Route 15 Overpass: Making the Mold

I mentioned last time that the main reason I wanted to learn how to do resin casting was so that I could duplicate the wonderfully-detailed bridge girders that Mike Redden made for me from photos I took of the Route 15 overpass. This overpass will anchor the north end of the Wethersfield scene and provide a nice - and prototypical - view block for hiding where trains head "to Hartford."

Well, after doing a test run using an old scrap load as a master (click here, here, and here for details on the steps involved), I decided it was finally time to tackle the overpass.

I started with Mike's Shapeways parts as masters, which I'd primed last October(!). Here I'm trying to arrange them as efficiently as possible for the mold. I determined that about 8.5" across and 4.5" front to back would make a good footprint/base. 

So I measured that all out on a piece of foamcore, cut out the base and then cut the sides at about 5/8" high. This would account for the thickness of the base (I glued the sides to the edges of the base rather than on top as I did before), the thickness of the parts, and still allow a 1/8-1/4" of rubber on top to cover everything adequately. In addition to hot gluing the sides to the edge of the base and to each other, I also ran a bead of glue inside each joint to ensure that the box was water rubber tight.

Next, instead of using hot glue, I decided to use quick drying Aleen's Tacky Glue to attach the parts to the base of the box. To (try and) ensure that no rubber would seep underneath the parts, I ran a bead of glue around the entire perimeter of each part to, hopefully, form a nice seal/barrier. I'm not too concerned about messing up the nice masters, since the Aleen's should just soak off with water. I guess we'll see.

After letting the glue cure for 4 hours or so, it was time to mix and pour the rubber. Here are the quick steps (but be sure to click here for a detailed post):

• Make sure the mold box is level in all directions
• Use rubber gloves
• (this time I didn't apply any mold release)
• Pour rubber mold material Part A into one cup and an equal portion of Part B in another cup
• Mix together in a larger, clear cup (so you can see that it's mixed thoroughly)
• Mix gently to reduce the number of bubbles
• Let the mixture sit to allow as many bubbles as possible to come to the surface (this material has a 10 minute work time from mix to pour)
• Pour the rubber into the mold from high up (12" +/-) if possible so you have a small, thin stream (again, to reduce bubbles), starting in one corner and covering the entire master. If you aren't comfortable pouring from that high - or if you can't maintain a steady stream - you can pour closer, just keep it flowing so as to reduce bubbles.

While I've enjoyed doing the videos, I wanted to try a new way to document these steps:

I set up my iPhone on a tripod and got a Bluetooth shutter release so I could take hands-free pictures during the process.

Here's the rubber mold material from the Micro-Mark resin casting starter set. Put some of Part A in one cup and an equal amount of Part B in another cup.

Then mix the two cups of material together in a third, clear cup. Be sure to scrape out all the material from each cup.

Then mix the two parts by slowly stirring them together. The clear cup helps you see how thoroughly you're mixing.

When it gets all thoroughly mixed together, you're ready to pour. Well, almost. Set the cup down and tap on the sides for a minute or so to encourage any bubbles to surface so they'll pop. Then pour.

This step is both the most fun - since it's cool to see it coming out of the cup and into the mold box - but also the most harrowing - since you're covering up, in this case, over $40 worth of parts with liquid rubber. Start in one corner . . .

and work your way around . . .

and all throughout the mold box, covering everything with hopefully enough material. You can see that I had extra cups waiting on standby in case I had to mix up more rubber quickly! You have about 7 minutes from mixing to pouring.

Use your stirrer to scrape out all the material - might as well be sure and use it all up!

The final step, like with the rubber in the cup, is to tap on either side of the mold box to encourage the bubbles to surface. And just because I have this handy-dandy camera & shutter release setup, I decided to do a video of this complicated process . . .

Tapping releases the bubbles and blowing across the surface helps them pop faster.

And here's what you end up with with your done - a nice, smooth swath of rubber. Whether it made a good mold or not remains to be seen. Until next time . . .

Wordless Wednesday #214

"Un-Molding" the Casting

So here's where we left off last time - resin poured into the rubber mold & a sheet of acetate laid on top and weighted down . . .

The video from last time seemed to work well, so instead of a lot of pictures and text, I figured I'd do a longer video of "unmolding" the casting . . .

As I mentioned, I'm not happy with the bubble-voids, but they're on the bottom of the casting where they won't be seen, so they don't really matter. I'm just happy that all turned out as well as I'd hoped.

Not bad for my first rubber mold/resin casting effort. Here you see the mold I made, with the master in the center, and my copy/casting on the bottom.

Now, all this was by way of practice for the real reason I got all this casting material and did all this practice in the first place. I intend to use the Shapeways parts that MikeR made of the Rt. 15 overpass and use them as masters for a bunch of additional girders so I can, yes, FINALLY(!) make some more progress on the north end of Wethersfield!

PS: be sure to let me know what you think of the videos. I'll never become a Vlogger, but sometimes I think having a video in a post instead of a lot of pics and text description is more helpful. So let me know your thoughts in the comments!

Molding Monday: Unboxing & Trimming the Mold, Pouring the Resin

So when we last left the mold-making process, I had just poured the rubber into the mold box and used a Rube Goldberg-like setup to hold everything in place (thanks DandHColonieMain for the observation). Click here to see that (and the rest of the previous steps).

Once the rubber cured (it's supposed to cure in 4 hours, but I left it overnight - well, for a bunch of days truth be told...), it was time to undo the Goldberg Press and unbox the mold:

You can see in the pic above how 1) I didn't have quite enough rubber to cover the master, and 2) how part of the master poked up as a result. This was actually a blessing in disguise since it gave me a point on which to place the weight to keep the master from floating (yes, floating) up through the rubber as it cured.

Next step is to remove the foamcore box, which is a simple matter of just peeling it away. But if a picture is worth a thousand words, how much would a video be worth?

Sorry it got cut off (phone ran out of space), but you get the idea.

Once I got the master out, this is what I was left with. Some trimming to do.

And, flipping it back over, you can see where I didn't have quite enough rubber to cover everything. I'll just put a piece of packing tape over the hole to keep resin from leaking through when I do the resin pour.

But, all in all, I'm really happy with how the mold came out - especially for my first time!

I just needed to finish trimming where the rubber had seeped under the master. Trimming was easy with a new x-acto blade - and here's how it looked when all that trimming was done.

Now for the fun part - mixing and pouring the resin. Here are the steps:

1. Put on some rubber gloves and make sure you have a nice, level spot on which to place the mold (of course, cover the spot with plastic or - as I did - use a piece of plate glass - to keep any resin from going where you don't want it to).
2. Gently shake the two bottles of resin - parts A & B - to mix the contents.
3. Pour equal parts of A & B into two separate cups.
4. Pour the two cups together into a larger, clear cup & stir gently and slowly to mix the two parts together.

Here, the resin is mixed together and the mold is standing by. I'm waiting a few minutes for bubbles to make their way to the surface. You have about 7 minutes working time from mix to pouring.

Like with the rubber for the mold, pour a long, thin stream of resin into the mold to reduce bubbles. Work from one corner to the other, filling the entire mold.

Overpour slightly so you're sure the entire mold is filled. You'll probably see some bubbles come up - I just blew on them and, when necessary, used a small brush to pop them. Next time, I may be a bit more aggressive with a toothpick.

To ensure that the back of the casting is flat, place a piece of glass or acetate on top. You can see here that it squished out the resin a bit. The last time I did this, I used plastic wrap instead of acetate - but that resulted in a very wavy back.

As a final step, I weighed down the acetate on the resin to make certain it'd lay - and stay - flat.

Now I just need to wait for it to cure. The instructions say that it should cure in 15-20 minutes (you know it's cured when it turns from clear to white), but to be certain I just plan to leave it overnight.

So far so good! I'll be interested to see how my first (well, technically, my second) casting comes out!

A Washboard - On the Valley Line Today

The other day I happened to be home when I heard an engine from the local railroad ("local" as in "through my backyard" - literally) blowing for the grade crossing at my street. I'm ashamed to admit that, while this is still a relatively rare occurrence this far south, I didn't bother running down the street to see it. I thought it was just a light engine move - perhaps HOTT - but I was wrong.

Turns out, the railroad was moving a "Washboard" - a former New Haven MU coach - down to the interchange for pickup. It would have made a pretty cool video, seeing it go over the crossing - especially since these cars ran only in the Electrified Zone between New Haven and NYC during the 1950s through the mid-1970s. I'll let others who are more knowledgeable on the West End weigh in with the particulars, but I think they were first delivered to the railroad around 1954 to replace multiple-unit electric coaches that had been around since at least the 1931 and earlier (some were still around from the 1909 delivery). I remember seeing them at Devon, CT around 1983, but I don't think they were in revenue service (IIRC, they were on a work/wire train). Unfortunately, I never rode in one.

But it was cool seeing an original piece of New Haven equipment still in its original paint - including intact stainless steel letterboard.

And having it go through my backyard and sit down at the interchange long enough for me to catch a few photos was a special - and very unexpected - treat. Here's wishing it a good future with a new owner that can restore it to its former glory. It was nice having it visit for a bit.

P.S. This isn't the first time an electric has gone by here . . . I can't believe it's already been over 2 1/2 years since the EF-4 left the Valley Line. . .

Wordless Wednesday #213

Molding Monday - Making a Rubber Mold

The rubber mold-making materials arrived from Micro-Mark and - as has been the typical story with this project - they sat in the unopened box for a few weeks. But this weekend I got a block of time to get them out and make my first rubber mold!

The photo above shows where I'd left off: master hot glued to a foamcore base and foamcore walls hot glued together to make a box (make sure all of the joints are sealed - you don't want any material leaking out).

First thing I did was get out the instructional video and watch it again. The process Dave Frary describes is pretty straightforward:

• Make sure the mold box is level in all directions
• Use rubber gloves
• Apply mold release to the master and the inside of the box. Wait to dry.
• Pour rubber mold material Part A into one cup and an equal portion of Part B in another cup
• Mix together in a larger, clear cup (so you can see that it's mixed thoroughly)
• Mix gently to reduce the number of bubbles
• Let the mixture sit to allow as many bubbles as possible to come to the surface (this material has a 10 minute work time from mix to pour)
• Pour the rubber into the mold from high up (12" +/-) so you have a small, thin stream (again, to reduce bubbles), starting in one corner and covering the entire master.

Straightforward in description. Execution was a wee bit different . . .

First, the mold release must've seeped under the master because it dissolved the hot glue holding it in place(!!). I wiped down the foamcore and the bottom of the master with a paper towel, and re-hot glued it.

Once that cooled, I mixed and poured the rubber, but then discovered that I didn't make quite enough material - it covered all but the "highest" part of the master! No worries (because: test).

And as if that wasn't bad enough, as I was pouring the rubber, I noticed that other parts of the master weren't being covered - it was like the master was starting to float up. . .

Because is WAS floating up! Yes, the hot glue had failed to hold and the master was floating on top of the rubber(!!!)

Now, that just ain't right.

So I pressed the master back down into the rubber and held it in place with a stirring stick in one hand, while I used the other hand to hot glue a couple scraps of foam core onto a block of wood.

If necessity is the mother of invention, desperation is the father of ingenuity. Resting on the ends, the wood block wouldn't have been able to press the master down, so the little white bits are the foamcore scraps used to fill the gap between the wood weight and the sticking-up portion of the master. Of course, the wood is either warped or the ends of the box aren't quite level with each other. So the handy dandy baby powder bottle is resting on one side to keep the wood tilted properly.

I have no idea how this is going to work out. I already figure that the part of the master touching the wood/foamcore is going to poke through the mold. It really can't help but do so. So I don't think I'm going to be able to pour any resin into this mold (hmmmmm.... unless I use some duct tape to seal the little hole . . .)

Ah well. Again - this is only a test.

A couple of lessons so far:

• Adhere your master to the bottom of the foamcore box using something that's impervious to mold release
• Mix enough rubber mold material to cover the entire master, with rubber to spare (it should cover the highest part of the master by at least 1/8" preferably more)

Despite these hiccups (hiccoughs?), I'm actually enjoying learning this process. Resin casting - like soldering or airbrushing - is one of those things that's so mysterious in the hobby and I'm glad to be confronting my fear of failure and enjoying the journey. At the end of the day, worst case scenario is that I'm only out a little time and money. And the longer I'm in this hobby the more I realize that that's the price - literally and figuratively - of getting over some of these hurdles and developing some really useful skills.

Of course, I may change my tune when I see how this thing actually comes out . . . stay tuned!