poor man's square broach

A new member was asking how to drill square holes so I thought I would share a process that I have used successfully in the past

for instance to make a 5/16" square hole in soft material or even in mild steel as long as it is not too thick I have taken a 7/16" NC starting tap and ground it square. the teeth will broach out the material to make a square hole. Care must be taken when doing it like this because the 60° cut angle is wrong for this application
press the modified tap through the holes
here is a drawing of how the tap would look
Attachment 9066
Attachment 9067
Attachment 9068
Ideally you would use a 5/16 sq piece of tool steel ground to the shape of a broach
like this
Attachment 9069

I like that idea. will now have to hank on to all non sharp taps for this purpose.

they are no replacement for a proper broach but in a pinch and with care you can make quite a few hole turn square before the teeth break off

A good and inexpensive idea, we have all old threading tools broken or used.

Quote:

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Originally Posted by Okapi

A good and inexpensive idea, we have all old threading tools broken or used.

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+1

I was just thinking that the other day as I was getting ready to toss a chipped 3/8" tap. I love thinking I'm not really hoarding, I'm just waiting to find the right re purpose :)

I am with you on keeping the broken taps, drills, etc. I keep anything broken or worn out and made from HSS in a box waiting for the right re-purposed tool.

All "old " mecanicians have a big tin bean can where we put all the "can be useful sometimes later"…
And when you need a small piece of very good steel to make a new centering pin for example, what better than a broken tap.

Very slick, Frank! Thanks!
---Joe

It'd not hoarding. It's the fuel of creativity waiting for sparks from your mind.
It works like this: A pile of treasure fills all available flat spaces. In recognition of this problem you use some of the stuff to create storage in the air volume above the other stuff. Cardboard, yellow carpenter glue, cutting tools, assorted spring clamps and a can of left over paint are needed. Now you have new flat space to fill.
Repeat the cycle; but take time to mark things for ID and make dividers for the little containers. Show someone your accomplishment and tell them it's not hoarding, it's creativity
2nd repeat cycle. Attach stack of storage containers to wall to keep gravity at bay.
Go into Michaels or Hobby Lobby and come out with nothing but some new storage boxes that were on sale.
You are beginning to feel artistic. Buy another can of mismatched paint; but a different color.
3rd cycle. There is no longer any space on the workbench except where the vise is mounted. You find a scrap piece of plywood and attach a stringer board to the back that will allow this new little mini-workbench in the jaws of the vise. Voila!! New flat space in thin air!
People you know are beginning to notice ..............

Nice, great idea.

Ralph

Gee, that takes a load off of my shoulders after reading some of the posts on here, I thought sure I was a hoarder, " wow" I had an inkling I was not one of those people that cannot throw anything away until it rots or molds. I will have to convince my wife to read this and quit pointing her finger at me and raising her eyebrows. Thanks folks, you just saved my marriage.

My grand father had a saying you keep something for 7 years if you have't used it by then you need to dig it out take another look at it then build a storage place for it label that space and keep it another 7 years. You will probably have used it or traded it by then for something else to keep for 7 years.
When he died at the tender young age of 97 there was this one storage space that had several dozen feet of hand made decorative molding that hadn't been produced in over 70 years. On of my uncles decided that since there was so much stuff some of it might have a little value to someone so they had an estate auction I wasn't at the auction but I heard that the hand made molding which was left over from a house my grand father had remolded was bought by the folks who owned the house for a 4 figure price how much of a 4 figure price I don't think I ever heard but I doubt if it was on the smaller side.
Hoarding? I don't see it that way as long as you eventually get around to using it or are willing to part with it at some time.

I've done a similar trick by pressing a spiral reamer through a length of seamless tubing to cut rifling into it for air guns (or regular guns, for that matter!)

Works much better than one might think.

Great idea. Need one some 6 x 6mm HSS insert.
Small problem....need a 8.5mm Tap. Is there an imperial size close to 8.5mm Diameter.

Attachment 20993

The closest thing would be a 5/16" but at /312 that is only be 7.9mm the next size being 3/8" .375 would be 9.5 which would probably be the best size to grind square if using a corse thread tap there should still be enough of the threads left to do the cutting.

Going to try it with a M8 tap. Can not take too long to file out 0.25mm per side with a needle file.
Still fantastic idea.
Will this handle changing a 6mm Dia hole in a 12 x 12mm bar I want to use as a boring bar. Bright MS as it is only to open up a brass bush.

That's a great idea. I will have to try it.

As an added thought, I have found that pawn shops in my area often have used taps available for 10% or 15% of their new price. Sometimes even less. I have purchased bunches of them and tumbled them in walnut shell media to clean them up. I have even gotten complete sets this way: taper, plug, and bottom taps; all the same brand and tolerance so they were probably purchased as a set originally.

Most clean up to a usable state, but those that don't could easily become square broaches. Heck, event the good ones could easily become broaches and at a low cost.

I wonder if the three flute ones could become triangular or hex broaches. The hex may require two passes.

How about a "D" shaped hole? Or one with a key? This has my imagination going.

Paul A, if you were to calculate the depth of cut required for a key-way grind 1 flute flat then grind the remaining 3 to the diameter it is feasible to make a key way broach the problem stems from the body of most taps having deep reliefs cut between the flutes. However since all of the threads would be ground off on the 3 flutes at best the bore would not be effected, at worst it might be scored but should otherwise remain un damaged You would want to use long taper taps for key way broaches.Non fluted machine taps might be best for this as well.

Way to go Frank....:O)

Don't try it on a piece of 22mm dia solid MS.

Attachment 21098

Fortunately I felt my little 5 ton manual press was struggling, so covered it with lots of rags and an old jacket so when it let go it was not too dramatic.

Ended up just filing it to square. Gave me a good start at least.

For thinner stuff I am sure it will work

I've never tried to use this method on anything thicker than 1 .5 times the square of the hole IE approximately 6mm square hole through 10 mm mild steel. and always a long taper a 1/2"20 tpi taper starting tap goes through 1/2" mild steel fairly easy but sometimes starting out with a size smaller tap to initially start the cutting process by removing part of the metal then finishing off with the size you need will reduce the risk of breakage.
This is the reason some of the draw broached I used to have were 30" long, for cutting a .75" dia. 6 spline while broaching through 2" thick materials

A great example of using what you to make what you don't have!

Use it up; wear it out; make it do; or do without! :-)