Ebook - Stirling Engine Plans - Part2.pdf - wszystko o Stirling engine - korand0

FizTextx

, FIZGIG

('A giddy girl', 'a firework', a 'whimsical idea', a 'whirligig', a 'spinning top', or 'a damp squib' ---

various dictionaries)

Some time ago I had this idea that I would design a hot air engine that a beginner could build with a

reasonable guarantee that it would work and using only the simplest tools. Fortunately the average 'first

timer' doesn't worry too much about the power his engine produces but is likely to be very pleased indeed

if it 'revs' easily.

So I set about building one myself, very simple, relying only on the accuracy of a 50 year old lathe, a

good four jaw chuck and a micrometer. And was very pleased when it hit 2000 rpm.

Then the hard part began, the drawings followed by the words and music. A second engine was built,

very similar to the first and with a similar performance, and this time I took notes of the machining

involved and possible alternative materials/methods. The next step was to edit and put them in some

kind of order and finish the drawings and here I must acknowledge the great help I've had from fellow

members of modeleng-list:- Dale Guenther for his initial web space and help with compatibility and

translating the drawings, David MacMillan for his valuable assistance with the instructions, Mark Barrett

(Jasper) for a short but essential course in Technical Drawing, and to Joe Dunfee for purging much of the

rubbish from my CAD files and the several other people whose comments and criticisms have been most

useful.

Dimensions are imperial and I've used vulgar fractions where a ruler is likely to be used and decimal

for those diameters likely to be measured with a micrometer. The present drawings should be regarded

as a 'beta release' . Completion reports are now coming in, and if/when some hero reports back that he

has built the engine exactly to the drawings, any comments will be taken into account and the drawings

will become Issue 1. ( Now done - see history file ) Minor modifications may be made to improve

legibility without altering issue number. Any material alterations will be recorded in the history file .

Alterations and additions to this text may be made at (almost) any time and won't normally be recorded.

In the 1999 Model Engineer Hot Air Engine Competition the following performance was recorded:-

Running on the simple meths/alcohol lamp, as in picture , 0.54 watts at 660 rpm. Off load speed,

1250 rpm.

Fired by a tiny 'kitchen' blowtorch (intended for caramelizing sugar) off load speed was just over 2000

rpm.

Disclaimer

INSTRUCTIONS

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These notes are intended to help the lad who has just discovered that he can't drill a hole in the right

place. (cheer up - join the club!) In the unlikely event of a hardened model engineer being interested in

such a crude engine he need only read the last couple of pages.

A 3" lathe (6" USA) should be able to cope easily enough but owners of smaller lathes should check

up on whether they could cope with the flywheel (although the engine would be happy enough with a

smaller one) and whether their four jaw chuck could handle the block. Other tools required will be a

micrometer, a steel rule, a scriber and dividers, together with a hacksaw and files.

Several sizes of drills, taps and dies are needed and a bench drill will make things easier. A medium

sized blowlamp/torch will deal with the silver soldering but, if you decide on the mild steel hot cap, a

larger one will be needed to braze the end disc.

Without precision measuring equipment, many amateurs work to "fit" rather than absolute dimensions.

This requires components to be made in the correct order or there won't be a part available to fit to! And

accounts for just some of the peculiarities in the following text---

LIST

1 The Bed

2 Crankshaft Bearing Tube

3 Soldering

4 Crankshaft Bushes

5 Cylinder Mounting Block

6 Displacer Etc

7 Hot Caps (Air Chamber)

8 Water Jacket (Cooler)

9 Cylinder

10 Piston

11 Crankshaft

12 Con-rod

13 Return Crank

14 Displacer Con-rod

15 Flywheel

16 Assembly

17 Notes

Drawings (Hit Back to return)

Parts List 1 (Hit Back to return)

Parts List 2 (Hit Back to return)

FAQs

The Bed Sheets 2 2a 2b (Hit Back to return)

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Cut the bed from either 2mm or 3mm (1/10" or 1/8") mild steel sheet and if you are unable to find a

suitable piece of metal locally remember that the firms who supply frame steel to model loco builders

will be able to help with 3mm material. If you intend to make the con-rod with the split big-end it is

essential that the piston stroke is truly perpendicular to the crankshaft and to ensure this the bed plate

must be flat.

Check it before marking out by first removing any burrs from the edges and holding it up to the light

with a steel rule laid across the surface. On the concave surface you will see a glimpse of light between

the ruler and the metal, and this is the side which you should mark out on.

Drill holes first, the relationship between the bearing tube hole and the block fixing screw holes being

particularly important. Then cut the outer shape. This is for appearance only and not critical, whether you

chain drill the curves and file them or attack them with an angle grinder is up to you. The next job is to

get that concave surface flat and after removing any burrs round the edge, a few strokes with a new file

laid flat on the surface should suffice.

Back to List -

Crankshaft Bearing Tube Sheet 2a (Hit Back to return)

It is important that the flange is exactly square with the hole through the centre of the tube and this will

present no difficulties to the experienced turner with half decent equipment. However, beginners often

have difficulty drilling long holes accurately and the combination of an inaccurately sharpened drill with

an imperfectly aligned tailstock can make it very difficult. So unless you are really confident, chuck the

rod and drill the hole first, starting truly in the centre at the flange end. Then remove it from the chuck

and make a mandrel to mount it on.

Chuck a length of 3/8" dia mild steel with about 3/4" protruding and turn this down to a few thous

(thousandths of an inch) over 9/32" dia and then use a fine file to put a very slight taper on it, so that the

tube, flange end first, will just force on for about 1/2". Squirt plenty of oil into the tube before supporting

the outer end of the tube with the tailstock centre, Then turn the outside of the tube down to 3/8" dia,

leaving the flange just over 1/16" thick. Finish this side of the flange with a single cut to leave it true.

Now remove from the chuck and knock out the mandrel. Chuck the tube gently by the 3/8" dia and take

very light cuts to reduce flange thickness to a bare 1/16".

Back to List -

Soldering Sheet 2a (Hit Back to return)

Support the plate horizontally with the tube hanging thro' the hole and three short pieces of silver solder

wire under the flange. Flux thoroughly and heat mostly from above playing the flame round the flange so

that it heats at the same rate as the plate. When you see the solder melt, move the flame to the underside

to `draw' the solder towards the heat. With reasonable luck a fine fillet of solder behind the plate will

confirm penetration.

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In the case of the thinner, 2mm or 1/10", metal we now need to make up the web and collar as shown on

Sheet 2b. These should be silver soldered together and the faces that will fit against the plate filed flat

before soft soldering on to it. After soldering you can use soldering iron to leave a fillet of solder along

the web which, after painting, will give a look-a-like casting effect.

Back to List -

Crankshaft Bushes Sheet 2a (Hit Back to return)

The bushes are turned to an easy sliding fit in the tube and either drilled 3/16" or drilled undersized and

reamed 3/16".

Part off the two bushes to length and glue into the tube as follows. Insert the, lightly oiled, length of

silver steel rod that will become the crankshaft through the tube to project from each end. Slide one of

the bushes on to it and enter this into one end of the tube. Slip the other bush on to the other end of the

rod and enter it into the other end of the tube. With about 1/32" of each bush in the tube, apply a tiny

drop of Loctite 603* to the first bush, close to the tube face and turn the bush, to distribute the glue, as

you push it home into the tube. Leave a bare 1/32" projecting, just enough to accommodate any fillet of

glue that oozes out and prevent it falling on to the shaft . Repeat with the other bush and leave for a few

minutes before checking that the rod is free. If it isn't, grip it in the vice to pull it out and use a pipe

cleaner to clean the bushes before re-entering it. If the vice won't shift it, use a blowlamp to destroy the

bond, remove the bushes, clean up and start again with an even smaller drop of glue ----.

*Loctite 601 was used on both prototypes but now appears to have been superseded by 603.

Back to List -

Cylinder Mounting Block. Sheet 3 (Hit Back to return)

Cut from 3/8" Aluminium bar and hold in the 4-jaw chuck to machine the sawn edges square, or, if bar

isn't available, cast an oversized block in a simple folded tin-plate mould about 5/8" deep and machine all

over in the 4-jaw. Begin by holding it by the edges and machining the first, concave, surface flat. Now

chuck it with this face firmly against one of the jaws and, with a small packing piece between the centre

of the opposite jaw and the other face, machine the first edge flat. Re-chuck it with this edge against a

jaw and packing against the opposite jaw to machine the adjacent edge and repeat for the third edge. The

block can now be held between opposite edges to machine the last one after which it can be chucked by

the edges to machine the other face

Finally check the dimensions and machine it down to the correct size, and to ensure that the two faces

are truly parallel, a parallel packing should be inserted between the block and the chuck face for the final

facing. A ring from an old ball race is ideal for this.

Mark out, and drill the holes for the cylinder and chamber fixing screws, the displacer bush tube and the

two screws to hold the block to the bed. Tap these two and the one for the tube.

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The only awkward job here is the skew hole. Hold the block at the correct angle in your drilling machine

vice and begin drilling with a small, say 3/16", end-mill. When this has entered to its full diameter,

replace by the same sized drill and continue thro'. Alternatively, drill from both sides, using a hand brace

and carefully skewing the drill. Either way, you will need to finish by filing the port to the shape shown.

Cut the register disc approx' 1/16" oversize from 1/32" sheet aluminium and flatten it by a good squeeze

in the vice. Chuck a piece of scrap material, about 1" diameter, drill a short 1/4" hole in the centre and

then face it to make a 'chucking piece'. Glue the disc to its face with Loctite 603 and hold it firmly in

place (with the tailstock barrel?) until the glue is set and then turn to size and drill or drill and bore the

centre hole. (There is less risk of breaking the glued joint if you drill a small hole and open it up to 0.2"

with a tiny boring tool.) Ensure that no burr remains round the hole. Remove from the chuck, heat

gently to remove the disc and drill a 3/16" hole to line up with the port but don't fix the disc to the block

until the displacer bush tube is completed.

Very sharp eyed folk may have noticed the laminar appearance of the block in the photo. This was an

experiment with the second engine to obviate the need for casting the block and it is built up from three

pieces of 1/8" aluminium sheet glued together with Loctite 601. The surfaces to be glued were first

roughened with coarse abrasive paper, the Loctite applied and the assembled pieces were then clamped

together in a vice for 24 hours before machining the edges as described above.

The tricky part was drilling the holes and, after the first attempt had broken one of the joints, it was

glued back together and mole grips were used to hold it together during the drilling of the four corner

holes. The port was drilled, and the two holes in the edge and the centre hole were all drilled and tapped,

by hand, while it was clamped in the vice.

Care is needed to keep the centre hole square with the surface, but the built up block certainly works and

could be an alternative to a bar or a casting.

Back to List -

Displacer etc Sheets 4 and 5 (Hit Back to return)

Drill and turn the displacer rod bush tube from 7/16" diameter steel rod. Again we have the problem of

drilling a long hole and in this case it can be dealt with by first turning the end down, cutting the thread

and turning the nose to fit the register disc before drilling. If the drill wanders make up a carrier from a

strip of metal with a tapped hole at one end to match that on the tube and turn the outside diameter taper

between centres, finishing by taking the tiniest amount off the full diameter at the thread end - just

enough to true it up with the hole.

Now hold it, firmly, in the chuck by this 'full' diameter to lightly skim the face behind the thread before

screwing the block fully home on to it. Check that sufficient 'nose' projects through to locate the register

disc, skimming off any excess, Use Loctite 603 to glue the register disc to the block and hold it firmly

(between chuck jaws and tailstock barrel?) until cured.

Remove the assembly from the chuck and hold the block in the vice to file out the port to approx 1/4"

dia, keeping within the limits shown on Sheet 3 and working from the disc side to avoid disturbing it.

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Ebook - Stirling Engine Plans - Part2.pdf

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