Stirling Engine : Laura

I had a few problems with the drilling and tapping today. There is supposed to be a 3mm diameter hole that runs down the side of the work cylinder but due to a miscalculation I broke through the side of the cylinder. You can just see a small hole on the side at the bottom of the cylinder in photo 3. Ever the pessimist, I was prepared for a stuff up of this nature and I had another work cylinder ready to go for drilling and tapping. The completed cylinder can be seen held in the vice with the frame and cylinder cover now screwed in place.

1. I am just curious if that small hole could be neatly repaired in some way or would you just ditch it ? The 3mm diameter hole is to allow heat/air to transfer between the work and displacement cylinders..........I think !

2. The two frames in the vice are supposed to be sealed together prior to assembly. The instructions recommend bathroom silicon. Would gasket goo do the job ? What would you use ?

3. There is no mention made of gaskets for the cylinder covers as would be required on a steam engine. Are they not necessary on a Stirling engine ?

Edited By Brian John on 28/12/2015 06:45:08

Edited By Brian John on 28/12/2015 06:45:31

Edited By Brian John on 28/12/2015 06:46:14

Edited By Brian John on 28/12/2015 06:49:19

Could you pop a bit of brass rod in the hole and use soft solder to hold it in place, or does it get too hot, otherwise use silver solder ?

I'm guessing that if there is enough meat left round that hole you could either simply tap a shrt thread and loctite a piece of threaded brass in there or plug with an interference fit rod or if really worried about heat expansion loosening the plug then heat the cylinder before tapping in a tighter interefernce plug that has been frozen first? Or to be really lazy just mix some epoxy with brass filings as filler. I;ve used epoxy as emergency gasket goo on my rc heli exhausts and it works fine at those temps.

No need to scrap that cylinder you will be ok to either press in a small piece of brass or soft solder a piece in because if your heating the hot end with meths it wont get hot enough to melt the solder , and a brass plug will expand at the same rate as the cylinder so no worries there either , as far as gaskets go stuff like the cylinder covers as long as the machined surfaces are flat and have a good finish should be able to fit together with no gaskets and seal , on all the 6 engines i have made so far i have not needed any gaskets anywhere i have just relied on good machining to create airtight joints , for the frames a silicone gasket goo used on car/motorcycle engines might be better than bathroom sealant as they are meant to seal at higher temperatures maybe something like "Hermatite" used for sealing crankcases etc , or maybe even make a thin paper gasket.

Edited By Kettrinboy on 28/12/2015 10:02:21

The stove top fan is to my own design, all the plans are in my top 2", as usual, I tend to just put things together to fit around the stuff I'v got, and the general theory of Stirling Engines. The piston is made from window weight iron, and has a skirt thickness of just over 1 mm, and a crown of 3 mm, the little end bearing is fitted to a 3/8 UNF hole in the crown.

Normally I don't use gaskets, but if one is needed I use Loctite liquid gasket (can't remember the number). I have in the past tried proper gasket paper with the idea of forming a thermal break, for example, between the hot cap and the cold end of a BETA motor.

Ian S C

I have plenty of the proper ''paper'' gasket material which I purchased for building model steam engines. I think I will use that for sealing the frames.

I will try to solder up that damaged cylinder ; I may need for for something.

.

Thanks, Ian

MichaelG.

Brian, I think the gasket paper may be a good idea. I finally completed my engine last night, and after an hour of frustration and burnt fingers conceded defeat!

I used silicon to seal everything, and either didn't do a good enough job, or over did it and bunged up the air passage.

I will pull it apart tonight and see if I can see anything obvious. I've checked all the usual things like good piston seal, everything free etc. so it's a bit of a mystery at the moment.

Andrew : I bought this kit as a project in how to use a lathe rather than mindlessly churning up scrap metal with no purpose in mind. I very much doubt that I will end up with a functioning Stirling engine

Brian, that was my purpose too, but it would have been nice to have something that works - how hard can it be?!?!?

It would seem that Stirling engines are much more difficult to build than steam engines. The fit of the parts must be just right. I also read somewhere that the gap between the piston and the cylinder cover at TDC must be as small as possible. I don't know if this is true but it is something to look at. The kit has been designed to make these adjustments.

Edited By Brian John on 28/12/2015 17:40:18

The gap in my displacer cylinder is tiny - I had to adjust the rod as the piston was hitting the end of the cylinder. I'll pull it apart later and see if I can see what's going on. I'll take the work cylinder cap off first and see if I can feel any wind coming up the hole from the displacer.

My next project is the Bengs Karl engine. It's an I.C. hit & miss engine - I'm much more confident with petrol and a spark!

I finished the covers and collar for the displacement cylinder today. I am not quite happy with the fit of the glass tube collar (part 27) so I may make another one tomorrow. I am not sure what went wrong there !

I am still a bit puzzled about the 16mm X 3mm recess in the end of the displacement cylinder (part 25). I was told it was to allow for expansion of the 20mm rubber collar which fits neatly in the recess of the glass collar (part 27). But having put it all together, I disagree with this theory.

It looks like you are making good progress Brian.

Couple things you can do to avoid drilling through bore again might be to make a drilling template, a circle of steel like a thick flat washer that fits over the end of the cylinder and has the hole drilled in exactly the right place. (If the first hole is not quite right, you can keep drilling more holes until you get it right. Use the lathe to mark the circle on the drill jig washer at the diameter where you want the centre of the hole to be.

Then make sure the bore is dead square to the end of the cylinder that bolts to the frame. These should ideally be machine in one set up to ensure perfect squareness. If not, you can make mandrel with a taper of about .001" that the bore fits over, without removing the mandrel from the lathe, and then machine the end of the cylinder square with the bore that is a tight fit on the freshly turned mandrel. An alternative to the taper is a neat fitting parallel mandrel and a spot of Loctite to hold the cylinder on firmly.

Then check/machine the other end of the cylinder so it too is square to the bore. This is the surface the cylinder sits on when drilling it.

I would sit the cylinder straight on the drill press table, perhaps with a pair of toolbit blanks under it as parallels so you can drill through the cylinder without hitting the drill press table. A nut and bolt and pair of washers with the bolt runnign through the bore and a T slot etc in the table will clamp it down nice and firm. This eliminates the cylinder getting out of square in the vice, which maye or may not sit perfectly square as bought.

I wouldn't use gaskets or silicone to seal. I would use a spray can of Hylomar gasket sealer to just mist a thin thin layer of sealer on the necessary surfaces. Let it dry out completely before assembly then put together in the normal manner. Allied Bearings carries the Hylomar. A little of it goes a long way. But it does not make blobs and strings inside the engine like silicone will.

Hopper, thank you for the information. The reason it went through the side is because I initially drilled the pilot hole in the wrong place. I should have left it as a 2mm hole (it may have still done the job) but I tried to ''move the hole over'' with a 3mm drill bit....that was never going to work. You can do that with 2mm thin plate but not when drilling through 27mm of brass. The drill bit just deflects and follows the original hole. I will see if I can salvage it with some delicate soldering.

The Hylomar sounds good. I was still uncertain what to do there ; I know it should not be anything thick.

NOTE : I think the 16mm X 3mm recess in the displacement cylinder is for the glass tube to rest on when it is inserted through the collar. The glass tube is 15.4mm OD.

Edited By Brian John on 29/12/2015 08:12:56

Edited By Brian John on 29/12/2015 08:13:21

Although I did not really need to, I made another collar (part 27) for the glass tube. How do I drill holes in the collar to match the holes which have already been drilled and tapped in the end of the displacement cylinder ?

My solution is to draw a 30mm circle on a sheet of paper with a compass then carefully cut out the circle with a pair of scissors. I then lay this circle on top of the cylinder and mark the hole positions on the transparent paper. This circle of paper can then be laid on the collar and the position of the holes marked with a punch.

I have used this method before with good results but it seems a bit primitive. Is there a better way ?

I was not going to make a meths burner out of brass as per the instructions (parts 31 and 32) but I realised today that I have not yet done any taper turning on the lathe . After thinking about how to do it, I realised that my lathe does not have a handle on the top slide wheel. This is going to make it difficult to get a smooth cut. Why would they leave the handle off the top slide ? The lathe instruction book actually shows a handle on the top slide wheel in all the diagrams. I think I am going to have to make a handle and drill/tap the top slide wheel for it as I doubt that I can get a good finish without it. Am I missing something ?

Edited By Brian John on 31/12/2015 10:06:20

You should not use the handle if you want smooth cuts, both hands or at least finger and thumb of each hand on the wheel and that way you can feed continuously . Using a handle can induce up and down movement which will show up on the finished surface.

Reason they did not fit one is lack of room and not needed as topslide is usually used for fine feeding only.

My lathe has 2 handles on the top slide wheel, a short one and a long one. The long one soon got a bump against the tail stock, and broke off, the short one got bent. Replaced the broken one with one that rotates, but as Jason says, don't use the handle when actually removing metal.

Brian, your coming along well.

Ian S C Happy new year in about half an hour.

I have now drilled and tapped the bearings supports and the base plate. I had a few dramas but I got there eventually. The main cylinder assembly is just sitting on the base plate at this stage. The instructions call for it to be soft soldered to the base plate but the more I think about it, the less I like that idea. If something needed to be readjusted it would be difficult to do it. Unsoldering is a messy business !

I am thinking of drilling and tapping the base plate and the cylinder support frame so that I can use some brass angle and bolt it all together with 2mm socket screws. Are there any problems with that idea that I have not considered ?

Edited By Brian John on 01/01/2016 06:16:22