tech: square holes old school

There was some discussion recently about square holes. Here's a crude way of making holes for carriage bolts. It's pretty quick, and involves a hammer, so it's the kind of thing I like to do.

I want use carriage bolts to attach the headlight stands on the Ferguson roadster.

Start by drilling 5/16 holes in the parts. The square broach is a 5/16 square tool steel lathe bit. I drilled a 27/64 hole in a scrap of shafting to serve as an arbor for the bit. It just presses into the hole. Then using a cut off wheel, I knocked the corners off the broach forming a rough pilot about 5/16 diameter in the center, and leaving sharp cutting edges at the corners.

Using a hydraulic press, push the broach into the part until it marks the corners of the square hole. (I'm using 1/4 in plate for these parts, on thinner stock, or aluminum, you may push the broach right through.) Then remove the tool and clean up the corners with a square nose chisel. The second pass with the broach finishes the hole except for some minor cleanup with a file.

Time for 8 holes including making the tool was about 2 hours. Crude but effective.

Jerry

 

Thats nice and simple. Thanks for posting it.

Any suggestions how to make a nice curved slot like for an alt or P/S bracket that must slide in an arc?

 

With a mill and rotary table.

 

cool just grind it off and It'll look good!

 

Lay out the arc.
Make a center line and two border lines.
A single center line works ok, but having a border to cut to can help.

Drill a series of holes where the slot goes.
If the slot is to be 3/8" + a touch, use a 3/8" drill.

Connect the holes with a die grinder and 1/8" abrasive wheel.

Do the final finish with a sharp flat file making sure a 3/8" bolts unthreaded section will slide along the arc.

Somewhat labor intensive, but it's not bad.

 

The secret is to cut the slot, BEFORE you cut out the outside shape of the bracket: Make a practice bracket out of 1/4 inch masonite first. I made one as follows
1. Get 3/16 in. thick steel plate big enough for bracket.
2. Layout outside shape of bracket and inside curve of slot you need.
(The centerline of the slot and the bracket may not be the same,
depending on what you need.)
3. Center drill and drill hole at each end of slot. I used 3/8 drill.
4. Carefully saw out slot with sabresaw and metal cutting blade,
18 teth per inch.
5. Finish file inside contur of slot.
6. Use sabre saw or band saw to cut outside shape of bracket.
7. Finish file nice and smooth.

 

I've used 1/4 x 5/16 bar stock bent over a piece of pipe. Then space them apart and weld the ends together. As they say, a little grinding and you're good to go.

 

That's the ticket!

 

There's a machine shop local(pittsburgh) that makes tooling to drill square & hexagonal holes.....Its WATTS Bros. tool & die, on Airbrake ave, in Wilmerding, Pa.....dont have the # handy, but sure it'll google....

 

now that is a killer idea...and I happen to have a bunch of different size lathe bits around...definately a good tech thread for those of us who're picky about what we do...should help with building equipment and machinery to give it that professional look...

 

If you dont have a mill and rotary table, use a compass (like you had in grade school and poked people with the sharp end). Map out your Arc, drill a Hole at each end, use a dremmel cut-off whell to cut out the center, then the sander disc on it to clean it up. Youll never know it wasnt done on a table.


Oh, not to hijack the post, so, I like the idea of the pilot for the square broach, I would have just tried to push the square straight through.

 

huh....I just use a square file....

 

I used the lathe bit for the square hole but I just heated the bracket to red hot and drove it through with a 3 pound hammer.