Making a sharp inside corner?

[Docmani]

Hi all,

I'm new to this board and fairly new at machining, so please bear with me.

I have a small Sherline mill and I've done a couple little things on it. I'm currently working on converting it for CNC.

I'm looking at cutting a couple new parts I need and I had a question. I'm looking at making the following part in aluminum (the one in the picture is resin cast):

http://www.resinparts.com/images/krfrontdiag.jpg

Simple enough, except for the sharp inside corners. There is no way to get a cutter at a perpendicular angle. Now, as a hobbiest, I'll probably end up milling a round corner and then filing it down.

I'm just curious if there is an alternative? How would a professional handle something like this for a large run? Filing each one by hand seems like an awful lot of work. Thats probably the way I'll go, I was wondering if I was missing some other method for accomplishing the same thing?

Thanks!

[Verfur]

Not that this will help you at home, Cut it on a EDM.

As it goes I would use as small of an ball nose end mill I could get down it and the file to suit. Thats how I have done it fore years.

[DieGuy]

Generally a sharp inside corner is done with a shaper or a broach.

[HuFlungDung]

As I learned from the Vcarve software advertised hereabouts, if you can grind a tool (even a spade type tool) with a conical point, and a cone angle that matches the taper angle on your part, and then withdraw the tool up the corner line, it will 'sharpen' the corner cut to a very small radius equal to the tip of your tool diameter. I just can't get over how nifty that concept is

[Tony Mac]

Hi,

The link below will run a short video that shows how a V shaped tool plumges from a corner into the material, then lifts into each corner in turn to form the concave pyramid having 'sharp corners'.

http://www.vectric.com/vectric/images/tmp/pyramid.avi

This technique can also be used to machine 'raised' features that include sharp corners.

Tony Mac

[CNCRob]

Hey Tony, I just tried the video link and I couldn't get it to come up, I was wondering if there are any settings I need to change to make it work. Thanks - Robbie

[Tony Mac]

Hi Robbie,

Sorry about that.

This link should work for you,

http://vectric.com/vectric/images/tmp/new.exe

Let me know if you still can't run the video.

Tony Mac

[CNCRob]

Thanks Tony, That link did the trick, it worked great.

[pauluk]

Hi,
The other thing that you can do to get what is effectively a sharp corner is to drill out the corner as shown. Drill the holes first then mill the pocket out. Obviously this is not practical with a significantly tapered hole, and won’t be suited to some jobs due to aesthetics or other considerations. It is advisable for parts which are fairly highly stressed, since it removes the stress raiser caused by a sharp corner.

[Tony Mac]

Hello Docmani,

Looking at your picture I can't decide whether the inner wall is vertical or is it tapered - larger rectangle on the top face taperng to a smaller rectangle on the back side?

If it is tapered then VCarve Wizard will do what your require and I have attached an image showing a similar example.

Hope this might help you,

Tony Mac

[Docmani]

The inside of that box is tapered (larger top, smaller bottom), although I was curious about regular non-tapered boxes as well.

I will definately give this VCarve a try. Thanks for the tips!