Potato cannon carriage #3: Trail, ramrod and major assembly

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Blog entry by JJohnston posted 08-08-2010 07:12 AM 7010 reads 2 times favorited 8 comments Add to Favorites Watch
« Part 2: Frame and elevating arc assembly and trunnion construction Part 3 of Potato cannon carriage series Part 4: Ignition »

We made a lot of progress today. Most of the painting is done, so we could concentrate on assembly. Here’s the lower trunnion assembly with the hanger studs and knobs complete. The potato projectiles are muzzle-loaded, so they have to be pushed down toward the combustion chamber with a ramrod. The ramrod will ride in a tube above the barrel, both to simulate the “recuperator cylinder” on the real thing, and because it’s so long, there’s no other place to put it. The smaller rings on top of the cannon clamp rings will hold the tube tight. It’s 1 1/2” PVC; the ramrod is a 1 1/4” x 48” dowel.

Here’s a shot with the cannon and ramrod tube assembled. The machine screw in the side of the cannon is an electrode/spark plug for the ignition system. There’s also one on the opposite side.

Here’s a shot looking into the breech at the electrodes. You can see my “R” marks (for Rear) chiseled into the trunnion parts here. Heh – you can also see my smaller, handheld cannon on the wall rack across the garage, above my car.

Here’s a shot showing the ramrod sitting atop the cannon. The yellow line indicates the proper projectile seating depth. There’s also some extra length so it can be used as a cleaning rod.

And here’s a shot with the ramrod in its tube. It still lacks the forward bracket holding the tube and barrel together.

Now the trail assembly is going together. At the end of each member, I ran a piece of left-over 3/4” threaded rod down through, and put a plain nut on top, and an acorn nut on the bottom for a foot.

Halfway along the right arm is a bracket to hold the breech plug, so it won’t have to be set on the ground.

I bandsawed a breech plug wrench out of 3/4” baltic birch ply. The plugs tend to get stuck on these, with overtightening and fuel residue; this should be easier on the fingers.

Here’s the wrench in its bracket.

It’s on wheels!

Here’s the start of the forward ramrod tube bracket. I’m going to split this one vertically through the centerline and put 2 screws through it horizontally. I’ve got the edges laid out; next step here is to drill for the screws, then split it, then cut/sand the curves and the taper. It’s a double thickness of 3/4” birch ply.

And here it is sanded and ready for paint. It was almost 9:30, and dark, when I got to this stage, so painting can wait until morning.

Next installment: Ignition

-- "A man may conduct himself well in both adversity and good fortune, but if you want to test his character, give him power." - Abraham Lincoln

8 comments so far

View flyfisherbob2000's profile


81 posts in 3185 days

#1 posted 08-08-2010 09:07 AM

sweet! makes my spud gun look low class by comparasion. Cant wait to see the rest

View kolwdwrkr's profile


2821 posts in 3788 days

#2 posted 08-08-2010 09:40 AM

HAH! That thing is kick a$$. My high school friends and I made one of these (obviously not as elaborate). It wasn’t firing one day so my friends dad took the cap off the back. He was looking inside it clicking the trigger to see if there was spark. Well there was still hairspray in it and it fired a big ball of fire into his face burning his eye brows off. That was the funniest thing I have ever seen and we laughed for days. LOL. Well done. Play safe!

-- ~ Inspiring those who inspire me ~

View docholladay's profile


1287 posts in 3257 days

#3 posted 08-08-2010 10:14 AM

That is cool. That is going to be hugely fun. I used to work in the automotive business and me and some guys in the shop decided to build one of these one day. Ours looked more like a shoulder mounted rocket launcher. We actually used compressed air to propell the projectile. What used a device use for setting the beads on big truck tires which had a valve that allowed us to deliver a large volume of air very quickly at about 150 psi (eventually blew out the pipe). We were shooting spuds quite some distance. Our record shot was several blocks away (that is as acurate as we measured). I saw a guy on some TV show make one similar to what we had and he fired one at a door mounted in a frame and it took the door down. It didn’t go through the door, it knocked the door open as if someone had kicked it open. Amazing what can be inspired by a bunch of guys with one too man beers on a Friday afternoon after work.

-- Hey, woodworking ain't brain surgery. Just do something and keep trying till you get it. Doc

View Dennisgrosen's profile


10880 posts in 3313 days

#4 posted 08-08-2010 01:12 PM

it´s realy begin to come together looks good
thank you for the toturial and the time you used to make it
I look forward to see the next installment


View Manitario's profile


2679 posts in 3081 days

#5 posted 08-08-2010 04:26 PM

very inspiring, I can’t wait to see that bad boy fire

-- Sometimes the creative process requires foul language. -- Charles Neil

View JJohnston's profile


1622 posts in 3489 days

#6 posted 08-08-2010 05:22 PM

Heh – there’s no shortage of “spud gun mishap” videos on Youtube.

-- "A man may conduct himself well in both adversity and good fortune, but if you want to test his character, give him power." - Abraham Lincoln

View Jim Jakosh's profile

Jim Jakosh

21718 posts in 3303 days

#7 posted 08-09-2010 06:56 PM

Very cool. You have to get a picture of it actually shooting. That would be way cool!
I was thinking about making a golf ball cannon because golf balls are truly round and fly so well.
Is PVC strong enough fot shooting a golf ball or should I use a steel pipe?
What is your propellent?

-- Jim Jakosh.....Practical Wood Products...........Learn something new every day!! Variety is the Spice of Life!!

View JJohnston's profile


1622 posts in 3489 days

#8 posted 08-10-2010 03:58 AM

I really don’t know enough about these to say whether or not PVC is suitable for golf balls; however, there’s loads and loads of info on the internet. I also don’t know if a golf ball would fly that well out of one of these, because it wouldn’t be spinning, and it’s the spinning (backspin, ideally) that makes a golf ball fly so well. This is more like a knuckle ball, with its erratic flight. For fuel, I’m using “Static Guard”. I’m told it leaves less residue than hairspray, and so far, in my little handheld prototype, it works fine (and leaves a fresh, clean scent, too). FWIW, I had a guy at work tell me today that ears of corn the right diameter make pretty good projectiles, too.

-- "A man may conduct himself well in both adversity and good fortune, but if you want to test his character, give him power." - Abraham Lincoln

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