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

I'm tied up with the dividing head project, or I'd love to join this one. But, I've been reading every word of the thread.

The 1 degree face seems like it would be hard to make, and then locks the user into using a precise length of broach. I was thinking that you could machine it square, and then insert a washer between the backing plate and body. The typical washer is .062" thick, but there are thin washers half that. On the bolt circle, you'd want a thick one, then a thin on the two neighboring ones, then no washer on the last.

Also, machining a shallow cup at each bolt hole in the body, along with a half ball on the socket head screws would account for the tilting.
 
Also, if you did it this way, remove the offsetting washers and you have a free live center.

(Watched Joe Py video a couple days ago, and was wondering why it looked so familiar.)
 
Shotgun said:
I'm tied up with the dividing head project, or I'd love to join this one. But, I've been reading every word of the thread.

The 1 degree face seems like it would be hard to make, and then locks the user into using a precise length of broach. I was thinking that you could machine it square, and then insert a washer between the backing plate and body. The typical washer is .062" thick, but there are thin washers half that. On the bolt circle, you'd want a thick one, then a thin on the two neighboring ones, then no washer on the last.

Also, machining a shallow cup at each bolt hole in the body, along with a half ball on the socket head screws would account for the tilting.
Click to expand...
The length of the bit doesn't have to be too precise, a few tens of thou is fine.

The problem with making the angle adjustable is that the angle is extremely important in relatio ln to the relief of the bit, AND then changes the offset. So you'd then have two adjustments you need to make.

Having the offset be adjustable is what most designs usually go with.
 
Ok, I think we're about ready to build, right? The only clarification seems to be that the body's 4 holes need to be tapped 1/4-28, and that the backing plate is 1/4-28 clearance holes (I specified 'G', but feel free to mess with that a touch).

Anyone else have other concerns/questions?

I got my HSS blanks in last night, but thanks to the dividing head project am likely a little bit of time from making my parts. Additionally, I still need 3 bit size/shape-requests from everyone. Options are basically:

-Hex: Any size up to ~.433 across the flats.
-Square: Any size up to ~.353 across the flats.

For me, I'm probably going to do:
1/4" Square
3/8" Hex
3/16" Hex
 
The ones you listed look good to me @ErichKeane. I think the drawing makes sense, so I should be able to cut from it fine. I'll work on a prototype and update here should I run into anything.
 
I got the steel in yesterday, cut a 1” slab off. I do want to clarify hole positions. I get they should favor the thicker side of the angled plate, but couldn’t you offset the holes on the body? This way the body and backing plate with more or less alight on the outside edge? Why the holes aren’t evenly spaced and just drill a bit off center….I’m perplexed.
As for sizes…are metric ok? I’d say 3, 4 & 5 mm ?CA28F479-DA7D-4311-9F7E-0B8C81B06307.jpeg
 
GunsOfNavarone said:
I got the steel in yesterday, cut a 1” slab off. I do want to clarify hole positions. I get they should favor the thicker side of the angled plate, but couldn’t you offset the holes on the body? This way the body and backing plate with more or less alight on the outside edge? Why the holes aren’t evenly spaced and just drill a bit off center….I’m perplexed.
As for sizes…are metric ok? I’d say 3, 4 & 5 mm ?View attachment 369897
Click to expand...
As long as there is an offset, yes. I chose to do it in the backing plate just because most designs seem to introduce the offset there. Doing the offset in the base wouldn't correct the ODs though, since it would still be offset.

I'm not sure what you mean by 'evenly spaced and drilled off center'? They are evenly spaced compared to eachother (a 1.4" 'square') AND are drilled off center (~43 thou toward the thickest side).

As far as the drill bit size, it is just clearance hole with some wiggle room for a 1/4-28, so it would have to be a 6.5mm at minimum.
 
1 big problem with doing the offset in the base is it would require its flange to be bigger to account for that. The bolt-circle is currently about the smallest size we can get away with to save from going too big on that part.
 
Alright, I’m gonna knock one out tomorrow, if all is well, how many more? 4 correct? Or was it 4 total?
 
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