# Building a Cracker



## MarinusK (Jun 24, 2015)

*Building a Cracker by Marinus Kruger*


Hi all,

I have been quite busy the last couple of weeks building a cracker loco from scratch. 
I will be doing a full write up on making the parts, going day by day.
Here's the progress reports of the days that I've spent working on it.

*Day one:*

Gears:
I first made up some gears in the lathe using the plunge cut method .I used indexed piece of paper the length of the circumference of the chuck marked out at 40 points and glued it to the chuck. The small pinion gear has 10 teeth, so I just used every fourth mark.They were made from bronze bar and the boss is made from 8 mm brass and soft soldered in. After soldering the were cleaned up with some thinners and put in the lathe to back off the two sides. The last step was to drill and tap the bosses M2.

Gear Shafts:
The gear shafts were made from some 4 mm round steel instead of 3 mm, because of availability. It was marked out, sawed off and faced at both ends.

Flywheel:
The flywheel was made from some 35 mm bronze bar. It was first turned to size and faced then it was drilled 3.2 mm and parted off. It was then put back in the lathe and backed out both sides. Lastly it was drilled and tapped M3.

Boiler:

The boiler shell was made from some 35 mm copper tubing with 1 mm wall thickness. It was put in the lathe, squared up the end, turned down to 34 mm up to the smoke box and parted off. 
Next was the boiler end plates made from 1 mm wall copper pipe, annealed and rolled flat. I used the dolly and die method to form the end caps. The holes for the flue was then drilled and the flue was cut out of some 14 mm copper tube as well as the chimney.

*Day two:*

Boiler parts:

The boiler bushings was made from some gunmetal bronze and the boiler was silver soldered at one go, using an oxy- acetylene torch.
After the boiler was pickled it got sandblasted and bushings were threaded. The boiler then got hydro-tested up to 140 psi, and held the pressure for about 15 minutes.

Miscellaneous parts:

The smoke box door was made from some brass and the buffer beam from a piece of scrap gunmetal.

*Pictures*










*Day three:*

Cylinder:

The cylinder was made from a piece of phosphor bronze, squared up in the lathe and put in the 4 jaw chuck to machine the round end and to bore the cylinder to 8.2 mm. It was then transferred to the milling machine to cut out the sides with a 6 mm end mill. After deburring the inside the port hole in the cylinder was drilled as well as the hole for the 2 mm pivot screw that got tapped M 2. The last few thing that needed to be done was to round the one side of the cylinder and polish the cylinder bore.

Port block:

The port block was made from gunmetal bar. A suitable piece was squared up in the milling machine and the sides milled. The back was cut away to allow for fitting into the chassis and the round part was cut with the boring bar in reverse. All the holes were drilled and the inlet and exhaust was tapped M3. 

*Pictures*











*Day four:*

Gas tank:

The gas tank was made from gunmetal bronze and copper tubing. I didn't want to use any of my bar stock, so I got a big round piece, about 20 mm thick and used a hole saw to cut two 26 mm dia. pieces. It was then chucked in the lathe, faced and turned to size. The lower part of the gas tank was very easy to make, turn 10 mm of the part down to 8 mm, turn around drill 2.5 mm and tap M 3. The top part was a bit more difficult, as the part to house the filler valve had to be 5 mm off-center and I couldn't chuck it on the 1 mm flange, so I drilled the hole for the filler valve, got a suitable rod and loctited it in place. I then used the tail stock live center and slowly began cutting it, took a while but got it done.

The copper body was made from 22 mm copper pipe with a 1 mm wall thickness. The hole was drilled using a 8 mm slot drill and the two end pieces was inserted to stop the copper tube from distorting. 

The gas control valve body was also made from gunmetal bronze. I had previously cut out a square block, 10 mm x 10 mm and used my homemade driving dog to make some round pieces. 

The silver soldering was done in two stages, first the lower part was silver soldered in and pickled afterwards. Then the top part and the valve body was silver soldered in. After it was pickled for a few hours it was sand blasted and the inside got washed out. 

The filler valve has a tread size of 5.4 mm and a 0.5 mm pitch, so I had to make a tap from a 8.8 steel bolt.

Boiler saddles:

The boiler saddles were made from bakelite. The boring bar was used to cut the radius for the boiler and just cleaned it up on the belt sander.

Steam dome and goodall filler valve:

The steam dome was made from 12 mm HEX brass bar and threaded M 8 to fit the boiler bushing.

The goodall filler valve was made from 10 mm HEX brass bar and threaded M 6 to fit the boiler bushing. 

*Pictures*


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## pickleford75 (May 3, 2012)

Good job.... so far your workmanship looks first class... keep us posted on your progress


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## xo18thfa (Jan 2, 2008)

Nice work. Cracker is a great engine. You will enjoy running it. I see you have not done the burner yet. It works pefectly

I did a Cracker scaled up to Ga 1. Great runner. Ended up doing a fuel car, just for looks


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## MarinusK (Jun 24, 2015)

Thank you pickleford and Bob 
I have already made a burner, the one included in the drawings of cracker. It works quite good.
I will see if I can post the next three days later today.

Marinus K


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## Joe Johnson (Jan 2, 2008)

Thanks Marinus!!


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## Phippsburg Eric (Jan 10, 2008)

Well done! I look forward to seeing more!


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## bille1906 (May 2, 2009)

Nice work Marinus and fast too
Can you take a photo of the cutting tool you used to cut the gears in the lathe


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## MarinusK (Jun 24, 2015)

Thank you Joe, Eric and Bill.

Here's the photo as requested:


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## MarinusK (Jun 24, 2015)

*Day five & six:*

Frames:

The frames were made from 2 mm mild steel sheet instead of 1.5 mm because of availability. The outline was marked out 2 mm oversize so that it wouldn't end up too small. I then cut it out with a plasma cutter and squared it up in the milling machine using a 4 tip fly cutter and cut it to size. The recess was cut with a 10 mm end mill down to half it's width. The top hole for the engine frame and bushing were marked out and center punched. It was then put in the milling machine with a broken 3 mm drill bit sharpened to a very small point in the chuck to locate the other holes using the x and y dials. The sharpened drill bit was centered on the previously center punched mark and carefully moved down 12.5 mm, marked out, moved 20 mm right, marked out, moved 40 mm left and marked out. After marking out the holes were center drilled and finally drilled 6.5 mm. The same was repeated on the other frame afterwards. All the edges were cleaned up with some emery paper. 

Running plate:

The running plate was made from 2 mm mild steel as well. The outline was marked out 2 mm oversize and cut out with the plasma cutter. It was squared up in the milling machine and side slots milled in with a 10 mm end mill. All the holes were marked out center punched and drilled. All the edges were cleaned up with some emery paper.

Buffer beams:

The buffer beams were made from 10 mm mild steel flat bar. First a piece of of 10 mm flat bar was marked out 10 mm to cut out square pieces, then cut to size and squared up in the mill. The drawings call for M2 screws to secure the buffer beams to the frames and running plate, but instead I made it M3, because my M2 taps are carbon steel and won't be able to thread such a deep hole in steel. The recess on the ends were milled away using a 8 mm slot drill and some cutting fluid. The securing holes were drilled 2.5 mm to tap M3 and the buffer's 3 mm. After the part was machined it was cleaned off on the belt sander.

*Pictures*


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## MarinusK (Jun 24, 2015)

*Day 7:*

Burner Body:

The burner was built up from brass and bronze. A piece suitable for the big end was turned down to 13 mm to fit the flue tube. The inside was bored to a dept of 12 and the remaining 2mm was drilled 6mm the top was then filed flat for secondary air. The smaller part at the back was cut from 6mm brass rod drilled 3.5 mm trough. The end where the jet fits was drilled to 5mm. The two parts were then silver soldered and cleaned up using a wire brush. The part was then brought over to the milling machine and the air holes were drilled at 4 locations around the "tube". 

Burner Nozzle:

The burner nozzle was made from a piece of 10mm brass. The piece was turned down to 9.5mm for a press fit in the body. The recess in the middle was cut using a parting tool and while still on the remaining stock it went over to the milling machine where the 8 holes were drilled. I drilled the holes without marking out any locating and without a rotary table, just used my eye sight.

Burner Jet:

The burner jet was made from a piece of 6mm brass bar. The part was turned down to 5mm and with a shoulder left at 6.5mm and the back part was turned down to 3mm with a shoulder.
The part was then drilled from the back with a 1 mm drill and left a 1mm wall at the end. The jet was then put in the milling machine were it was "drilled" 0.2 mm with a 1mm drill that had been ground to a very sharp point. 

The nozzle was press fitted into the big end and the jet just pushed into the back end. The burner was tested using propane and it worked great outside the flue as well as inside.

*Pictures*


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## MarinusK (Jun 24, 2015)

*Day 8:*

Dome:

The steam dome was made from 21 mm bronze bar. It was turned down to 15 mm, 13mm from the end with a 3 mm radius HSS bit. The end was then filed to a radius while the machine is running, DO NOT TRY THIS CLOSE TO THE CHUCK, YOU CAN GET SERIOUSLY INJURED!! The dome was then parted off and wrapped with a piece of paper to protect in when put in the chuck. The dome was drilled 8mm and bored 14mm to a depth of 4mm and the end rounded off. The part was then put in the milling machine, protected with wooden blocks, cut the radius of the boiler with the boring head. The dome was then filed around the bottom to suit the radius that just had been cut. It was later on sanded and polished.

Chimney:

The chimney is built up from two pieces of scrap brass. The chimney body was made from 15 mm brass bored to 13mm. The top ring was made from a piece of plumbing fitting turned down to 17mm filed round and parted off. The two parts were then silver soldered together. After silver soldering the boiler's radius was filed at the bottom and the chimney was pushed onto a taper piece of steel and put in the lathe to sand and polish the chimney.

Cab:

The cab was made from 0.7 mm brass sheet. The cab was marked out and cut out using tin snips. the radius around the boiler was cut using the boring head and the piece supported using wood. The window holes were drilled and the edges rounded off on the belt sander. The top part and sides were bent in the milling machine vice. The lower support angles were made from a piece of scrap bronze milled into an angle and cut to length. It got drilled 2 mm and soldered to the cab. 

*Pictures*


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## MarinusK (Jun 24, 2015)

*Day 9:*

Burner support:

The burner support is made from a small piece of bronze. I made it just to lock the burner in place. First a piece of 4 mm bronze was cut out to size and sides cleaned up. The 6 mm hole was then drilled and the top and bottom holes that was drilled 1.5 mm and tapped M 2. The top edges were given a radius on the belt sander. The piece had a deep mark on the one side that if sanded clean the part would've been too small. I then decided to mill it away at a depth of 0.2 mm. It was then sprayed matte black and the part protruding was sanded clean using fine sandpaper on a granite table.

The top locking screw is made from 2 mm bronze brazing rod. The thread was cut with a M 2 die and the part was bent and cut off.

Piston:

The piston was made from a scrap piece of gunmetal bronze bar. The part was turned down to over 8 mm and the con rod part was turned down to 3.5 mm. The piston was then made a press fit in the cylinder and the piston got sanded with a wooden block with some 1000 grit sanding paper until it was a sliding fit in the cylinder, the same was done with the con rod end. The 2 mm hole for the crank pin was drilled and the two sides were filed flat and cleaned up with some sanding paper.

*Pictures*


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## MarinusK (Jun 24, 2015)

*Day 10:*

Wheels:

The wheels are made from a piece of mild steel bar. The piece was turned down to 26 mm and the rough shape was turned. The wheel profile was then machined and the boss at the back was cut using a parting tool, taking light cuts. After the recess at front was cut with a radius HHS cutter it was drilled 4 mm and parted off, this was repeated 4 times as there are only 4 wheels. The bosses at the back was drilled and tapped M3. The recess at the front was then sprayed the same black as all the other parts.

*Pictures*


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## MarinusK (Jun 24, 2015)

*Day eleven:*

Crank assembly:

The crank assembly was made up from stainless steel and brass. The crank was cut from brass bar turned to 13 mm and drilled 2.5 mm. The piece then got the crank pin hole drilled in the milling machine. The crank disc then got parted off and the two sides were milled away with an angle. 

The crank shaft was salvaged from a broken CD player's slider shaft. The shaft is very hard so I used it as a reamer as well. The shaft got press fitted into the crank disc and a suitable 2 mm piece of steel was press fitted for the crank pin.

The cylinder block was reamed with the crankshaft as well as the back support bushing while it was assembled on the frame.

Steam delivery tube:

The steam delivery tube is made up from brass and copper. Two small rings had to be made from brass. The copper tube and brass rings were silver soldered together and after it was cleaned up with some files and sanding paper it was bent to shape. 


All the brass and bronze parts were cleaned up and polished. Some of the parts received a layer of clear coat.

*Pictures*





























_*Video of engine's first steam run:*_


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