Any better minds than mine?

Okay…slow down the hoards of better minds. <snerf, snerf>

I am cutting 6 of these panels in 0.125" Luan. The areas contained in the RED box needs to be cut at a 75° per side, while the areas contained in BLUE need a 90° cut. My thought was to cut everything at a 90° cut, then somehow delete the areas in BLUE and re-cut the areas in RED with a 30° V-bit with no offset which would give me a 15° angle.

Anyone have a better, or easier way to do this?

I believe the easiest way to do this would be to:

  • duplicate / break open, then close and offset the geometry which needs the V cut so that that can be cut w/ a V bit (and preview properly) — tool engagement should be low enough that the connected part at the straight edge will hold things in place okay

  • a straight cut / follow path should address the base cut.

Hang on, tutorial coming up.

Can you put that into english? :wink:

Thanks @WillAdams. I appreciate that. I am attempting to build a mini “Airstream” trailer for bicycle, using composite construction, and this is the domed front.

P.S. HERE is a link to how the dome was laid out. I had to do a bit of fiddling to create a half hemisphere, but it was remarkably easy.

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Here is the file: sphere 32.dxf (72.1 KB)

That, is very cool!

Okay, never mind the part drawing:

Instead, open the .dxf in LibreCAD, export as MakerCAM SVG, open in Inkscape, re-save as PDF (I’ll think better if I use Freehand — once we’ve got the numbers for this worked out we’ll re-do it in Carbide Create).

Imported file:

Delete down to just one half of one part:

Presumably it was intentional to have a curve rather than line segments, so we re-draw:

Exactly. The line segments let you set up If you use the link that I provided, you can get a perfect .pdf. the line segments (rings) are used when using glue tabs.

I used 32" diameter, 10 “rings” and 12 segments (since I need 6 to make a half-hemisphere) 0 glue and 0 margin.

Okay, I couldn’t get the generator to work (not inclined to switch browsers), so we’ll roll with what we have thus far:

The next thing to do is work up how wide the offset should be:

Draw up a 30 degree V shape, a rectangle of the correct height, and do a Boolean operation to get the required dimension:

0.06699 inches, 1.7015mm (or folks w/ actual educations can just use math)

We’ll just use 1.7mm (the 0.0015mm can go towards the glue line) and we need to offset by half the dimension — I prefer to do this twice, once w/ the full dimension, the second time with the halved:

You could use math, and would prolly come up with a more precise answer. I was thinking about this approach though, which is the kind of thing I sometimes do (probably out of mental laziness, in part) but it occurred to me for the first time just now that what you get with this graphical approach is a built in visual check on the reasonableness of the calculation that you don’t with a strictly mathematical approach. Here’s to thinking with the right side of the brain!

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Btw, it would be cool to end up from this with a pattern for making globes (textured with exaggerated topo data perhaps?).

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Break open the path along the straight line for the middle path:

then delete the extraneous points which define the straight.

@WillAdams here is the hemisphere in .pdf format. template_sphere_32_in.pdf (9.6 KB)

@tito I’d rather let the computer do the work. And…yes, you could easily use THIS to create a globe.

Also @WillAdams are there any “gotcha’s” if I lie to CC and tell it that I am using a ball nose bit, but slip in a V-bit to do “no offset” cutting? and get my 15° bevel per side?

I would worry about the toolpath calculation, and getting the positioning accurate — doing it as a V carve allows one to get a preview, which I prefer.

So, for the V carve, take the center path and expand it by the desired diameter w/ rounded ends:

Draw in a line which will be used to cut the base:

and snap it to the endpoint:

then select the entire line and offset it by one-half the endmill diameter which will be used for this cut:

If desired, extend the line and break it up so as to create tabs.

Delete everything which is not needed, export to PDF, convert to SVG, et voila!

(And then we get reminded that Carbide Create doesn’t do well importing lines…)

The SVG:


(will need to be scaled down 0.75 assuming the size of ~25" x 8.25" is correct)

And one eventually gets a file which sort of previews okay:

sphere32.c2d (196.4 KB)

I’ll try to find the time to redo that in Carbide Create later.

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Ooh @BoscoBob… Super cool tool there!