Heisler Boiler Construction IV
Nelson Riedel, Nelson@NelsonsLocomotive.com
1/20/2014, last updated 01/26/2014

The Heisler has been in operation for several years and most the bugs have been worked out.  It was finally time to finish the project.   In this page we describe

  • Steam Dome

  • Sand Dome

  • Boiler Jacket

  • Changes to the steam supply pipe at rear of steam dome

  • Changes to the throttle linkage 

  • Smoke Box Door Hinge & Dogs

Sand Dome:   The sand dome uses Allen Models aluminum castings part # M221/2.  There are two castings, the base and the top.   The user must supply a tube that fits between the two pieces.  A ~2.75" length of 3" steel pipe with the OD turned down from about 3.5" to about 3.35" was used for the tube. A short stub was turned on both castings such that the tube was a snug fit over the stub.   A  plate was welded across the tube and the tube was secured to the bottom casting with a couple 4-40  screws as shown in the photo.  Note that the tube appears to have part of the side cut out in the photo -- that is an illusion possibly caused by part of the flash being blocked.  The dome is secured by a 3/8" threaded rod through the center hole of the plate into a nut welded onto the top of the boiler; a coupling nut is used on the upper end of the rod.  A second threaded rod is secured to the top casting as shown in the photo.   That second rod with top attached is screwed into the upper end of the coupling nut.    

Changes to pipes out of rear of steam dome:  In the original design and construction the two 1/4" NPT couplings at the bottom rear of the steam dome were fitted with 3/8" compression adapters, one for a 3/8" tube to supply steam to the steam manifold and the other to house a O-Ring seal for the 3/16" throttle rod; see  Boiler Construction II.  These compression adapters were too bulky, the holes required through the  steam dome cover would be too large and there was insufficient room for the boiler jacket and insulation to slide underneath.   These problems were solved by inserting 1/4" NPT to 1/8" NPT bushings in the couplings in the steam dome and screwing 1/8" NPT stainless pipe nipples into the bushings, see photo above.     The upper pipe in the photo is the steam supply line.  On the very left of the photo a piece of hex is visible; the hex was silver soldered to the pipe to provide a means to install and remove the pipe from the steam dome.  The end of 1/8" pipe was turned down to 3/8" just beyond the hex so that it would fit into the 3/8" tube compression fitting used in the previous arrangement.   (Compression fittings are large but much smaller than and less expensive than unions and seem to seal better.)  The 3/16" throttle rod of the original design was too stiff to easily flex as necessary between the coupling in the side of the steam dome and the throttle lever.  The solution was to reduce the throttle rod to 1/8" diameter to make it more flexible.  The rod is run through the 1/8" pipe which serves both to limit the flexing of the rod and to move the bulky compression adapter used to hold the seal to the rear and into the cab.   The photo below shows the rear part of the 1/8" pipes.   This is a much improved design; wished I'd thought of it the first time.       





Steam Dome Cover: The steam dome cover uses Allen Models aluminum castings part #M219/2.   The center part of the cover is a ~2.5" length of 5" OD 4.5" ID aluminum tube purchased separately.  Very short stubs were turned on the castings that were a snug fit to the ID of the tube.   A slight taper was turned on the outside of the tube to match the slightly smaller OD of the upper casting.  The  lower casting was attached to the tube with 4-40 screws as shown in photo above.  (Note that part of the side of aluminum tube appears to missing in the photo; that is an illusion.)  The slots for the pair of 1/8" pipes extending out the back were then cut through the bottom casting and part way into the aluminum tube.  The cover is held in place  by a pair of screws through the top into threaded spacers secured to the top of the steam dome as shown in a previous photo.   The cover in turn holds the lower part in position.           

 Boiler Jacket:  The jacket was made of 24 gauge (.024") stainless steel.   It was cut and rolled on a 3-in-1 brake, shear, rolling tool.   (Shearing the stainless was hard on the shear blades and dulled them to the point that they need to be replaced - replacement at ~$80/blade appears to be cheaper then having them sharpened.  26 gauge would have probably worked as well and been easier to cut.)   A double layer of 1/8" self adhesive cork sheets (McMaster) were used for lagging.  Spacers/supports for under the jacket were made of ~ 3/4" wide rings sawed off the scrap from the fire box tube (rounded part of boiler) and 1/4" square bar stock for the flat section parts.  These spacers were positioned under the jacket joints and just in front of the cab.  (The very front of the jacket rests on the rear of the smoke box tube.)    The spacers were tack welded to the boiler - in hindsight, high temperature epoxy would probably been a better alternative than welding.          

 The assembly process was to first join the boiler and the smoke box with  4 - 1/4" FH screws.   The screws go though holes in the rear part of the smoke box tube into threaded holes in the boiler tube.    (The holes are in front of the front tube sheet so no leaks but behind the front edge of the jacket so they are not visible.)   Next, the spacers were attached.   Next, the cork sheets were cut and pressed into position between the spacers.     The stainless jacket pieces were then cut and attached.   A pattern of heavy paper was made for the center section to help in the cutting and fitting.  Unfortunately, no pictures were taken of these steps.     

Photo above shows the finished jacket.   The flange under the boiler is about 1/2" wide and the screws are 1" long 6-32.   Longer screws were used in a couple spots initially until the jacket was pulled tight.   It was a challenge to figure out a way to pull the rear section tight.  The lower part of the jacket over the side of the firebox is behind the slotted frame stiffeners where there is very little clearance and virtually no access.  The solution was to make the parts of the jacket behind the stiffeners separate pieces secured with a couple  button head cap screws at the bottom.   3/16" square brass bars were attached to the top of the flat part and the bottom of the rounded part with 4-40 FH screws through the jacket into the bars.  Three 4-40 screws through clearance holes through the upper bar into threaded holes in the lower bar tied everything together and permitted the jacket to be tightened down.  The bars and gap are behind the upper frame bar and the upper part of the stiffener and are not noticeable unless one is standing on their head.  The walkways hide the top of the brass bars.   The bands are 0.020" X 1/2" stainless strip stock (McMaster).

  Smoke Box Front:     


The two photos above show the smoke box front after the hinge and dogs have been added.  The upper photo was taken just after the hinge and dogs were attached.   The lower photo was taken after the locomotive had been operated for about 20 hours with the hinges and dogs in place --- and it looks suitably dirty.   This second photo was taken from a different angle to show the depth of the hinge and dogs.  Originally, the hinge pieces were intended to be made from 1/4" thick bar stock.    After looking at the actual thickness of the 1/4" stock held against the smoke box front it was decided to cut the width to 1/8' bar stock.  The drawing in the Boiler Design III page had been updated to reflect this change.  1/8" wide slots were milled into the cast iron smoke box front for the hinge parts which were secured with high temperature epoxy. 


Smoke Box Door Dogs:  The design of the dogs in the drawing above was settled on after several trials of slightly different dimensions.    The dogs were machined on the ends of  length of 0.25" X 0.22" bar stock milled down from 0.25" square stock.   The first step was to make rough saw cuts for the larger notch on the end.   That big notch was smoothed on the mill and the second smaller notch cut on the mill.    The hole was then located and drilled.   Next, the bar was held in the vise and the edges rounded to resemble a casting using a small sanding drum in a rotary tool.    The dog was then sawed off the bar stock and the saw marks smoothed with the sanding drum.   It takes a while to get setup to make the first one, after that it goes pretty quickly.  I made a dog at each end of the bar to speed up the process.   The dogs are secured with 4-40 studs (held in place by Loctite)  and nuts.

The number plate shown in the photo above is discussed in the Finishing Details section.

 This wraps up the description of the construction of the boiler fittings.    


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