# Thread: How do you cut square inside coners?

1. ## How do you cut square inside coners?

Ok, I am haveing fun learning my new machine a CNC Taig. But now I need to start making parts. How do you machine a square inside coner?

2. One method, which depends on whether you can tolerate it cosmetically, is to use a small diameter tool for the final finish on the outside of the pocket, and when the corners are reached the tool moves out a small distance at 45&#176;, just enough to take out the normal radius that is left.
This depends alot on your application.
Al
.

3. Originally Posted by Al_The_Man
One method, which depends on whether you can tolerate it cosmetically, is to use a small diameter tool for the final finish on the outside of the pocket, and when the corners are reached the tool moves out a small distance at 45°, just enough to take out the normal radius that is left.
This depends alot on your application.
Al
.
I`m not sure I understand how that works?

4. IOW if you used, say a 1/8" endmill to get the corners as close as possible to a right angle, then move outward from the corner at 45&#176;, this causes a small semicircle out from the corner, if you were making a pocket for a rectangular item to fit into, this would relieve it enough for it to drop into, this is one method I use to, but maybe not pretty.
Al.

• Originally Posted by Astroguy
Ok, I am haveing fun learning my new machine a CNC Taig. But now I need to start making parts. How do you machine a square inside coner?
You CAN'T

Al's method is a workaround to allow a square part to fit through the aperture.

Square holes are made by broaching, EDM or filing.

• If you mill around the inside of the square with a 2" diameter tool, it leaves a 1" radius in the corner. The distance from the edge of the tool to the corner of the rectangle is the ((square root of (1^2 +1^2 )) minus 1) or the square root of 2 - 1 which is approximately 0.414". So when the tool is tangent with both side of the corner, you could move on a 45° towards the corner to remove the remaining material from the corner. Of course the smaller the tool that is used the less the deviation from square.

• Originally Posted by Al_The_Man
IOW if you used, say a 1/8" endmill to get the corners as close as possible to a right angle, then move outward from the corner at 45&#176;, this causes a small semicircle out from the corner, if you were making a pocket for a rectangular item to fit into, this would relieve it enough for it to drop into, this is one method I use to, but maybe not pretty.
Al.
Duh, OK now I see. Thanks guys, I have learned so much here.

• We call those corners "mouse ears". They work fine in the mold business.

• ...or, you could use a square hole drill, I kid you not

http://www.integerspin.co.uk/polygon.htm

• Darebee is right squared corners are made with broaching cutters, EDM's or filing.

You could try to cut the pocket and then come back with a smaller diameter cutter to lessen the corner radius but it will still require broaching or filing to get them truely square. If you can get the radius as small as possible first it lessens the amount of filing needed to square things up.

Bowman

• Originally Posted by Astroguy
Ok, I am haveing fun learning my new machine a CNC Taig. But now I need to start making parts. How do you machine a square inside coner?
Astroguy,

I guess the real question now is ,"Do you really need square corners, or do you need a hole that something square will fit into?

Alan

• Maybe he just needs a deliberate stress raiser

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