milling question

Sep 20, 2008
1,668
2
0
Clearwater, FL
web.tampabay.rr.com
for the machinists out there....well jim and ret

can you mill a square tapered hole to fit onto a 3piece bottom bracket?
It's called a broach. You drill a hole first, and then use an arbor press to push a broach into the hole. The broach shaves the metal out of the corners. This is also how straight key slots are cut.

It could also be done with a wire EDM, but it would be expensive.

The milling machine will always leave a radius in the corners.

Jim
 

Retmachinist

New Member
Oct 21, 2008
637
1
0
Urbandale Ia
for the machinists out there....well jim and ret

can you mill a square tapered hole to fit onto a 3piece bottom bracket?
I'm not sure what you mean "to fit into a 3 piece bottom bracket?" Milling wouldn't be an option. There are ways to cut square holes, broaches, E.D.M.'s, lazers, water jet, also not sure why you need a tapered square hole? Explain.

John
 
Sep 20, 2008
1,668
2
0
Clearwater, FL
web.tampabay.rr.com
I think he's talking about the pedal crank shaft.

I've got the 3 piece set-up on my Spoilers. The shaft is square and tapered at the ends 2-3 degrees.

The hole in the crank has a corresponding square, tapered hole so that the crank is forced onto the taper for a positive fit. There is a bolt that draws the crank onto the shaft.

Jim
 

junkyard

New Member
Jan 6, 2009
82
0
0
st.petersburg fla
It's called a broach. You drill a hole first, and then use an arbor press to push a broach into the hole. The broach shaves the metal out of the corners. This is also how straight key slots are cut.

It could also be done with a wire EDM, but it would be expensive.

The milling machine will always leave a radius in the corners.

Jim
you said the magic word....expensive

ok even tho i love the clean look of the bottom bracket jackshaft im probly gunna try to use a steel hub like i did on my electric drive conversion

thx for the info
 

junkyard

New Member
Jan 6, 2009
82
0
0
st.petersburg fla
I'm not sure what you mean "to fit into a 3 piece bottom bracket?" Milling wouldn't be an option. There are ways to cut square holes, broaches, E.D.M.'s, lazers, water jet, also not sure why you need a tapered square hole? Explain.

John
yes what jim said....to fit onto the bottom bracket like the crank would....sorry for any confusion

edit:the idea was to make a piece for one side to mount 2 freewheels back to back and a piece for the other to mount the larger sprocket to the engine......both pieces would bolt onto a standard bottom bracket

but the idea revolved around making the square tapering hole like a crank arm has
 
Last edited:

Retmachinist

New Member
Oct 21, 2008
637
1
0
Urbandale Ia
I think he's talking about the pedal crank shaft.

I've got the 3 piece set-up on my Spoilers. The shaft is square and tapered at the ends 2-3 degrees.

The hole in the crank has a corresponding square, tapered hole so that the crank is forced onto the taper for a positive fit. There is a bolt that draws the crank onto the shaft.

Jim
O.K. I am with you guys now. I thought at first he wanted to cut a tapered square hole through the bottom bracket, just tapered at one end. I couldn't figure out what you could use it for.
Got it now.

John