Want to have a little mildly dangerous fun this weekend?
Make your very own Ping Pong Blaster!
This is basically a small, handheld potato cannon that shoots ping pong balls. It uses denatured alcohol as fuel, and makes an incredibly satisfying "FWAP!" when you fire it. I've sent sent a few ping pong balls over 50 feet with it.
Like anything that involves combustibles, it should only be used outside with caution and common sense.
Want to make one? It's not that hard. Let's get to it!
Step 1: Critical Components
There are two necessary parts.
One is a replacement igniter for gas grills. I purchased a Brinkmann brand igniter for about $12 USD.
The second part is a "Bulb Type Battery Filler" which I purchased at an auto parts store (O'Reilly) for about $6 USD. The outer diameter of the open end of the bulb portion is just over 1 3/4". The inner diameter stretches to snugly fit a standard 40mm table tennis ball.
Step 2: Pattern
I made up a basic pattern and cobbled together a prototype. After testing and tweaking the design a bit, I drew up the final pattern which is linked below.
I recommend printing this pattern onto stiff paper and cutting out the pieces to trace onto the the wood. This works better than using spray adhesive to affix the pattern to the wood, as the handle portion needs to be used to lay out three separate pieces.
When you print out the pattern, print directly in actual size with no scaling.
If you have the precise thicknesses of wood noted in the next step, everything should work out well. If not, the various notched areas in the pattern marked with dashes ( - - - ) will need to be modified to fit whatever materials you are using.
Step 3: Lay Out Pattern Pieces
Trace all the pattern pieces onto the correct thicknesses of material. I used plywood for everything but the grips, which are made of MDF.
The circular piece and the horseshoe piece are made from 10mm or 3/8" material.
The main handle piece is made from 3/4" material (actual thickness was 11/16", or 17mm).
The two grip portions are made from 1/4" material.
The circular piece has five cross hatches, which should be punched through with a nail set to assist in pre-drilling holes later on, and for centering a hole saw when cutting out the center circle.
Step 4: Cut Out Pieces
A scroll saw, band saw, jig saw, or even a handheld coping saw could be used to cut out these pieces. I used a band saw with a 1/4" blade.
Prior to cutting out the circular piece, drill out the center hole with a 1 3/4" hole saw. Use scrap wood underneath, or cut halfway through and then flip the piece to finish the other half.
Step 5: Test Fit, Make Adjustments
You may need to nibble away a little here and there to get all the pieces to fit together nicely.
Ultimately you should have a hand piece that fits together as shown. No glue or screws are added at this point.
Step 6: Fit Igniter
On the pattern, there is a line indicating where the center of the igniter should run. Trace your igniter over this area, and cut out. The igniter should fit snugly, so cut the opening a little small initially and then remove material as needed to open it up for a nice fit.
Cut an opening for the wires just above the back end of the igniter. I used a small carving bit on a dremel to do this, chewing a little away at a time with the tool angled from either side of the hand piece. Another option would be to simply drill a 1/4" hole through the backside of the hand piece, catching the back end of the igniter cut-out, and into the bulb support area.
Step 7: Glue on One of the Grips
Use clamps and wood glue to attach one of the grips. Try to get all the edges as close to flush as possible.
Step 8: Screw on Second Grip
The second grip is attached with short screws into pilot-holed, and countersunk holes. Use clamps to assist in initial positioning before drilling pilot holes.
Step 9: Shape Grip
Both sides of the grip can now be shaped with whatever suitable tools you may have. I used a coarse sanding drum on a dremel, which kicked up a lot of dust. If you do it this way, be sure to wear eye protection and a suitable mask. I followed this by hand sanding with 220 grit sandpaper.
Other options for shaping the grips could be careful routing, knife carving and sanding, or using files and rasps. Or you could just sand off the sharp edges by hand and call it good.
The marked areas in the second photo show where I recommend removing material to make an especially comfortable grip.
Step 10: Detail Sanding and Initial Assembly
I gave all the individual pieces a light sanding to remove the saw blade marks using a benchtop spindle sander, and followed with 220 grit hand sanding to gently round over any sharp edges.
When the pieces are sanded to your liking, assemble them together and fasten with four short screws through the front, circular piece. Pre-drill and countersink these screw holes through the marks made earlier.
I used 5/8" screws to attach this front piece, as well as the grip piece.
This is the finished state of the hand piece, but it needs to be disassembled to apply finish and add the other components.
Step 11: Finish
Finish the pieces as you see fit.
I finished them simply with paste wax, but you could coat with lacquer, shellac, or any other finishing product.
Step 12: Add Igniter
The igniter is now installed. These types of replacement igniters come with wires that have connectors built in. Trim the two wires to about six inches in length
Connect wires to ingiter, and feed them through the hole that leads from the handle to the bulb support area. Fit igniter into opening, and use a small amount of hot glue to hold it in place.
Replace grip and fasten with screws.
Step 13: Prepare Bulb
I tried a few different variations on how to connect the wires into the bulb to create a consistent spark.
The best way I found was to use two 1 1/2" #6 machine screws, tightened in place with nuts on the inside of the bulb.
Use a soldering iron with a pointy tip to melt two holes through the bulb 90 degrees apart.
Strip about an inch and half off of the end of each wire, and wrap each wire onto the top 1/4" of each respective screw. Use heat shrink tubing to fasten wire in place onto end of each screw. This method provides a lot of contact area and ensures an excellent connection. (I tried just tightening the screws over a single wrap of wire, but the spark wasn't very consistent.)
Push the screws into the bulb and fasten in place with nuts. To simplify getting the nuts onto the screws inside the bulb, you can depress the side/back of the bulb next to each screw and push it so its end is near the opening.
Don't over tighten the nuts; they should just be finger-tight. Ideally you want the two screw ends to be as close as possible without touching.
Now test it out!
Does it spark? Consistently?
If not, check your wiring and make sure all connections are solid.
If it is sparking consistently, you are now ready to start blasting some ping pong balls!
Step 14: Fuel and Other Tips
I tried various fuels, but had the most success with denatured alcohol.
I like denatured alcohol because it doesn't smell terrible and it burns clean without leaving any glue-like residue. Best of all though, is that you can make 6 or 7 shots with a single fueling!
To fuel the bulb, put about 5 drops of alcohol in. Swirl it around and shake the blaster to spread the fuel around the walls. If you hold it upside down, there shouldn't be enough alcohol to drip out.
Twist and push a ping pong ball into the opening, but no more than halfway in.
Aim and fire!
Check to see if the fuel remained lit. If so, quickly and sharply blow out the now-lit fuel from the side of the opening. Not from directly on, or you may create a burst of flame and singe your eyebrows!
To refire, move the blaster through the air to circulate fresh air into the bulb. Don't blow in it to clear it out--it needs to be fresh air. Replace ping pong ball and fire again.
Don't fret if the blaster doesn't fire. The necessary fuel/air/spark combination is delicate. The method I've described seemed to produce the best results for me, but you can surely play around with it and figure out what works for you.
If you make one, I'd love to hear how it goes. Tips, suggestions and comments are wholeheartedly encouraged.
Have fun and be safe. Thanks for taking a look!