Heisler Truck Design IV - Brakes
 Nelson Riedel, Nelson@NelsonsLocomotive.com
1/29/2010, last updated 01/30/2010

Truck Brakes: The design of the truck brake component was postponed until the trucks were fabricated to make it easier to determine how the linkages and beams would fit around the gearing. 

  
Overview: This is a photo of the brakes on MRSR91.   The design uses long levers which pivot at the shoes and at the adjusters to create large forces on the shoes. This design appears to have been used on all the Heislers.
This is a photo of the finished model brakes.   The HM220 shoes are aluminum.   The plan is to glue brake lining to the shoes after they become worn to the exact shape of the wheels. Part HM221 is the Brake Shoe Hanger.   The adjuster is made up of parts HM222 Brake Adjuster Male and HM223 Brake Adjuster Female.  Part HM233 is the Brake Hanger Pin, part HM234 is the Brake Shoe Pin and part HM235 is the Brake Adjuster Pin.
This photo shows the cotter pin that holds the Brake Hanger Pin in place.
This is a photo of the under side of the front truck --- the axel pump is visible on the right.  The brakes on the front and the tender trucks are identical and driven by air/steam cylinders.

Part HM224 is the Brake Beam.  Parts HM225 serve as short brake beams and links to the Cylinder Link parts HM227, HM228 & HM229.   The cylinder piston rod screws into the Cylinder Link.

The cylinder mounts to the upper side of the HM237 Brake Cylinder Mount.

The HM238 Brake Cylinder Mount Spacers hold the Brake Cylinder Mount away from the Axel Bear Caps to permit the truck to flex on uneven track.    


 

This is a photo of the middle truck.  The pair of spur gears take up the space where the brake cylinder is mounted on the front and tender trucks.   The brakes on this truck will are used for the park brake function.

The HM224 Brake Beam is the same as used on the other two trucks.  

Parts HM226 Brake Beam & Link are shorter than the similar parts on the other two trucks.

The HM230 Clevis, the HM231 Clevis Rods and the HM232 Park Brake Link provide the linkage to the park brake levers.  The park brake lever mechanism is described in the brake section. 
 

HM220 Brake Shoes:  The brake shoes are machined from aluminum bar stock.  The shoes are attached to the brake beams with 8-32 socket head cap screws threaded into the beams.   The screw head fits in to the 0.266" hole and the threaded part of the screw fits into the 0.156" hole.         

HM221 Brake Shoe Hanger:  The brake shoe hanger is made from 1/8" X 3/8" CFS bar stock. The tab fits into the slot in the truck side and insures that the hanger will not slip out of the truck side if the shoes are severely worn.   Recall that the wheels were machined from castings by Allen Models and the wheels are slightly under scale.   The Martin Model wheel castings are probably slightly larger and would likely permit a 1/4" larger wheel diameter.   If that is done, the tab should be left off the hanger.       

HM222 & HM223 Brake Adjuster:  These parts can be machined from brass, Bronze or steel.    

HM224, HM225 & HM226 Brake Beams:  These parts are machined from 1/8" X 3/8" CFS bar stock.

 

HM227 Brake Cylinder Link Upper:  This part can most easily be made by silver soldering pieces of 1/8" X 3/8" CFS bar stock, 3/8" diameter CFS rod and 5/32" diameter CFS rod  together.
HM228 Brake Cylinder Link Lower: This part is machined from 1/8" X 3/8" CFS bar stock.
HM229 Brake Cylinder Link Middle: This part can most easily be made by silver soldering a piece of 3/8" square CFS bar stock and a piece of 3/16" diameter CFS rod together.

 

HM230 Brake Clevis:   This part  is similar to the brake adjuster parts and can be machined from brass, bronze or steel.

HM231 Brake Clevis Rod: This part is simply a piece of 3/16" diameter CFS rod threaded on each end. 

HM232 Park Brake Link:   This part is machined from 1/8: X 3/8" CFS bar stock.  

HM233 Brake Shoe Hanger Pin, HM234 Brake Shoe Pin and HM235 Brake Adjuster & Clevis Pin:   These parts are all machined from 3/16' diameter CFS bar stock.

Brake Cylinder (HS207):  The brake cylinders are off-the-shelf Clippard #UUR-14-1-1 shown above.   This cylinder is reverse acting in that the shaft is fully extended in the idle state and moves into the cylinder as pressure is applied.    There is an external spring that returns the piston to the idle position when pressure is removed.  Mounting is via a bronze sleeved 1/4" hole at the back of the cylinder.    The piston is 7/8" diameter and all parts are stainless steel.   The stroke is 1" and the seals are Vinton to tolerate high temperature steam.    

HM237 Brake Cylinder Mount: The brake cylinder mount is loosely attached to the axel bearing caps via the Cylinder Mount Spacers described below.  The Mount also shields the cylinder and associated plumbing from objects under the truck during a derailment.  The Mount can be fabricated from steel bar stock.   I uses scrap pieces of 3" channel. 

HM238 Brake Cylinder Mount Spacer:  This part is machined from 3/8" hex bar stock.  Similar sized round or square stock may also be used.   A 6-32 hole are drilled and tapped in each of the Axel Bearing Caps above the mount.  A FH screw is installed in each cap with the head on the bearing side of the caps.  The Spacer is then screwed onto the screw.  The screw is long enough to extend ~ 1/4" beyond the spacer. The spacer is secured with Loctite.   The 1/4" holes in the mount fit over the 0.23" shaft of the spacers --- it's a loose fit which allows the mount to accommodate movement in the truck sides.   The Mount is secured with Nyloc nuts. 

Alternate Shoe:  Several years ago I purchased the brake components in above photo from Howard Gorin (www.themachineryworks.com) at Cabin Fever with the thought that they might be usable on the Heisler.   Unfortunately I forgot about them until I had finished fabricating the brakes.   The shoe on the left is cast aluminum and shoe holder on the right is cast brass.  The shoe is retained in the holder by the brass strip that is inserted from the top.  This shoe is nearly an exact match to the shoe part of HM220 shoe described above.   If I had it to do over I'd probably design an brass piece that could be silver soldered to the holder to provide a way to attach the hanger and to the brake beams.   The ability to easily replace worn shoes is very attractive.     

The plumbing of the brake cylinders and the mechanical link to the park brake handle will be described in the Brake Section. 

This wraps up the design of the trucks except for the gearing.  The gearing is covered in the Gears & Shafts Design section.     

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