Saturday, July 13, 2019

Webster Update #3, Fumbles, Recoveries, Fumbles and Learning

It has been a couple of weeks since I did my last update on the engine, so I thought I'd do one of those.  The two side plates that hold the various parts of the engine in place are completed. 

The two side plates are the shinier pieces in the foreground - the larger piece in the background is the base plate they screw down onto with the two tapped holes visible on the bottom edges facing the camera.

I've been making things out of wood for much longer than I've been machining metal, and one of the prime lessons that sunk into my brain 40 years ago was, "the secret to a good project is how you recover from a screw up".  (I think it could be extended to life in general - the secret to life is how gracefully you recover from a screw-up.)  I want to draw your attention to the large hole that's closest to the camera on the lower left, this is where the camshaft that opens the exhaust valve goes.  The hole is dark and has a wide rim so it looks different from every other hole.

It looks different from the other holes because it's a ball bearing and it's a ball bearing because I was recovering from the way I screwed up that hole.  The drawings call out the hole should reamed to 0.250".  Everyone is familiar with drill bits for making a hole but I'll wager only people who work in metal are familiar with reamers (in-depth article - pdf warning).  The rule of thumb is that a drill bit will tend to make a hole that is neither perfectly circular nor perfectly perpendicular to the work.  For a hole with a requirement for an exact size, a slightly undersized hole is drilled and that's followed by a reamer which removes a small amount of metal but helps make it more highly circular and straight through the work. 

The problem is that I grabbed the wrong reamer out of my set and ruined the hole.  The way out was to make it bigger and put something in the hole to sleeve it (or make another side plate - which I'd really rather not).  Since the hole carries a .250 diameter cam shaft, I used a ball bearing I had from my Duclos engine.  That required a 0.375" hole, which was easy.  I paid more attention to grabbing the right reamer. 

While putting the ball bearings into this assembly, I started thinking about ball bearings for the other holes, which are reamed 0.500".  I took a quick look at the drawings to see what part goes there and it's the "other" big shaft in an internal combustion engine, the crankshaft.  A quick look told me that it's a 0.500 cold rolled steel piece (which I've already bought and is in the pile 'o parts).  It was easy to find 0.500 inside diameter ball bearings that look just like this set.  Unfortunately, I'm not prepared to mount it.  It requires a 0.750 hole, which means I need a 0.750 reamer and a slightly smaller drill bit.  Ordered everything. 

Which was another screw-up, although only a waste of money (to the extent ordering some tools is ever a waste of money, which is only if you never need them).  I bought the drill bit, reamer and four ball bearings that I don't need.  Maybe I need to design a bigger engine.

A closer look at the drawings while trying to figure out how this all goes together showed me a suggested set of ball bearings for those half inch holes.  It turns out the crankshaft is really 5/16" diameter - 0.3125" - I read the diameter of a collar it goes in.  Those bearings are on order today. 

I started a conversation with a guy who has built one of these on a forum I hang out on and he said I can't use the ball bearings in the second picture.  My concept is wrong: the shaft doesn't rotate.  It's fixed in the side plate and the parts that go on the shaft rotate on the shaft.  This makes fixing that hole easier.  I'll turn a sleeve and hold it in the side plate with red LocTite.  I could use the cam shaft as the drawings say or turn it onto the 3/8" piece that goes in the screwed up hole.

I've already started on the next part, the flywheel, while I wait on parts for the sides.  The flywheel blank is that piece of tool steel I de-rusted in vinegar a few weeks ago.  That stuff is interesting to turn, by the way.  If I cut off a tiny cut, like .005", the chips go from the bright silver of the metal to gold or amber colored.  If I take off .010", they come out deep cobalt blue.  Rather interesting stuff.  At .005 or .010" at a pass with cubic inches to take off, it will be a while.


  1. Maybe I need to design a bigger engine.


    Great recovery, BTW!

  2. Generally, when drilling/machining, if anything steel turns blue it was overheated. As long as the bigger parts don't turn blue you are usually okay. Better to use more lube/coolant, or cut less deep. You may be changing the temper of the surface you are working. Vary the numbers to get a better outcome (speed/feed/depth/bit profile,material)

    1. I have a "speeds and feeds" calculator, but with my manual lathe it's hard to turn those numbers into practice. I can't set "1.8 IPM" by a command statement - I get a feed rate that's geared to the RPMs and that's all I can get.

      All I can do for coolant is dribble cutting fluid onto it, or spray some WD40.

      I need to part it off, to go from 2" thick to 1.125, and I think the chances of doing that without breaking my tool are just about zero.