Cutting sharp square internal corners , newbie

Hi all new to all all this , I've just got machine working and have few questions,

How do you go about cutting square internal corners ?

im trying to cut g10 3mm and 1.5mm carbon sheet, can anybody recommend good bits for such tasks and give a guide to spindle speeds ect , there is some fine detail in some parts I'm trying to make , is using very small bits a problem with such materials ?

thanks in advance , just trying to get started on my cnc adventure

I have Chinese 6040 machine and am using cut 2d at moment

Simple answer is that you can't cut a square internal corner with a round tool! What is generally done is either you accept round corners and machine the mating part to fit, or you machine a relief in the corner by over-cutting slightly so that there is clearance for the sharp corners of the mating item.

You say that you are using Cut2D. I use Cut3D and it has a feature that lets you add these fillets to a design. It's very much a 2D feature so I would be surprised if your software didn't include it as well. There is a choice of style of fillet, even, and it's as simple as selecting the tool and clicking on the corner on the drawing. Using a small tool, the result is fairly discreet.

EDIT: Just been checking and it's VCarve that has the filleting feature, not Cut2D/Cut3D. You can add these fillets manually, of course.

search ebay for drillman , he has the best bits to cut composite sheets

For Cut2D I just drawn the overcuts in CAD as my version of Cut2D doesn't automatically do this operation.

But Cambam has an option to overcut the internal corners to allow something with square corners to fit inside, but you will have gaps on the outside as Neale mentions.

Scroll halfway down:
http://www.cambam.info/doc/plus/WhatsNew.htm

Or if I need dead square corners in wood I just file them square by hand - you could do the same in carbon fibre?

I know this is off topic slightly but on metal you can broach square holes, you can spark erode square holes (or whatever shape you machine the eroder bit to be), and if you have a look at John on NYCCNC you will see machined square holes being made using a special broaching device:

(scroll to 11:30 for the machining operation)
https://www.youtube.com/watch?v=-MidOdzxT7k

Quote:

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Originally Posted by Blackrat

search ebay for drillman , he has the best bits to cut composite sheets

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is he in the uk or is it on eBay us , found one quy called drillman1 but was in texas?