Building a Drop Trap
Lisa A. Pierson, DVM
Back to Drop Trap/Remote Control Trap page.
Video - Drop Trap in Use
April 22, 2007
These instructions are a work-in-progress. Keep checking back for more pictures and instructions.
Please drop me a line if you are successful in building one of these or have any questions.
This page illustrates how to make a folding drop trap out of PVC pipe. Wood is easier to work with but I prefer using PVC pipe. Putting flat hinges on a round pipe is definitely much harder than it is on flat wood but PVC is lighter than wood and I hate sanding!
Please pay attention to how you are placing your screws - keeping the cat's safety in mind. The 4 corner hinges are applied with the head of the screws on the inside of the trap but because I use the bulkier nylon lock nuts, I have to reverse that for the side hinges otherwise they will not close properly. If you are using thin, flat nuts and cutting off the excess machine screw tip, you may be able to keep all heads of the screws on the inside of the trap.
Make sure that nothing sharp is on the inside of the trap.
As you are building this trap, it is very important to use a square ("L") and pay attention to what needs to be parallel and what needs to be at a 90 degree angle otherwise the trap will not fold properly.
The materials for this trap will run about $100 without the netting. (I get netting donated to me.) If you purchase netting from Gourock that will run you another ~$30 for a total of ~$130.
It takes me about 20 hours to build one of these but I am not known for my speed. I stand around a lot....staring at it....hoping that it will build itself. The only thing that pushes me to keep building these is the knowledge of how much suffering will be prevented when a drop trap is used to manage the feral cat population.
Front/Back Frames, Side Pieces
Start by making two end frames using 1" PVC pipe and 90 degree 1"
elbows. The long poles are 44" and the short ones are 10".
Using a hammer, tap the poles into the elbows so that they are seated
firmly. (Be sure to do this with all of the PVC pipe and
fittings.) Lay them down on a flat surface and make sure that they
are properly aligned and are 'true'. If they are not, then just twist
them into alignment.
Make the 4 side pieces using both 1" PVC pipe (horizontal piece) and
3/4" PVC pipe (vertical piece). Note that there are 4 - 90 degree
elbows that are 1" x 3/4" and 4 - 90 degree elbows that are
3/4" x 3/4".
The 1" PVC pieces are 20" long and the 3/4" vertical pipes are 10" long.
This is the most challenging part of building this trap. The hinges must be applied correctly or the trap will not fold properly. I use 8-32 machine screws and nylon lock nuts which are much easier to use than liquid threadlockers such as Loctite. The machine screw lengths that I use are 1 5/8", 1 3/4" and 2" - all pan or round head. I use a Dremel tool and cutoff wheels to cut off any excess length from the screws if necessary. Most of the time I am able to match up the screw length with the application so that I don't have to cut many of them off. A 2" screw is usually needed when going through the pipe and elbow and a 1 5/8" screw is usually needed for the front tip of the hinge but sometimes a 1 3/4" screw is needed there if tightening the front part of the hinge makes the side piece bowtie in. If you are not using the nylon locking nuts, and are using smaller, flatter nuts, you may need shorter screws.
Do not over-tighten the screws.
The hinge pin must be perpendicular to the ground.
This is an example of what you do not want. Note how the hinge is
out of alignment in two planes. It is both tilted and rotated.
Again, the hinge pin must be perpendicular to the ground.
You can loosen/tighten the two back screws as needed to level out the
hinge, but if it is rotated, that means you did not drill your holes
properly.
This hinge is applied correctly. It is parallel with the PVC pipe
(not rotated) and is flat (not tilted).
This hinge is applied correctly but note that the board has not been
trimmed very accurately. I like to keep any light coming through
the trap to a minimum since a panicked feral cat will start pushing and
clawing at any light source with the hope of escaping.
Hinges applied correctly. Note that the two vertical pieces are
parallel and perpendicular to the ground.
These hinges were not applied as well as they should have been.
Note the gap between the two vertical pieces and see how the end frame
tilts backward. However, when the net is put on, it will pull the
trap together nicely.
Apply the side hinges - remembering to use the L to
keep the trap square. Check both sides of the trap to make sure it
is square before applying the hinges.
There is a more detailed picture below of this part of the trap. The snap is optional since most of the time the trap 'bowties' in enough so as not to allow the hasp to pop up when the trap is dropped. If in doubt, however, use a snap (or a screw or nail as shown in another picture below) to secure the hasp.
This hasp is 1 3/4" in length and is 3/4"
wide. The length really does not matter but the width does since there
is not much room on 1" PVC pipe. Note how the small piece of
the hasp is applied very close to the end of the pipe. It is best
if the long flat part of the hasp is as far back as possible because
when it is flipped forward, it will catch up when opening the trap.
BE CAREFUL when opening these traps as the hasps are often in the way
and need to be flipped back before the trap can be opened.
Also, there is not much room on this small piece (hidden from view by the snap) for two 8-32 machine screw heads to sit side-by-side. And there is not enough room at the bottom for the bulkier nylon lock nuts. For this reason, I use 6-32 machine screws instead of the 8-32 screws. I then use the small nuts (with Loctite) that come with the 6-32 screws which will fit side-by-side on the underside of the trap.
Alternatively, if you don't have 6-32 machine screws, you can use a Dremel to file down one side of the head of one 8-32 screw. Then they will fit side-by-side. You can then stack the larger 8-32 flat nuts on top of each other.
This is another tricky part. Note the hinges below and how the top
one (Stanley Heavy Duty 4") has two holes that are close together whereas the lower one (National HD 4") has the two holes further apart.
Now, note the picture above where I have the machine screws placed
through the hasp. The National brand of hinge allows for that but
the Stanley does not (unless you drill another hole in the hinge).
The Stanley hinges are fine for the corners.
Measure the distance between the the elbows taking into consideration
how far the top 3/4" PVC pipe pieces will insert into the elbows.
Divide that distance by 2 and that will give you the length that you
need to cut the top pieces. The length of each of the 4 top pieces
should end up being ~20". You would like for them to meet
together without more than a 1/2" gap between them. Brace the elbows while tapping the PVC
pipe into them securely so as not to put too much pressure on the hinges. (I just brace them with my leg.)
Note that the side and back panels are placed on the INSIDE of the trap but the front panel with the door is placed on the OUTSIDE of the trap.
I first made these traps with hardboard - using 1/4" for the front panel due to the weight of the door and using 1/8" for the other 3 sides. This resulted in a trap that was 29.5#. I actually like using a trap this heavy and this is what my personal one weighs but other people may find that too heavy. In order to make it lighter (23.3#) I now use 1/4" Coroplast for three of the sides but that is not readily available for most people. It is lightweight, is very durable and is very easy to work with. It can be cut with scissors. If anyone is going to make several of these traps, it would be well-worth sourcing. I get mine locally at Plastic Depot in Gardena, CA.
Important note: Do not fit the panels so that they are flush with the ground. Otherwise, they have the potential of acting as a guillotine on a cat's tail. This is especially important for the 2 side panels at the front where the cats will be sitting and eating. Cats often have their tails out past the perimeter of the trap. Fit the panels so that they are just slightly above the lowest point of the PVC pipe radius. Since I use 12" high panels, this works out well. (If you were to fit the 12" panels flush with the ground, they would not meet the top PVC pipe rail.)
As an added safety measure, I add a ~3/8 - 1/2" spacer to raise the trap up in order to create a gap in case the trap were to come down on a tail. See the Safety for the Cat section below for more comments about the needed safety gap.
If you want to try and use 1/8" hardboard for the door panel instead of the 1/4", this will cut 2# off of the weight. You won't have the 1/4" material to make the door but I suppose that you could use the 1/8" hardboard to make small sliding door.
With the dimensions of this trap, the panels are 12" high but measure the length for each one. I fit each panel so that it goes over the hinge pin to close the gap in the corners as much as possible.
When securing the 3 rear panels in the back half of the trap (1 long and
2 short) just use 3 - 7" cable ties on the sides and secure the bottom front
corners (of the short side pieces) with a couple of 4" cable ties as
shown in the next picture. Don't waste cable ties on the bottom or
top of the 3 back pieces at this point in time because you will be
turning the trap over and applying carpet strips to the bottom of the
back half of the trap and you will be attaching the net to the top later
on.
Be sure to tuck the cut ends of these 4" cable ties inside the pipe or else
they will catch on the netting when you try to open the trap.
Keylee supervising the carpet installation on the back half of the trap.
The carpet really does dampen the noise when the trap drops and will scare the
trapped cats less and the cats around the trap as well.
It is hard to see in this picture (below) but I did secure the front
ends of the carpet with 2 - 4" cable ties on each side - drilled through
the ends of the pipe near the center hinges. Note in the picture
above - right side - that I also drilled right through the elbow to
secure the carpet. At other times, I have just applied glue to the
end but that will probably wear out in time. Some may think that
drilling through the elbow will weaken it but, so far, so good, on my
own trap. If you are worried about the integrity of the elbow,
then just use cable ties just surrounding the elbow and don't drill
through it.
When using 1/4" Coroplast, I use 8-32
1/2" machine screws with a washer on the other side. If you are
using 1/8" hard board and are
not using the bulkier nylon lock nuts, you will need to use shorter screws
and possibly more washers to act as spacers - with the bottom line
being that you do not want the screw tips protruding into the trap where
the cats can hurt themselves. So you will either need to use the
right size screw and nut/washer combination or cut the screw tips off
and file them smooth. (Note that the carpet is just on
the back half.)
For the side hasp - some may want to use a clip like that shown on the bottom hasp in a picture above, but in cold weather, I find that keeping it simple works better. When my hands are cold, I do not want to fool with a snap so I just use a machine screw tied on with string as shown. If you have extra 2" screws left over, this would be a good place for them.
Inside of side panels with 13 nylon lock nuts.
See here for an update to the door design.
I use 1/4" hardboard for the front panel. If you have been accurate in your measurements up to this point, the front panel should be 46" long and 12" high but double check the measurements of your trap.
Cut a square out of the panel 9" x 9". This size door
works well with a trap that is 10" x 12" like a Tomahawk 608. If
your trap is smaller, then you will want to make the door smaller.
Just note that the smaller the door, the less enticing it will be for
the cat to go through it. It can be very frustrating to be
standing there with a cat that refuses to leave the drop trap and go
into the wire trap.
I like to put a radius on the bottom edge of the inside of the door panel to ensure
that the bottom of the sliding door slides nicely to the bottom of the
door frame tunnel.
I use old molding scraps to make the door frame. It is very helpful to have the back of the molding flat so that the spacer lies flat up against the molding. Most ornate molding is not flat on the backside so using door stop for both the frame and the spacer works the best.
The molding in the picture above happens to be 1 3/8" wide and the door stop that is acting as a spacer is 3/8" thick and 5/8" wide. (It will be listed as "1/2" x 3/4" door stop" at the lumber yard.) The sliding door panel is made from 1/4" hard board. You can pick whatever size of wood you want to for the frame but just make sure that the spacer is 1/8" thicker than the thickness of your sliding door. That way, the door will slide very easily. I like the door 'sloppy'. In other words, it fits very loosely from front to back (the 1/8" gap) and from side to side. When you are trying to rapidly get the door down before the cat goes back into the drop trap from the wire trap, you do not want a 'sticky' door. It needs to be able to slide very freely.
I cut the correct lengths of the 6 pieces and then use wood glue to attach the spacers to the molding. You don't have to do 45 degree 'picture frame' cuts like shown in the picture. You can just do straight cuts and it will be perfectly functional. The wood glue is just to keep the two pieces together well enough so that they don't slip when drilling the holes for the machine screws that will be used to attach this door frame to the hardboard panel. Allow at least 1 hour for the glue to set before drilling the holes. Put the door frame onto the front panel BEFORE attaching the panel to the trap.
This view of the back of the panel shows how I use small screws and washers to attach the velcro piece
(3/4" wide, 6 1/2" long)
to the front panel. (I use the small screws that came with the
small hasps.) Make sure that you cut off and file smooth any
part of the screw tip that protrudes otherwise your door will hang up on
them. The 'hook' part (2" long) of the velcro is glued to the sliding
door. (Superglue should work but I am using a quick
bond glue from a hobby shop that works very well. Both are
cyanoacrylate but the glue that I get from the hobby shop seems to bond
faster and stronger than the brand Superglue.)
Note in the above view where the machine screws attaching the door frame are placed. The bottom ones need to be as low as possible and the top ones need to be down a bit from the top otherwise, the nuts will meet the PVC pipe and create a gap. It does create a gap at the bottom but the gap is less if you put the screws as low as possible.
Pick a screw length taking into account the thickness of the molding, spacer and hardboard so you don't have to go to the trouble of cutting off the excess screw length.
Update: I have found that some traps have a wire loop on the sliding back door that is quite prominent. This prevents the metal trap from being pushed firmly against the frame of the drop trap and also makes it hard to slide the metal trap door up and down. See below for a modification that I have made. The relief area is 1 1/2" wide.
I find it easier to put the eyescrews and bungee cords onto the door frame after the panel has been attached to the trap. Crimp the bungee cord hooks onto the eyescrews so they won't get lost.
After you have attached the front panel to the trap, it is time to put the netting on the top. The picture below shows a 5/16" dowel threaded through 5/8" netting for a side panel. If you order the golf impact (not golf barrier) netting from Gourock, your netting will be larger (3/4") and so you can use a slightly larger dowel....or just stick with a 5/16" dowel. (Note on the Gourock net: The square mesh is easier to work with than the diamond mesh. It will cost $8 more but may be worth it for the ease of working with it.)
This dowel will be tucked under the PVC pipe and then the side panel plus the
dowel/net will be cable tied into place. I use needle nose pliers
to reach through the net to grab the end of the cable ties.
I like to start with the back panel and then do the front panel next, followed by the 4 side panels. Applying the netting is a bit tricky. You don't want it too tight at the corners because then it will be pulled too tightly when the trap is closed, but you do not want it too loose at the corners either. After the netting is put on, I carefully examine all four corners and reinforce the netting as needed by drilling through the PVC corner pieces and attaching the netting with more cable ties. (See picture below.)
To reinforce the corners after the net has been put on all 4 sides, drill your holes through the PVC corners and then thread the cable ties with the trap open - estimating where to go through the netting but don't close up the cable tie yet. Tighten them when the trap is in the CLOSED position because you may have to alter where the cable ties go through the netting. Otherwise, the netting at the corners may up being too tight when the trap is closed which will stress the netting.
Never underestimate the ability of a feral cat to get out of a small gap!!
This picture shows two cable ties (please use the black ties, not the white ones) going through holes drilled into the corner PVC pieces securing the net at one corner. You may need 1 or 2 ties at each corner depending on how close your other ties are to the corner. Most of the time, I get by with just one extra cable tie per corner that is passed through a hole in the PVC 90 degree piece.
Some corners, however, have not needed any extra support. Just
think like a panicked feral cat and use your judgment. Better too
many cable ties than too few!
There is no doubt in my mind that many feral cats have had their tails damaged by drop traps. I have watched many cats sitting under traps and observed that their tails often extend beyond the trap perimeter. This is, of course, more apt to happen with the smaller traps. I have had people claim to have "never hurt a cat's tail" but the bottom line is....how would you know? It is not like you can readily examine feral cat's tail after it has been trapped! The veterinarian doing the surgery is not going examine or radiograph the tail so, again, drop traps HAVE injured tails without it being appreciated by the trapper.
Obviously, the heavier trap, the more damage will be done to the tail but even a 13# trap hurts if dropped on your finger from several inches above. Try it! Believe me, it hurts.
For this reason, I want a 1/2" gap created between the PVC pipe and the ground at the side pieces in the front half of the trap.
Be very careful to not have your 1/8" hardboard panels act as a guillotine on a cat's tail! The hardboard should NOT be flush with the ground. It should be above the bearing surface of the PVC pipe. If there is going to be any contact between the trap and the cat's tail, better that it be the PVC pipe than the sharp edge of the board!
This trap is so large that if you do catch a cat's tail, it will be toward the end where it is thinner. If you use a trap that is smaller (3'x3') then you may very well bring the trap down on the thicker, base of the tail and even a 1/2" gap will not protect the cat from an injured tail. This is another reason why I like larger traps.
To create the gap, I cut small (~1" x1" give or take) squares of carpet and stack 3 - 4 together and cable tie them to the two front corners of the trap and also near the ends of the front short PVC pipe pieces - near the center hinges.
A stack of 3 carpet squares on the front (using thin indoor/outdoor
carpet) acts as a spacer. I use 4 for the stack near the center hinge.
Bottom of the trap. Note the stack of 3 carpet squares to the
right (front of the trap) and a stack of 4 to the left near the center
hinge. Depending on the thickness of your carpet, use as much
carpet as you need to get a ~1/2" gap in case the trap comes down on a
tail.
I really can't imagine a cat pushing its way through the gap between the vertical PVC pipes at the corners but if they pushed hard enough, they may get their head through and injure themselves. If the trap is not constructed properly, there may be more of a gap than there should be. Also, there is 'play' in all hinges so we can only make that gap as tight as wobbly hinges will allow.
For added reinforcement, I add an 11" cable tie (or hook 2 - 7" ones together) as shown (with the tab untrimmed). Note the placement of the cable tie as shown in the lower view taken from inside the trap. It is snug up against the side 3/4" PVC pipe but it is ~2" from the front 1" pipe. This is to allow for the way that the trap closes.
Note: Do not tighten this reinforcement cable tie when the trap is open. Tighten it only when the trap is closed. This will result in the tie being a bit loose in the open position but if the tie is too tight while in the open position, the trap will not close.
The first handle that I used was simply made from romex electrical wire and a 4"
piece of 1" PVC pipe. This did end up pulling through one of the
ends of my very heavy (29.5#) traps so then I started using chain (with
machine screws and washers) wrapped with duct tape plus a piece of PVC
pipe. If you prefer a smaller handle then use the 3/4" pipe.
Or try a piece of 3/4" pipe on both handles. (Update: I
tried using 3/4" pipe on both handles and did not like it as well as
using the 1" pipe on just one handle.)
I bend the ends of the chain to a 90 degree angle so that it stands up
better.
Attach eye bolts (I used 1/4" but you can use smaller ones) to the back panel as shown. Use 4 washers for each side of the 2 eyebolts. This provides a place to hook your bungee cords and also keeps the trap closed. You will have to cut off the ends of the bolts and smooth them with a file.
Use all 3/4" PVC pipe with 4 - 3/4" T's and 2 - 3/4" 90 degree angle pieces.
Cut 1 - 8" pipe and 2 - 12" pipes and 2 - 1 7/8" (or a bit shorter) small pieces. Construct as shown using the 1 7/8" pieces to attach the 90 degree angle pieces to the T's. (Drive one end of the small piece into the upper T and then slip the 90 degree piece on.) Use a hammer to tap the pieces firmly together.
Use 50' of soft rope - one that will lie flat and straight.
You may want to use PVC pipe glue to construct your stand. For the ones that I am handing out to the public, I choose not to in case the U shaped part breaks. If it breaks, a person could easily go to Home Depot for a replacement.
The drawback about not using glue is that the stand will shift around when it is banged on the ground as it is pulled rapidly out from under the trap. This is not a problem but you do have to make sure the stand is 'true' and aligned properly before re-setting the trap. It just takes 2 seconds to twist it back into proper alignment and I have to wonder if it was glued....and there was less 'give' to the stand pieces....would it be more apt to break? PVC is pretty darn strong so it probably would not break. It is your choice to glue or not to glue.
The 90 degree elbow should face forward as shown - not the other way around.
Make sure that the trap is perfectly centered and that the stand is perpendicular to the ground. Put a mark on your trap to show where the exact center is of the trap. I actually do this with my first cable tie when putting the carpet on.
I find that I catch more cats....and catch them much more quickly.... if I use a trail of food in addition to the main bowl of food placed in the center/front of the trap. Make sure that the bowl of food is centered to lower the chances of a tail getting caught under the trap. Also, use both dry and canned food. Some cats do not like canned food yet that is what we most frequently use for our bait....assuming that all cats love canned food when many are dry food addicts.
May, 2007
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