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
Thanks for reading,
bob prohaska
Harley cranks are built up of a pair of flywheels , a crankpin (con rods are fitted and mounted before assembly) , a pinion shaft to drive the cam and auxiliary items (oil pump, timing ignition , etc) and a sprocket shaft for power output .By inference , since this motor is a direct take off of radial aircraft engines , they would be made the same way . The crankpin location in that example was located by simply measuring the offset - carefully ...
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Snag
General-purpose engine lathes. That's the way engine rebuilders do it today.
Faceplate fixtures (or special, dedicated fixtures) on the spindle clamp the ends of the crank in an offset position so that the crank throws are centered.
Without special fixtures, it's very tedious.
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.
-jsw
These are stiffer and don't damage a drill jig hole in mild steel as quickly as longer-fluted bits:
You can make a crankshaft using nothing more than 2 center points a scale, a pair of calipers, a hacksaw and file if you want to do it manually.
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.
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.
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
That's fascinating stuff, Eric. I remember seeing photos and drawings like that in the old machining books we had in the McGraw-Hill library (going back to 1877, the year of _American Machinist's_ founding). I spent many lunch hours pouring through them.
They used wood in a lot of places where we wouldn't think of it today. Also, speaking of crankshafts, they often used threaded steel spacers, where necessary, to keep the cranks spread open then they were under end-to-end pressure between centers.
Modern high-speed steels were developed roughly between 1910 and 1930. Before that, with rare exceptions, most machining was done with plain high-carbon cutting tools. They were hard, but they couldn't take any heat. So drilling, turning and milling were done slowly -- very slowly.
My original notion was of a large billet with center holes on the main axis and every crank throw axis, the question being directed at how the throw axis centers were found. Clearly, that's not how it was done.
Thanks to all who replied, I was thinking in the wrong way!
bob prohaska
Clever inventors amd mechanics have been making crankshafts for a very long time:
-jsw
Amazing. The Romans had much of what we do today.
Yummy! Now we can have roast pig.
The Renaissance was a return to Rome's level. Europe didn't advance beyond them in most ways until about 1800. One century later we had cars and airplanes.
-jsw
That century covered a lot of ground 8-)
Some of the ploughwork is chronicled in
It's available as a very good free E-book and quite fascinating to wade through. It'll be old news to most following this thread, but if not the book is well worth a look. One of the more striking parallels is between toolmaking of the 1800's and electronics of the 1900's.
Thanks for reading,
bob prohaska
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