Resin casting out of production kits

[Ed Kapuscinski]

So, my downtown York scene is going to require a bunch of the IHC storefront kits.

I've build a bit of a stockpile, but I'm concerned about burning through them.

So, to that point, I've thought about making some castings of the major components (ie, the walls that face out and some of the detail sprues).

What do I need to know to start doing that (aside from that I'm breaking the law if I sell any of them)?

Is the Smooth On pourable kit the place to start? The Micro-Mark one? Something else?

Am I going to need a pressure pot?

[chicken45]

I think pressure pots are a good idea. Especially in n scale where an air bubble could be catastrophic.

[peteski]

For single flat open molds a pressure pot would be an overkill. It wouldn't hurt, but it shouldn't be needed. At least I'm assuming that is what Ed wants to do. Sort of like the old Magnuson Models Hotel kit was made.

There are many resins available out there. Micro-Mark stuff is just repackaged resin (from Smooth-On, IIRC) with much higher price tag.  I started with Alumilite (back when they only had one type of resin available). Nowadays I usually work with Smooth-On stuff, but Alumilite also has a fairly extensive range of products available. Then there are other brands used by the "real" kit manufacturers.

[Rasputen]

How many of these are you planning to make?  Also, how thick are the kit walls?? I recommend a vacuum chamber for making molds, even for rubber where the instructions say it isn't necessary.

[wazzou]

I single molded flat castings of a bunch of DPM front walls, just squish molds.  I was careful in mixing the resin to limit bubbles and the working time allowed time to pop most if not all with a pin before the flash point, put a sheet of glass on the mold with a heavy weight and very little flash resulted. 
I can scare a couple castings and/or molds up and take a picture if you'd like.

[chessie system fan]

I've always needed a pressure pot.  Otherwise my resin turns into practically a foam, but then I live almost on the Gulf of Mexico.  How many kit parts do you need?  You're looking at ~$60-70 (resin + mold material + shipping) just to get started.  For what you're talking about, casting does best with bulk items.  If you need ten of something it's worth it.  If you need two or three of something it's probably not cost effective. 

[Ed Kapuscinski]

I've always needed a pressure pot.  Otherwise my resin turns into practically a foam, but then I live almost on the Gulf of Mexico.  How many kit parts do you need?  You're looking at ~$60-70 (resin + mold material + shipping) just to get started.  For what you're talking about, casting does best with bulk items.  If you need ten of something it's worth it.  If you need two or three of something it's probably not cost effective. 

Thanks for that Aaron. That's a really good point. I hadn't really thought about that. At the going eBay prices, that'd be 4-5 kits beyond the current stockpile.

I guess I should figure out how many I'm REALLY going to need before I go further.

[thomasjmdavis]

For a structure (as opposed to a car or loco shell), something you might consider is casting in hydrocal rather than resin, which can help hold down the expense- and it seems a bit more forgiving.  Unless you need the strength, although I have been surprised by how durable hydrocal is, a big improvement over plaster of paris and such.

[peteski]

For a structure (as opposed to a car or loco shell), something you might consider is casting in hydrocal rather than resin, which can help hold down the expense- and it seems a bit more forgiving.  Unless you need the strength, although I have been surprised by how durable hydrocal is, a big improvement over plaster of paris and such.

Except the wall thickness ends up about 10 foot thick!  At least in most of this type of kits I have seen.  You have to get creative installing windows and doors so they don';t look like a medieval castle.

I don't see a problem with low-volume casting (open mold, no pressure pot).   A trial size Smooth-On resin and RTV kits were about $25 each (last time I bought them).  Yes, you will probably end up just using small portion of those trial size kits, but you will have some nice resin castings.  I've molded about 20 N scale golf carts and bumper cars and that barely made a dent in a trial size resin kit. But it was well worth it.   I really wish that they sold half-size trial kits for casters like me. 

[Angus Shops]

I don't use a pressure pot and I don't have any issues with bubbles, unless I'm using old product or I trap air in the mold inadvertently. I use Smooth On products now exclusively. I would use an open mold that I would slightly overfill with resin and then I would place another flat piece of the mold material (I use the flat side of old clapped out molds) over top (starting at one side and sort of "rolling" the top down so that air doesn't get under it) and then weight it down with a piece of wood and a bit of pressure. When the resin is cured remove the top and inspect for bubbles; any bubbles can be opened up with a hobby knife and filled with a drop of resin applied with tooth pick. When satisfied the finished part can be removed from the mold and you should have good useable part with a repeatable constant thickness and a nice flat rear surface.

I'd start with the smallest kit you can find; you'll get a lot of parts and there isn't much sense in having a lot of resin left over. I'd also recommend getting one of those little digital scales that measure in 1/100's of grams for accurate resin mixing. I mix resin in those little plastic measuring things that come with cough medicines and such; I came across a package of 100 and they've lasted for years. The cured resin doesn't stick to these things and can be popped out. I decant the resin parts (A and  B) into plastic squeeze bottles (easy squeeze out a gram or three and minimizes the number of times the the original packaging gets opened; air and moisture reduces the shelf like of the product). Place the little plastic cup on the scale and turn the scale on and it will 'zero', squeeze in a equal weight of each part, mix thoroughly with a tooth pick, and pour. If you have 5 or 6 not too complex open moods and enough 'tops' you should be able to pour them all in one go. If the mold has a lot of surface complexity you may need to use a tooth pick to tease out the odd little air bubble that nestle into the deeper crevices of the mold before you put the top on.

Have fun, Geoff

[narrowminded]

Wondering what durometer experienced folks have arrived at for their mold materials?  And then which casting resins do folks like? 

I see so many choices but not a lot on specific recommendations.  A lot of "more of this", less of that" and many other generalities.  I would guess the size of the mold, the intricacy, etc, will effect this and those guidelines, without a starting reference point, aren't very useful. 

[SandyEggoJake]

Ed, you might give Lloyd Kluesner of LloydsLayouts.com a call.  At last month's Great Train Show at Del Mar, he patiently gave me a 1:1 primer on casting with the Alumite product line.  He uses it extensively and also reps for them, I guess.

He listened to all my stupid q's and offered to mentor me as I am working on reproducing some parts I've modified from a shake the box kit for personal consumption.

He seems to really like a two part mold pour method, where he uses a thicker (heaver) resin to coat the inside of the mold, then follows it up with a foamier resin backer, that fills the space.  That way he gets crisp details on the front, but with lighter weight.  Given some of his molding are fairly large mountain ranges, such is critical.  But it might also be a cost thing as the foamier backer resin can be stretched farther and trimmed off easier.  You'll have to ask him on the specific products he recommends for your application.  Their product line is extensive.   

One product that Alumite product I found since (have ordered but yet to try) looks especially nice for learning to cast or doing small one off runs ... "Amazing Remelt".  As I understand it, it is essentially a reusable mold material.  So  after you are done you can reuse the material again and again to mold something new.   

[peteski]

He seems to really like a two part mold pour method, where he uses a thicker (heaver) resin to coat the inside of the mold, then follows it up with a foamier resin backer, that fills the space.  That way he gets crisp details on the front, but with lighter weight.  Given some of his molding are fairly large mountain ranges, such is critical.  But it might also be a cost thing as the foamier backer resin can be stretched farther and trimmed off easier.  You'll have to ask him on the specific products he recommends for your application.  Their product line is extensive.   

I suspect that Ed doesn't want to cast entire building as a single solid casting. I suspect he just wants to copy the walls, which means they won't be any thicker than few hundredths of an inch. I don't think that the foam-filled casting method would work or would be needed here.

[mighalpern]

ed:
I needed to copy the power plant wall to make a large power plant for my layout.
I first made a box for the wall section, then placed the wall in the box and poured the 2 part micro mark casting silicone rubber.  once cured i used the alumite product the make the walls.  i learned 2 things.  First i am super allergic to the dust of this alumite when i sand the rough edges and such and 2.  if you pour thin walls it need extra heat to set evenly.  So i have tried using a heat gun on the mold once poured and that works ok, and also i have tried to put the mold in the oven and heat the mold evenly before pouring and after pouring.  I have had mixed results in that some walls stay very flexible, like they haven't cure hard, but when they do come out, the details in N scale brickwork is picked up really nice