Making molds for plaster?

[scott]

I think we're going to try to mold our own plaster tunnel portals, so that we can fit trains with pantographs.

 

Anybody know what makes a good material for carving out a mold?

[CaptOblivious]

Latex. Carve up a master positive from, say, plaster or styrene, or whatever. Get some of Woodland Scenics make-a-mold kits, and go to town.

[scott]

That makes sense--I hadn't thought of latex.

 

I'll check out the make-a-mold kits.

[inobu]

Funny, I did not read this thread until tonight. I have been working on this for a few weeks and may have the setup that will work all around. The front has a buffer area that will extend from the mountain side, the arc cuts allow for the abrupt turns in either directions inside the mountain. Not sure if it needs to be extended to give a deeper look.  

 

Measurements:

 

The clearance is 57mm at the top, the pantograph are 43 to 47 mm or so and it can clears both rail sides.

The slab in the center represents a SE double track which is 57.5mm, the tunnel width is 80.66 mm.  

 

[smg id=793] [smg id=794]

 

 

I going to see how much it is going to cost to produce these. Need to find out if it is worth while to do.

 

Inobu

[Hobby Dreamer]

Hey inobu 

 

That rocks!! Great job...

[inobu]

Thanks,

 

I was thinking that my measurements were off until I saw this video. Look at the children above the tunnel and the guy to the left.

That puts things into prospective.

 

I think I'm going to add a walk way into the tunnel

 

 

Inobu

[scott]

That's a nice design, Inobu--what are you going to make it out of?

 

On the much-less-professional front, my first attempt at an original cut/carved out of plaster ended up with a bunch of broken pieces. So maybe I'll try another material, or give plaster one more try; I dunno.

 

So far I only need portals for single track. Also, I was making the opening about 60mm high in order to accomodate really tall sprung pantographs. It might look a little big, but I can live with that.

[CaptOblivious]

That's a nice design, Inobu--what are you going to make it out of?

 

On the much-less-professional front, my first attempt at an original cut/carved out of plaster ended up with a bunch of broken pieces. So maybe I'll try another material, or give plaster one more try; I dunno.

 

So far I only need portals for single track. Also, I was making the opening about 60mm high in order to accomodate really tall sprung pantographs. It might look a little big, but I can live with that.

 

Plaster is fiddly stuff. You have to get the mixture just right. Also, forget about WS's way overpriced "Lightweight Hydrocal", and go for the Wal-Mart special in the craft section—it's much stronger.

 

Here's a guy I used to buy a ton of stuff from for wargaming terrain. He has excellent tutorials on working with plaster:

http://hirstarts.com/

and even mold making!

http://hirstarts.com/moldmake/moldmaking.html

[inobu]

That's a nice design, Inobu--what are you going to make it out of?

 

On the much-less-professional front, my first attempt at an original cut/carved out of plaster ended up with a bunch of broken pieces. So maybe I'll try another material, or give plaster one more try; I dunno.

 

So far I only need portals for single track. Also, I was making the opening about 60mm high in order to accomodate really tall sprung pantographs. It might look a little big, but I can live with that.

 

I'm going to use plastic.

 

Plaster will be hard to work with unless you have the mold already. A block of Foam board may be better 6 to 10 lb weight. It can be sanded fairly easy but sturdy enough the hold shape. That's one way

 

Not sure how much you want to go into it, but find something with the general shape you want, use bondo (stuff for car body) to give you a surface to sculpture. Carve it, sand it and primer it. This should give you the first article to mold.

 

Inobu 

[scott]

Thanks, guys. For the regular portals, I'm going to try the Bake-N-Carve clay that's mentioned on the Hirst Arts site.

 

For curved portals, I had thought of using really heavy cardstock, but so far haven't found anything quite heavy enough. Plus cardstock must be popular with the tacky-scrapbook set, because it's getting expensive...

[scott]

Latex. Carve up a master positive from, say, plaster or styrene, or whatever. Get some of Woodland Scenics make-a-mold kits, and go to town.

 

Sooooooo...I've been working with the WS latex rubber for a few days now, and it seems to take forevvvvvvvvvver to dry. Is it better to build up lots of very thin coats rather than globbing on enough to make a stout layer? (The instructions on the bottle don't really say...)

[qwertyaardvark]

I was under the impression (according to what little of the instructions on the bottle i read) that you were supposed to brush on several "thin" coats. I would define thin as perhaps 1/8" or less. After letting that one layer dry, add more layers as necessary for rigidity. They recommended a minimum of three layers, and unfortunately you do have to wait a full day between layers. For additional rigidity, add a cheese cloth or bandage material between layers.

[scott]

Yeah--my bottle mentions using at least three layers, but somehow fails to mention how thick they should be or how long they take to dry. 

[scott]

Well, I've been at this on and off (mostly off) for the last couple of weeks or so, and finally have something that looks merely poor, rather than like utter trash.

 

 

Making the original out of plaster turned out to be a bad idea:

 

 

 

Top row: molds

Bottom row: (L) plaster portal fresh out of mold (bottom bar gets cut out); © clay original; ® smaller portal in plaster

 

 

First examples with paint; they looked better with the first wash--I should have taken the pictures then before I started messing with them:

 

[Yes, I know they look really rough and fakey....]

 

Along the way, I gave up trying to do the fine details (such as they are) on the clay originals--there were too many setbacks. It's easier to carve details into the plaster after the portal comes out of the mold. I also have one more original (somewhere...) with an overhanging top "beam."

 

For the larger portal, I tried to things to make life easier--making the original and mold deeper than the plaster versions would be, and leaving a bar across the bottom of the opening. This keeps the clay original from moving/squishing the opening. The bar can be cut out with a hacksaw blade.

 

Bigger pictures in this photoset.

[CaptOblivious]

Mate, they might not look like much, but this is real progress! I'm very excited to see this. Let me encourage you to keep trying...

[scott]

Thanks! Now, if I hadn't broken the last two portals I made, I'd feel better about it...  :-P

 

The bigger portal is workable, with some caution. I'm re-doing the mold for the smaller one, since it got warped.

[scott]

Here's a somewhat better result. (The paint was is still drying, which is why it looks wet.)

 

[CaptOblivious]

These are pretty big and chunky castings. If you are having a problem with your casts breaking, I suspect there is something amiss in your plaster mix. In my experience, plaster castings can be extraordinarily robust (which is why gamers, who manipulate their scenery extensively, prefer plaster to materials like hydrocal, which is comparatively fragile). But only if you get the water-plaster ratio exactly right, which can be tricky. Plaster can also be made to hold a surprising amount of detail, but your mold has to be stiff enough to transmit it; this may be a limitation of latex that I didn't know about when I suggested it.

 

Anyway, your latest result is looking quite good!

[scott]

Thanks--as for the breakage, I think I was just being too rough when cutting out the "bar" under the opening. Lesson  learned...at least plaster isn't too expensive at the hardware store.

 

Otherwise, the 2:1 plaster:water ration recommended on the bucket seems to work OK. One of the ones I broke had a slighty watery-er mix that I tried to make it easier to fill the mold without voids. I'm not sure if the mix was the problem, or just my handling.

 

The latex seems to capture more detail than I expected--including the fine scratches from the sandpaper I used to flatten the face of the clay original. Ironically, since I haven't been carving details into the originals, there aren't any *wanted* details for it to capture. Maybe I should work on carving and flattening the unbaked clay. But so far that's been really difficult. It might take some sort of box-mold for the clay to get the sides and faces straight.

[scott]

I've put the latest update on the portals in the layout thread rather than here.