Heisler Frame Construction Part I
Nelson Riedel, Nelson@NelsonsLocomotive.com
6/30/2006, last updated

It was the spring of 2006.   The miscellaneous engine parts had all been fabricated and the boiler was being made so the next thing was to finish the frame design and construction.   Five weeks volunteer teaching in Central America where there would be a lot of free time to work on the frame design was coming up in two couple weeks.    The  design and fabrication of those slotted stiffeners that distinguish the late Heislers filled those two weeks.  

Center Stiffener:  The design of the stiffener is documented in the Frame Design II page (done after the stiffener was actually built).  The stiffener is too complex to machine as one piece.   However, after a bit of thought it became obvious that it could be build by soldering together a bunch of relatively simple parts.  If the part is small and requires a lot of machining, brass or bronze is a good choice.  For larger parts, steel is cheaper and hence preferred unless considerable machining is required.  Kozo Hiraoka is an expert at the technique of modeling castings by silver soldering together smaller pieces.  Many of his techniques have been used to make these and other parts for both the Shay and the Heisler.    

For this center stiffener, not much intricate machining is required so steel was the choice.  (It also helped that all the required maternal was on hand.) 

The drawing on the right identifies the three part types that make of the basic stiffener ( a fourth part is added later).  Part A is the back plate shown in more detail below.  The horizontal bar part B is a 5.813" length of 1/8" X 3/4" CRS bar stock.  Two horizontal bars are required.  The six vertical bars (part C) are 6.53" lengths of  1/8" X 1/2" HRS.   HRS rather than CRS is used because the edges are rounded, saving the effort to round them to make the stiffener resemble a casting. 
This drawing shows the stiffener back made from 1/8" steel plate.  There was no obvious way to avoid cutting those five long slots so, being the most difficult, this  piece was made first. 
Two stiffeners are required. The back  plates can be cut in one operation to minimize the effort.  The photo shows  milling those slots in the pair of back plates.  The plates were sawed from a larger sheet and the top and bottom milled smooth with the height exactly 5.437".  The length was left about 1/2" too long.  The two plates were bolted together with a couple 4-40 screws on the one end.  The other end was held together with a clamp.   A 1/2" starter hole was drilled near the end of each slot.  A 5/8" mill was then used to cut the slot in both sheets using one pass.  The cutting was slow and a bit of lubricant was used.  The chips are like little needles that took a few weeks to dig out of my hands.   The mill X-Y table helped to make the slots fairly accurate.
Next, the HM405B horizontal bars were attached to the plates.  The bars were cut extra long.   One 2-56 FH brass screw per slot was used to attach the bars.  The bars and plates were accurately positioned and clamped and then a trap drill run through both pieces at the same time.  The clearance drill and countersink were later used on the back plate. 

A center punch was used to make prick holes on the mating area of the pieces to give a slight separation for solder to flow into.  The pieces were then pickled and flux applied to the joints.  The photo shows soldering the bars to the plate.  A half dozen  small pieces of solder was laid at the joint between the bar and the plate ---- in the top of the photo.  The assembly was then rotated 180 degrees and the other bar soldered.   


After the horizontal bars had been soldered to the back plate, the assembly was cleaned in the pickling solution.

The next step (shown on the right) was to mill 1/8" wide X 1/8" deep slots in the front side of the horizontal bars at the correct position for the vertical bars.  Note that this cuts the horizontal bars into five pieces plus stubs on each end that will be trimmed off with the extra length.  The solder holds each piece in place. There is also a screw into each piece that will hold it in place during subsequent soldering.  

The next step was to cut the 6 vertical bars (HM405C). Note that there is extra length that will be cut off later.   The edge of each bar that mates with the backing plate was cleaned and flattened using a belt sander.  
Next, one 2-56 FH brass screw was used to hold each vertical  bar in position.   Again, punch pricks were used to keep the pieces separated slightly.  The whole assembly was taken apart and cleaned in the pickling solution and then the joints were fluxed in preparation for soldering.   The photo shows the back of the assembly and the position of the screws.
This shows soldering the verticals bars.  Three short pieces of solder were placed at the upper side of the joint between each vertical bar and the back plate.  The assembly was then heated until the solder flowed into the joints.  The assembly was then cleaned in the pickling solution, positioned upside down from photo, the joints fluxed again, short pieces of  solder placed at the joints and then the heating process repeated.
The next step was to cut off the excess length of bars and back plate and clean  the assembly.  The back side of the trimmed assembly is shown at right.
The front side of the trimmed assembly.

Modified Stiffeners: The basic center stiffener design was later modified with the addition of a bar (HM419) along the bottom that interfaces with the center boiler support.  This modification is described in the Frame Design III page. The bars are lengths of 3/8" X 1/2" bar stock  The recesses were rough cut on the band saw and finished on the mill.  The lower 1/2" of three of the vertical bars were rough cut out using a rotary tool abrasive disk and then finished on the mill.  A  #2 FH screw into the bar from the back holds the bar in position while it is silver soldered to the rest of the assembly. This time short strips of .004" thick flat silver solder and flux were sandwiched between the bars the the rest of the assembly and then the assembly heated.    The photo below shows the two stiffeners after the modification.

Note that the stiffeners are no longer identical since the added bar is off center.  The left stiffener is on the left in the photo.    The left stiffener will require further modification to accommodate the reversing bar rollers.   The right stiffener will be modified to accommodate the lubricator.   The holes to attach the stiffeners to the frame side and to attach the center boiler support to the stiffeners must also be drilled.  Those issues will be dealt with later.

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