Friday, September 20, 2019

Webster Update #5

While waiting on circuit breakers for my radio troubleshooting, I returned to the flywheel saga I mentioned in Update #4 and last Saturday.  It's now finished. 

Once I saw this picture in the camera, I saw a face in the flywheel and now I can't unsee it. 

Now I call the flywheel Mr. Bill.  Mr. Bill's nose (the flywheel's, not the puppet's) is drilled through for the 5/16" crankshaft and the end is reamed to 0.500" diameter by 3/16 deep.  This was my first puzzlement of the last week or so.  I ordered the gears specified in the prints and thought I just used them as provided.  Wrong.  The gear is very different in size from the drawing I have.

The answer was that I needed to machine the gear's hub to meet the dimensions on this print.  Note the upper right says this is a "light press fit into flywheel".  I accomplished that today.  I drilled and tapped the hub for a #6-32 setscrew, used that to fasten the gear to a little scrap of shaft, and used that shaft to hold the gear in the lathe's chuck so I could reduce it to size.  It's now done.

I think the inner web of the flywheel will get painted like I saw on another guy's model.  Flat black wrinkle paint.  I'm set up to do powder coating, so I found a paint I could use. 

I also made a brain dead simple part - the crankshaft itself.  This just needed to be cut to length, so a quick cut on the bandsaw followed by facing and cleaning up the ends on the lathe.  It will get hard soldered (brazed) into a piece that I have yet to make - or yet to decide on how it should look.  The drawing looks like this and I'm focusing on the rectangular tab seen in all three views here:

A couple of builds I've been seen change that little rectangular 1-1/4 x 1/2 tab turns into a rather intricate piece designed to better balance while the engine is running.  One divides that tab at the center of the big hole, and replaces the bottom with a semicircle about 1" radius.  The other replaces the tab entirely, with a sector of a triangular wedge, heavier below the center of the big hole, and tapering to about that half inch dimension of the rectangular piece. 

Not including this part, which is either a simple hour or so, but maybe a full day for the fancy part, I've completed four pages of parts for this engine.  There are 13 pages of parts; nine more.  Not all of them need to be made; so as a rough guess, I've made about a third of the parts.  Most of the rest are smallish parts (like the parts of this crankshaft).  The biggest part left is the piston, so I think that will be my next task. 


  1. I looked at the crank, and counterweight for the piston.

    I suppose running at the speed this runs at, vibration isn't much of a problem.

    Nice work, SiG!

  2. I didn't even know there was a wrinkle powder coat paint.
    Every time I learn something, I also learn just how much I don't know.

    I wonder if anyone has off centered the flywheel's lightening holes so that they would act as a counterweight.
    I've looked at a fair amount of old steam or gas engines and never seen that done.

    Nice work.

    1. Like you, I've never seen that done. My guess is that you can't change it enough that way but I haven't run numbers.

      The property we're changing is called the moment of inertia and adding or removing mass changes it with distance squared. That means the adding or removing the same amount of metal has more effect the farther from the center you change it. This flywheel is 3-3/4" diameter. The outermost half inch of radius is 3/4" thick, and the inner web (where the holes are) is 1/4" thick for that reason so it would take removing a lot more metal to affect its MOI compared to removing it farther out. This is why a lot of flywheels have spokes or ribs, which we make by drilling out metal.

      But that says instead of those weight removing holes in the web, we could remove metal in the rim.

      Gotta dig out my old Dynamics book and play with some numbers.

    2. And to add way more complexity than is needed, the counter weight location would also have to move along the radius of the flywheel as a speed changes because I think the counterweight effect changes with RPM changes.
      I haven't seen that either. But I wondered if there were self adjusting counterweights and I found the correct term is called a dynamic compensating counterweight.

      And no, I don't want to scale it down nor build it. That would be the path to madness.