Casting AC&Y 3900 Series 50' SS Box Car

[Sokramiketes]

That sounds like deja-vou all over again.  I seem to recall Daniel, in an earlier thread casting ,showing a similar photo and DKS making a similar statement.

Cool story, bro.

[pjm20]

Cool story, bro.

[SAH]

Great looking model Daniel. 

My first master did not include the "skirt", or whatever the proper name for the extension beneath the bottom sill is.  I had trouble completely filling the mold.  I then shaved off all the interior support and glued styrene sheet to the interior of the car sides to extend the box.  For the 50' SS box car I used 0.040" sheet.   The sides become rather thick which I don't particularly like.  I made another mold using a 40' Arnold steel reefer the other day but used 0.020" styrene to build the box.  The reefer has gusset plates at the sill and I wanted to see how that feature plays into the casting process. 

In both cases I sand the bottom of the extension so it's dead flat and use glue stick adhesive to fasten it to the mold bottom plate.   The mold material did not leak inside the master in either case.  I'm not using pressure but my gut says the result will be the same as far as leakage goes.  The glue stick adhesive allows easy separation of the master from the bottom plate.  Going forward I'll use 0.020 styrene for the skirt.

[daniel_leavitt2000]

The reason for the clay is that the exterior of the mold is being cast right side up... that is to sat the car is right side up when I pour the rubber. If the interior of the car was empty it would 1. collapse or 2. fill with rubber. To avoid this the car interior needs to be solid. After the exterior of the mold is dry, I remove the platform, insert the interior of the master and cast the interior of the two-part mold.

Maybe I am over-engineering the master, but it was a lot of work and a lot of people helped out. I don't want to ruin it,

[chessie system fan]

Why not do the interior side first?  Or at least fill it with enough mold material so it doesn't potentially collapse on itself.  It seems like that would be less work.

Or another idea would be to cast it hanging upside down to get the outer mold half.  Just put a temporary dam made of scotch tape around the bottom of the car (now the top of the mold) so the mold material doesn't overflow into the interior.

[DKS]

The reason for the clay is that the exterior of the mold is being cast right side up... that is to sat the car is right side up when I pour the rubber. If the interior of the car was empty it would 1. collapse or 2. fill with rubber. To avoid this the car interior needs to be solid. After the exterior of the mold is dry, I remove the platform, insert the interior of the master and cast the interior of the two-part mold.

Maybe I am over-engineering the master, but it was a lot of work and a lot of people helped out. I don't want to ruin it,

As noted before, the interior need not be solid if there are vents to equalize pressure. You could simply glue the "casting platform" to the bottom of the box, and drill holes up through the box into the platform interior; then vent the casting platform into the interior of the master.

Sometimes rubber may get inside the master anyway, and that's never been a problem for me; I'll simply pull it out by running a sharp knife along the inside edge of the master to separate it. Then, sometimes I will deliberately allow the rubber to get inside, because it's too complicated to prevent it from happening, and I'll simply remove it afterwards. I've never lost a master as a result.

The key is to make sure there are no sealed interior spaces, since these could collapse. As long as there are provisions to equalize pressure, there is no risk of any damage, even if there are leaks where rubber can pass.

[SAH]

That makes sense to me David.

I bought a pressure pot on Saturday.  I guess that means I'm all in.   

Q regarding mold material.  I used micro mark  1-1 resin for my trial shots.  It worked fine but the blue part was much thicker than the white part, to the point of being "gloppy".  It would pour but in chunks.  Is this normal?  I used it within 1 week of arrival. 

Steve

[DKS]

I used micro mark  1-1 resin for my trial shots.  It worked fine but the blue part was much thicker than the white part, to the point of being "gloppy".  It would pour but in chunks.  Is this normal?  I used it within 1 week of arrival.

You must mean 1:1 mold material, not resin. The blue part is normally much thicker. It should not pour in chunks, however. Be sure to stir both parts thoroughly in their original containers before mixing them together.

BTW, hopefully you'll migrate to Smooth-On Mold Max at some point. Infinitely better than Micro Mark 1:1.

[peteski]

BTW, hopefully you'll migrate to Smooth-On Mold Max at some point. Infinitely better than Micro Mark 1:1.

+1  I use Smooth-On  OOMOO RTV rubber. It is easy to mix and work with, and it sets quickly (almost too quickly).  This is for simple molds. For more complex molds, Mold Max RTV is even better.

[SAH]

You are correct David.  I meant mold material.  Thanks for the info.

After the mold material container is opened, what kind of shelf life can I expect?  What is the best way to store it?  I see myself as a sporadic caster (just like my modeling intervals) and would hate to see a container of the stuff go bad after using just a small amount.

Peteski - Since I've no reference point, what constitutes a complex mold?  10 being very complex, where does the 50' SS boxcar I've been testing with fall on the scale?

I can see how resin casting can become a hobby within a hobby.  There are a lot of projects I've wanted to tackle where resin casting figures in the process.

[DKS]

After the mold material container is opened, what kind of shelf life can I expect?  What is the best way to store it?  I see myself as a sporadic caster (just like my modeling intervals) and would hate to see a container of the stuff go bad after using just a small amount.

First, as a sporadic user, you should probably get smaller containers of material, even though it will cost more. I'd get the trial-size containers from Smooth-On, which have about as much material as standard size containers from other companies. I store mine in my workshop, which is the family room, so it's kept at room temperature at all times, and I make sure the lids are on good and tight. It might also be worth your while to get a container of Extend-It, which is a gas that displaces oxygen in a container to extend the shelf life. You might expect to see the mold material lasting from 9-12 months. Casting resin lasts about twice as long.

[peteski]

After the mold material container is opened, what kind of shelf life can I expect?  What is the best way to store it?  I see myself as a sporadic caster (just like my modeling intervals) and would hate to see a container of the stuff go bad after using just a small amount.

Peteski - Since I've no reference point, what constitutes a complex mold?  10 being very complex, where does the 50' SS boxcar I've been testing with fall on the scale?

I can see how resin casting can become a hobby within a hobby.  There are a lot of projects I've wanted to tackle where resin casting figures in the process.

I should have been clearer. To me a simple mold is either a 1-piece (open) mold or multi-piece mold with no deep undercuts.  That was in a reference to the OOMOO RTV, which is easy to work with but not very robust (it doesn't have great tear strength).

I also don't do great amount of casting and I even the trial-size quantities are a bit much for me. I end up discarding good portion of the uncured resin because it becomes unusable. When moisture slowly gets absorbed over time (even when following the manufacturers recommendations to keep the moisture out), that will cause gas bubbles to form when the resin sets.

[SAH]

I've been working with my test castings over the last month or so.  More or less trying to see what works  for underframes, weight, painting, detailing, etc.  Here is what I've come up with for the Con-Cor 50' SS 1-1/2 door box car


Close to a SP prototype.  I discovered my decals set was in bad shape, as in cracked.  It's only about 30 years old.   


The Omaha Western is a freelance I'm guessing.  The decals came as a sample set from Rail Graphics many years ago.  Maybe a RW member knows who the owner is.  It works pretty well on this car.


The Arnold reefer casts.  These are both Clover House dry transfers set on decal film prior to application.  Works OK but the Solvaset attacked the colors a bit.  Both are proto schemes but likely not for this car nor the era I'm modeling.  The CREX model will go on my display shelf.  The URTX car will likely get weathered and run on the AC&Y.


With these few under my belt it's time to tackle the subject line cars.  A new mold rubber supply is on the way.  We'll see what happens.

[peteski]

These look great!

[wcfn100]

Yes, very nice.

How's the shrinkage? 


Jason