[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?

[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
.

[Astroguy]

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?

[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°, 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.

[DareBee]

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.

[acondit]

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.

[Astroguy]

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°, 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.

[DJPLAST]

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

[Robin Hewitt]

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

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

[Bowman]

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

[acondit]

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

[M100]

Maybe he just needs a deliberate stress raiser

[alconatech]

go old school try a shapper

[Skyshark]

I was curious about this myself because I wanted square corners for a project I'll be working on. After doing a ton of research this morning, it looks like there is a company that makes the Square Hole drill bits, but they recommend that you only go 2x the size of the square for depth. They are sending me a catalog, so I'm going to check it out and will report back with any findings.

[Rodm1954]

Have a look at the part you are mating to the pocket and see if it is easier to radius the corners to match the pocket.

[AMCjeepCJ]

http://www.rotarybroaching.com/

That'll do it!!

[RICHARD ZASTROW]

I bet that's why they made the slotting/broaching attachment for BP's.

Then there is tilting/swiveling the head at a compound 45 deg. angle with a 90 deg. incl. angle end mill (ground to sharp point). Don't think it applies to the Taig CNC though.

I'd vote for the corner broaching if a true square corner is required.

[NC Cams]

Square holes can be rather sexy - they can also be great sharp cornered places for cracks to start propogating from. This is especially true in material that is to be subsequently hardened and/or moderately/highly stressed.

The "how to" make a square hole has already been discussed. However, the best way to prevent the square hole from causing problems later is to use the round hole in the corner trick.

Moreover, by doing this, any torque applied to the part thru the hole applies the foce into/thru the "flat drive" method - Snap-on made a lot of money selling wrenches and sockets that use this trick and it is also used in fits-all combo/metric-imperial wrenches that show up in TV telemarketing ads.

The reduced stress concentration from the rounded corners provides a lot of incipient charm as opposed to a sexy but "why bother" truly square hole.

[Robin Hewitt]

After doing a ton of research this morning, it looks like there is a company that makes the Square Hole drill bits

If you get one working you will post lots of pics won't you, maybe a movie?

I think it will only drill, won't round out a corner. Looking at the theory I think the tip needs to bite in to metal to keep it on track corner to corner

[arie kabaalstra]

The Mouse-ear trick is the most commom used method to create square or rectangular holes.. i must stress though, EDM is used to make em, BUT!!..WITH "mouse ears, because an EDM wire still is 0.25 mm thick in most cases, creating a 0.32 mm wide cut, thus a 0.16 mm corner radius...
slightly bigger is better, we'd make 1mm holes on the corners at least..

Stress relief is important here..

a hole can really prevent a crack, it's an old trick used by motorcycle racers, when after a crash the windshield was cracked, simply drill a 4 mm hole at the end of the crack, and the crack won't crack any further..