Heisler Main Frame Design I
Nelson Riedel, Nelson@NelsonsLocomotive.com
3/17/2005, last updated 02/23/2007

The frame ties the major parts of the locomotive together.   During the design process quite a few parts were made slightly over scale, usually by rounding up dimensions.  It was also desirable to provide a slightly greater space around the engine to ease maintenance.   The net effect of these alternations is that the overall length of the frame including the sills is 61.5", about 2" or 3% over exact scale.  The Cass 6 frame drawings can be scaled by any who are offended by this deviation from exact scale.     

This page describes the design of the model frame sides and frame bolster.  This design was updated in June 2006 to reflect some minor changes made to better match the boiler and match with the additional frame components described in the subsequent frame design pages.   The page was updated again in February 2007 after the frame was actually fabricated.  The major change with this update was to show a machined frame bolster to substitute for the cast bolster originally planned.

Diamond Frame: The photo below  shows the diamond frame of a late Heisler that is somewhat smaller than MRSR91.  Having the cab and boiler off reveals details normally hidden.   The vertical casting next to the smoke box saddle is a mount for a duplex air pump.     

The photo at right shows the front stiffening plates on MRSR91.  Note that there is a plate on both the inside and outside of the bars.   (On Cass 6 there are single front stiffening plates on each side --- on the inside of the frame bars.)
This photo shows the rear stiffening plates on that  smaller Heisler.  Note that double plates are used, one on each side of the frame bars.    The box-like part is the support for frame side channels under the outer edge of the cab.
This shows the cast center stiffeners used on the late Heisler. These same type stiffeners are used on MSR91.  (On Cass 6 the center stiffeners are double plates, one on each side of the frame bars.)  The painted (primed) part in the photo is inside the cab.  Note also that there are two castings, one that is inside the cab and the other that is mostly to the front of the cab.  I decided to deviate from this design slightly and use a plate stiffener inside the cab where it isn't noticeable and then make a slotted  stiffener for the part in front of the cab.  One stiffener design should be usable on both sides.   I should be able to assemble the frame without the slotted stiffener and hence defer that part of the design.

The frame side bars shown in the drawing above are made from 9/16" cold rolled or cold formed steel bar stock.   Saw cuts will be made about 75% of the way through at the point of each bend.  After all the bends have been made the gaps will be filled with weld and then ground and/or filed smooth.   

The stiffening plates shown in the drawing above are all cut from 1/8" thick steel plate.   Four of the rear plates (HM402) and four front plates (HM404) are required.   Only two of the middles plates (HM403) are required. 

The drawing above shows the assembled frame side.  The initial plan was to use 1/8' steel rivets to attach the plates to the side bars but however, in the end 6-32 button head cap screws were used to simulate the rivets.    Drawings with exact rivet (screw) screw locations are given in the construction pages.  

Frame Bolster: The photo below shows the tender frame bolster on the smaller late Heisler.  Note that the bolster is hollow..    

The photo at the right shows the joint between the Cass 6 front bolster and the frame side.  Note that the top of the bolster cross piece lines up with the joint between the two frame bars.  The part that extends above the cross piece provides a flange for bolts running through the upper frame bar to the bolster clamping plate outside the frame.  This flange is not provided on the tender bolster.
This photo shows a top view of the bolster-frame side joint of the smaller late Heisler.
This shows the left front bolster mounting bracket on MRSR91.   The six bolts on the left go through the frame bars into the smoke box saddle.   The ten bolts on the right side go into the frame bolster.

The drawing above shows the model frame bolster.  The model is solid rather than hollow like the prototype.  The same casting design  can be used on the tender if the portion of the tabs that extend above the body are removed.  Photo at right shows the upper side of the bolster pattern.
This photo shows the under side of the bolster pattern.    The tapered pads mate with the rollers on the truck bolster.

The goal for this page was to get enough of the frame design done so that the bolster pattern could be fabricated since the castings are the long lead time items.  The majority if not all of the remaining frame parts will be fabricated from stock sheet and bars.

Update February 2007: The process of making casting molds proved to be more lengthily than originally thought and the interval to obtain the castings from the foundry has proven to be very long and in some cases,  apparently forever.   The frame fabrication was essentially complete except for the bolster so the bolster design was given a second look and found to be fairly easy to fabricate from bar and angle  stock.  The following is the bolster design actually used on the frame.     

The main part of the bolster is a 1.25" X 2.5" HRS bar.  The ends are finished with 3/16" X 1.125" bars stock and 3/16" thick angles.  A 1" X 1" X3/16" angle was cut down to the correct size.  The end plates and angles were attached to the bar with 10-32 FH screws.   Pieces of 1.125" X 3/16" bars were  welded to the bottom for the truck roller pads.  The bottom was then turned to give the main bar the correct thickness and the pads the correct slope.  The cylinder that extends below the main bar to mate with the truck bolster was made as a separate piece and then attached the main bar with a couple 10-32 screws.     Note that the rear bolster has a 1.875" diameter X 3/8" deep recess in the top.  This recess will allow the use of an external retaining ring on the truck bolster pin and have the top of the pin below the  top of the bolster so as not to interfere with the electrical compartment under the oil tank.   A hairpin clip will be used on the front truck pin and the clip will be above the bolster to permit access.

Bolster Brackets: The three drawings above show the brackets that clamp the frame sides to the bolsters and smoke box saddle to the frame sides.  These brackets will be made by soldering or welding 1/8" thick angle to 3/16" CRS bars.   

More frame parts are described in the subsequent frame design pages.