On Tue, 27 Jun 2017 17:42:27 -0400, Ed Huntress
wrote:
On Tue, 27 Jun 2017 17:12:10 -0400, "Jim Wilkins"
wrote:
"whit3rd" wrote in message
...
On Monday, June 26, 2017 at 6:40:30 PM UTC-7, bob prohaska wrote:
How were crankshafts made before the development of specialized
machine tools?
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.
That model was turned on centers, with two center-drilled pivot
positions at each end. Then, the ends were cut off so the finished
item doesn't show where the centers were.
Probably forged or cast rough items were similarly turned on
centers.
After you finish the ends, the evidence is gone.
https://books.google.com/books?id=Kc...xtures&f=false
This is the kind of fixture they used in the early days of car and
aircraft manufacturing. Start at about 3:30 and you'll see what it's
about in a few seconds.
https://www.youtube.com/watch?v=WnP_STFjtK4
You see the fixture are work again starting at 4:11; this time, for
grinding.
This not for models; I think Bob's original question was about real
crankshafts.
Greetings Ed,
I have seen a picture, years ago, of a large single throw crank
shaft being turned and using, I believe, oak fixture plates on the
faceplate. In fact, the faceplate itself may have been wood too. Maybe
wood bolted to a cast iron hub. Nevertheless, some sort of hardwood
was being used to fixture the offset. Not only that, wood was used as
a support between the faceplate and the throw and another piece of
wood fixturing was used at the center, so that the throw was centered
just as it was at the faceplate. The fixturing at the center end of
things was a disc with a female center in it and with a wood support
between the disc and the throw, similar to the faceplate setup. The
picture wasn't great but it looked like there was some sort of
shimming between the wood and the throw.
I turned the throw on a 3.5 hp Clinton engine some years ago to
clean it up after I ran the engine too low on oil. This was a small
crank. I used a 4 jaw chuck and I seem to remember there being a
center already drilled into the throw that I was able to use. Since I
didn't balance the setup I had to run the job real slow. But the old
picture I saw had stuff attached to the faceplate that I assume was
for balancing. Since the picture was so old they probably didn't have
tooling that could be run very fast anyway so maybe balance wasn't
that big of a concern. On the other hand though the men making that
kind of stuff back then were certainly craftsmen for the most part so
the balance was probably very good. Especially considering that many
of the machines they were using weren't that rigid.
Eric