Hooked on "Miser" Stirling by Jerry Howell

I have been lurking around here for several months, and I must add, enjoying every visit. I am really a novice machinist, learning something every day. I am fascinated by the "Miser" Stirling engine due to the fact that it runs on just hot or cold and does not require any external fuel source to operate.

I ordered Jerry Howell's print set and misc pieces for his "Miser". After a lot of research I am finally going to start the build, one part at a time. I have a small CNC mill and a small lathe. I do not have a 4th axis on my mill, but I do have a 3 jaw chuck indexer that will help with some of the round part machining and drilling on the mill.

Now that I have decided to jump in, I spent this evening making a materials list for the engine. Was quite surprised that one did not come with the prints. Maybe he figures that most just go to the junk box corner and dig through until they fine what they need, but, when you are new to the whole process, the junk box is very empty!

From what I can see, most of the materials can be purchased on line in small quantities. I have already discovered "Speedy Metals" and wonder if any of you have other favorite on line suppliers that sell in small quantities, at reasonable prices I must add!

In looking through the various kinds of steel, I have no idea what is meant by mild steel. I see it listed by various numbers and have no clue as to what is mild and easily machinable. Maybe someone can fill me in one what to purchase in this area. Or, should I use cast iron where it is suggested instead of mild steel? Boy, do they get an arm and leg for that stuff! That is why I am considering "mild" steel.

I am sure I am going to need to ask a lot of questions as I start to build the engine. Any advice any of you may have to offer would be appreciated. I plan on doing a lot of pictures and updates to here on a regular basis, once I actually start destroying pieces of metal and cutting tools.

I thought I would start by attaching the material list that I generated this evening. It sure will make buying it piece by piece easier for someone who does NOT have a big junk box full of good stuff to choose from like me. I am a very detail oriented person and probably will spend more time researching, looking, planning, and scheming then I will machining. But I will stick with it and get it done!

I do plan on doing a lot of .dxf drawings for many of the parts so they can be processed into GCode for the mill. If anyone thinks that would useful information to have I will post either the .dxf files and or GCode on here from time to time as I create it. I am quite well versed in AutoCAD and will probably use it to develop some of the files. Incidentally, I do use CamBam for most of my CAD/CAM processing. To drive the mill I use Mach3.

All comments and suggestions greatly appreciated.

George







View attachment Raw Material List For Miser Stirling.doc

That is a tricky one to start on. It will definitely put your skills to the test. Did you get a piece of graphite for the piston. Very little friction, very close fit, no taper are very important on the cylinder and piston. You may want to do a test cut on your lathe and make sure the head alignment is good (ie. no taper on a cut)

If i remember correctly a perfect slip fit is .0005" per every half inch. This transaltes to very tight tolerances.

Have fun and be patient!

Hi Jadecy:
Yes, I realize this is going to be a difficult first project for a novice. I did get the graphite piston with the parts kit from Jerry. I do plan on doing a lot of checking to make sure I have a good cylinder. Appreciate the advise.
George

George, as far as mild steel goes...see if you can find some 12L14 leaded steel. Its vary easy to machine and gives a nice finish. Having made a couple of half scale misers a few years back I can understand your fascination with it...one of my favorites too. It is a challenging build but do-able if you take your time. The piston fit is critical but other than that there can't be any binding anywhere!! Good luck on the build and please post pics as you progress.

Regards,
Bill

Hi Bill:
Thanks for your comments. I will look into 12L14 and I do appreciate your input.
I am a photo nut as well, so you will definitely see a lot of pictures as I get into the project.
George

George,
You will have fun with the Miser build. It will require careful work to keep the friction as low as possible and yet be air tight with close tolerances.

I would suggest that you do use cast iron where it is called for. It is messy to machine but can be lapped to a very smooth finish. Cast Iron has a very low coefficient of friction so it makes for a smooth working engine with low drag.

Avoid hardware store aluminum at all costs. It is soft and difficult to machine. Not too bad to turn, but it can be difficult to drill and tap. For general purposes, 6061 aluminum is suitable for anything you will be doing on the Miser. It is the most commonly available engineering aluminum and about the lowest cost. If you get into IC engines later you may want to use some 2024 or 7075 aluminum, but they are two to three times the cost and there will be no need for them with the miser.

When mild steel is referred to it is normally 1018 that is being referred to. 12L14 is suitable substitute for 1018 for most applications. It does not weld well and is difficult to case harden, but it is one of the easiest steels to machine, particularly on smaller machines. It costs about twice what 1018 does but it is well worth it in my opinion. It is very forgiving of many common mistakes that the beginning machinist makes.

For brass, brass 360 is about the easiest to machine material there is.

You have already discovered Speedy metals. They give good service and have a wide range of materials. Shipping should not be too bad to your location. Although I use others also, Speedy is my supplier of choice when I have to order material.

Gail in NM

Hi George;
When they say "mild steel", it can mean almost anything that is not in the higher carbon content steels.
1018 is the one we think of most often, I think. It could also be A36, which people often call hot rolled.
Try to stay away from A36. It doesn't machine very pretty compared to 1018 or 12L14, other things
being equal.
Personally, any place that mild steel is called for on model engines, I would use 12L14 for it's superior
machining characteristics. It's similar strength to 1018. The two places I use most for metals, Speedy
Metals and Online Metals, show almost the same price for either 1018 and 12L14. The cost difference
is almost nil.

I think you should use the material called for in the plans. If it says use CI for something, use it! I can't
imagine you having to buy much of it for that engine! If it says aluminum, without a spec, then what
Gail says: 6061.

Follow Jerry's prints and do as he suggests in the notes, and you'll end up with a runner.
Good luck!

Dean

Well today I fired up the lathe and turned out a couple of test parts. Wanted to brush up on my skills a bit and see what I could turn out in a couple of hours of time. Looks like it is not going to be too difficult to turn out, mill, and drill a small part.

Here is a picture of the first couple of trial parts. I say trial because I think I can make them a bit more uniform in size.

Comments, suggestions, and criticism welcomed.

George

Pictures look like they are made from copper, but it is brass. Too warm a light source on the pictures. Will try to do better next time.

A few thoughts: make the cylinder out of something that won't rust (brass, for instance). I used cast iron, which made a beautiful cylinder, but after sitting around for an extended period the bore roughened up slightly, enough so it wouldn't run until I cleaned the bore.

My favorite "mild steel" for machining is 1144. 12L14 machines easily, to be sure, but in my experience it's a rust magnet.

McMaster-Carr www.mcmaster.com sells a variety of metals in small quantities. Not the cheapest place around, but the selection is hard to beat and their service is great. The best bet would be to find a tame steel supplier who will tolerate small purchases.

As Gail says, it takes careful work. As close to zero friction as you can get, but with no looseness anywhere. But when you get it to run on the palm of your hand, it sure is a thrill.

George_Race said:

Here is a picture of the first couple of trial parts. I say trial because I think I can make them a bit more uniform in size.

Comments, suggestions, and criticism welcomed.

Click to expand...

Well, I think those look pretty good, George!
You mention you would like to make them more uniform in size. I suppose you may be thinking of the
top left part of each piece, so they would look identical.
I don't know how big these pieces are, but assume fairly small considering the engine you're building. A profile tool ground from HSS will cut the ends on these so they look exactly the same. Grinding the tool would take longer than the turning on the parts. Profile tools work especially well in brass.

Dean

Hi Dean and Mainer:
Thanks for your comments. Dean, to give you an idea of size, the lower round part is .125 in diameter. The hole in the flat spot is .081 in diameter. Pretty small parts. Yes the top of the oil cup is different on both pieces. I want it to look more like the one on the left, a smaller ridge on top. I don't think I will go to the trouble of making a profile tool, would be very small and difficult to grind. Should not be any problem to get them both looking very much alike.

Mainer, I appreciate your comments on rust. I would like to make all of the parts out of aluminum and brass to prevent rust. We have a lot of temp change here in Michigan, and humidity levels can leave everything just dripping. Rust is very quick to form on bare steel parts in this part of the country.

George

Are those oil cups for the Miser? If so, be careful. Most LTD Stirlings are run dry because even the low viscosity of light oil can overcome their minute power output.

In a similar vein, if you use ball bearings, flush all lubrication from them.

My half-scale Miser runs just fine with absolutely no lubrication.

Made a full size Miser about 12 or 13 years ago and wanted it to be brass and copper. Wasn't sure about a brass cylinder, thinking it might tarnish and the piston fit might not be right in a tarnished cylinder. Made the cylinder out of brass and lined the cylinder with stainless steel. The stainless polished up to a nice finish and has never been a problem. Since then made a couple of half size Misers with stainless steel liners and they have been no problem either. The stainless was mystry stainless from my scrap bin and it did machine nice.

I made Jerry's Miser as my first engine two years ago. If you can build yourself an airplane you can build this engine. I left out some of the detail on the column because I thought it beyond my skills at the time and didn't want to buy more tooling than I already needed to buy. If you screw up, just get some more material and try again. I was pretty lucky in that I only needed to redo a few pieces and the engine ran right off the bat (with the normal tuning).

I used 12L14 for all the steel and brass and aluminum as called out. I had my aluminum anodized, looks great.

Have fun and show progression pics as you build.

Ken

I'd like to build a Miser one day George. Other than that I don't know much about them. Looking forward to seeing your build progress.

Best wishes
Steve

I agree with Marv....there is little if any need for lubrication and even 3 in 1 oil will gum up over time. As to the rust issue, I have had no problems after many years, but this isn't the kind of model one leaves out in the elements. I found a doll display base and glass dome at the local hobby store, made a new base out of UHMW and keep it under the glass 99% of the time. I do try to run it at least monthly just to keep things loose. I also used 12L14 for the steel parts.

Regards,
Bill