Model of the Month October 2008
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
Tony Bird
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