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?:confused:

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
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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
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I`m not sure I understand how that works?

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.

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?:confused:

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.

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.

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

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?:confused:

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 :)

go old school try a shapper

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.

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.

http://www.rotarybroaching.com/

That'll do it!!

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.

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.

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 :D

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..

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

I had a square piece I needed to fit in a pocket but I ended up rounding off the corners of the piece this time. But in the future that may not be an option.

i think you're now going about it the right way, most of the time square corners are a design flaw, yeah you see them but not all that often. the few times i've needed them, i've made a broach, used the lathe as a shaper, filed or fabricated - mill a slot, silver solder or brazed a piece over top creating the square, then machine the outside. For all the problems they create, and the difficulty in machining them, you're best to design around square holes/pockets if you can. rectangular pockets, even with rounded corners, are still a pita. can you go one step further and mate the parts cylindrically? or just mount face to face, bolt, then pin it to accurately locate? design to the simplest way to make it

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 :D

When I get the catalog I'll post pictures and contact information. I'm thinking I'll try making the squares first, then using end mills to remove the rest of the material I don't need. We'll see.

Has anyone tried a home EDM machine for making square corners? I wonder how difficult & accurate that's be.

EDM does square corners, as has been stated. It works pretty well. Very expensive per hole, though.

A different option not many people seem to be aware of is that jig grinders will do square corners with an attachment, and not only that, will put draft on those corners as well, from the skinny side of the hole.

EDM does square corners, as has been stated. It works pretty well. Very expensive per hole, though.

A different option not many people seem to be aware of is that jig grinders will do square corners with an attachment, and not only that, will put draft on those corners as well, from the skinny side of the hole.

do you erode with sqaure wires?.. even EDM machining has a radius, there's always a gap between the wire and the workpiece.. a chamfer of fillet of 0.5 mm can fix the problem though, and that's barely visible, but is your part is square, and has sharp edges, you still have to "mickey-mouse" you contour.

If it were me, I'd just get the Square drill bit set out. In my shop their kept right under the Sky hook, and behind the Prop Wash. :) :) :)

Speaking of Square drill bits, a place I worked at a while back, had a box-stretcher, first thing all the new welders had to do was learn how to use it, the problem was finding the dang thing.

Most times it was time to go home for the day (before they found it) Ahhh, always tomorrow. :)



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Speaking of Square drill bits, a place I worked at a while back, had a box-stretcher, .

That reminds me, being in the electrical game, we always used to keep a "cable stretcher" somewhere in the workshop, just in case, though the apprentices always had trouble finding it... hard to get good help.

Russell.

has anyone, by any chance seen my folder with lost items?.. i used to keep it in my archive, but it's gone missing.. :)

Sometimes that folder gets moved into the folder for next weeks incoming emails, if you wait a week it may re-appear :D

Astroguy, I just picked up one of these little squares yesterday and it has the inside-corner cut in as Al is explaining. Click on this picture for a larger view and look at the inside corner... http://woodcraft.com/family.aspx?familyid=20077

Cheers,
-Neil.

yeh, I remember being sent to the tool store to ask for a "long-weight" and a long wait is what they gave me.

yeh, I remember being sent to the tool store to ask for a "long-weight" and a long wait is what they gave me.

That's a good one. :)

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Has anyone tried a home EDM machine for making square corners? I wonder how difficult & accurate that's be.

I made a home EDM machine and it cut well but was very hard on the copper electrodes. After having made it I was told that the tools were burning out because I didn't use a low current spark to initiate on a separate circuit.

I may fix it one day, but having an EDM on the shelf means I have not broken any taps or sheared any bolts since :D

do you erode with sqaure wires?.. even EDM machining has a radius, there's always a gap between the wire and the workpiece.. a chamfer of fillet of 0.5 mm can fix the problem though, and that's barely visible, but is your part is square, and has sharp edges, you still have to "mickey-mouse" you contour.

Didn't know "EDM" meant wire EDM exclusively.

I guess nobody uses sinker EDM anymore, because that's what I was talking about. And having seen holes produced by such method, I know it can be done.

As others have hinted at, the goal is to anticipate how the part can be made and then design it to use standard and achievable manufacturing processes.

In other words: Avoid square holes and shafts unless there is a really good reason. If it cannot be avoided, a square shaft can be ground flat square and parallel on a surface grinder. Grind a chamfer on each corner that is bigger than the inside radius that you are able to machine into the pocket. There you go !

My question is: What purpose does the square feature serve ? Could it be served by a round shaft with a doweled joint or roll pin providing the torque coupling ? Or is it a linear application (straight line motion with guidance against rotation ?

?????????


http://www.toolstation.com/images/library/stock/webbig/50532.jpg


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Square holes can be rather sexy


I am so confused be this statement. What is is pertaining too???:confused: :confused: :confused:


Anyway,
EDM, Shaper, or a small drilled hole in the corner and cleaned out with an end mill. Granted it won't be a sharp inside corner, but the radius will be as small as the drill you use.

Astroguy, I just picked up one of these little squares yesterday and it has the inside-corner cut in as Al is explaining. Click on this picture for a larger view and look at the inside corner... http://woodcraft.com/family.aspx?familyid=20077

Cheers,
-Neil.

Thanks!

That reminds me, being in the electrical game, we always used to keep a "cable stretcher" somewhere in the workshop, just in case, though the apprentices always had trouble finding it... hard to get good help.

Russell.
I got an 8' board stretcher here in the shop, I'm relay want to save up for a 12' one next

A rotary broaching tool holder (http://www.slatertools.com/rotary7.htm) should fit on your CNC machine. To make the square hole using this tool, first pre-drill a hole to the flat-to-flat dimension, then use a broach of the same dimension to take out the square corners. The best way to understand how this works is to watch the video.

http://www.slatertools.com/video.htm

http://www.rotarybroaching.com/images/p_squbro.jpg

wow, I watched the video. Pretty darn impressive!
Steve