Rotary Broaching a Hex Key Recess on a Mini Lathe

Whilst busy working on something entirely different, I wandered off on this hexagonal hole cutting tangent. Essentially I wanted to be able to make an Allen key recess.
Rather than double the length of the original project, I’ve separated it out as a stand alone film.
Cutting small a small hex recess in a blind hole is relatively easy using a simple tool that can be knocked up from materials lying round the home shop.
Credit for at least 50% of the design goes to Mike at Mikes Workshop. Take a look at his web site. There’s some real gems in there for the bench-top machine tool user.
mikesworkshop.weebly.com/
Mike’s rotary broaching tool can be seen in action here:
• Rotary broaching video...
Although I’ve yet to try it, the same technique can be used to make holes in various other shapes including polygons, splines, Torx etc.
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POST UPLOAD UPDATE:
Thanks for all the comments and feedback :-)
I've read them all, but I’ve not the time to respond individually. There’s some good ideas and advice for me to try next time.
In response to queries about the white material in my tin can brazing hearth:
It’s called ‘Insulfrax S Blanket’ ceramic fibre. It’s available from eBay (in the UK at least). There’s a thin piece of steel sheet in the bottom of the can (where the part sits) to help prolong the blanket’s life where the flame hits it directly.
Note: some types of ceramic fibre are bad for the lungs (in the same way as asbestos is) so I’d recommend at least gloves, mask and ventilation when handling (what ever the type of fibre -just to be safe). I only handle a small amount, infrequently, and Insulfrax S is body soluble so think my precautions are enough.
As for how the broach works:
Consider if the broach and brass were in-line on the same axis. You’d be in an arbor press situation, with all corners cutting simultaneously. The rotation would contribute nothing.
The key is the 1 degree offset and the relief on the broach.
This allows the small contacting part of the cutter to present a shearing action to the inside of the pilot hole as it rotates in the brass. As the work turns so does the cutter, presenting a different cut profile as the broach rotates.
The cutter has to be free to rotate or it would just act as a boring bar and inefficiently cut a circular hole.
I’ve not tried it, but I imagine as the number of sides increases, and the shape tends towards a circle, the less effective the tool will become.
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Made with subtitles -click the CC box.
Shot: HDC-HS700 1920x1080 50P AVCHD
Edit: FCP7 ProRes 422
Mic: C01U

[@tenlittleindians]

We experimented with using a cnc lathe to do the broaching. We used a commercial purchased broach that looks very much like yours and we mounted it rigid in one of the collet holders in an AmeriSeki lathe. We drilled the hole in the part to max diameter and plenty deep to allow for a place for the curled chips to go. We programmed a spindle lock and fed the broach into the hole on center. We thought the machine might alarm out under the pressure but it had no problems. We did put a stop in the program so we could brush on cutting oil before each hole. We made thousands of parts like that back in the 90's.

[@chipmunkshavenuts]

I've recently made a rotary broach not very long ago to do a 10mm hex in steel. Made the broach out of tool steel, didn't make the hex much longer than the depth I wanted to keep from thinning it out with the relief angle. I also center drilled the other end. I hardened in oil as specified for that tool steel, used a torch to draw to straw color. For use, I just adjusted the tail stock slightly to the side, and used a live center in the center drilled spot on the back end, and used the tail stock to push it against the hole in the steel, with the broach just floating between those two points. Worked great!

[@Deltarig]

Awesome! Rotary broaching is definitely a massive achievement in the world of machining. It takes a gifted person to come up with an idea like this, the first time I saw it work it changed my way of thinking. The principals and the concept are invaluable. Great video.

[@deucedeuce1572]

Yeah, it is a brilliant idea. It's not even easy to imagine how the parts work and move. If you didn't know, most people wouldn't be able to figure it out. I'm not normally confused when it comes to mechanical things... but this one took me a minute to figure it out (when I heard about them a couple years ago).

[@cognitivedissonancer]

Excellent video, well shot, edited, and narrated. It's great that you include your entire process, and not only successful highlights. The included references are also a nice touch! Keep up the good work, it has been a pleasure.

[@mikedrop4421]

It appears that This Old Tony has been a strong inspiration for this channel down to the camera angles, on screen graphics and subject matter. I'm super excited about this channel. Finally the YT algorithm recommended something I want to watch! Edit: he's even wearing a black sweatshirt like TOT always does. This can't all be coincidence. Well done good sir I'm loving the videos.

[@oskarGoesTubbe]

We need more of The Recreational Machinist's content. :)

[@jklmnop8607]

I've never had to create a hex recess before, but for my work as a machinist/engjneer/problem solver, this looks like an excellent addition to my bag of tricks for incorporating into possible future projects. Thanks. You just never know where the next idea will come from.

[@WeCanDoThatBetter]

Great job! Never seen a rotary broach built this way without real bearings. Interesting approach.

[@tomsmith3045]

Fantastic video, thank you! I love that you are building functional tools with home sized equipment, and even more that you demonstrated approaches that didn't quite work out. The former demonstrates what's possible, and the latter is going to save many people quite a bit of time, as well as imparting us with more knowledge.

[@mikebarton3218]

Just stumbled across this channel. Wow what have I been missing! I subscribed and now I'm going to catch up on your content. Great to have a British channel to watch. Thanks. Mike

[@joycemiller4716]

Why not English

[@calumbmx1]

Only just found your channel, love the ingenuity required working in a mini machine shop! Waiting for the next episode

[@c0rificus]

You have a very calming and reassuring voice which makes the things you are saying easier to digest. Good video!

[@donsmith9797]

That's an awesome little side track, loved it.

[@philipbarker7672]

At last I found another machinist channel to gorge on. Good work.

[@CM-xr9oq]

At last? How about Abom79, oxtoolco, AvE, Keith Fenner, This Old Tony, Robrenz, NYC CNC, Edge Precision,

[@philipbarker7672]

C M I did say another. I also watch the others.

[@davewilliams6172]

@@philipbarker7672 I'm glad I am not the only one with a growing list of channels...just wish I could spend as much time in the workshop as I do on KZbin.

[@par5endos562]

Fantastic presentation. Video, narration, content, it's all a pleasure to watch. Well done!

[@dennisjewitt3809]

Great video full of practical use and without time wasting

[@Preso58]

Hey, great result! That looks completely doable in my shop. Thanks.

[@samcoote9653]

Found this channel through Facebook, enjoying so far! love the content! :)

[@joksutube]

I love the smell of hot metal and coffee in the morning. Very well done and thank you.

[@baraw87]

Keep up the good work, your videos are nicely shot, very well narrated, and to the point! Please keep the content coming!

[@lawrencedavidson5550]

This was in my recommended and glad it was.. I will use this method on some of my projects. Thank you... Subbed.

[@michedmck]

Beautiful production, yielding excellent results! I have been wanting to make a broaching tool for some years now, but have always been mystified by the mechanism required to cause the broach to "wobble". Your method precludes the use of the wobble method. I will copy your design unashamedly! Thank you indeed!

[@jaspermcconnell6417]

I really like this version of the broaching setup. I built one that uses a MT in the tail stock and the 1 degree offset puts a lot of stress on the tail stock as it tries to turn off center

[@stylr882]

Great channel. You have nailed it with the format. Informative and entertaining. Like a British This Old Tony :)

[@3maticod]

agreed. Finally another machinist to add to the sub list!

[@colleenmolley244]

Fascinating,I could watch this all day

[@edgeeffect]

The title sequence is ace... I love that fly cutter and micrometer turning into an "R". The video itself is well shot too and the narration is neither to hurried or too meandering... good to see you leaving your "stupid" mistakes in too... 'cus we all make them. All in all great stuff, hope to see more... keep up The Great Work. (AND this is the clearest and simplest explanation of rotary broaching I've seen)

[@ensen89]

You can take a small drill bit and drill a 6 hole pattern inside your 4,62mm circle. The small holes should be tangential to the hex. That removes a lot of material and makes it easier for the broach.

[@index7787]

What a clever way to broach. Who the hell thought of that first.

[@binness]

I have no idea, however it as been used for over one hundred years, Hemingway Kits in the UK will sell you the plans

[@linginfelterh]

What gems one can find by looking around the KZbin. Loved your switchbox. Quite the design. Great job on the vids, you have a new sub. Looking forward to more great content.

[@howardhughes6311]

You need a fillet at the corner of the broach, that's why it broke. You had a sharp corner and it became a stress riser. Nice job on the video.

[@user-fn5bl6jz7z]

история тгрушнк

[@lsubslimed]

I agree that the corner or shoulder shield have a decent radius to it to distribute the stresses, but it actually looks like it broke near the base of the shaft rather than right at the base where it would have broke if it was caused by a stress fracture at that cross-sectional transition... unless I'm seeing it wrong?

[@jklmnop8607]

A lot of factors come into play here. I think he got it right on the choice of heat treating method. In the first go round, his part spent too long in the furnace and experienced grain growth. You're right about the corner radius, but also, be careful not to make the tool longer than necessary. It's a cantilever beam, where longer equals reduced rigidity.

[@tobinator999]

As a mechanical engineering student, taking a machine design class, I found this particular comment thread super interesting!

[@ronstar8857]

Very nicely done. I learned quite a few tips watching. Thank you for sharing!

[@fmdc7442]

I love all the demo and job, thank you!

[@Cactusworkshopchannel]

very interesting! I knew the technique but I didn't think it would be this "simple" cheers!

[@oldschoolengineer58]

This video is impressive, the narration is spot on one of the best on you tube, nice clear british accent (instead of the usual Yankee or Aussie). so i have subscribed thanks for sharing

[@theonlybuzz1969]

Excellent job I will be remembering this information for some of the custom jobs that I produce, thanks for showing us this, very impressed indeed and I just feel like nipping into work and produce one just to experiment with, this would be great for those not off the shelf fasteners, thanks again...Phil

[@JohnJones-cp4wh]

When making the broach, use a corner radius cutter to avoid a sharp corner, that will extend the life of the broach.

[@DudleyToolwright]

Wonderful narration and well shot. The video was really well paced and shot. I think you are going to give Clickspring, the channel, a run for it's money.

[@mikedrop4421]

You are right about most of that but it's not Clickspring who's got the competition incoming.. It's This Old Tony. These videos could be played without sound for the majority of TOT fans and we'd all buy it as something Tony made a year or so ago.

[@DudleyToolwright]

@@mikedrop4421 You make an excellent point.

[@AMRAMRS]

@@mikedrop4421 You are extremely wrong man. This man couldn't time travel on the lathe

[@mikedrop4421]

@@AMRAMRS that's exactly what a timelord would want you to think. Besides, I think he uses the mill for quantom jobs

[@newmantoolsinc]

Great video. I used this to show various tools being used to my son.

[@rbpercussion89]

Woah. Everytime I think I've seen the limits of the mini lathe I see something like this

[@thlee3]

Awesome content. Great editing and cuts!! Great tutorial.

[@core4365]

This is my favorite video on the internet

[@markhobster8113]

great work and this will help a lot, I was thinking of buying a rotary broach kit but ill be sure to try my hand at this one, cheers fella and the pie in the oven to make extra use of the heat is exactly what I would do ;)

[@clist9406]

That was a lot of work , nicely done

[@judd_s5643]

I believe Chris of Clickspring has set the Bar in editing/narration of “machinist” type videos and I believe this video is equal in quality. Excellent work, very informative and enjoyable to watch!

[@DursunX]

i havent touched a lathe for 30 yrs.. this video awoke my curiosity. excellent tutor

[@colinnorthcott9219]

Thanks for the great video, you explain what you are doing very well.

[@goldeee666]

amazing work well done thank you for posting

[@EDesigns_FL]

This video came up on my recommend list and I'm glad it did. Considering how great your narration and production are, you're likely to get a lot more subscribers very soon. Your like Clickspring, but with more relevant content;)

[@ifell3]

Wow nice result!! You know about the dangers of that wool stuff and inhaling fella.

[@nexoxenigma3805]

Nice video! My hex collet block also doesn't have even corners, but I prefer to grip it on the flats with the vise, so I use a couple 10mm round HSS tool blanks as parallels so the block rests on the flats, not the corner.

[@StevesProjects]

Enjoyed that. Hardening and tempering at different degrees within the same work piece is always tricky, I've had plenty of similar failures.

[@GaryMcKinnonUFO]

Mad skills pal! Thanks for sharing.

[@musicmaneman38]

That was awesome! Angular broaching a blind hole.

[@DubsnSubsSessions]

Subbed. Great technique I would never have thought of! And nice to watch a UK video that doesn't sound like an old man trying to speak between nasal sprays...

[@pigpig19d]

nice! have never heard of rotary broaching. thanks for the video

[@MicroRCFiend]

Awesome little video and super interesting. Thank you, i'll be having a looksy at your others

[@Workshopfriend]

Very well produced. Thank you.

[@PropKnucklesFPV]

If you keep it up, your channel will get big!

[@TechGorilla1987]

What a wonderful video! I happened upon this randomly. Thank you!

[@Zakamooza]

i have the same lathe! very useful , please make more videos on it ! subscribed

[@jodyolivent8481]

Nice job and keep up the awesome videos!

[@mrayco]

Last week I have made hex abroach I used drill bit tail I machined it as well and hardened it ,, I had success without broken it… ..thanks for sharing.

[@n0f8r]

fascinating stuff - and thanks for the rotary broach explanation in the description - I would never have guessed what was going on.

[@TheRecreationalMachinist]

Glad you enjoyed it

[@Just1GuyMetalworks]

Nicely done!

[@BBB-ly8ro]

Brilliantly done.

[@wezzzvanderlinden2019]

Nice poliangolar!! nice job!!

[@TSODInc]

Loved it, Great Timer!

[@argentknight7557]

Thank you Sir, this video have made Me very motivated to make one rotary broach.

[@hugostiglitz6914]

I only managed to do this a couple of times and although was easy on brass.just couldn't manage steel unless I used an induction coil. Also, I never cut the hex all the way down the entire length of the tool. Just the tip and the rest just slightly smaller diameter than the diameter of the original hole. It also still needs a corner radius where the tool diameter increases. Having said that yours seems every bit as good with a little modification.

[@OFICINATERAPIA]

Really really great job!

[@BurtonsAttic]

Nice work!

[@pgs8597]

G’day, well presented video of a nicely made tool. Cheers Peter

[@Kevin-gx8lc]

Well done. Keep it up! Greetings from Southport!

[@mxcollin95]

Nicely done sir! 👍

[@woodscreekworkshop9939]

Great quality video and content!

[@russtuff]

Nicely done

[@protospace270]

Well done!

[@dwightcarlson7136]

Looks like something to try to just prove it can be done. Excellent video!

[@Jonhenrysneip]

Great video. Tools we all wish we had 😀

[@TheAwesonymous]

You sound like a narrator on a TV documentary. Nice.

[@robertfensome9293]

Awesonymous RC

[@MikeHughesShooter]

I love it! these are amazing videos

[@matthasaname]

Utterly brilliant.

[@bobuk5722]

Wow! Such a simple, elegant design. BobUK.

[@daos3300]

now we know what sean bean does in his spare time ;)

[@johnambler3107]

Great video. Very interesting 👍

[@CreaseysWorkshop]

Excellent video

[@RenoLaringo]

Wow, it takes some serious imagination and logical sense to only think of such a method. I didn't know of this technique. Thanks for this very comprehensive video. I also really like the narration. Very well done sir.

[@binness]

Look up rotary Broach, a UK company called Hemingway Kits will sell you the plans, and by the way I have nothing to do with them

[@RenoLaringo]

@@binness Thanks mate, I definitely will !

[@cheewurz]

Amazing!

[@clintchapman4319]

Great video Bud!

[@VanoverMachineAndRepair]

Nice video very well shot

[@felixdostie9024]

Great video!

[@robertofranciscoromerorami5373]

Tremendo vídeo!!

[@abimanyu9887]

amazing video

[@hendriyawativinny802]

I love this video, love so much

[@kinnikuzero]

Just found this channel, subbed.

[@grottonisred6541]

Excellent video...

[@dalejones4186]

New sub. Great video. Thanks for sharing.

[@robertpartsmade5832]

Spot on well done 😎😎

[@yellowsupra88]

Great video

[@snowiethetoolguy]

Great tip. I can see me using it

[@Airgunfunrich]

Great video👍