Making a Single Tooth Square Broach

[carrdo]

From a long forgotten Canadian inventor, master mechanic, hobbyist and TSME (Toronto Society of Model Engineers) member (from his private publication) "The Master Mechanics' Manual, Volume One by Le Comte de Millimetres" (George Barrett).

One can make ANY regular or odd size square broach with this method but there is a limit to what thickness one can broach with it (1/8" in mild steel). In desperation, I have made a number of these over the decades mostly in 01 (drill rod) and HSS as I have the grinding equipment to do it.

George doesn't go into a lot of detail in his publication but I will fill in the blanks.

Here it is.

to be continued.

 

[Tom O]

I believe I saw some of those in my Dads toolbox.

 

[carrdo]

Now to the actual making. I am presuming that the broach is being made from drill rod and is hardened and tempered after forming. The series of photos I think is self explanatory and shows what I did to make one. Only one note, it is important to make the 10-15 degree "hook" indentation as shown on the tool's cross section. The "hook" is the backward facing curved part of the cut. Think of it like a bird of prey's curved beak. Hook cutting edges are very efficient slashing tools although they need to be modified for metal cutting. End mills also have a curved "hook" or a "rake" cutting edge but that is for another topic.

One has to grind the slim long nosed lathe tool as seen in the photos to make the "hook".

to be continued.

 

[carrdo]

To finish. I think that the photos say it all.

 

[gerritv]

A useful tool.
It would be interesting to see the rest of George's notebook.