Drill a square hole..
 

Drilling square holes. http://upper.us.edu/faculty/smith/reuleaux.htm A little break from the political morass. ( I enjoy the read, but prefer not to enter the fray)

david 89 turbo cab

Have you seen the moment arm on aftermarket Porsche swaybars? There's a square hole where the torsion bar fits. I have always wondered how to make this square hole. Do you think this is how they accomplish it? If not, how? I think I can build these sway bars for about $200 + some time at the milling machine. The blocks and collars can be purchased from an industrial supply house. Same story with the rod ends and links. Jürgen

http://www.pelicanparts.com/catalog/...Sway_Bar11.jpg

My dad built a timber-frame home that required a square-hole drill press device. The technique described above is far cooler, but the thing built by the nice boys at Mikita worked just fine, drilled really nice square chunks out of stuff. Seems like it was a normal round bit right down the middle with corner-cutter doo-dads -- little sharp horns that sliced the corners out of the corner-space and pushed them out into the middle. Worked a lot easier than it sounds. :)


Dan

Those square holes were most likely cut with a broach. Same way keyways, hexagonal holes and many other odd shapes are cut. Basically if you want to make a square hole 1"x1", you drill a 1" round hole, and insert the broach( a long bar of tool steel with one end 1" in diameter and many teeth each on slightly more square than the next until you get to the last tooth which is 1" square) and ram it through with hydraulic pressure.

5axis's way is much cooler, however.

There are many ways to make a square pocket. Everything from wire EDM (leaves the wire dia/2 corner radius) Sinker EDM (square electrode with sharp corners will make sharp corners) As mentioned by Anton, a more old fashioned production method is broaching (a form tool with progressive steps is pressed through the hole) and a very old school method, using a die filer. (sort of a jig saw for files) I think the arms for your sway bar are aluminum so they would probably be broached quite easily. It's fast and accurate. A great machine tool accessory found on some old bridgeports was a shaper head. It reciprocates a lathe type tool and shaves away the material with each stroke. It was often used to cut internal key ways.
Another way to overcome fitting a sharp square into a pocket is to mickey mouse ear the corners. That is to drill a relief hole so that the sharp falls into the cleared area. It is also much easier to mill since the end mill is not trapped in a corner.

I kinda dig the old shaper attachment when I have time to play.




We often pick corners with a ball mill down to a .020 radius in some deep pockets.... 5 axis indeed..

5, given the other machining operations needed to make the sway bar arm, I think it is CNC milled. How did that machine actually cut the square hole?

Perhaps the last thing you said.

"A little break from the political morass."

What, you're just too afraid to broach that material ? :cool: cough-cough. . .oye:rolleyes:

and for those who want square plumbing fittings...

http://forums.pelicanparts.com/uploa...1087975743.jpg

Forgive me, but what good is threading a square fitting?

Makes a good joke....

Some fluids flow better in square pipes/fittings. Also, if the fitting is round, and the debris is square, it will clog easier. Very useful in cities with old water systems...

;)

I just checked the price on a 1" broach, and they're $433 from Mcmaster. Ouch!!! Plus, I don't have a press big enough to fit a 24" tool. I think milling the square hole with an end mill would be the best. Perhaps it's not the quickest way, but it's cheapest for me. :)

Something like the sway bar mount could be done will in a mill with one tool change. Once the basic dimensions of the hole are achieved, just process the corners with a small diameter end mill. The slight radius in the corner is not an issue as the clamping force is on the flats, not the corners. 5Axis also mentioned the broaching machines, and yes they work well. These were WW1 technology and can probably be had for scrap prices.

You got me achhhhh.... SmileWavy

Back to square holes: That $400 broach is cheap compared to the machine time to make a perfectly square hole, or corner pick down to a very, very fine radius. They would be my first choice for that job. You may be able to call around and borrow/ rent one for a small donation of some sort.(perhaps liquid) That depends on your persuasive abilities. To mill that down to a small corner radius where the corners are not significant I would use the mouse ear method. It will prevent the small end mill from pulling against the two adjacent walls and overloading the flutes. The extra clearance in the corner can be almost imperceptible and you won't get a digger on the wall from the cutter sucking in.

http://forums.pelicanparts.com/uploa...1088038965.jpg

political morass
 

. . .and why would you want to broach material like that ? . ..I hear its just a stress riser . :cool:

Well, I could borrow a broach, but if it's 24" long, I have no way to press it through the aluminum arm.

Actually, I was brainstorming about a new way to fasten the arm to the bar. What if you drill a 1/4" hole in the arm and the round bar and use a pin to attach the two. Let me draw it up and post later. The only advantage I see to the square drive is the fact you can change to larger/smaller sway bars while using the same links and arm.
Jurgen

One of these will do for pushing a broach. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=33497
I used a similar one to make key ways. It does not take long to index the supports upward and resume broaching. Repeat until finished.

My friend Island may be able to help you out with pinning the bar in place. I don't know if a 1/4" dia. pin in shear will be sufficient?

A easy way to key a shaft is to drill and ream along the length of the shaft, on the seam of the mating parts for a pin. This arrangement places the entire length of the pin in shear. Think of it as a easy to make key way
http://forums.pelicanparts.com/uploa...1088110846.jpg

Wow, great idea. I'm an amateur machinist, so I'm still learning how to think outside the box. :)

Now, I have a really wild idea: cockpit adjustable rear sway bar. Jurgen

In our business we manufacture wood doors and windows using mortise and tenon joinery. The mortise machine is essentially a drill press with the bit surrounded by a four sided chissel.

Also good for pressing out pedal cluster roll pins, I imagine...