Router an angle...

LowRider CNC Advice
1

Hi,
The spars of my plane are 2400mm long (there are three of them), and 187mm deep. That’s the easy part.

Both the top and the bottom have to be cut at an angle. The top needs to be at 8.2 deg, and the bottom at 3.3 deg.

Can the LR2 do this? And if so, how?

Duncan

Spar.png

2

You could prop up the other side and then cut it straight. You’d need to already have it cut to width.

sin(8.2deg)*187mm=26.7mm
sin(3.3deg)*187mm=10.8mm

You could also make an stl and have it carve out the wedge you want removed, but it will end up being a stair step and you’d need to sand it flat.

This is a pretty trivial operation on a table saw though. I have a wixey digital angle guage that would set up the angle in 30 seconds and we could rip them in a few minutes. What material is it?

3

I agree with Jeff. If it's just square stock, the table saw will be much easier to do this with. Also, you'd need to flip the pieces to do both angles anyway.

4

Thanks guys. I suspected as much. The material is DOW blue foam, so very easy to cut, but not very stiff, and it flops about a bit. In case you’re wondering, it will be covered with carbon fibre. I don’t have a table saw, unfortunately.

Jeff, you mentioned a stl file, which would allow the router to carve away the offending wedge - how does this work? If I used very small incremented passes, there wouldn’t be a lot of tidy up work to do. I’m going to go in search of stl-type instruction on the web, but please feel free to suggest an approach which would work.

Thanks,
Duncan

 

5

STL is a file format that CAD programs produce to define a 3D shape. Any 3D CAD program should be able to make it. Probably the easiest though would be tinkerCAD.

6

You could also just draw a line on the top and use a hand tool to cut from the line to the corner. You would use the same math to determine the distance from the end to the line:

sin(8.2deg) * thickness = distance from edge.

So if your material was 20mm thick, it would be 2.85mm.

7

Hi Jeff,
I have it! Using your formula, I will align two straight edges (one at the corner, and the other offset), and simply hotwire the wedge off. Elegant, and no mess.

Thank you.

Duncan