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:

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.

Cracker Boiler


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.


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.


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.


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.


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.


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

Tony Bird