Heisler Main Frame Design II
Nelson Riedel, Nelson@NelsonsLocomotive.com
Initial 5/20/2005, last updated 02/23/2007

It's been over a year since the Frame Design I pager was first published.  The boiler is being fabricated and the foundry is in the process of casting the engine parts.   It would be nice to make the frame now so that there would be a place to mount the engine when it is finished.  Normally the frame sides would be constructed and jointed together with the frame bolsters.  Unfortunately, the frame bolster castings will likely not be available for many months.   An alternative is to fabricate the saddle, sills and associated fixtures and use them to hold the frame together until the bolsters arrive.  So, it's time to finish the design of the diamond frame and then design those sills and associated fixtures.   

Center Stiffener: The cast center stiffener for MRSR91 is shown in the photo on the right.  There are actually two castings on each side. The rear casting is mostly in the cab.  The joint between the to castings is between the 4th and 5th vertical slot.   I decided to make the part of the stiffener inside the cab out of smooth plate and make a single slotted stiffer design with five slots. The same design will be used on both sides.  The protrusion on the bottom is additional support for the boiler mount.  This support will be added as a separate part later.  (See Main Frame Design III)

The center stiffener design is shown on the right.  It is a good aesthetic match to MRSR91  but is also simpler in detail.   The recesses on the back side fit over the frame bars.  Bar and plate stock are used to build the stiffeners.  See the frame construction pages for more information on fabrication. (In this case the stiffeners were actually built before the design was documented.)

Saddle:  The saddle was the next most complex piece so it was tackled next.  Photo at right shows the saddle on a late Heisler that is a bit smaller then MRSR91.  This photo was taken from the right front.
This photo taken from the right rear shows that same saddle on the smaller Heisler.  Note that  the back is flat and there are bolt holes to attach the smoke box on the front and side but not the back.  Also note that the center exhaust port that connects to the nozzle is square.  I'll make that part round on the model---- square holes are just too hard to drill. Note that the front coupler support goes under the saddle.  The top of the support and center bottom of the saddle are the same height as the top of the frame bolster and the joint between the two frame side bars.
This is a photo of the MRSR91 saddle taken from the left front.   Note that some of the pipes and the back of the steps are identified.  Also note that I don't know the purpose of one pipe.  Also note that there is a difference between this saddle and the one shown in the previous two photos where the curved top joins the base.  I plan to model this design

The drawing above shows the saddle design.   The plan is to assemble it from stock bars, plate and a piece of tube.   The center will be a steel block sandwiched between 3/16" thick steel plates silver soldered to the front and back.   The vertical passages will be drilled from the top.   The horizontal passages will be milled from the bottom.  The bottom will then be covered with a 1/8" thick plate. The sides and bottom plate as well as the 1/2" angles on the bottom will be silver soldered in place,   The two flange like  exhaust openings will be separate pieces silver soldered to the center block.  More detail will be shown in the construction page.   This drawing was updated on 1/9/2007 to reflect minor changes made when the saddle was fabricated. 

Rear part of frame:  Much of the rear part of the frame is obscured by the coal bunker on Cass 6 and the oil tank on MRSR91.    The photo below shows the rear part of the frame of a late Heisler.  The MRSR91 frame has an identical structure albeit a bit larger.   Note that the seam between the two frame bars is even with the top of the rear sill, the bolster and that cross piece.  The upper frame bar extends about half way across the top of the rear sill.   The bottom of the cab sides and the bottom of bunker/oil tank sides are also even with seam between the two frame bars.  The bottom of the oil tank rests on the top of the upper frame bars.   I decided to not have the cross piece on the model: I want to keep that area as free as possible to accommodate oil, atomizer and feed water plumbing.   The plan is to have the bottom of the oil tank about 2.5" above the top of the bolster.  The igniter circuit and coil as well as a sealed lead acid battery will housed in the space between the bottom of the oil tank and the top of the frame.  

The Cass 6 floor is even with the seam between the two frame bars as shown in the photo on right.   The side bar sticking up 4" off the floor is not elegant.  I wonder how many  crew members tripped over the bar and fell out of the cab.
The photo shows the MRSR91 floor which  rests on top the upper frame bar.  This is a more elegant design which I'll use on the model. The floor on the model will be a sheet of 1/8" plate.
This photo shows the MRSR91 frame side channel that supports the outer part of the cab and fuel tank.  The channel is 8" high which scales to ~1.07"  Note the gap between the top of the channel and the floor.  This gap would the 7/16" on the model. I decided to use a 1.5" channel and make the top of the channel even with the bottom of the floor.  The higher channel and the use of a 1/8" thick floor will obviate the need for the braces and brackets in the photo.

Rear Sill:  The drawing above shows the rear sill design.  The sill will be made from 1"X1.75" bar stock.   The angles are attached with 6-32 screws.  The nose pieces are attached with a 4-40 screw each from the rear to hold the pieces in position while they are silver soldered to the bar.  (This drawing was updated 1/9/2007 to reflect minor changes made when the sill was fabricated.)    

Swivel Pocket: This piece will be made from 1/2" X 1.25" HRS  bar stock     The two 3/4" pieces between the long bars are held in place by a pair of 10-32  socket head cap screws and then silver soldered.   The pocket is attached to the frame bars with four 10-32 socket head screws .

Link Pin:  This is the Cass 6 link that connects the locomotive to the tender. The link pin hole is about 1" below the link center line.  The link looked like a replacement that was forged locally.  The droop is necessary because the pin hole in the tender coupler pocket is below the link center line.   I've always thought the Cass 6 tender was tilted up slightly at the front.  I now suspect that this apparent replacement part has less than the required droop to make the tender level.
This photo shows the Cass 6 locomotive - tender connection.  The height of the pin in the tender coupler pocket is clearly below the center line of the link.
This photo shows the MRSR91 locomotive - tender connection.  In this case the pin appears to be below the centerline of the link by a bit more than on Cass 6. (The MRSR91 tender also appears to be level.)   Note that the top of both sills are at the same height.     Also note that the link cross-section seems to be rectangular and there is a shoulder between the locomotive sill and the tender part of the couple.  This looks like a factory provided part.

This drawing shows the tender coupler link design.  The main part of the link will be machined from 1.25" square bar stock.  The disk will probably be cut off a length of  1.25" diameter bar stock.

Frame Side Channel:  The frame side  channel shown in the drawing above is a length of 1.5" X 1/2" X 1/8" channel.  The only machining required is to mill out the fillets on the inside corners for about 1/2" back from each end.  This is done to provide a good mating surface for the angle brackets that are used to attach the channel to the rear sill and the side channel support. 

Side Channel supports:  The side channel supports are cut from 2" X 2" X1/8"angle  The support bolts to the frame side bars.   A 1.25" length of 1/2" X 1/2" X 1/8" angle will be used as a bracket to connect this support to the side channel. 

The sketch shows the spacing of the rear bolster, center stiffeners and the side channel supports.  Note that there is a 3/32" gap between the stiffener and channel support for the front of the cab.  This matches the design of the MRSR91 cab front.  

The front sill and boiler support designs will be described in the Frame Design III page.