Heisler Boiler Design III
Smoke Box Front, Smokestack & Firebox Door
Nelson Riedel, Nelson@NelsonsLocomotive.com
12/30/2008, last updated 02/27/2010

The drawing above shows some of the holes that must be drilled in the smoke box. 

The 2" diameter hole in the top is for the smokestack.   Additional holes are required to secure the smokestack to the smoke box.  The smokestack can be used as a template for those holes.       

The 13/16" holes are for the steam supply lines to the cylinders.   Four additional holes are required to attach the steam supply plates over these holes.   The steam supply plates can be used as templates for these holes.

The 1.25" hole in the bottom is for the exhaust nozzle to pass through to the saddle.  Additional holes are required to pass the screws securing the exhaust flange the saddle.   

Smokestack: The MRSR91 smokestack is shown in the photo above left.    I decided to use a casting  from Allen Models, part number M211/1.  The casing is aluminum and easily finished with a file and Emory paper on the lathe and on the belt sander.  The approximate  finished dimensions are shown in drawing above right.  

Photos of the Cass 6 and MRSR91 smoke box fronts and doors are shown on the right.   They seem to be identical.    I have not been able to find a suitable off-the-shelf casting for the smoke box front and door so it was decided to make one using a 8" diameter 1.5" thick cast iron disk from McMaster-Carr as shown in drawing above.    The door and front will be made as one piece.  The hinge is not functional - for decoration only.   The hinge will be made from flat bar stock and held to the casting with screws from the rear.   The design of the door dogs is deferred until I get a better close-up photo and measurements (a good excuse for a trip to Cass). Seven of the holes around the outside are tapped 4-40.  These will be fitted with studs and nuts for decoration.   The remaining five holes will be used to attached the smoke box front with 4-40 screws into threaded holes in the end of the smoke box tube.

Fire Box Door: The MRSR91 fire box door is shown in the four photos above.   The door incorporates a draft vent with a damper controlled by the small lever on the left side.   The draft air enters from the bottom.  I assume that the plate with holes facing the fire box is a grate to minimize flame bursts from  going through the door.

The fire box door base squares up the surface around the weld fillet. 

This drawing shows how a suitable door can be made using a piece of square tube and a piece of round tube. 

The round tube (or round bar stock) is machined to fit with the base and the square tube.
The square tube is cut to match with the other pieces.
The rear plate is cut to match with the square and round tubes.  Small brass screws on the back side are used to hold the three major pieces together for silver soldering.
This simple latch is silver soldered to the round tube
This hinge is screwed and then silver soldered to the round tube.
The hinge base is attached to the door base

A damper plate must be cut to fit inside the square tube and handles for the latch and damper must be designed.  These designs were done after the rest of the door was fabricated.  See the Boiler Constriction I page for more details of the fabricated door.