Hex Broach Material?

[pacifica]

Was that a multi toothed broach or eccentric rotary?

eccentric rotary

 

[TTD]

Thank you for the words of wisdom, guys…greatly appreciated . Certainly gives me some food for thought…

 

[TTD]

Here is a video that may help with the machining.

Thanks for the vid. That’s actually the exact video I watched that prompted me to try making one myself. Probably won’t turn out near as pretty as his, but if I can get it to work that’s all that matters.

 

[TTD]

Wouldn't it be easier to rough machine the broach with the material annealed then harden and final grind the cutting edges

You are quite likely 100% correct, Greg.

My thought process however (and I’m probably wrong so feel free to correct me) was to skip the annealing, roughing, hardening/tempering steps altogether. Seeing as the hex I’ll be starting with will already be hard (if I decide to go with 4140HT), I was actually going to just chuck the hex in my 3-jaw, cover everything to keep grit away & have at it with my McGyver-ized, redneck tool post grinder that’s mounted on the compound while hex is spinning in the lathe. Hone edges once done & give it a whirl.

Looks good on paper, but I also know how reality likes to kick me in the head from time to time. Guess I’ll see what transpires…

To be perfectly honest, I really don’t need a hex-shaped hole…I can/should do what any sane, normal person would do & just turn the end down for a .001”-.0015” press/shrink fit & call it a day…may end up going that route anyways if this adventure doesn’t pan out. A lot less work & aggravation for sure, but I like challenges & apparently have nothing better to do with my time! A home-brewed hex broach is just another project for me to try.

 

[TTD]

The question stated that he wanted to make a push broach, if that means that he wants to make a multi toothed broach, it would have no problem broaching through 3/4" of steel.

Yes, it would be a multi-toothed broach similar to the one in clickspring’s video, just hex shaped.

Spent some quality time on the computer drawing out different options & came up with these #’s:

All options @ .003” increments (.0015” DOC per tooth)
1.0* taper = 34 cutters @ .086” spacing. Max LOC = 2.836”__ 9 cutters engaged @ .750” LOC = .024” stock removal
3/4* taper = 34 cutters @ .115” spacing Max LOC = 3.781”__ 7 cutters engaged @ .750” LOC = .018” stock removal
1/2* taper = 34 cutters @ .172” spacing Max LOC = 5.672”__ 5 cutters engaged @ .750” LOC = .012” stock removal

This pic is for a 1/8” square HSS broach not a hex, but dimensions for tooth spacing, body taper, relief angles etc are basically the same.

 

[pacifica]

Yes, it would be a multi-toothed broach similar to the one in clickspring’s video, just hex shaped.

Spent some quality time on the computer drawing out different options & came up with these #’s:

All options @ .003” increments (.0015” DOC per tooth)
1.0* taper = 34 cutters @ .086” spacing. Max LOC = 2.836”__ 9 cutters engaged @ .750” LOC = .024” stock removal
3/4* taper = 34 cutters @ .115” spacing Max LOC = 3.781”__ 7 cutters engaged @ .750” LOC = .018” stock removal
1/2* taper = 34 cutters @ .172” spacing Max LOC = 5.672”__ 5 cutters engaged @ .750” LOC = .012” stock removal

This pic is for a 1/8” square HSS broach not a hex, but dimensions for tooth spacing, body taper, relief angles etc are basically the same.

My opinion: If you go to the trouble of accurately machining the broach then why wouldn't you do it in a permanent metal? Like hss or s-7(made for dies and punches)tool steel, and harden.