Model of the Month October 2008
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Model of the Month October 2008 |
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A pair of Crackers by Tony Bird
Cracker was designed and built by Ernest Glaser and Felix Heufke in 1996 and 6 free drawings are available on the Internet at: http://home.iae.nl/users/summer/16mmngm/Articles_htms/Cracker.htm.
Two Crackers have been made. For the first most of the drawn
dimensions were used only being altered to suit the materials available and my
construction techniques. If the drawings are followed exactly I am sure
that the locomotive built will perform as well as the one made, which is very
good for such a small locomotive.
The techniques used and described in the
construction are certainly not the only way and possibly not the best way that
Cracker could be built, but they worked for me.
Boiler
construction.
The boiler was made from a 35mm diameter copper tube cut into three
lengths; 85mm long for the boiler barrel, 20mm long for the smoke box and 40mm
long for the tube plates. A length of 15mm copper tube 78mm long was used
for the flue. The ends of all the tubes were trued in a lathe and the
barrel was drilled for its two bushes and the chimney.
The other two 35mm
diameter copper tubes were cut through their length and annealed. One was
flattened and cut into two 40mm lengths to form the tube plates. . They had
their corners cut off before being formed over a steel former to make the tube
plates. These plates had their ragged edges turned off and were turned to
fit the barrel in the lathe. They were then drilled and bored offset in a
4-jaw chuck for the flue tube to go through them.
The other tube had a hole drilled in it for the chimney before being cut
and annealed. It was then sprung out to go over the boiler barrel and
projects 2mm beyond it to form a recess for the false smoke box door. (Different
from drawing)
The boiler was then assembled and silver soldered together and tested for
an hour at 80psi. A standard filler valve is fitted.
Chassis.
One frame was marked out and cut to shape with a piecing saw from 1/16”
sheet steel. Pilot holes were drilled for the axles along with tight
clearance size holes for the screws that hold the frame to the buffer beam.
Another piece of 1/16” steel with a straight edge was lined up with the cut
frame’s straight top edge and glued to it with Loctite Stud Lock. Holes
were drilled through the buffer beam holes of the frames and the frames were
bolted together. While together with the pilot holes as guides the holes for the
4 axle bushes were drilled through both frames. The second frame was cut
to shape using the first frame as a guide and both frames were filed to shape.
Then they were marked for outside and front before removing the bolts and
separating by heating. After cleaning up they were blued. The axle
bushes were glued into place using Loctite Retention. These bushes came
from IP Engineering but could easily be made.
The buffer beams weren’t milled they were each made from two pieces of
steel bar machined to size in the lathe, glued and riveted together before
drilling a hole for the couplings.
The set up to drill the buffer beams from the frames was as follows.
Axles (with no wheels) were fitted into their bushes in the frames and were
sandwiched with two 1” wide pieces of steel held together by screws between the
frames. The buffer beams were then lined up and glued with Stud Lock to
the frames and being held in place by strong elastic bands going along and
across the chassis while the glue set. With the elastic bands removed the
chassis was clamped to a piece of wood which held it vertical in a sideways
position for drilling the screw holes using a pillar drill. First a light
drill with a clearance drill followed by the tapping drill. Before
separating the buffer beams the holes were tapped 8BA. This system has
been found to keep the frames square and four wheels on the track without the
complication of clamps, which can move in use. Clean the taps after use as
any Stud Lock left on them is very difficult to remove if it is allowed to set.
The smoke box door has been made and is a push fit in the boiler.
An old oak draw front was used to make the boiler supports, as no paxolin was
available. The boiler also sports a steam dome made from a 22mm copper
stop end which had been domed and polished, it was put away ‘safe’, lost then
found and used on Cracker Mk2.
Gears.
The wheels and axles sets used were I P Engineering’s ‘0’ gauge 24mm
diameter. These were unaltered the width between the frames being altered
to accommodate them and their bearings.
The four gears were from Hobby’s being: one Ref.EB1 10 teeth 5mm diameter
and three Ref.EB7 40 teeth 20mm diameter. These gears had to be drilled
and reamed from 3mm to the axle’s 1/8” diameter and drilled and tapped for grub
screws before removing and replacing one of the wheels from their axles to fit
them. The pinion on the crankshaft was glued on using Loctite Retention
the spacers being 5/32” K&S brass tube left loose. The intermediate axle
between the wheels also used the same tubes as spacers.
The fly crank is not to the drawings being balance and held to its shaft
with a grub screw. The port block is also not to drawing and will be
described in the cylinder section. Note unaltered 22mm copper stop end
used as a steam dome, still hoping to find domed one.
Cylinder
and Port Block.
The cylinder and port block are different to the drawings but the
dimensions are the same. Alterations: First the cylinder assembly, to drawings
and construction but with added cut away on port face to reduce friction.
Piston, to drawings with ‘O’ ring added. Crank, made as fly crank and
secured by grub screw instead of being glued or pushed on. Port block,
major differences, made thicker so inlet and exhaust pipes go straight into
block. As drawn seemed a little complicated.
Cylinder
tube.
A piece of hexagonal brass rod was cut over length and one of its flats
marked to line up with No.1 jaw of a three jaw chuck. In the lathe one end
of the rod was faced, centre drilled and then drilled slightly undersize for the
bore for half its length. The rod was turned around in the chuck lining
the marked flat up with the No.1 jaw. It was faced, turned to length,
centred, drilled through and reamed to size. A wooden lap was made and the
holes were first lapped with fine valve grinding paste and finished using a new
lap charged with ‘Brasso’ (A liquid used for polishing brass which is slightly
abrasive).
The bored rod was mounted on a shellac rod chuck between centres on the
lathe and its outside turned to size. The resulting tube was mounted
tightly on a turned piece of dowel whose other end was held in a vice. The
tube was marked out for the cut-outs, which were made with a round and a flat
file. Filing the wood and brass away together. With the tube removed
from the dowel the rough edges of the cut-outs were removed and the tube was
lapped again with ‘Brasso’.
The cylinder port face was made from a larger piece of hexagonal brass
rod, which was bored through to the OD of the tube, using the same technique as
used for the tube, but without the lapping. The rod was then mounted
sideways in a 4 jaw across its flats and its protruding pointed angle turned
nearly through to the bore. It was turned around and it’s opposite side
also removed. It was gripped by its freshly turned faces and end set
square so that the hole for its pivot screw could be drilled and tapped (note it
is off-set). The port face was turned to thickness from the bore and the
cut-outs made. For a twin cylinder engine the same would be done to its
other side. Removed from the lathe it was cut lengthways using a piecing
saw and cleaned up with a file, this gives one or two cylinder port faces
The
port face was bound to the tube and lined up before soldering them with
plumber’s soft solder. The nearly finished cylinder was lapped with ‘Brasso’
for the last time pushing the cylinder up and down the lap as the piston would
do.
Port Block.
The front of the block was made from 1/16” sheet brass to the drawing but
5mm higher. A piece of 4mm brass was silver soldered to its top end to
give thickness for the inlet and exhaust pipes.
Piston.
The piston was made from stainless steel in a 3-jaw chuck on one setting.
Turned to diameter then the slot between the piston and the cross head cut,
followed by the slot for the ‘O’ ring. While still in the lathe the flats
on the cross head-made with a file. Removed from the lathe the hole for
the crank pin was drilled in the crosshead. The nearly finished piston was
cut from its rod and faced to length in the lathe.
Assembly.
A jig was made as shown on the drawing which was then used to drill the
inlet and exhaust ports half way through the port block. The same jig was
bolted to the cylinder to drill its port hole through to the bore. Holes
were drilled the port block for the inlet and exhaust pipes to connect to their
relevant port holes. The inlet pipe is in the top of the block and the
pipe from the steam dome soft soldered in. The exhaust pipe comes out of
the right hand side of the block and is a push fit.
A cylinder cover was made and glued into the cylinder with Loctite
Retention. To finish the engine a bolt and spring was used to hold the
cylinder to the port block. Take care that this threaded rod does not
deform the cylinder’s thin wall by bottoming on it.
Air and
Steam Tests.
With the boiler and chassis finished Cracker was run first on air then
steam. While running on air the tension on the spring holding the cylinder
to its port face was adjusted so the cylinder lifted off the port at about 25psi
so it could work as a safety valve. For the steam test a pencil blowlamp
which was about the same size as the burner to be made was used to fire the
boiler. The steam test was very successful the burner kept the engine
running until the boiler was out of water which took about 10 minutes.
Gas Tank & Burner.
The gas tank was made as drawing. The gas valve seemed a bit
complicated going through the gas tank so a valve of the same type that I use as
a regulator or gas valve was used with a copper feed pipe to the burner.
The burner from the pencil torch had been so successful was used instead
of making one.
Finished.
So Cracker was finished. It had been steam tested and all that was
left to do was a track test. So on a very damp Saturday morning Cracker
was taken to the Cardiff Model Engineering Society’s garden railway. It
was steamed up in the clubhouse and discussed with other members while running
on blocks. Still running it was then taken to the garden railway where it
did 6 circuits of our 150-foot long track before running out of water. The
gas tank far outlasts the water but as it has a filler valve this isn’t a
problem.
Cracker MkII
With the success of Cracker both in performance and interested created
at exhibitions it was decided to build another.
Some bits were stock items:
IPE wheels, gas jet, gas valve, Goodall valve and couplings. Other parts
were left over from Cracker’s construction, there had been enough 35mm tube to
make two boilers so extra plates had been flanged when making Cracker. The
system used to make the port block created two of them. Only one had been
used not both which are usually used on most locomotives. Extra buffer
beams had been machined when making Cracker and enough 1/16” sheet steel was
available to make the side frames and footplate. The polished copper steam dome,
which had been ‘lost’ also, came to light.
There were only two areas where things could be altered or improved on
Cracker. One was self inflicted, the fitting of an ‘0’ ring on the piston,
this meant every time the boiler was topped up it was a good idea to lubricate
the cylinder as ‘0’ do not like to go without oil. As designed this
probably wouldn’t be necessary. The other was the burner it worked very
well but was difficult to light when fitted in the flue of the boiler this had
been got around by making it removable. The burner’s gas tank was also a
bit unsightly on the footplate.
So with Cracker Mk2 improvements were addressed. First a lubricator would
be fitted. The designers of Cracker had had similar problems with their
burner so had designed and built a poker type to replace it. This was
copied from drawings supplied by Felix Heufke and the gas tank was positioned
between the frames.
Then things got a bit out of had and the original design concept left
behind, a pressure gauge, regulator and safety valve was fitted along with
provision to fit a gauge glass as yet to be fitted.
The frames had to be lengthened by 10mm to accommodate the gas tank but
other than this the general construction was the same as used on Cracker.
With its higher chimney and larger cab I think Cracker Two’s lines are quite
pleasing.
All in all both of these little locomotives were fun and simple to make
and have a surprising good performance.
Conclusion
I do not know of Ernst Glaser and Felix Heufke’s intentions in designing
Cracker but I think a good guess would be that it was designed as simple
locomotive using the minimum amount of parts which was quick to build. If
this was the case I think they have succeeded.
Cracker when run in will pull five or six light wagons and even managed
to push cracker Mk2 until its cylinders were fitted. Its speed is the fast
end of slow the lack of regulator doesn’t worry it at all and the
cylinder/safety valve works well. I chose to alter the construction of
some of the components but if the drawings are followed it will be just as
successful.
Cracker wouldn’t be a bad first loco. With so few parts a result
would be seen quite quickly also like the loco described some parts could be
purchased. A larger version using a single double acting cylinder (Mamod
or I P Engineering) with all the control fittings could be made and it would be
surprising if it didn’t work very well.
If I can be or any help to anyone
interested in making a Cracker email address is
gaynorandtony@btinternet.com
Click here for September 2008 'Model of the Month' - NWNGR 'Gowrie' by Nigel Town
Click here for August 2008 'Model of the Month' - Clogher Valley Steam Tractor by Neil Ramsay
