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Building a Simple Spark Arrestor by Alan Olson

October 20, 2005

To construct this simple spark arrestor you will need some
strip material and some fine mesh screen. You can use
styrene or brass for the strip material and brass or nylon
mesh for the screen. You can assemble everything by using
medium viscosity CA glue. If you are handy with a soldering
iron, you may want to assemble the arrestor with low
temperature silver bearing solder. This solder is easy to
work with and very strong.
The basic arrestor is made up of a top and bottom ring,
four uprights, a screen wrapper and a screen disk.
I suggest that you use 1/8’ wide x .040 thick material for
assembling a styrene version and 1/8” x .020 material for
brass. The screen can be found at hobby shops and craft
stores.

Step 1
Find the diameter of the smoke stack top lip; this will be
the most important measurement.

Step 2
Decide how tall you want the arrestor to be. Short, squat
versions were referred to as pancakes, while tall and
narrow versions were called shotguns. If you don’t have any
idea about this dimension cut a piece of paper into a strip
about ¾” in height as a starting point. Wrap it around the
stack lip to form a tube. Use tape to hold it in place
while you look at it. This will give you an idea of how the
arrestor will look. Adjust the height of the paper to suit
your needs. Use the height you choose for the length of the
four uprights.

Step 3
Form two rings to fit around the stack lip. Do this by
drawing a circle on paper that matches the lip diameter.
Add four evenly spaced marks on the circle to locate the
uprights. If you are using CA, place some waxed paper over
the circle to prevent the glue from sticking to the paper.
Cut the strip to a length that is longer than the
circumference of the drawing. Carefully bend the strip
material around your finger until you have a ring. Cut the
formed strip to length so that it matches the drawing. Join
the ends together to complete the ring.

Step 4
Cut the four uprights to length. Set one of the rings over
the circle drawing and glue or solder each upright so that
they are positioned over the cross hair marks. Some
prototypes had the uprights fastened to the inside edge of
the rings and some were attached to the outer surface. If
this is your first attempt at a spark arrestor you may want
to build the version with the uprights on the outside. Make
sure that the uprights are at 90 degrees to the drawing
surface.

Step 5
Attach the top ring. Make sure that it parallel to the
bottom ring.

Step 6
Measure the distance from the top edge of the lower ring to
the bottom edge of the top ring. This will be the height of
the screen. Next measure the circumference of the inner
face of the ring and add 1/8” for an overlap seam to that.
This total will be the length of the screen.

Step 7
Cut the screen and test fit it into place. You may what to
bend the screen material between your fingers to form a
curve to match the rings. The screen should sit between the
upper and lower rings and have an overlap at the ends.
Attach one end of the screen to one of the uprights. Make
sure that the screen rests up against the inside surface on
all of the uprights. Overlap the free end of the screen to
where the screen has already been attached to the upright.
The rings, uprights and screen will now form a tube. Test
fit this assembly onto the smoke stack.

Step 8
Cut a disk of screen material that matches the top ring of
the arrestor. Once this is attached the arrestor is ready
to paint.

Step 9
Once the paint is dry, the arrestor will be ready to mount
onto the stack.

We feature this and other locomotive detail crafting in our
video “Scratchbuilding Locomotive Detail Parts” hosted by
Alan Olson