Return To Non Combustion Gallery 

Bob Verhaeghe,     Merritt NC

The Miser Engine is a Jerry Howell design of a Low Temp Stirling Cycle (Hot Air) Engine.  The cylinder has a .600 dia. bore and a .625 stroke.  The fly wheel is 5 1/8 in. dia. and the base is 6 3/8 in. dia. 
    The drawings and "HTF" materials kit were given to me this past Christmas by my son.   I started off by making a plastic model of the fly wheel.  This was to get some experience with using my new rotary table.  I band-sawed the disc out of a flat piece, turned the O.D. and cut the center sections to the drawing.  Then mounted the flywheel and the rotary table and proceeded to machine out the spokes and engravings on the outer rim.  This all turned out to be fun and educational.


   My next step was to make up some of the smaller parts.  The center support column of the engine was one that took some time and also the use of the rotary table.  Milling the flutes on the tapered column required tilting the rotary table and setting the upper surface of the column level under the cutter.  Here I used the height gauge.


     At this point, with several of the parts made, I was able to see some progress as to what things would look like. 


Here, I've come to realize that the fly wheel is too thick.  Jerry's drawing called for .375 in. wide and the material that I had was .480 in. thick.  I didn't think that this would make any difference, but I was now faced with re-locating and re-drilling the screw holes in the main frame or making a new fly wheel.
Jerry's material call out for the fly wheel material was aluminum.  I had the aluminum and decided that to make a new fly wheel according to drawing was the better way to go.


   Feb. 12,  2005
  The making of the aluminum flywheel....
     Here I show the sequence that I used for machining the new flywheel, which is also the way Jerry's instructions said to do it.  The only note that I made when making the plastic flywheel was to use a 3/16 cutter when machining the spokes.  This allows one to work up to the 1/8 in. radius in the corners without hitting the other side of the spokes at the hub area.  
One  tip on making the flywheel.... 
   Do the math and make notes on the drawing for all the angles before making any cuts.
      The next steps were to do a final assembly and check out.  This was interesting to see all the parts come together and get ready for the first test runs.
     Everything looked good....I had one or two tight spots that were corrected and the engine was test run.
AMAZING.....Last thing to do is to paint and polish.
     The finished engine.....Makes a nice centerpiece for the dining room table too.
Feb. 19, 2005

 When I first started to get the engine running ,  I was using a microwaveable hot
plate used for keeping food warm on a table.   That was too much heat and made
the engine run too fast.   (see pic. on the table)  The hot plate  temperature was
as high as 130 deg's.  It would run the engine for about an hour after heating  the
hot plate in the  microwave for 2 min.  RPMs would start out about 150 RPM and then slow
down at the end to approx. 20 RPM or so, then stop.   It was at this time I figured that there
was a need for some sort of running stand.
Feb 25, 2005
     The running stand was made from styrene bead foam, about 1 1/2 in. thick and 8 in. square.   The cutout hole is 5 1/2 I.D. and there is a cardboard bottom.   The inside was lined with some alum. foil.   The lamp is just resting on the bottom and held in place with a 1/16 dia. dowel.
    The new run stand works much better, as the engine runs slow & steady and is nicer to watch. 
Now it can be fine tuned with a steady source of heat.  ---- guess I should take some
temp. readings for the record!  ---- I like to know things!!
    Feb. 28, 2005
    Balance is most important!!!  I have just finished making a running stand
with a 4 watt bulb for heat.   At first the engine would just about run and
it appeared to have trouble because of being slightly out of balance.  I added a small piece
of solder to one of the flywheel spokes and that got it running.  It is now
running at 42 RPM and is steady.  Guess I will have to do some fine 
tuning of the balance disk to finish the engine!  Jerry Howell says to let the
engine run 24-7 for a month or more, then fine tune everything.  I'm think I'm getting 
close now.
     Feb. 30, 2005
    The Miser----   The heated base, I call it the  "Running Stand", (my son said that is an oxymoron) is working better than I thought it would.   The 4 watt bulb makes more heat than I need.  Temperature at the engine base was taken and the reading was 108 deg's F. With the engine sitting over the lamp the engine wanted to run at 115/120 RPM, that was still too fast! ----  I'm now sliding the engine base back off the cutout hole so some of the heat can escape and also some of the engine base isn't exposed to any heat at the back. (see attached pic.)  At present, the engine seems to have steadied out @ 42 RPM.   That is getting down there and really looks good.   Now I'm  thinking of getting a dimmer sw. to see if a speed control can be achieved and then get the engine back on the center of the Stand.
     The engine is running 24 hrs. a day and when someone comes over it is nice to have a working piece of the  hobby in action without noise, smoke, smell ,etc.  Although you do have to explain how it works!!  (LOL)  That is just part of the fun though.   
     This should be the completed project except for the final tuning that will be sometime in the future. 




Copyright 2005,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.