Brian Naughton's Flat Floor Arched Tunnels
by
Brian Naughton
1/17/2006
input by Lawrence Lemke, concerning the forming of the floor from a single tube of PVC pipe.
The main advantages are :
1. It allows for wider entrances, up to 4 inches, for better access by the birds.
2. The wider inside porch makes it much easier for three hatchlings to comfortably fit across the
entrance.
3. The tunnel and dam has all of the accepted benefits by providing extra protection from predators;
as well as maintaining dry nests by channeling the water back to the outside.
Here is a write-up of the steps that I use to make these arched tunnels and, I hope, may be a source of
information for this or other projects that someone may use. The procedure is fairly simple, but needs
some time.
It helps to have a reasonable amount of workshop equipment, but it can also all be done by hand. This
sequence would not be profitable to make for sale, but it gives another alternative for the hobbyist.
All of the components are made from 4” PVC Sewer and Drain pipe that is reheated and formed into
the needed shapes. The pipe is approximately 3/32" thick and is strong enough for each application whereas
Schedule 40 pipe, although much thicker, would be too heavy for this tunnel.
The individual components are shown in #2, and comprise of a 2 ½" tunnel, integral inside porch 3 ½" wide,
and outside porch 5" wide, and an entrance plate that is 5" wide and a minimum of 4" high. The length of the porch
is just over six", which is a 3 ½" porch outside and 2 ½" inside. The pipe, cut in half lengthwise, will give
the required 6+ inches as described later.
A double thickness of ½" X 5" is used for the dam.
I am able to use a 12" mitre saw to cut the PVC. All cuts should be made slowly, and with safety as a
main concern.
A simple 2 ½" cut makes the tube to be the arch ( #3). Cuts at 5 ½" make tubes to be converted into the
plates for porches and entrances.
Cutting the tube lengthwise needs care. When the first cut is made, measuring 4 3/8" around the circumference
(#5) will give three right size plates for entrances when they are finally trimmed and when slit into two pieces will
give two plates of 6+" for the porches (#6).
These plates are slightly oversize since there may be some distortion in the flattening process that requires
trimming to size.
A 10' tube will yield 15 tunnels, and at a present cost of $6.50, gives tunnels for about $0.45 each
Flattening the pipe is done by heating the PVC for a couple of minutes to about 350 deg F until it is pliable (#7)
and then clamping between two MDF boards until cool (#8). I have an old toaster-oven for this job.
The entrance plates can be made using the cut 4 3/8" wide material or be purchased ready-made from Sandy.
Working with the flat PVC sheet, it is best to first establish a square corner by trimming two adjacent sides that
are already nearly square. Use these two sides as the base for the other dimensions.
If you plan on making very many tunnels, it is worthwhile to make templates since most of the dimensions
are not super critical.
The arch is formed by preheating the 2 ½" tube as described above and forced, when pliable, over a form.
The dimensions of the form I use, is shown in #9 and also shown in use in #10.
A small block is clamped across the base to flatten the arch (#11). Remove the arch when cool and stable - do
not allow it to get too cold otherwise it will be very difficult to get off the form. Make sure that the warmed
tube is placed evenly spaced from the top over the form which will help later in preparing to glue
things together.
The shape of the arch can be “fine tuned” while it is cooling to get a symmetrical shape of the sides and
lower radii.
The porch plate is cut (#12) to the dimensions mentioned above, leaving it a little longer than the 6" to allow
for trimming to match the rear of the tunnel and give a good double thickness edge to which to glue the dam.
The porch is placed inside of the tunnel for it to be the same distance below the entrance both inside and outside.
The porch and tunnel are glued together using PVC clear cleaner and cement as shown in #13, making sure
that the outside porch is pulled close and central to the front of the arch. The inside porch is narrower than the
base of the porch and provides good channels for water to flow to the front.
When the glue is set, the excess inside porch can be trimmed to match the arch.
The entrance plate is trimmed (#14) to the desired height above the porch and glued to the front of the arch (#15).
Care is needed to insure that the entrance hole is central to the arch.
The entrance can be clamped in place, but I use a full gallon paint can on top while holding the outer edges of the
porch against the outside of the edges of the entrance.
When set, the excess entrance plate can be trimmed (#16) to be close to the arch and then sanded to have a good finish
(#17). I prefer to use a spiral cutting bit in a rotary tool for working with PVC.
After sanding the arch, the corners of the porch are rounded (#18). and the lower rear of the arch sanded smooth
and flat for attaching the dam.
At this point, I find it most convenient to put the traction on the inside porch. The traction consists of cleaning the porch
with PVC clear cleaner and adding a smear of polyurethane adhesive (PPCA) using an old comb to stroke a pattern (#20).
Immediately sprinkle the surface with sand, tap on a hard surface to set the sand and shake off the excess.
When set (about 24 hours), remove any excess from the channels and scrape the rear surface clean to prepare for
adding the dam.
The dam can be made of a piece of schedule 40 or two pieces of S&D glued together, cut to 5" long and ½" wide.
In #21, the piece of PVC under the top of the arch is simply to keep the arch level while the dam is setting.
When set, remove the excess dam on the ends and sand to match the profile.(#22).
The edges on top of the dam are sanded with a slight radius for comfort.
The outside porch is now prepared for the traction surface by cleaning with PVC cleaner and smearing a light coat of
PPCA (#23) before combing in the pattern (#24) and applying the sand.
The top of the arch should be done in a similar manner since this is a favorite resting place for the birds.
The 3/16" drain holes are drilled at an angle to enter behind the entrance plate to give maximum drainage
from the inside porch. (#25)
Finished tunnels with traction surface on top of the arch (#26) and the inside rear is sprayed with Krylon Camoflage
Ultra flat brown to remove any brightness around the inside of the entrance (#27).
The tunnel provides an internal perch when the tunnel is fully inserted as in the above SG (#1b) but also acts as an
external perch as shown on the natural gourd (#1a).
Further Application
A shortened arch can be used to hold any entrance to a Super Gourd where inside and outside porches are
already installed.
The arch fills in the curvature in this area and covers any previous entrances cut into the gourd. (#28)
Is all this effort worth it?
You decide !!!!!!!
