Spare Parts #13 - Making A Square Broach

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Making A Square Broach, by Clickspring.

It's not necessarily a common event, but when you need to make a square hole, it can be difficult to get a precise result. One of the best methods to achieve a professional cut is to use a custom made broach, so in this video I go through the process of making one from scratch.

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A very special thank you to patron Dan Keen.
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Abbreviated Transcript:

00:06 No matter what your style of metal working project might be, every now and then there's a need to form a precise square hole.
00:21 A pilot hole locates the exact position of the desired square, and then the broach is forced through the workpiece.
00:53 And that's because, all of the teeth prior to the last tooth collectively prepare the opening for the final tooth to set the dimension, so within reason, we can tolerate some small errors in those teeth, providing that the very last one is correct.
01:26 Its much too long and slender to be turned between centers, so I'll need to form the features by incrementally extending the work from a 4 jaw chuck. And the other key feature is the pilot diameter, which must be centered on the square, so I'm taking care to center the raw stock prior to forming that cylindrical shape.
01:48 I have the work reasonably well centered to begin with, so that when I position the dial indicator, the error that I see for each jaw is quite small I then use 2 chuck keys in opposition to each other, to move the work, so that the dial reads directly between the original 2 readings for both jaws.
02:13 Once its close, I move the zero reference to that point, so that becomes my target when I start to center the other two jaws. Once the work gets close to being centered, the errors start to sit nicely either side of that zero reference, and it gets easier to pull it into position.
02:53 But even doing this quickly, you can see that it will take a fair amount of time to do this for every cut, so there's a strong incentive to bypass this centering process if we can. For now though, the work is centered, so I can make a start on cutting that pilot diameter.
03:39 Next I'm using the first groove position to register the tool after extending the work, and then I'm using the hand wheels to advance the tool the required amount to form the next groove. Now inevitably I will have introduced a small eccentricity to each of these cuts, and the teeth won't be precisely spaced either. But as I mentioned before, they don't really need to be.
04:14 Providing I don't introduce any gross errors, It's close enough for the final result, and by accepting a small error, I can move through this part of the process very quickly.
05:14 The total amount of metal to be removed, is determined by the difference between the pilot diameter and the diameter of the circle that just encloses the final square. That metal removal must now be shared across all of the teeth, so it determines how much I feed out before cutting each tooth, and that in turn ends up determining the broach depth of cut.
05:32 The diameter difference also gives an indication of how many teeth are required to keep the chip load manageable.
06:15 At this point all of the features of the broach have been formed, so it can now be quench hardened, and on this occasion I'm using the tray that I recently made for the current clock project.
07:07 In an industrial setting a broach is far more likely to be pulled through the work rather than pushed like this, and there's a real risk of fracture using an arbor press in this way, so be sure to take it carefully.
07:19 Make sure the broach is perfectly vertical before you push it through, and as always have your eye protection on. But even with all of the compromises, its still a great way to use home shop tools to quickly shape a precise square hole.

Making A Square Broach, by Clickspring.
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" a small eccentricity"? Dude... there are robots that are less precise than you! Awesome skills. Subbed on the basis that a shop made square broach is an awesome McGyver tool!

TheWtfnonamez
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as a retired blacksmith, I love watching your video. takes me back to the productive days that I miss.

dmmdmm
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We had to learn to broach a square hole to make a hacksaw in our first semester of school. We were the first class to get a broach while all the other classes had to use a file. The 10mm broach we used had a nice pricetag of around $750. I was quick to make my tasks on the lathe and asked my teacher if i could make my own broach for fun, but he said it is almost impossible to make one...
Gues i'm gonna do the almost impossible on my own lathe soon :D

rasmus
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I have no intention on ever making a broach or even have the need for one and I still watched this all the way through. Amazing production. Everything about this video was in perfect detail it seemed.

tions
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I have no idea why I needed this information but I don't feel disappointed at all. Now I know how to make a square hole.

Lunageldia
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That has to be the cleanest machine and workplace I have ever seen.

depenthene
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There's something very satisfying about watching the broach work through that sheet in the final shots and making that perfectly shaped hole; thanks for the video!

RedHillian
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These videos are never boring. Well sometimes they are but boring in the right way.

dg-hughes
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I love that every little piece you make feels like its own project. When I make things, I always look at the project as a whole. This video showed me that even one small piece of that project should be a project in itself and care should be taken for every little piece. Your work is always impressive. Thanks for the video.

kamitsuna
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Clickspring, the only channel I always click like before even watching the video, a guaranteed quality and informative production. Always a pleasure to watch you work.

jimbrockie
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Tool maker, Clock maker, Film maker, Narrator. Wow, thanks Chris keep 'em coming!

insidemyshop
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Who can actually dislike clicksprings videos? This content is top notch and fun to watch

IntegraDIY
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Never mind the tool porn or the actual results (both of which are just brilliant), your explanation of the path to the result always makes watching your channel worthwhile, Chris. Thank you. Greetings from sunny Adelaide!

greaser
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Of all the videos I watch - your dominate in: Interest, Delivery, Production. You have it nailed.

mrenrollment
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The toolmaking videos are just as interesting as the clockmaking videos.

Flumphinator
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I shivered when you showed the used broach. Too many flashbacks of metal splinters cleaning them.

rich
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Who new such a broach could be made like this? So simple, yet such sophistication. Thank you.

roylucas
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Chris, as a metallurgist, I was very pleased to see your care while heat treating, especially in regards to oxidation when austenitizing steel. I just would like to suggest that, when using bulky trays like this one to hold the boric acid (clever idea), bear in mind that the mass of the tray might reduce too much your heat flow (quench speed) and therefore the final hardness of the tool. That is also influenced by your oil temperature and viscosity. A cutting tool like this broach will last several hundred times more in 62 HRC (Rockwell C) other than 54 HRC. The file test is nice and useful, but being qualitative, it will never tell you the difference.
Finally, please let us know the song or music name in the video's description. I see several people in all of your videos asking the very same question.
Kind regards!
Marcelo

MMorenoBrazil
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It's not just Chris' videography or the Hugh Jackman accent. The CAD overlays really add a lot to the educational value of the content. As always, well done Chris!

thomasutley
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Hoi Chris, as grandfather age 68 i´m helping grandson age 10 who discoverd thechnic. For his to toy he needs a square hole. This video will help to explane him. Next step we will do it together in my hobby garage. Regards from the Netherlands

jenvanleest
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