Resin casting tutorial/information?

[Ovidius Incertus]

I looked in the tutorials section here and didn't see anything on the first few pages.

 

Anyone have a recommendation for a good source for information about molding and then casting resin bits?

[Olis]

Well, there's plenty on Youtube for press moulding (here's an example) and the old casting videos by XanderXereus still seem to be up.

[SquigBait]

If you are in the US, I strongly recommend and stand by Alumilite products. I used to work at a metal casting company making masters and we used their RC3 resin to great effect. It is easy to use in that it is equal parts A and B parts, it flows really well and picks up detail exceptionally well, sets and cures quickly, and is strong enough to survive the temperatures and pressures of the vulcanizing process for making rubber molds. This translates to a user friendly resin that stands up very well to use and abuse on the gaming table. You can find their tutorials on their website at http://www.alumilite.com/store/pg/13-How-Tos.aspx

[Ovidius Incertus]

How much casting can one get out of various sizes of casting kits?  It seems like the silicone goes quite quickly, based on how thick the molds are in some of these video tutorials.

 

If one is interested in starting out casting torsos/heads/arms, how big of a starter kit is necessary?

[Carlson793]

Using the Alumalite Mini Casting kit, I was able to make a mold of the doors and faceplate for a Red Scorpion Rhino. Based on Alumalite's volume calculator, you'd get 6-8 casts with the resin included in the kit. The Super Casting Kit contains four times the Mini's material.

 

A product I'm starting to experiment with is ComposiMold. It's microwaveable and, unlike silicone rubber, reusable. Melts to the consistency of honey (with roughly the same stickiness if/when you get some on your hands).

[Subtle Discord]

If all you are doing is small things like heads, torsos, arms, man-portable weapons, etc., then a smaller kit will be more then enough to do several moulds. But as you have noted, as soon as you get up into even a medium or large size mould the rubber usage will go up significantly. Note that RTV rubber and resin plastics have a shelf life. Rubber will slowly get thicker-and-thicker until it becomes useless, and resin will turn to slush in the bottle. There are aerosol products that can add a gas layer to a container to extend the life, but it only slows the inevitable. You generally have about 1 year from opening the container before you lose it. Plan accordingly.

Reusable mould compounds are not horrible, but they will be less accurate and require more trial and error to get really nice results if you're after really faithful reproductions. Complex objects will likely have much more prominent mould lines that will require a bit more cleanup. For simple press moulds they can do very well, but they will also struggle with some details where proper RTV rubber will produce amazingly accurate results no matter what they shape or level of detail.

It all depends on just how serious about making copies of something; walk this path carefully, resin addiction is real (I'm proof of that) and it will cost some money to satisfy the itch. But seriously, small scale casting it not extremely expensive if you keep it simple (considering the cost of this hobby in general) but there is a cost involved. I use SmoothOn products and I buy the RTV rubber by the gallon at roughly $225 CAD; it's a 50/50 mix so you get 2 gallons of final rubber. A quart measure is $44 CAD (again double the actual rubber) and I would guess that you could get 5-10 small moulds out of it. ~$5-10 per mould in RTV rubber is not too bad as long as you're going to make a few copies that will make it worth while.

Finally, as a shameless personal plug, have a look in my Legion Rising W.I.P. thread for my misadventures in resin casting. If you go way back in the thread you can find my earliest moulds and see how I started out just wanting to replicate a single scratch built part. Once you've got the skill at your disposal it can be really powerful; make one, cast a bunch, can save a ton of labour. Even if it's a hobby, time is money, really. Saved time is currency you can use on other projects.

Edit: Interesting! That mould making product is not what I though it was. Something like that, if you're willing to go the split mould method for harder objects, could produce very good results. The fact that it becomes a proper pourable liquid is key to it working well. I wonder just how warm it needs to get?

[Carlson793]

Edit: Interesting! That mould making product is not what I though it was. Something like that, if you're willing to go the split mould method for harder objects, could produce very good results. The fact that it becomes a proper pourable liquid is key to it working well. I wonder just how warm it needs to get?

130° F (not to exceed 200° F). That's about 30-45 seconds in the microwave per 10 oz, and probably not quite as warm as what's coming out of your homes water heater. I was able to make a couple quick-and-dirty clear Culexus Assassins with it, which I need to revisit using more detailed mold making practices (vents and channels and such - I was rushing to get them ready for a tournament).

[Ovidius Incertus]

Thanks, fratres.  I think I will start with the Alumilite kit and see what sort of trouble I can get up to and experiment with the reusable mold material after I get my footing.  Maybe get some Instamold to mess around with GS press molds first.

 

Quick questions:

 

About orienting a torso into a mold: is it best to put it into the clay chest side down and then put vents in at the arms (like some FW torsos) or to press the torso in at an angle and vent into the waist socket (like some older FW torsos)?

 

Heads should go face down so any mold line is on the side/top of the head and not bisecting the face?

 

And how thick of a mold do you want for relatively flat pieces like vehicle doors?  If the mold is too thin, you'll get warpage?

[Carlson793]

Heads should go face down so any mold line is on the side/top of the head and not bisecting the face?

 

And how thick of a mold do you want for relatively flat pieces like vehicle doors?  If the mold is too thin, you'll get warpage?

While heads would be best bisected (giving you a few long mold lines to remove instead of many short ones), I think that would have the potential to kill the face details (especially the mouth grill),

 

For doors, I think a silicone thickness equal to the doors on each half (so the entire mold is about triple thickness of the door) gives a good foundation (though add a couple pieces of cardboard when you wrap the mold for casting to avoid any flexing).

[Subtle Discord]

I would remember the simple fact that bubbles will rise; try to orient the object in such a way that if a bubble does get trapped it will be as least noticable as possible. That way you can hopefully hide it during the assembly of the parts or it will be easier to fill and repair.

 

Without using pressure and/or vacuum you will need to be careful and creative with your vents to maximize the release of trapped air to avoid bubbles; orient the object to work with these considerations. The simplest rule of thumb is that you'll want the bubbles to be on the bottom of the object, whenever possible. A bubble that forms on the bottom of the foot of a model is not a problem compared to a bubble on a toe, for example.

[SW1]

I second the warnings over how addictive casting can be. I've had fun making tiles for a board and currently casting enough parts to cover an 8' x 4' board. It's not cheap covering that area with a minimum thickness of 5mm of resin. :lol:

[Subtle Discord]

On the subject of mould thickness. To avoid warping to the final object best practice is a thickness of 1cm beyond the highest point. So a simple flat armour plate would be moulded best by a ~2cm mould. Now, that isn't a 100% hard rule, and you can make a bit thinner in many cases. Additionally you can cut Masonite boards to place on each side of a mould and wrap the whole thing with rubber bands to apply flat even pressure to the mould to ensure it doesn't deform. I recommend this in general, unless the mould is very large, and you can use just the rubber bands. Doing that will let to get away with even thinner moulds, but I would still make them reasonably bulky. Reducing the flat armour plate from the earlier example to ~1cm would be the lower limit, to give you an idea.

 

Edit: to answer the specific question of how to vent a torso, since it makes a good example. Forge Worlds uses at minimum (likely Pressure as well) Vacuum to degas their resin; the vacuum applied actively pulls the gas out and also lowers the boiling point of the liquid plastic further boiling the trapped air out. With that method it is easy to get away with a single large gate at the bottom of the torso, since it is an active process that will force the air out. In your case it might be safer to add the additional vents out of the side to provide all the air escaping paths possible. A few extra vents in areas where you worry the spot might catch a bubble is always better then discovering a trap zone after the mould is made; you have to either modify the mould by manually cutting it, or make a new one with more vents.