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' .
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
) Minor modifications may be made to improve
legibility without altering issue number. Any material alterations will be recorded in the
.
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
, 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.
INSTRUCTIONS
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (1 of 14) [8/18/2003 9:07:31 PM]
FizTextx
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,
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
(Hit Back to return)
(Hit Back to return)
(Hit Back to return)
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (2 of 14) [8/18/2003 9:07:31 PM]
FizTextx
Cut the bed from either 2mm or 3mm (1/10" or 1/8")
sheet and if you are unable to find a
suitable piece of metal locally remember that the
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.
(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".
Soldering Sheet
(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.
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (3 of 14) [8/18/2003 9:07:31 PM]
FizTextx
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.
Crankshaft Bushes Sheet
(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
Part off the two bushes to length and glue into the tube as follows. Insert the, lightly oiled, length of
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.
Cylinder Mounting Block. Sheet
(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.
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (4 of 14) [8/18/2003 9:07:31 PM]
FizTextx
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.
and
(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.
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (5 of 14) [8/18/2003 9:07:31 PM]
FizTextx
Finally file the 3/16" x 3/16" square flat on the top of the tube to accommodate the lubricator screw, drill
its centre and tap 7 BA. (The correct procedure here would be to mill the flat or counterbore the hole to
give an accurate seating for the screw. However the air pressure is extremely low and the trace of oil on
the thread gives an adequate seal.) The screw thread must be short enough to prevent it touching the
rod.
Two displacers are possible. The original engine used an aluminium 'Steradent' (denture cleaning
tablets) tube and a heater/air chamber made from a length of bicycle frame tube. This was very
satisfactory but after recommending it to friends I was told that the aluminium tubes were no longer
available, having been superseded by plastic. So for the second engine I bought a matching pair, heater
and displacer, of stainless steel tubes from
. Of near identical sizes, these could be
substituted without any difficulty. However they are really intended for much more powerful pressurized
engines running at higher temperatures and whilst this is no disadvantage with the heater cap, the
displacer is really too heavy for Fizgig although it does have the slight advantage that it is fireproof and
already the correct length.
However, I then discovered that the aluminium tubes are still available, used to pack a more powerful
grade of Steradent for coping with nicotine stains etc, and one of these was used for the second engine.
The safest way to cut the tablet tube is to chuck a length of broomstick and turn it down until the tube is
an easy push fit to well beyond the cut. Grind the sides of a Junior hacksaw blade until you have a
toothed knife blade then, with your hand steadied by the tool post, bring this gently down on the tube in
the correct position. Any slight rag on the cut end can be removed by lightly rubbing it on flat emery
cloth.
Glue the end disc to a chucking piece with Loctite and turn it to a snug fit in the tube, drill the centre and
tap 7 BA while it is still in the lathe. Remove from the chuck before heating gently to destroy the glued
joint.
Check that your length of 3/32" steel is truly straight and protect it by several turns of paper when
chucking it to cut the threads with a tail-stock die holder. Screw the lock nut on to it and face it down to
1/32" thick before applying a tiny speck of Loctite and screwing on the disc. Then use Araldite or similar
epoxy resin to glue the disc into the tube.
The bushes are turned to an easy fit in the displacer rod tube and drilled 3/32" or drilled and reamed as
described for the crankshaft bushes. (in this case drill 2.3mm. - 0.003" undersize) Both can be made
together and "parted off" using the ground Junior hack saw. Glue them into place using the same method
as for the crankshaft bushes.
When the glue has hardened slip the displacer rod into the bushes and twirl it - the hot end of the
displacer should run true within a few thous, if not, very carefully bend the rod where it enters the disc,
until it does. (bending it whilst pushed well home in the bushes is probably very bad practice - but it
works) Finally, the displacer should be immersed in hot water to check for leaks. There should be no leak
at all from the tube joint although a very small leak, several tiny bubbles per minute, from the centre is
acceptable and may even prevent internal pressure bulging the end if you overheat the engine.
A problem arose on my last engine with streams of bubbles from the side of the tube and this was found
to be due to serious internal corrosion. Apparently the cleaning solution is extremely corrosive to
aluminium and if any dampness gets to the tablets they will start to eat their way out through the tube!
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (6 of 14) [8/18/2003 9:07:31 PM]
FizTextx
(Hit Back to return)
The hot cap can be either stainless or mild steel and I used the stainless steel cap for the second engine to
confirm that the metal could be easily soft soldered to the jacket.
The mild steel cap can be made from any piece of tubing that can be turned and bored to the correct size.
A tolerance of plus/minus five thous is allowable here and internal finish is not important - I was able to
use a length of bicycle frame tube, ignoring the internal weld, for the first engine. The tube wall should
be turned down to about eight thous thickness between the strengthening bands to reduce heat leakage
along it. The disc closing the hot end should be brazed on using either brass wire or a high temperature
spelter such as Sifbronze.
(Hit Back to return)
To avoid the need for accurate marking out and drilling of the base, make the inner sleeve first and
although the bore should be an accurate fit on the register disc, its finish is not important. Next cut out
the base, oversized, and use the four jaw chuck or the face plate to bore the 1 7/64" hole to fit the reduced
end of the sleeve and counterbore it to accept the 35mm jacket.
Remove from the lathe, fit the inner sleeve into its hole, counterbore side, and then fit the assembly on
to the register disc/block.
Clamp together firmly while you scribe the base around three of its sides and mark out for the holes with
a 7/64" drill through the holes in the block. Dismantle, and before cutting and filing the base to size,
mark out the remaining side and drill the four screw holes.
The metal for the top ring should be drilled, as big as you can, before carefully cutting out and filing
close to the scribed outer circle. Now hold in the chuck and bore out the centre hole to fit the top end of
the sleeve. Remove from the lathe and clean both sides thoroughly before soldering the sleeve into it.
Now chuck it by the sleeve, with the bore running true, to take very light cuts reducing the outside
diameter of the disc to fit into the jacket, and not forgetting the very small chamfer.
The jacket is made from copper in the prototypes and although the dimensions are not critical, a 35mm
Delco pipe coupling from the local DIY store is ideal for the job. It is recommended that all component
parts are made and fitted together in a trial assembly before the stub pipes are silver soldered in as the
copper will be very soft after this operation and measurements difficult.
Drill the two holes in the sleeve 1/4" and then open them up to nearly 5/16" using a file tang as a reamer
to give a sharp taper. A similar taper filed on the ends of the stubs will then allow them to be jammed
tightly into position for the silver soldering. If any part of the stub projects inside the sleeve it must be
filed flush.
To solder the cooler together begin by thoroughly cleaning, fluxing and tinning the outside of the inner
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (7 of 14) [8/18/2003 9:07:31 PM]
FizTextx
sleeve at both ends and, if not already fitted, solder the top ring on to it. Clean and flux the inside of the
copper before sliding the inner sleeve down into it, to project from the bottom. Weight the inner sleeve to
hold it squarely in the base, and solder to it. Now wind a couple of turns of solder wire round the sleeve
and make sure that the stubs are correctly orientated before fitting the outer sleeve down into the base
counterbore and heating from beneath until a silver ring appears around the outside of the joint.
Clean and flux the end of the cap before fitting it into the top ring and weight it to hold it square whilst
soldering it and the outer sleeve to the ring.
Cylinder Sheet
(Hit Back to return)
This is cut from a length of drawn brass tube. Be careful to avoid distorting it when you saw off to
length and wrap a turn of paper round it to help prevent it slipping when held lightly in the chuck. Face
both ends, then bore or scrape and polish a tiny taper inside the outer end to help with inserting the
piston. The steel flange should be marked out and drilled before cutting out - it will give you something
to hold on to. The centre hole should be drilled only well undersized and, after cutting out, bored to about
a couple of thou's bigger than the tube. It can be held in the four jaw chuck and squared up by eye with
sufficient accuracy for this.
Roughen the end 1/8" of the tube with coarse emery before Loctiting it into the flange. Stand both on a
piece of cling film or similar on a flat surface to cure. Cut the gasket from a thick brown envelope.
Piston Sheets
and
(Hit Back to return)
The engine in the photo uses the solid piston, it was quick to make and certainly runs OK but it is
grossly overweight and the vibration probably slows the engine down by several hundred RPM. So,
unless you are really in a hurry, the lightweight piston is recommended; altho' it is more complicated,
each individual operation is inherently simple.
Begin with the shell, boring 1/4" over length to the finished I/D and then turning the O/D, also over
length, to within a few thou's of cylinder bore size. (by this time, folk with worn lathes should have set
the top-slide to turn truly parallel) Now advance the cross-slide, a thou' at a time, reducing just the end
1/8" of the piston and trying to fit the cylinder over it. After each unsuccessful attempt, and without
adjusting the cross-slide, cut along the full length before trying once more - and then advancing another
thou' and reducing the end 1/8" again. As soon as this 1/8" enters the bore take no further cuts with the
tool but remove the last thou' using (in order of preference) a diamond file, an oilstone or an oiled strip of
fine emery cloth on a flat strip of metal. Keep the abrasive moving from side to side and check frequently
with the mike to keep things parallel. Aim for a very light push fit in the bore, but don't lose too much
sleep over it, off load, loose pistons work nearly as well!
Do be extremely careful to avoid jamming the cylinder on the piston.
When you are satisfied with the fit, turn off the end 1/8" and, using a pointed tool, turn a series of oil
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (8 of 14) [8/18/2003 9:07:31 PM]
FizTextx
retaining grooves, about five thou's deep and spaced 1/8". Bore the little recess to take the head disc
before parting/sawing off to length.
Received wisdom suggests that loose emery embeds itself in soft metals, so, if you have been using
emery cloth, it will do no harm to scrub the shell thoroughly in petrol, using an old tooth-brush.
The head disc can be glued (Loctite) to a chucking piece and turned to an easy fit in the recess, drilled
and countersunk. Use heat to break the glued joint, clean any remaining glue from the back of the disc
and ensure that it is both clean and flat, with the sharp edge removed, before Loctiting it into the piston.
More experienced machinists may elect to make shell/head in one piece, in which case they might, with
advantage, reduce wall thickness to about 0.025", and its probably safer to do this after finishing the O/D
to the cylinder bore.
The holes to be drilled in the yoke must be at 90 deg's to each other and the easiest way to ensure this is
by starting with a rectangular block of metal. This can be cut from the same stock as the cylinder
mounting block and accurately 'squared up' in the four jaw chuck. After marking out, return it to the
chuck for drilling and tapping.
The gudgeon pin hole should be drilled 1/8" (or drilled and reamed) right through, the nearest metric
drill in this case is 3.1mm, approx. 0.003" undersize. Tap the shell fixing screw hole after you have
sawn/filed out the slot for the con-rod; noting that this will need to be 3/16" wide for the steel con-rod.
Finally, saw and file to the outside shape.
(Hit Back to return)
Begin by marking out, drilling, tapping and then cutting out the disc. To turn the edge of the disc I
chucked a short stub of steel, turned it down to 3/16" dia and threaded it to match the disc. A thick
washer was slipped over it and the disc screwed on to hold the washer firmly against the chuck jaws.
Next, chuck the 3/16" silver steel shaft and thread it. Screw on a nut, as far as it will go, and face it down
to a bare 1/8" thick before putting a dab of Loctite on the projecting thread, screwing the disc on to it and
facing back any remaining thread flush with the face of the disc. This face should now run true. If it
doesn't you will have to correct it by a very light facing cut using an extremely sharp, pointed tool,
removing any tool marks afterwards by rubbing the disc on a sheet of abrasive paper laid on a flat
surface.
Use a 1/4" drill held in the fingers to very lightly countersink the crank pin hole to accommodate the
small fillet on the pin.
Its not a bad idea to check the geometrical accuracy of the bed at this stage. Slip the shaft into its
bearings and lay the edge of a steel rule across the face of the disc. The squared end of the ruler should fit
perfectly against the front surface of the mounting block. If it doesn't, turn the crank 180 degrees and try
again. If this reverses the error, the face of the disc must be re-machined. If not, either the block or the
bearing tube is slightly askew, correct by carefully bending the bed, without straining the block fixing
screws.
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (9 of 14) [8/18/2003 9:07:31 PM]
FizTextx
Finally, saw the disc to shape as shown, and I found the lead balance weight a useful addition to reduce
vibration.
and
(Hit Back to return)
The steel con-rod is a much better looking job, the engine will run quieter and the split big-end will
allow wear to be taken up. However the long bearing can cause binding and it is not recommended unless
you are 100% confident of the alignment of all your previous work. The spacers, item 29 will not be
required.
Otherwise, fit the simple aluminium rod, with the spacers, which can accommodate minor errors without
too much difficulty - and you can always change to the steel rod later if you think the performance
justifies it.
To keep the working pressure of a Stirling as high as possible, "dead space" must be kept to the
minimum and the length of rod shown should keep the piston clearance at TDC down to 1/32". However,
any clearance, from a few thou's up to 1/16" is acceptable. Outside these limits it may be possible to
correct by slotting the block fixing screw holes in the bed. If not, you will have to make a new rod after
very carefully measuring between the crank pin and the gudgeon pin with the piston sitting on a 1/32"
spacer against the block.
Both holes should be reamed to give a quieter running engine. (initially!) However, Fizgig is no lady
and, being double acting, will hammer her bearings at an alarming rate; by now you will be impatient to
see results and drilled holes work just as well.
Return Crank Sheet
(Hit Back to return)
If everything were made precisely to the given dimensions, this crank would result in a phase angle of
approx' 95 deg's; roughly in the middle of a very wide range of angles over which there would be no
detectable difference in performance. So don't worry.
Displacer Con-rod Sheet
(Hit Back to return)
Use aluminium strip and double over at the "big-end" before drilling, to give a larger bearing surface.
The long thread in the knuckle joint is to give help in obtaining the correct clearances at either end of the
displacer stroke. If you still can't get them right you'll have to make another con-rod ------
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (10 of 14) [8/18/2003 9:07:31 PM]
FizTextx
(Hit Back to return)
Being a double acting engine, i.e. non-snifting, Fizgig works happily with any flywheel you care to hang
on it. In fact the prototypes run at high speed with no flywheel at all! A simple wheel, spoked or not,
around 3 1/2" diameter and secured by the traditional grub screw is all that is needed, although Sheet 13
shows my own favourite method of fixing, as used on the prototypes. The pulley may only be wishful
thinking - keep your fingers crossed. Sheet 14 shows a much simpler lead flywheel. The large diameter
boss is to allow for a long grub screw to reduce the risk of stripping the thread in the soft metal.
Assembly
With a mean working pressure of less than 4 PSI it is essential that our engine runs with the absolute
minimum friction, and this includes oil drag. The lovely silky smooth feel of a well made steam engine
which "ticks over beautifully at only 5 PSI" simply won't do for a Stirling engine. Our aim must be an
engine which feels "loose" albeit, ideally, with no perceptible play in any of the bearings. Or, if we can't
quite achieve this, "loose" with the minimum play.
The first requirement is accurate alignment and the earlier check should have ensured that the cylinder is
square with the crankshaft. Assemble the piston and con-rod, smother with Molyslip and slide it into the
cylinder. Use more Moly to insert the crank-shaft into its bearings but don't oil the crank pin before
sliding the big-end on and screwing the cylinder to the block with a couple of lengths of 7BA studding.
Now turn the shaft over and check that the big-end is sitting about 3/32" from the crank disc and is
perfectly free to slide, although perhaps only 1/32", sideways throughout a whole revolution. If it isn't
and binds slightly, turn the cylinder upside-down and try again. If this doesn't do the trick, turn the rod
over, or the piston etc etc. If you can't find an ideal combination, then settle for the best and, with luck,
any tightness will disappear after the running in.
This may well be required anyway. So now unscrew the cylinder to remove the big-end from the pin and
fit one of the spacers before replacing it. Molyslip the pin, slip the other spacer on and fit the return
crank to allow a few thou's side play at the big-end. Refit the cylinder and check that the shaft turns
freely - (hopefully now with that silky smooth feeling!) couple up to the lathe or similar and motor the
engine at several hundred RPM for 5 mins or so.
Now strip the engine, use a dry clean rag to clean the Molyslip and all traces of oil from the cylinder and
piston, and reassemble. Without the air chamber fitted it should be possible to twirl the crankshaft freely
with finger and thumb.
of light oil should now keep the piston happy, clock, sewing machine, typewriter or thin
cycle oil will do but don't use motor oil or WD40. Re-fit the return crank, setting the clamping screw so
that it can be easily turned on the crankpin with light finger pressure and set it to approx' the angle
shown on
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (11 of 14) [8/18/2003 9:07:31 PM]
FizTextx
Use the same light oil on the displacer rod before sliding it into its bushes and couple it up to its con-
rod/crank-pin. Hold the air chamber in place and adjust the length of the displacer rod together with the
throw of the return crank to give about 1/64" clearance at the hot end of the chamber and 1/32" clearance
at the cold end. Tighten the return crank clamping screw and the air chamber may now be screwed to the
block with two more lengths of 7BA studding, using an oiled paper gasket to seal it.
As a final check, and to delay the dreaded moment of truth for a few more minutes, hold the chamber
and both joints under hot water and turn the crank to TDC. Any bubbles appearing at the joints should be
investigated before proceeding any further.
The first run of any hot air engine is always a special occasion. (perhaps best attempted in seclusion!)
The great Dr Stirling himself probably knew the same apprehension as things warmed up, and the same
feeling of amazement when it actually ran!
Clamp Fizgig's bed in the vice and apply a small torch flame to the side of the heater. Turn the crank a
few times to distribute the heat along the displacer and then give it a flick in the forward direction - i.e.,
that in which the displacer leads the piston. At the third or fourth flick the engine should keep running
and within 25 to 30 seconds it should reach 1500 RPM or so. Keep your hand on the jacket and as soon
as it becomes really warm, 30 to 40 seconds, remove the flame.
If all is successful, fit the engine to a baseboard with a water tank and connect this up to the stubs on the
jacket. Note the bottom stub is shorter to reduce the sharpness of the bend in the plastic pipe. Fill the
tank with water and, fired by a simple spirit/alcohol lamp, the engine should run indefinitely ------
Finally, I must apologise for the nit-picking detail in this text. Most hot air engine builders will admit to
having built the occasional dud and I can certainly claim to have built my share. These failures (my own
and others) were sometimes due to a silly little detail and I have attempted to recall and overcome these
and forestall others in this write-up.
NOTES :-
The Model Engineering Web Site gives a list of suppliers at:-
http://easyweb.easynet.co.uk/~chrish/ads-
Sterling Stirling (Julian Wood) is at:- 15 THE PILL,
CALDICOT,
NEWPORT,
GWENT.
NP6 4JH - UK
Tel 01291-421095
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (12 of 14) [8/18/2003 9:07:31 PM]
FizTextx
BA and BSF threads have been specified simply because screwing tackle in these sizes is readily
available from model engineering suppliers (and others) in UK. Some folk may think the use of the odd
BA sizes rather strange. However I agree with Stuart Turner that 7 BA fitting 3/32" and 5 BA fitting
1/8" is rather convenient. There is no reason why other threads covering the same or similar diameters
should not be used - whatever taps and dies happen to be available in your part of the world.
If you don't posses a reamer its a very easy job to make one from the same diameter of silver steel that
you intend using for the shaft. Cut a 4" length, put a small chamfer on the end and file a diagonal flat as
shown in the sketch. (Sheet
Hit Back to return) Harden the end and then temper to straw. Check that
the rod is still straight by a couple of very light strokes on an oil-stone with the flat upwards and then
turn it over and stone the flat face to a high finish. Drill the hole 4.7mm (0.0025" undersize) then hold
the reamer in the tailstock chuck with the flat upwards and enter just the chamfer in the drilled hole
before starting the lathe and pushing it through gently. Withdraw and restart several times to clear the
tiny pieces of swarf but don't stop the lathe with the reamer in the hole. These reamers work well in
brass, gun metal and cast iron. They do NOT work with drawn phosphor bronze and I've not tried them
in steel.
To avoid making reamers, a very close fitting hole can often be drilled by beginning with the undersized
drill and then following this at low speed with a nominal sized drill which has seen sufficient use to just
dull the extreme outer points/edges. Try it on a piece of scrap first.
Silver Steel (UK) = Drill Rod (USA) High Carbon Steel, centreless ground to close limits and usually
available in 13" or 1 metre lengths.
Mild Steel = Low Carbon Steel and comes in two varieties, Bright (BMS) or Cold Rolled and Black or
Hot Rolled.
Bright Mild Steel is clean to handle but has built in stresses which can cause slight distortion after
cutting, it also tends to crack if bent sharply. In rod form it is always a thou or two under its nominal
size. Free Cutting Mild Steel (FCMS) or Leaded Steel, containing a small percentage of lead, cuts
smoothly and turns to a high finish.
Gudgeon pin (UK) = Wrist pin (USA)
Oil very sparingly with the lightest oil you can find and normally before a run just one drop each will
suffice for the piston and the displacer rod. However, after some use the big-end will probably
appreciate the change to a thicker oil. Unfortunately it will throw this in all directions and if/when a drop
finds its way into the cylinder it can cause a mysterious drop in performance. Strip, clean and re-
lubricate the piston with its single drop of light oil.
Copyright FMCollins 30/06/99 - Mick Collins, who will attempt to answer any questions at:-
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (13 of 14) [8/18/2003 9:07:31 PM]
FizTextx
http://www.btinternet.com/~sylvestris/fizgig/FizText.htm (14 of 14) [8/18/2003 9:07:31 PM]
Document Outline
- btinternet.com
Wyszukiwarka
Podobne podstrony:
Ebook Stirling Engine Homemade From Soup Can
Two Cylinder Stirling Engine
Low Temperature Differential Stirling Engines(Lots Of Good References In The End)Bushendorf
Coffee Cup Stirling Engine Instructions
Performance optimization of Stirling engines
Buid A Can Stirling Engine
ANALYSIS OF STIRLING ENGINE PERFORMANCE
An experimental study on the development of a b type Stirling engine
(make) Stirling Engines Diy
Two low temperature Stirling engines, WSZYSTKO O ENERGII I ENERGETYCE, SILNIK STIRLINGA, WIADMOŚCI
Design and performance optimization of GPU 3 Stirling engines
(ebook pdf) Engineering Numerical Analysis with MATLAB FMKYK6K23YGTTIMP3IT5M4UO4EKLFJQYI4T3ZRY
Stirling Engines DIY(2)
eBook DIY Woodworking Plans Guide To Wood Finishing
(make) Stirling Engines Diy
Roelf Meijer Co Gen System With Stirling Engine Patent (#5074114 1991)
working theory of Stirling Engine
więcej podobnych podstron