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 taz on July 20, 2011 at 2:37pm

Do your arcs need to be offset to one side or the other of your re-entrant corners?

Otherwise you could set up a test to generate "points" (small circles) at the re-entrant corners and drill those out first as part of your toolpath sequencing...

Permalink Reply by Elliot Mistur on July 20, 2011 at 2:48pm

For the pieces you see in the example file, I may actually just do points like you say. But there is a huge number of cut sheets I am doing where the circle does have to be offset to one side, because then the extra missing material isn't visible on the other side, which I need. They are simpilar pieces, but they are the same principle with a few differently oriented inward corners.

Permalink Reply by taz on July 20, 2011 at 3:03pm

Before I saw your reply, this is the quick "test" I came up with. The [Crv Length] component isn't technically necessary.

Automatically offsetting to one side or the other based on visible edges would be hard to figure out rules for...

Permalink Reply by Elliot Mistur on July 20, 2011 at 3:17pm

This is great help, thanks! It helps me understand a bit how grasshopper thinks too. I am in europe so I can't try at my office til the morning the next step, but I already had problems with it. It is to move the circle edge to the current center so there is only a minimal arc left, and the inward corner touches the new location edge of the circle.

If I was going to draw the corner in rhino I would draw a bisecting angle from the center based on the two edge lines of the inward corner and then move the circle along that line from the end (the inward side) to the current center.

I think the easiest way to do it is just move these cirlces after they generate and then trim it out? but i had trouble bisecting and trimming.

Permalink Reply by Elliot Mistur on July 21, 2011 at 1:57am

Taz, what is the button in the middle with the cpr then Ci and Co?

I have to use the 8.0009 version

Permalink Reply by Chris Tietjen on July 21, 2011 at 4:59am

Intersect>Region>Trim with Region

Permalink Reply by Chris Tietjen on July 20, 2011 at 4:32pm

If your inside corner radius is going to be the same as the radius of your tool I don't see why you would want to go to the trouble of drawing these semi-circles. Just run the cutter straight into the corner the distance of the radius using an offset and centerline cutter path as shown above. Are you trying to get Grasshopper to generate the G-code or just the tool path?

Chris

Permalink Reply by Elliot Mistur on July 20, 2011 at 4:44pm

This also makes sense. I am only generating the tool paths with grasshopper. Some one else is milling for me and wanted closed curves, but this looks much easier I will try to get it generated like this i think. thanks again.

I may post some more questions tommorow. I still need to do tolerances for materials to slot into each other (offseting cuts to make them slightly bigger), so I may try to use taz's definition to find the interior corners and offset all of those curves.

Permalink Reply by Chris Tietjen on July 20, 2011 at 6:34pm

You shouldn't really need closed curves as most cnc software is happy to chain open curves to produce a profile.

Chris

Permalink Reply by taz on July 20, 2011 at 6:59pm

This works well too, but from the JPEG posted there seems to be a specific user (visual) choice of which corner line gets run out so automating the process might be difficult...

These are 2 different conditions: