Machining Styrene to make small models

[ALAN2525]

I'm trying to make some scale models from styrene and having some difficulties joining the edges.

For 90 degree corners I'm engraving the fold lines with a 90 degree V point tool "almost through" and then folding along the line and using some poly cement to make the joint.

The problem is where I have a corner which isn't 90 degrees, ideally a 5 axis machine would be able to cut the exact angle on the edge of the sheets. I only have a 3 axis machine and wanted to find something in between a basic 2.5D solution and having to model each sheet in 3d and then machining the parts out with the requires angles on the sheet edges.

I hope this illustration helps to explain what I'm refering to:

The image shows the resultant gap when the sheet is bent to angles less that 90 degrees.


http://img152.imageshack.us/img152/3767/image1sr1.jpg

[GaryCorlew]

You don't say what the degrees are for the other bends but this site may help you with most of them http://www.toolstoday.com/c-320-chamfer-bits.aspx

[braidmeister]

I've done this sort of thing in the past with Dibond AL faced plastic. You need a bit with 100-110° vee to 'over-bend' the corner to get your 90° angle. Be sure to check angles on router bits, they vary as much as 4°, unlike end mills, which are always spot on.

It's just a 2D cut, no 5-axis needed. Get the proper angle bit, set a vector on the centerline of the joint & machine along vector.

-Brady

[ALAN2525]

I didn't make it clear but the 90 degree V bit works for bending 90 degree corners. The problem is obtaining bends less than 90 and avoiding a large gap which would require some kind of filler.

The smaller angles vary so it wouldn't be able to find a cutter with the correct angles to cut all of them.

I can get away with most of those bends but on some you'll be able to see both sides of the bend so I need to try to find a way of making the edges butt up more precisely. I could always make the parts to the sive of the longest edge and then file to the correct angle with a needle file but that defeats the point of using cnc.

[braidmeister]

If this is a $ making venture, then get custom bits ground. Something like the Her-Saf type insert bits come to mind. They may even offer you a custom angle.

-B

[ALAN2525]

The angles all vary so I can really justify getting custom bits ground for each edge.

It'd also take forever to machine too as I'm using an EGX-300 so no automatic tool changer etc...

[ALAN2525]

I guess i'll have to model the parts in 3d and then machine them all!

That would take so much longer than a simple 2.5d toolpath!