"bob prohaska" wrote in message
news
How were crankshafts made before the development of specialized
machine tools? I've looked around on the Web and found no
description that doesn't rely on purpose-built machinery.

I did find http://modelengines.info/goldeng/const/crankshaft.html
but I can't figure out how the author located the offset center
holes in the blank.

Thanks for reading,

bob prohaska

The holes in the ends can be identically spaced with a simple drill
jig. They don't have to be parallel to the blank as long as it will
clean up. If you want the throw exact you can turn two disks to the
diameter equal to the throw which you can measure and adjust to
micrometer accuracy, put drill bushings in their center and press them
together to make the spacing jig.

I found it easier to locate and drill the first hole, hold its disk in
position with a dowel pin, put the second disk on a chucked dowel pin
and move the table until the disks touch.

A multicylinder engine might need temporary spacers in the throws to
stiffen them.

http://www.wright-brothers.org/Infor...903_Engine.htm
"The crankshaft was made out of a block of machine steel 6 by 31
inches and 1-5/8 inch thick. I traced the outline on the slab, then
drilled through with the drill press until I could knock out the
surplus pieces with a hammer and chisel. Then I put it in the lathe
and turned it down to size and smoothness."

-jsw