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Author Topic: Cannon! (Arming the Hammerhead Castle with light Naval Artillery)  (Read 6676 times)
Matthias Gladstone
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« on: April 04, 2013, 11:43:27 pm »

I jokingly remarked to a friend a few weeks ago that the next time I saw him i'd have a cannon; me being me, I mused on this for a while before deciding to make it happen:


It's a 1:1 scale replica of a generic 18th-19th century swivel gun, cast in polyurerthane resin. A friend of mine cut the pattern on wood using a lathe, and i've spent the past day and a half feverishly making an RTV silicone mold (not cheap!) and casting it. It'll be mounted on a tripod when finished. Obviously, it's fresh from the mold and hasn't been cleaned up yet.
The wooden pole you can see is the "core" which defines the bore. It's only bored to about 4" for the sake of strength.
I cast this one for myself, but I will be casting them to order eventually.
-Matt
« Last Edit: April 05, 2013, 12:14:43 am by Matthias Gladstone » Logged

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IGetPwnedOften
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« Reply #1 on: April 05, 2013, 12:44:46 am »

If I could offer a tip here - I've made moulds of many large items in the past, and my uncle showed me a great method to do it cheaply.

If you get a big bucket of water, like one of those 5 gallon paint tins, and then get some tubes of cheap silicone sealant, you basically dump all the sealant out of the tubes into the water and it turns almost into putty. Add two layers of thin metal around the edge of the piece to create a flange so you can separate the mould into two halves. Ideally to do this you should cut a slot all the way around the item and push the metal into it so it forms a perfect seal with the piece.

Work the wet sealant into a ball with your hands and then you use that to cover the item you want to mould, making sure you cover the metal flanges too, and leave it until it has completely set, and there you have your mould.

You can also strengthen it with fibreglass and wooden battens once it's dry if you plan to use it repeatedly.

It can be a touch on the messy side, but it's much cheaper than using silicone rubber.
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Drew P
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« Reply #2 on: April 05, 2013, 04:14:51 am »

IGetPwnedOften,thanks for that lesson! I would assume one has to coat the object being made into a mold with a release of some sort,yes?
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« Reply #3 on: April 05, 2013, 07:56:44 am »

How much are we going to piss off Gideon with that. And you keep telling me the society has too much weaponry
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Esteem Punk
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« Reply #4 on: April 05, 2013, 11:01:23 am »

I've seen the water method done as well. Although detergent was added. I was told it was a catalyst to make the silicone cure faster.
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IGetPwnedOften
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« Reply #5 on: April 05, 2013, 01:14:00 pm »

It's been a while since I made a mould like that, but I seem to recall we didn't need a release when creating the mould as the silicone didn't stick to the subject as long as it remained wet, but it probably wouldn't hurt to give the subject a thin coat of Vaseline, which again is way cheaper than most release agents.
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Drew P
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« Reply #6 on: April 05, 2013, 01:50:23 pm »

o,good,there's plenty of KY around at work

Excellent! I just remembered that we used Murphy's oil soap back in college for plaster molds. Too much of a mess and not easy enough to control.

Thanks!
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Fat Spider
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« Reply #7 on: April 05, 2013, 07:53:31 pm »

The problem with Vaseline is it makes a mess of the Master and it's also very difficult to apply without also leaving some form of texture (brushmarks etc), and RTV Silicone been what it is will pick up every mark. Release sprays are much better and well worth the money for anyone intending to make several moulds.

In use an RTV Silicone mould doesn't really need a release agent for something like Polyurethane resin although it is beneficial in helping to prolong the life of the mould especially if the cast has a lot of texture.

I've not heard of the idea with the Silicone sealant, but that stuff isn't cheap either.

As for doing things on the  cheap, Plasticine makes an excellent temporary mould for small objects, the Spiders on my Nerf were cast using an impression of a silver charm.
Spoiler (click to show/hide)

PS: nice job on the Canon, I can't imagine the true size but the thought of how much RTV you must have used makes me wince!
« Last Edit: April 05, 2013, 07:55:25 pm by Fat Spider » Logged

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« Reply #8 on: April 05, 2013, 08:29:36 pm »

If you make molds fairly frequently then vinyl rubber can be a much more economical alternative to silicone. It isn't any cheaper to buy but you can re-melt old molds to reuse the material quite a few times. This also means that, if you need to make a number of castings you can recycle the production mold once it starts to get a bit ratty.

The downside is that it's poured hot which means that you can't use anything too heat sensitive for the master. Having said that it's often helpful to make a master pattern from your original rather than take your final mold straight off the original in any case. For example for hand and face casts it is common to take an impression with palatinate, immediately make a plaster cast from the alginate and use that as your master.

Using skin molds with a plaster or fiberglass jacket can also be a good way to make expensive flexible mold materials go further.

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Matthias Gladstone
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« Reply #9 on: April 05, 2013, 09:26:53 pm »

Cheers for the advice guys, but the images you can see above are of the prototype casting. I made the mold on wednesday evening:

I went for RTV silicone purely because i've got experience using it - nothing about this project has been cheap, so I decided to use the most reliable method I knew.
-Matt

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Maets
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« Reply #10 on: April 05, 2013, 09:42:25 pm »

Very interesting. What is the size?
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Captain
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« Reply #11 on: April 06, 2013, 12:50:30 am »

I have a small carronade and bronze mortar but I have been wanting a swivel gun for some time.  Preferably bronze, about a 1" or 1/4# bore, and cheap. 

Have you seen?  http://www.hernironworks.com/cannonprice.html   or  http://www.fortvauseoutfitters.com/artillery-bronze 
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-Karl
Matthias Gladstone
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« Reply #12 on: April 06, 2013, 01:19:11 am »

Interesting; sadly you can't own a working cannon over here without a smoothbore and blackpowder license (i'm sure you could claim "obsolete caliber" but I wouldn't want to try it).
I'm going to try casting one of these with a bronze powder filler; this should give a finish similar to the guns you linked to.

Edit: about 42cm cascabel to muzzle. It's around the size of the smaller swivel guns. Bore is just over an inch. I wanted it about 25% longer but we were limited by the wood available.
« Last Edit: April 06, 2013, 01:40:12 am by Matthias Gladstone » Logged
Professor J. Cogsworthy
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« Reply #13 on: April 06, 2013, 01:59:58 pm »

What is the silicon to water ratio?

how many tubes are you talking here?
 ( let's say for a 5 gallon bucket.. .)
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IGetPwnedOften
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« Reply #14 on: April 06, 2013, 04:13:02 pm »

As I recall, and this is going back several years now, as there was three of us making the moulds and they were big moulds (we were casting copies of old wooden porch pillars), we basically had one person constantly pumping tubes of sealant into the bucket and the other two were taking it out and working it onto the subject, so I would suggest a similar method.

As long as you're reasonably swift you can keep adding as you go along rather than trying to do it all in one go.

By the way Matt, sorry for totally hijacking your thread. Maybe we could get these posts split out into a separate thread?
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Fat Spider
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« Reply #15 on: April 06, 2013, 06:48:32 pm »

Sorry to continue with the hi-jacking, but was the silicone the cheaper acrylic based stuff or the real stuff that smells of acetic acid when curing?

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IGetPwnedOften
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« Reply #16 on: April 06, 2013, 07:51:31 pm »

I'm not sure - my uncle bought it, but I'd say most like the latter as it did give off an acidic smell while curing.
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Captain
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« Reply #17 on: April 06, 2013, 10:17:10 pm »

Interesting; sadly you can't own a working cannon over here without a smoothbore and blackpowder license (i'm sure you could claim "obsolete caliber" but I wouldn't want to try it).
I'm going to try casting one of these with a bronze powder filler; this should give a finish similar to the guns you linked to.

Edit: about 42cm cascabel to muzzle. It's around the size of the smaller swivel guns. Bore is just over an inch. I wanted it about 25% longer but we were limited by the wood available.


 Embarrassed  Here we use spare cannons as submarine weights. 



Cannons are like microwaves and internet; once you have it it is hard to live without them. 



This is my little bronze grenade launcher/mortar.  There was a shoulder fired version and they fire basically the same size ammo as a Coehorn.  While a Coehorn is supposed to range out to maybe 1,600 yds these little ones are good for maybe 400 yds.  They are as loud as much larger cannons.   Grin  These folks sell a kit for the shoulder fired version:  http://www.therifleshoppe.com/ 
 
We used to go to a cannon shoot in North Carolina.  The host built a detailed sailing ship model manned by rubber rats.  It was on a pulley system in a lake and the ship was maybe 8' long.  You have to fire chain-shot!  It will even skip off the water like a stone. 
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Matthias Gladstone
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Call me Ishmael


« Reply #18 on: April 08, 2013, 02:35:29 pm »

Finished and painted:



-Matt
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IGetPwnedOften
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« Reply #19 on: April 08, 2013, 02:47:35 pm »

That looks great  Grin

I suppose if you wanted to simulate firing it you could always drop a banger into the muzzle...
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Matthias Gladstone
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« Reply #20 on: April 08, 2013, 03:12:23 pm »

It's only bored to about 4". Wouldn't want to risk it though.
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Major Willoughby Chase
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« Reply #21 on: April 08, 2013, 05:03:58 pm »

A lovely project, reblogged almost instantly to my Facebook (well, the advert version), fantastic to see something new being created. Well done!
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Matthias Gladstone
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« Reply #22 on: April 09, 2013, 04:09:28 pm »

Thank-you very much!
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RJBowman
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« Reply #23 on: April 21, 2013, 06:05:45 pm »

Cheers for the advice guys, but the images you can see above are of the prototype casting. I made the mold on wednesday evening:

I went for RTV silicone purely because i've got experience using it - nothing about this project has been cheap, so I decided to use the most reliable method I knew.
-Matt




That is a huge amount of silicone rubber. I would have used latex with a plaster mother mold.
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IGetPwnedOften
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« Reply #24 on: April 21, 2013, 06:21:29 pm »

Doesn't latex tend to shrink over time? I've cast some bits in latex (the kid's hands and feet mainly) and after a while they all shrank to about 2/3 of the original size.

I have to say if I wanted a mould to last so I could re-use it, I'd stick with silicone.
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