Truck Design IV - Brakes
Nelson Riedel, Nelson@NelsonsLocomotive.com
1/29/2010, last updated
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.
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
|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
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.
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.
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
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.
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.
Cylinder Link Lower: This
part is machined from 1/8" X 3/8" CFS bar stock.
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
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
|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
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
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
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