Heisler Truck Design I
Nelson Riedel, Nelson@NelsonsLocomotive.com
3/17/2005, last updated 01/30/2010

Updated 1/10/2010 to show the side rod as machined from bar stock rather than cast.    

The wheels, axles and rods are the subject of this part.   The photos below show Heisler wheels with axels.  Note that the gears are in two pieces that bolt to a carrier on the axel.  I assume this design is to permit changing broken gears without removing the axels.     

 

Wheel: The drawing above shows the scaled Cass 6 wheel.

 

The drawing above shows the dimensions of the wheel casting obtained from Allen Models (Allen Part # D3)  The casting is one or two percent too small to make the 5.36" diameter exact 1.6" scale of the 40" wheel.  However, no problem, as suggested by a friend, slightly worn wheels are being modeled. Another option is to use the castings for the wheels only and add separate tires. That seems like too much work.  A second source is Martin Models - http://www.martinmodels.com.  The Martin  wheels were produced from the drawings on this website and are slightly larger diameter than the Allen wheels.  Gary Martin was at 2009 Cabin Fever and said he had some of the wheels on hand.  They are not shown on his website so interested parties should use the contact information on his website to inquire.

The dimensions of the finished wheel is shown above. The tread profile is identical to that Ken Schroeder used on his shay and conforms to the BLS wheel standards. 

Rod: This and the next photo are of the Cass 6 rod.
This top view of the rod end shows the shape of the rod end as well as the grease fitting  

 

The drawing above shows the scaled Cass 6 Rod.  There is an error in the shape of the ends; the diameter of the part of the end next to the wheel should be smaller than shown ---- see photos above.      

The drawing above shows the rod design which will be machined from bar stock.  A grease nipple will be screwed into the hole. 

 

Sleeve Bearing - HS200: These SAE 841 oil impregnated bearings are pressed into the ends of the rod with the flange on the wheel side.  The OD is1/2", ID 3/8" and length including flange 3/4" The flange is 11/16" OD and 1/16" thick.   After the bearing is pressed into place, an oil hole is drilled in the top and the inside reamed 3/8"

Thrust Bearing - HS201: This SAE 841 thrust bearing is used instead of a washer under the crank pin nut. The washer dimensions are 5/8" OD, 1/4" ID and 1/16" thick.

Crank Pin - HM200: The crank pin is machined from  3/8" diameter drill rod.  The pin is positioned in the wheel such that 3/4" of the 3/8" diameter extends out from the edge of the wheel.  The pin is secured to the wheel with Loctite and held in place by a screw 10-32 from the back.
Crank Pin Nut - HS203:  The prototype uses a slotted nut with cotter pin on the crank pin.  Cotter pins are difficult to use on the small model shaft so the thin (jam) flex top locknut show on the right was selected. This nut is self locking. 

The sketch above shows the how the pieces fit together on the crank pin. 

 

The three drawings above show the the axels.  The non geared axel is turned from 7/8" cold rolled steel stock.   The geared axel is turned from 1" cold rolled steel.    The position of the 1" section of the geared axel is the only difference between the outside truck and middle truck geared axel.  The keyways on the two ends are rotated 90 degrees from each other (quartered).    

The drawing above shows an assembled non geared axel.   The bearings are the industry standard #6004 for 20mm shaft diameter.  This bearing has a 42 mm OD and 12mm thickness.   The spacer (HM203) is made from mild steel rod or tube.  The ID is 3/4"+ and OD is ~1".  The critical dimension is the thickness of 3/16".  Note that the 7.125" wheel inside spacing matches the BLS wheel standard of  7.120"-7.140"   

This wraps up the wheels and axels.   We're now ready to deal with the remaining truck components.

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