I will show you how to build a net gun out of materials available at any big box home improvement store. This net gun is capable of firing a 90 square foot net 15 to 25 feet using 80-100 psi of compressed air. The net is reusable, assuming your prey doesn't destroy or run off with it. The launcher section is modular and can be removed in case you want to use a different design or add attachments. Thread on some 1" PVC pipe and you have a Christmas Cannon, or check step 11 for how to build a tennis ball launching attachment.
The net gun is similar to many pneumatic launchers, but instead of launching a single projectile, it launches four tractors that pull the net through the air. The tractors are based on the fact that the neck of a standard soda bottle fits very well over the outside of 1/2" PVC pipe. The cost to build this will range from approximately $40-$75.
Before you begin be aware that this project uses PVC pipe in an application it is explicitly not intended for. PVC is meant for water, not pressurized air or other gases. The problem is not the pressure, this project uses pressures less than half the working pressure of any PVC component, but the failure mode when pressurized by gas. If the PVC is compromised, by dropping, impact, or other means, it shatters into sharp pieces that are ejected by the pressurized gas. An excellent discussion and demonstration here, make sure to watch the video through to the end.
Nearly all of these items can be picked up at your local home improvement retailer. It is probably worth buying a full 10' length of 1/2" pipe, for all the other sizes see if you can buy shorter lengths or scrap. Alternatively, get some friends together, share the costs of the full length pipes, and build a lot of net guns. The tire valves are available at auto parts stores. The net is addressed in detail in the next step.
All PVC fittings are slip fit unless otherwise noted
All PVC pipe and fittings must be SCH-40 (SCHedule 40) unless otherwise noted
All PVC pipe should have a PSI rating of 200 or greater, absolutely no cell core ABS DWV pipe
1 1" MPT (Male Pipe Thread) to 1" slip street elbow
1 1" elbow
1 2" to 1" reducer bushing
1 2" cap
1 2" coupler
1 foot of 1" pipe
minimum 9" length of 2" pipe
**1 valve stem, prefer a .453" as it corresponds to the readily available 7/16" drill bit
optional 1 pressure gauge
**There are two standard size automotive valve stems, one for a rim hole sized .453" the other .625". These two sizes correspond to fractional drill bit sizes of 29/64" and 5/8" respectively, the much more common 7/16" bit can be substituted in place of the less common 29/64". Additionally, most common drill indexes stop at 7/16" or 1/2" and do not contain the larger 5/8" bit.
3 2"(ish) wood screws
Wood scrap for base, a 16" length of 2x4 should work fine
4 13" lengths of 1/2" pipe
1 1/2" cross
2 1/2" tee
4 1/2" street elbows
4 1-1/2" pieces of 1/2" pipe (coupler joiners)
1 1-1/2" pipe 9" long
1 1-1/2" coupler
**1 1-1/2" to 1/2" reducing bushings
** 1 1" MPT to 1/2" slip
** these transitions usually can't be made with one adapter, just make sure the starting and ending dimensions are correct.
Memphis Net and Twine sku# 263 1lb minimum order is enough to make 7-8 nets
OR a substitute net computed using the net math spreadsheet and instructions in step 2
Nylon mason's twine (#15 or smaller), kite string, or some other thin durable rope
4 per net 16-20oz carbonated soda bottles
4 per net zip ties > 4" long
Hot glue/silicone/wax to pour in bottles to add weight
Optional additional items needed for high performance net tractors
4 per net 3/4" couplers
4 per net 3/4" caps
4 per net 8" lengths of SDR-21(Class 200) 3/4" thinwall PVC note: regular 3/4" SCH40 will NOT work!
4 per net 12" lengths of non-adhesive 1" ID foam pipe insulation. Pipe insulation is generally sold in 6' lengths.
PVC pipe cement and primer
PVC safe pipe joint compound (pipe dope) such as this
Sand, at least two cups worth (for bending the launcher arms)
2 1/2" pvc caps (for bending launcher arms, not part of gun)
Epoxy for modifying sprinkler valve
Thread locker (Loctite)
Saw, for cutting PVC pipe
Heat gun, propane torch, or candle for bending PVC
3/16" and 7/16" (or 5/8" see the **note in the pressure chamber section) drill bits
Dremel tool, or similar, with a sanding drum
Wrench for 1/4" npt hex nipple
Large adjustable wrench or channel-lock pliers, for tightening the trigger valve
A compressor or pump capable of attaching to a Schrader tire valve and attaining at least 80 psi
I ordered my net from the Memphis Net & Twine Company. If you have your own favorite gill net vendor, you can probably order an identical item from them. I have NO financial ties to MN&T other than being a satisfied purchaser of their retail products.
Here is the link to the product page on the MN&T website. Below is the exact info from my order information page, shipping is not included in the price. One pound of this net (minimum order) will make 7 or possibly 8, 9-1/2 foot square nets.
Description: 3 in. sq. mesh, 12 ft. deep
If you would like to try an alternate net part number please read the Alternate Net Substitution section below.
Optional Net Math Section
You may have noticed that the catalog description lists the net as 12 feet deep while I have claimed it is 9-1/2 feet square, why the difference? Let us first deal with a hypothetical net that has 3" mesh and is 3 meshes deep. You might think 3 x 3 equals a 9 inch deep net, but that would be incorrect. Visualize the meshes as diamonds stacked point to point and NOT squares stacked like bricks. Reference Fig 1 and it becomes apparent that the depth of our hypothetical net is nearly 12-3/4 inches. To extend this example to MN&T sku# 263, 27 x 4.24 equals 114.48 inches, divide by 12 and we get 9.55 feet deep. So where does MN&T get the 12 foot depth figure? They are building a certain amount of droop, when used in a fishing application the diamonds will be longer vertically than they are wide.
I have included a spreadsheet that will allow you to enter different figures to see what size net you will end up with, and how many nets you will get from a pound of that particular net. If the spreadsheet returns a zero for waste material, you may want to subtract one net from the total expected. The default numbers in the spreadsheet are for MN&T sku #272.
Alternate Net Substitution
I will use MN&T catalog and part numbers in this example, but as long as you know the correct variables, any net vendor should work. Using the spreadsheet is important, if you don't own MS excel, consider downloading OpenOffice. An excellent free MS office replacement that will allow you to view and edit the Net Math spreadsheet.
Please consult Fig 2 or have the spreadsheet open for this example. The top section of the spreadsheet contains a section called Mesh Count Estimator. This will help you calculate the mesh count you need to reach a desired net size. In this example I have entered 3.5 (3-1/2" mesh) in the Mesh size cell and 9.5 in the Desired depth cell. This should closely match the sku #263 net's overall size but with a 3-1/2" mesh instead of 3". The computed result, 23.03 appears in the mesh count cell. As fractional net meshes don't exist, just round to the closest integer, 23 in this case. Next, we will browse through the MN&T catalog for a 3-1/2" mesh net 23 meshes deep.
Go to the multifilament net section of the MN&T web catalog, then select #208 twine size and browse through the 3-1/2" mesh part numbers to find a net closest to the 23 mesh count. Part number 272 fits our specification perfectly.
Now enter all the information from the 272 page into the yellow cells on the Enter line of the net properties section of the spreadsheet. The Square depth cell tells us this net will be 9.43' square. This is also the spacing for the knots of your spreader string in step 9. The Knot cut point shows we need to count 46 knots and then cut between knot 46 and 47, the Cut length cell tells us knot 46 should fall at 161" on stretched netting. We can also assume that because the overall weight of the 272 net is slightly less than the 263 net, it should fit fine in the net holder.
I would advise waiting to build the net holder part of the launcher section if you try any radically different mesh, twine, or overall net sizes. Once you have the net constructed, fold it up and make sure you have the correct size PVC holder.