Machining a mechanical governor from stock

Peter van der Linden, January to March 2008, De Anza College

The engine kit came from PMR Research in New York. I found their website by doing a google search on "steam engine model kit". The kit cost $120, and included a full set of engineering drawings along with the unmachined castings and stock needed.

I also bought a similar kit for a mechanical governor from PMR. I decided to start by making the governor. I (correctly) saw this as simpler than the work needed on the engine, and I wanted to practice and get more experience before tackling the more difficult pieces.

When I got the kit, I matched each piece of stock to the corresponding component on the engineering drawing. Some of the pieces needed a couple of attempts before I had everything correctly accounted for.

1. The governor has 7 main parts:
  • a revolving central spindle,
  • a suspension arm "T" piece at the top of the spindle, from which hang
  • a pair of weight arms
  • each ending in a brass ball weight.
  • a driven pulley at the bottom of the spindle
  • a guide sleeve in the midsection of the spindle
  • a pair of weight links, fixed between the guide sleeve and the drawn arms.
There's also a return spring between the t-piece and the guide sleeve. This spring applies a counterpressure when the guide sleeve is raised by the spinning weights. The spring did not require any finishing.

The picture shows an example finished governor (not mine).

2. The brass ball weight is held in a collet, with a collet stop behind, to stop it being pushed back. Center drill, drill, and tap the hole.

For drilling, the lathe speed is ???

There are three parameters that define the cutting speed for a material:

  1. Surface Speed: the rate at which metal comes into contact with the tool at the cutting point, expressed in SFM: surface feet per minute.
  2. Feed Rate: rate at which the cutting point moves transverse to the workpiece.
  3. Cut Depth: how much material is removed in a given pass.
RPM for machine = speed/circumference.
Speed is the recommended cutting speed of the material.
Circumference of the workpiece (equals pi x diameter).
You can use meters or feet, but stick to the same units throughout.
Recommended cutting speeds:
brass 200 feet per min
mild steel 110 feet per min.
aluminum 100 feet per min
cast iron 70 feet per min