This page is dedicated to anyone ( but especially the technically minded ) interested in knowing how this engine was made.
Click on the enlargement button ( move mouse to middle of picture ) to get a closer, more detailed look at the pictures and sketches. To get back to regular size, press the Escape button on your keyboard.
This is my second Stirling Model, a simpler version of the first, utilising only one flywheel instead of two and making the " Power " - and " Displacement " Units more compact. I kept the speed ( RPM´s ) similar to the first Model ( fast enough to keep you from falling asleep, but slow enough to be able to visualize the movements ) allowing a better understand of the functioning processes. I had a lot of fun building this one.
There are no Patents, Copyrights, Design Rights or anything of this nature on this Stirling Model and there won´t be in the future. Then by International law, anything presented to the general public before Patents, Copyrights and the like have been applied for cannot be granted said rights.
I´ve added enough pictures, technical drawings and comments here to help anyone to be able to understand how I made this model. The decription, however, of how I did it is not a recommendation that you use the same working methods that I use. Please use your own discretion and methods of machining and read the disclaimer at the end of this writing.
I have no objections of anyone downloading pictures, technical drawings or texts from this Website as long as they are for your own personal use. I only ask that you do not change them in any way or spread them around ( especially through the internet ). Thanks for your understanding. Dave
( See " Copying The Prints " under " General Information " ).
Apologies to all of you who are using the English System, but I live in Germany and all my machines are based on the Metric System. So all the parts and technical drawings are based on and given in Millimeters ( abbreviation = mm ).
None of the drawings have tolerance specifications. The general tolerances I used for most of the machined parts of the Model are plus / minus 0.1 mm ( one Tenth of a Millimeter ), and a lot of those parts don´t actually require such close tolerances. But by considering the function of the part in question, a practiced machinist can usually decide what tolerance range could or should be used. When in doubt, just use the smallest Tolerances your machines can manage. There are, of course, exceptions like the fit between Power Cylinder and Piston, but I´ll talk about them as we go through the different drawings. For other tolerances, such as the spacings between the columns, you can use the Scales that I have added to the drawings. They are fairly accurate.
The Technical Drawings
I know I´ve broken a lot of rules making these drawings, but it was never my intention to make perfect sketches by the book. My only goal was to make them understandable without getting bogged down in detail.
For those who are not familiar with Metric Thread Specifications, here a few infos:
All thread specifications in the sketches are given starting with the capital Letter M for Metric. Example 1: M38 X 1 Example 2: M10
The first example is an example of a Non-Standard-Thread, which is always specified by the letter M followed by the nominal diameter size ( 38 ) followed by X followed by the pitch ( 1 ) in mm.
In the second example ( M10 ) only the nominal diameter size is given, the pitch is not. This specifies Standard Thread. Hier are the pitches of a few Standard Metric Threads.
Nominal Size Pitch
For the Tap Drill Sizes for all Metric Standard and Non-Standard-Threads use the following formula: Nominal Size minus Pitch = Tap-Drill-Size.
Example 1: 38 - 1 = 37 mm
Example 2: 10 - 1.5 = 8.5 mm
So Let´s Get Started
I´ll now go through the Pics & Sketches and comment on the things I think would help to understand the structual, constructional and or functional aspects of the parts represented by the drawings.
The first Pics & Sketches should give you a good overall idea of how the machine is constructed. I´ll be refering to some of them as we go through the other drawings.
All of the dimensions framed in little boxes will be dependant on the size of the Test Tube and the O-rings being used. I got my tube from Ebay, and I have no idea where it came from originally.
So the formulas at the bottom of the sketches must be used to calculate the necessary dimensions for other tube sizes. If the tubes to be used are significantly larger or smaller than the one I
used it may be necessary to adjust the dimensions of the power cylinder. If so, then go by the volume displacement- and not the diameter differences.
If the O-rings to be used have to be stretched a lot ( not recommended, ideally the O-rings should be 1-2 mm smaller in diameter than the test tube ) to get them over the tubes, they will decrease in thickness. So dimension E may also have to be adjusted to accommodate this. Here´s what I did. I stretched the O-rings over the glass. Then, using a Vernier Caliper, took a measurement of the outside diameter of the O-rings and added one tenth of a mm.
The aluminum cooling unit will be the most difficult and time consuming part to make. Most critical is cutting the gaps between the cooling fins. Aluminum tends to build up on a cutting edge greatly increasing the cutting resistance. If there is slack in the cross support this increased resistance may even come to a point where the slack is drawn out of the cross support causing the cutting tool to be pulled suddenly into the Aluminum causing a gashing or gouging effect and ending up braking the cutting tool and damaging the cooling unit. My tipps:
1.) Adjusting the height of the cutting tool to a little above center helps prevent it from being suddelny drawn into the cooling unit ( this is no guaranty, but it should help ).
2.) Use a cutting fluid. Better still, is using lots of it.
3.) Draw the cutting tool frequently out of the cutting material and check for and remove build-up.
4.) Trying another material for the cooler like brass or bronze would greatly reduce the danger of gouging.
If Aluminum is used for cooler and the nut, keep this in mind. Aluminum rubbing against Aluminum, especially in a dry state ( and especially thread ), has a tendancy of galling. What is galling ? It´s like this. When the two aluminum parts rub against each other ( again especially in a dry state ) the peaks of the microscopic unevenness start to tear and roll around ( in this case ) in the gap between the inside and outside threads and begin gouging into neighboring peaks. When this effect snowballs and produces chips larger than the gaps between the threads, the movement of the threads will become blocked. Usually at this state there is no more going forward and also no more going back. One can try ( hoping against hope ) using spray-oils to help loosen things up again, but usually it is all too late, and the result is that the two parts will have to be made again. So always make sure:
1.) that the surface quality of the threads are as good as you can get them.
2.) to coat the thread surfaces with oil before using ( thick oil is better than thin ). Be careful not to get any oil on the O-Rings.
3.) to cut these two threads liberally to avoid a tight fit.
I´ve also considered using Brass or Bronze for the nut ( I have never experienced galling between Aluminum and Brass or Aluminum and Bronze ).
The O-rings I use are made of Viton Rubber. This material has very good chemical- and heat resistance qualities, and after running the motor about 40 or 50 times there is not the least sign of melting or any other damage to the rings.
The Shore Value ( Shore = 80 ) is the specification of how soft ( or hard ) the rubber is. I assume Shore 80 is a spec that is commonly used in a variety of applications, and works just fine.
If oil gets on the O-rings they may not be able to hold the glass heating unit ( test tube ) in place. Mine just popped out one day traveling about 8 inches in the air before ending up making a beautiful brown to black burn mark on one of my wife´s kitchen towels. So it´s very important to keep the O-rings and all parts that come in contact with them absolutely free of oil, grease and the like.
I decided to hollow out the Aluminum displacement piston to make it lighter saving wear on the Bronze Bushing. In order to achive this I made it out of two segments connecting them with thread. I added a ventilation hole to prevent pressure build-up.
For cutting the test tube to its final length I wrapped it in a soft piece of neoprene rubber and chucked it up ( very lightly ) in the lathe. Running the lathe at a rather low speed I used a Dremel - Tool with a Diamond - Wheel to make the cut. After this preliminary cut I then used the Dremel again ( this time with a fine sanding disc ) to smooth up and round off the jagged edge.
These two processes require a very light hand with `` feeling ´´. I cannot ( for safety reasons ) recommend this method of cutting the test tubes. I only offer here a description of how I do this operation. It would be much better if a qualified glass cutter were to make this cut. Or maybe someone who works in a chemistry lab?
I use a vacuum cleaner to suck up the glass dust generated in this process being very careful to position the dremel so as to direct the dust directly into the vacuum cleaner nozzle. I also use a dust mask just in case any of the dust gets by the vacuum cleaner. Safety glasses are always a must for any type of work ( see disclaimer ).
Milling The Cooling Unit
Because I don´t have a milling machine I do all my milling on the Lathe. Pics 39, 40 and 41 show how I did this. The milling depths and other details are given in the technical drawing.
TO BE CONTINUED
THIS SITE UNDER CONSTRUCTION
( COULD TAKE A WHILE )