Making cannons from non-traditional materials

[JPZ66]

I have been informed by a highly reputable source, that powder is better suited for metal castings so I will avoid that.

It was suggested that I use a combination of Vaseline and Isopropyl alcohol as a release agent. I am going to try this in the next couple of weeks and will report back with my results.

Sherry,

 

Try it and see what works best, but in my experience, using many different types of resin, the vaseline is highly likely to inhibit the cure if there is any noticeable quantity of it in the mold cavity...... See my post above about powder. If you do not wish to powder the mold, then I would suggest using the mfg'r recommended mold release spray.

 

If you are talking about using vaseline over the master before pouring the rtv mold itself, then yes....vaseline or a thinned version of it works great so that the rtv silicone rubber does not stick to the master part. Be sure there is no porosity in the master either. Any sort of wood or other porous material used for the master part must be sealed and polished or buffed up to as nice a finish as you can get. The rtv rubber will capture the smallest flaw left on a master part, and be in the curd mold. When you later start casting parts, that flaw will be on each and every part. Even including such tiny flaws as brush marks or fingerprints.

 

Having done casting and mold work in the past for many 'cottage industry' companies in the scale modeling community....cars, trains, boats, planes, figures and many other items, for such companies as The Laughing Whale / Blue Jacket, Copper State Models, Liberty, Squadron, Tom's Modelworks, Fisher Model and Pattern and more, both in resin production and pewter, I'd like to think I gained some decent understanding and experience with the materials and the processes

 

 

Joe

[tkay11]

That's a great explanation, Joe. Thanks very much for the info. I hadn't thought of surface tension.

 

Tony

[newbuilder101]

Okay, I think I'm ready to fire my cannons.......................out the window that is!

 

I have tried casting with mixed results, none of which has yielded the end product that I deem acceptable for mass production! I have come to the conclusion that the biggest challenge has been casting at such a small scale - 1/96. These things are tiny! The problem arises in trying to pour/force the resin into the 2 part mold. Because the scale is so small, the pour hole has to be kept relatively small as well, and thus the problem. Just out of frustration, I tried filling the cavity in each half mold and then "slapping" them together.....believe it or not, this gave the best results, but still not exactly what I want. I will try to post a pic of the trials later. The diluted Vaseline worked quite well as a release agent and sticking was never an issue. 

 

For the curious, I used polyester casting resin and RTV rubber molds.

 

I may keep experimenting, or try something totally different - I am DETERMINED to make these things myself!

[hexnut]

If you prefer metal, there are low-temp tin-bismuth alloys that work with silicone molds:

http://www.micromark.com/casting-metal-type-280-75-ozand135-cubic-inch,8331.html

I haven't done this in a while, but as I recall, they flow nicely, just add some wires and cones to your master for pour and vent areas.

 

As Druxey mentioned, Micromark also sells resin and various casting media.

[casper1961]

Hey Sherry...I saw your posting regarding the results or lack of so far in casting the cannons.

 

For this size casting I definitely would be painting the resin on both sides of the mould, (if you made your mould properly, you should have a fairly good size reservoir to use) Why?

 

Once you have painted both sides of the mould with resin, and "slap" the 2 parts together, in your case I would stand the mould vertically and pour some leftover resin in the reservoir and squeeze the mould halves together like you are giving it CPR, squeezing the air out and drawing the resin into the mould, pumping it vigorously. This is if you do not degas the resin with a vacuum chamber or vibration.

 

This usually works very well...messy?...can be!

 

How many barrels do you have in your mould? If you have several, this comes in handy in that you may have 4 in the mould and each casting get 1 to 2 that are perfect...still better than carving each....as you do more of this you will find little tricks that make it work better each time.

 

How long do you have for setup time before the resin starts to turn solid? 5 minutes? 10 minutes?

 

Steve

[EdT]

Sherry,

 

I have never had much success with casting resin on a small scale, but have cast thousands of miniature figures in metal using epoxy molded patterns.

 

You have not shown a picture of your mold, but I assume you have included vent passages from the bottom of the molded part up and out the top. These are essential to get the air out of the mold and allow the resin to get in. You should not need a big hole if the mold is vented. If you have already made the mold and need to add vents, you can cut them with a knife or a carving gouge. Even with vents you may have bubbles especially with resin. If so, try tapping themold after pouring to work the bubbles out. You can do the same when you pour the RTV to make the mold if you are having bubble problems in the mold rubber.

 

I use a vacuum degassing chamber to remove air from the rubber and a centrifigal molding machine to get the mold filled and any air out, but miniature figures have deep and complex undercuts. Obviously you do not want to go that far to cast a few guns. Guns are fairly simple.

 

I would recommend the low-temperature alloy route suggested by hexnut. The weight of the metal helps drive the bubbles out. If you use metal you may want to dust the mold with talc before pouring. This will help with degassing. I assume you are only using the vaseline solution to coat he pattern when making the mold. I would not use it when casting regardless of the material.

 

Hope this is useful.

 

Ed

[newbuilder101]

Thank-you everyone for taking the time to help!

 

Bob: I haven't totally ruled out metal yet. If my next few tries with resin don't work, then that may be next.

 

Steve: I did paint both sides of the mold first, but will try "CPR" on it next time. Goodness knows they certainly need resuscitation! 

I've made a couple of 2 barrel molds, and the setup time is about 8-10 minutes.

 

Ed: I am seriously considering metal as an alternative, but would like to give the resin another couple of tries using the advice given. 

I've included a few photos of my molds and some of the rejected barrels. 

 

The barrels look better in the photos than they really are, at least they don't look good to me. 

 

 

[realworkingsailor]

Just a thought, what about casting the canon barrels as halves in a flat open mould, and then gluing them together?

 

Andy

[newbuilder101]

 That might just be worth a try!

[realworkingsailor]

I'd say also leave off the trunnions as well, just mould a little dimple as a drill start point. They're easy enough to make with wire afterwards.

 

Andy

[Remcohe]

Sherry, like Ed mentioned, adding a vent will greatly improve your results. I see your mold lacks one now, you can just cut one with a knife. 

 

Remco

[EdT]

Sherry,

 

I would take vents up both sides of each barrel and add vent passages from the ends of the trunnions into those. In looking at a closeup of your casting, it appears you may have some mold alignment problems as well. If you used vaseline in the mold before pouring the resin, that may account for the incomplete filling. These are all common molding problems. Again, I think you may find lo-temp metal to be easier t0 work with.

 

Good luck. Casting is a journey.

 

Ed

Edited June 19, 2014 by EdT

[gjdale]

Hi Sherry,

 

Just found this thread via your San Felipe log. I'm afraid I can add precisely nothing to the knowledge base here, but I'm fascinated by the process and will follow your learning journey with great interest. Good luck!

[newbuilder101]

Thanks again for all the input! Judging by all the advice given, I think my next step will be to make a brand new mold with plenty of vents and try again.

[Remcohe]

I would also turn the cannons 180 degrees so the wide end is closest the pouring hole, the other way around adds the risk of trapping air.

 

Remco

[hermies22b]

Hi - All complicated. Fast way is paper. What you do afterwards is up to you.

[allanyed]

Hermie,  What do you mean fast way is paper?  Can you post a couple photos?  Thanks

Allan

[GrandpaPhil]

I like to carve cannons from dowel rods.  It works well for me.