Prewar Workshop: “Drilling” square holes

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Recently I was making wheel hubs in the workshop and a question that kept rising from a lot of people that saw them was how I made the square holes. It’s actually a very simple operation that I want to show you.

This can be done in various ways, I will show the simplest way for the home shop. It’s called broaching. For every size square (or keyway for that matter) there is a different size broach. For the square hole, you drill a round pilot hole that’s the size of the broach start (the size of this is usually printed on the broach or easily measured). Then you put the broach in the hole in the press and press it through. In this operation, a couple things are very important.

First, make sure the square is lined up straight the way you want it. It’s easily overlooked and your hole will not be aligned. You can use an aid for this like a ruler, a machinist square or just eyesight if it’s not too important.

Second, make sure the part is laying straight in the press, not tilted in any way. This will make the broach go through unevenly and might wear it, break it or produce holes out of tolerance.

Then make sure the broach is straight in the hole, underneath the press. This is very important otherwise when you start pressing, the broach can bend and break. Especially on smaller size squares, this can easily happen.

Last and probably the most important: keep it lubricated very well with cutting oil. You’ll reduce the tool life and surface finish significantly if you don’t.

For a keyway the operations are the same. The only difference is that you need a guide for the hole to guide your keyway broach and shims to place behind the broach to deepen the key you just made. A broach need to pass through multiple times with everytime a shim added until you get the correct depth.

I hope this clears it up. It’s a very simple operation that saves a lot of time over simply filing the hole square and gives much better tolerances and finish. A photo album can be viewed here https://goo.gl/photos/fbdmQvYoSZhM3GTe7 For questions please comment or e-mail to [email protected]

Article by Jos van Genugten

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