11am

This is great, thanks!

Permalink Reply by Pieter Segeren on July 22, 2011 at 9:17am

you're welcome, but can you get the path for the drill from this?

Permalink Reply by Elliot Mistur on July 22, 2011 at 9:27am

I am developing various different tool paths and the ones i'm working on now don't require it, but it will help me call out what I need, I'll keep you posted if when I use it further

Permalink Reply by Hannes Löschke on July 22, 2011 at 4:30pm

Did you get some feedback from your manufacturer?

I came to realize the importance of "closed outlines" in a larger laser cutting project. The machine gets some DXF files for input and starts to trace the lines in the order they come. So let's say you drew a section of a staircase with a lot of short lines. Those lines do not necessarily stay in the order you drew so the laser might start at the bottom, cut one line, move to the top and cut another... taking a lot of time just travelling around.

Creating closed curves will at least order all the lines so the machine can easily flow along the outlines. All I do is select all cruves in rhino and run a join before exporting the file.

...what I mean to say is that your arcs may just create toally unwanted results if the curves your export are tool paths.

Permalink Reply by Elliot Mistur on July 23, 2011 at 4:21am

I will be doing tool paths to cut on lines now, which are offset outside the piece by the radias of the drill bit for some things, so when you lay the pieces together the lines of two pieces will be on top of each other which is a problem like you say because then it will double cut, and do all sorts of random travels. I am trying to figure out a good way to clean now.

The closed polylines does insure well sorted tool paths, but we are still trying to discover the most efficient process