Introduction: "drill" a Square Hole

This is a short vid showing how to make a quick and dirty broaching tool to make square holes.


legamin (author)2014-04-12

having been thoroughly bored but impressed by the statistical analysis of static and dynamic material loads and strengths during my grad degree in physics...I would recommend that anyone unfamiliar to what can occur under extreme dynamic loads (since you slipped over some of the tedious of the 'heavy' work), should familiarize themselves by talking to someone with experience or at least reading about it. I've had my forehead sliced cleanly open by a shattering shard of tool grade steel that I was hoping to press into a brass plate but in retrospect might have misjudged the size of hole required by a few ten thousandths.... But if you live through it, (and don't get so scarred that you can never be gainfully employed...but that's a DIFFERENT story!...), then you will learn a new skill and go on to self betterment.

I would have loved to seen the entire 'boring' process (forgive the shop humor). But it would give better understanding of just what the stresses are and if a person wants to risk it in their own shop at their current experience level.

-scarred and impressed... Thanks.

Well said legamin. Thanks!

lime3D (author)2015-03-18

I've been on intructables for a while now, and I'm getting pretty tired of self-proclaimed experts nit-picking every instructable they read. I read this one and found it interesting.

I too noticed the speed of the drill, but so f$%king what?

If you have a compliment, great. A legitimate question, great. But rather than tell an author how wrong they are, via the comments section, send them a private message, or even better, write your own instructable!

So my question is....

What do the grooves in the broach tool do for you. What happens if you don't cut them in?

arduinoversusevil (author)lime3D2015-03-18

Good Question!

It's like the hex hole instructables, the broach just mashes through the steel and it makes the hole nasty. If you cut nice sharp grooves then each groove takes a little cut out of the steel and leaves a nice crisp hole. Sort of like tiny nibbles instead of a big old bite...

Also, if the material is thicker, you'd never get the tool through because you are trying to remove too much material in one go.

rickharris (author)2014-05-01

I think I could have filed it out with less effort.

Hi Rick,

To file a square, slide fit 3/8" hole would take considerable, practice, care and patience. I'd like to see you do it, as a comparison. Please post a vid if you do.


texdanl (author)2014-04-14

Notes to all. I have 30 years experience as a job shop and ship yard machinist. The drill speed was actually about right for drilling mild steel with a coolant medium. The chips come when the speed and feed is right and you get long curly shavings when it is wrong. I knew immediately that he had used a coolant...steel on steel does not smoke!

If this sort of thing breaks your little hobbie vice then you need to upgrade to better tools. I use my steel vice as a press all the time and did so in the shops as well. The deep socket was a great use. I guess he COULD chuck up a piece of 4140 heat treat in a lathe and make something to do that job but if you are only doing this once or twice a socket is great. Good steel and generally hardened and tempered.

I have actually done this and made my own broaches the only difference being that I made my broach and then hardened it and tempered it. I ground it on a die grinding machine and it was perfectly sized to + or - .001" and used for making broached holes on a drilling rig.

You can broach a hole in hardwood but it needs to be made with a more aggressive bite. Look at the difference between a hack saw and a wood saw. The only safety thing that I would add to this is to make SURE that you wear good safety glasses. I never saw his face and assume that he was so GREAT ibble!

Fred82664 (author)texdanl2014-04-19

BRAVO ! Some people just need a brain and use it to think beyond the box

Pkranger88 (author)2014-04-14

arduinoversusevil, I'm glad you showed us the overall process, but I think there are a couple points you might consider.
1: Explain the options a person has a little more. For example, you can actually drill a square hole with an oscillating 3 fluted tool like:
2: If you're going to point out the fab of a square broach, you might point out the key considerations a person should have, such as taper angle, material, jugs for grinding etc.
3: If you want to make sure that your broach goes in straight, you need a collet. A square broach makes it more difficult, but you can make one out of 2 pieces of stepped aluminum that hold just the top.

But otherwise, I congratulate you on solving a problem that most would throw their hands up in the air over.

MSHAG (author)Pkranger882014-04-14

that is one badass video you've got there.

Pkranger88 (author)MSHAG2014-04-15

Thanks! I wish it was mine. But I can't take credit.
I found this a while ago. I have a Bridgeport Series 1 and it would be nice to have this adapter for making switch panels for square bodied switches.

Hi PK,

You'll note that it is a cartoon. Not real.

It would work in your BP, but never in a million years with a hand drill.

Is that a bet? :)

All day, any day! 1" mild steel 3/8" or larger square? 100 clams?

keldredge (author)2014-04-15

No, drill speed too fast, no flood coolant, or even a shot of lubricant during the procedure.

Dutch6 (author)2014-04-14

You forgot to SHOW how to make the broach. Once you have the broach the rest follows.

Thanx Much, Dutch

caruncles (author)2014-04-14

I always wondered how that was done. Now do a video on making the broach! Thanks to the poster who mentioned the drill bit-chisel for wood. Learned something there, too! Thanx!

Smelter_uk (author)2014-04-13

The perfect example of how to ruin the thread on a vice. They are intended for work holding, not crushing!

Hi Smelter,

Indeed, rules is rules? You're aware that there is a shear pin retaining the nut that is designed to fail if the designed clamping force is exceeded?

Yes I am aware of that pin. I have also met in my working life, a number of vices that have the thread worn out just in one spot!

gungajin (author)2014-04-14

Having almost a degree in mechanical engineering, and despite being a very practical, hands-on person with a higher than average readiness for risk-taking I totally agree that this is a kind of kamikaze approach. It will work as long as the stress on the tool is lesser than the stress on the workpiece, but it can just as well explode into your face.

and7barton (author)2014-04-13

Considering the time spent making the broach, surely you'd have got the job done quicker, by simply using an existing square file.

acoleman3 (author)and7barton2014-04-14

there's no guarantee the hole will be square to itself or the walls will be square to the surface of the metal. besides, i can make one of these about 20 min and it would take at least another 10, if not longer, to file it. even if it only saves 5 min, it's worth it

SANDBOX1 (author)2014-04-10

OUTSTANDING!!!! That was slick. I will be trying this soon.

Cool, let us know how you make out. I got a comment from a viewer that the broach shattered on his attempt. I think a uniform taper and the sharpness of the cutting edge in the relief slots are critical. Cheers!

this can be dangerous for sure, just like anything in a shop can be.

Like he just said, a user had a tool shatter, make sure you are aware of the types grades and any heat treatment on the steel you are using and if you are using a bunch of scrap be careful. A good pretest would be to try and use the broach to scratch or dent the steel you want to force it through it should be easy to do if not or if the edge/corner of your tool gets deformed at all you may want to select a softer "target" for broaching or use aluminum for the "target" . It seemed to me that you used a high grade tool steel with a high rockwell hardness for the tool and since you pushed it through in a vice and hammered it out relatively easy you had a very soft steel as your "tool holder" (not to mention how quickly and forcefully you drilled through it). No a vice isnt the "proper" tool for that job but it does have a few advantages, the first is they are everywhere, the second is, the force you can produce is pretty limited compared to even the smallest of shop presses, the third is, its slow so you can hear and feel what is going on so if you are barely making a "dent" you can back off and abort its really easy to put critical stresses on steel and end up with jagged steel flying at you.

Cool instructable its a neat at home solution to that problem

acoleman3 (author)abrown392014-04-14

doing some research on steel types and heat treat methods would be a damn good idea. if it shattered, then it sounds like the operator didn't draw the temper back after it was hardened.

snoopindaweb (author)2014-04-13

Where's a will there is a way. Thank You. ~(:-})={>--- ]

TwoWindsBear (author)2014-04-13

How about an 'ible on making the broach?

townsend1212 (author)2014-04-13


Why spend $8 when I can take 8 hours to make it?

kjlpdx (author)2014-04-13

i see no way to assure the square hole sides are parallel to the edge of the piece. the hand ground taper is certainly not accurate. the broach may actually have twist to it, who knows?

arduinoversusevil (author)kjlpdx2014-04-13

Agreed, maybe I just got lucky.

cqaigy (author)2014-04-13

Nice video, thanks for posting!

Nikiniku (author)2014-04-13

I had never heard of this idea, not to mention the tool, before. I then tried Amazon to see about purchasing such tools "readymade". There are many tools for different purposes called "broaches," but SETS of tools for this purpose are among them. Perhaps most instructive is the following: Broaches are cutting tools that can be pushed or pulled through a component to make key, square, hex, and other hole shapes. Most broach styles have teeth that increase slightly in cutting edge size and distance from each other to the end of the tool so they complete the full cutting process in one operation: roughing, semi-finishing, and finishing. Keyway broaches are specifically designed to make keyways. Rotary broaches, also known as wobble broaches, create shapes in blind holes.

typogenerator (author)2014-04-13

Nicely done. The high drill speed adds to the excitement. :-)

Also, another use for astroglide.

jwl41085 (author)2014-04-11

That drill speed is way to high

Indeed, it is too high.

zawy (author)arduinoversusevil2014-04-13

And was he also not using a lubricant, not even water, as the other thing to do to keep it cooler and thereby save the drill bit? Also, he seemed to be filing both ways whereas I have been told you want to file only against the teeth to save the file.

arduinoversusevil (author)zawy2014-04-13

Hi Zawy,

I used plenty of lube throughout, as witnessed by the smoking chips. Omitted in the vid for brevity.

In regards to filing; I use down pressure on cutting stroke, no pressure on return stroke.


RedBinary (author)jwl410852014-04-13

Ha! Yeah, I was shocked!

kjsrocks (author)jwl410852014-04-13

+1 for drilling metal you need it much slower

tstump (author)2014-04-13

Could you run this through wood to make a square hole as well?

arduinoversusevil (author)tstump2014-04-13

Hi tstump,

Not sure if this would work for wood. But there are mortising tools to do this in wood. Of course for larger holes you really only need a sharp chisel.

Johnkaye (author)tstump2014-04-13

There are square wood boring tools. Used in a drill press it is a drill inside of a four sided chisel. The pressure from the drill press pushes the four sided chisel into the hole as it is drilled.

TheDivineImpulse (author)2014-04-12

nice to se you on instructables, i saw the video on youtube in the subscription box a time ago...its a diy broach.... nice

Mihsin (author)2014-04-10

Great work.

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