Group Project: Rotary Broach-- Building complete, all shipped out!

ErichKeane

Making scrap at ludicrous speed.
H-M Lifetime Diamond Member
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Aug 3, 2017
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Ever wanted a tool to make Hex or Square heads in a bolt head or something? Surprise, its a $1500 tool! BUT, not that difficult to make!

I've attached what I think we can base our plans off of, it seems like a decent design, though I think some of the dimensions are wacky/don't make sense tome. I likely will want to spend some time trying to CAD it or something to make sure we get the dimensions right, but first we need to find ~4 members (Additionally, I'm pretty heavily into the dividing head project, so I'd like to get done with that work before I start my piece).

It looks like it is mostly lathe work, with 2 of the pieces requiring a mill, and nothing particularly large, so it should be cheap/easy to make and ship around.

Currently signed up members:
1- ErichKeane
2- GunsOfNavarone
3- ttabbal
4- T Bredehoft

Looks like we have all 4! Just about all the parts are made, except for the broaching bits, which ErichKeane is still working on. The rest of the parts are just awaiting assembly!

Final edit: All the parts are made and shipped! Congrats everyone!
 

Attachments

  • BroachRotary - Sheet1_8.pdf
    58.8 KB · Views: 166
Last edited:
How do you feel about amendments? Not necessary for everyone, but that appears to have a .6245" arbor, I guess I'd go .750 as that is a better fit for both my manual mill and CNC mill....HOWEVER, I could see using it on my lathe too. What makes best sense for tailstock use? I don't know, MT2?
EDIT-
Would we be making the actual bits? Do we need someone on board with a hardener?
 
How do you feel about amendments? Not necessary for everyone, but that appears to have a .6245" arbor, I guess I'd go .750 as that is a better fit for both my manual mill and CNC mill....HOWEVER, I could see using it on my lathe too. What makes best sense for tailstock use? I don't know, MT2?
EDIT-
Would we be making the actual bits? Do we need someone on board with a hardener?

I'm totally open to amendments :)

I have a lathe tailstock chuck I'd like to use it with which goes up to 5/8" (though I have a larger one, so .750 would work for me too). That way we could use it on both the mill and lathe. I suggested 1/2", since I know a lot of lathe chucks only go up to 1/2" and it is a common collet size, but that would depend on who else wants to participate. I think we could probably get away with doing that 'to order' if the person doing that part is willing.

As for the bits, typically they are just ground out of HSS rod, which doesn't require hardening, just grinding! I think we'd want to make at least a starter-one or two for everyone, since they tend to run about $100 each otherwise! I have the surface grinder to do the sides, but the central-relief I just don't quite have yet, so I'd have to figure that part out. I probably need some sort of die-grinder holder for my lathe to grind that part.
 
I have watched videos on the cupped center. Easily done on a grinding wheel.
 
I have watched videos on the cupped center. Easily done on a grinding wheel.
If you've got a good video, I would love to see it! I have an 8" grinder (plus I guess a 4" tool grinder I could use...).
 
Shank diameter. a 3/4" boring bar holder could be used to hold it in an Aloris type tool mount. Or, half inch with a sleeve.

Where does material come from? I'm considering joining the project.
 
If i got into this project the great thing for it being a mt2 would be it could fit my tailstock and my mill. But idk if i can sign up for this one. I will be watching though as even when you come up with the drawings i may "borrow" them to make my own.
 
Questions....lots of dimensions missing....what provision is made for thrust bearing surfaces? or is that the "grease"?
 
I was wondering the same thing, however, if you have seen the AVE guy on Youtube, it did it with two divits (one off center) in a couple of pieces f steel...with a ball bearing sandwiched between the two. It's a crazy simple device, but yeah, if we could find plans that made a higher level tool, that's awesome.
There is a British company that makes these and everyone copies those...I'll see if I can't find those plans or instructions, something.
 
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