exspanding cast resin kit.

exspanding cast resin kit.

Postby jmass » Mon Feb 20, 2012 5:07 pm

a long while back someone made mention of a cast resin kit that enlarges the item. anybody remember the name of the stuff? joe
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Re: exspanding cast resin kit.

Postby areibel » Mon Feb 20, 2012 5:43 pm

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Re: exspanding cast resin kit.

Postby AstroGoat760 » Tue Feb 21, 2012 1:38 am

Am I right in thinking that the expanding resin might be a good way to duplicate N scale figures and such to be approximately TT scale?
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Re: exspanding cast resin kit.

Postby Arseny » Tue Feb 21, 2012 3:24 am

Maybe it's better to SHRINK H0-scale thnigs, not EXPAND N-scale?
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Re: exspanding cast resin kit.

Postby areibel » Tue Feb 21, 2012 9:21 am

I tried the shrinking stuff (Hydrospan 400) but it doesn't work well. It doesn't reproduce the small details without them getting distorted, it doesn't always shrink at a uniform rate and the resulting item is really soft and rubbery, so you can't do much to modify anything. If you had a basic shape you wanted to add detail too it might work, I'm trying to shrink an HO scale fire engine to TT and it's been a bear but I'm getting closer. My first experiment was shrinking an HO scale diesel, that was a disaster!
I think Elmer McKay tried the expanding stuff to try to go from N to TT, but I think he had similar problems. Both of the materials (the shrinking and the expanding) rely on water to work- the shrinking stuff you mix water with it before you cast, then wait for the excess to evaporate off to shrink. The expanding stuff you cast it, then soak in water to make it expand. The problems I had were all related to the item I was casting- if it didn't have a pretty uniform shape and cross section it wouldn't shrink at a uniform rate. If it distorted you couldn't get it to correct, it was trash.
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Re: exspanding cast resin kit.

Postby Rob M » Tue Feb 21, 2012 9:58 am

After reading this thread last night I did some googling and found out you can add naptha (lighter fluid or Coleman fuel) to rtv silicone when making a mold and it will shrink as the naptha evaporates. A 1:1 ratio of silicone mixture and naptha is said to shrink about 20% in a week or so. From what I read it is a much more reliable process than the hydrospan. You can add less naptha to get less shrinkage. So, for TT it would need to be a two-step molding process. I’m going to give it a try today with some HO E7 side frames.

This process also works the other way around. You can make a regular rtv mold and soak it in naptha to enlarge it but you end up with a softer mold that is only good for a few castings.
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Re: exspanding cast resin kit.

Postby Rob M » Tue Feb 21, 2012 10:08 am

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Re: exspanding cast resin kit.

Postby Rob M » Tue Feb 28, 2012 4:24 pm

Well, it took a few trial & errors but I now have a TT scale side frame for an E7. I ended up expanding an N scale mold of one in Coleman fuel and then casting it with Smooth-On 300Q. That stuff cures so fast it doesn’t have time to react with the solvent.

Now if I just had something to put it on
Last edited by Rob M on Wed May 02, 2018 4:49 pm, edited 1 time in total.
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Re: exspanding cast resin kit.

Postby TTTerrific » Tue Feb 28, 2012 5:03 pm

Rob,

I'm very impressed with the results. Good photos, too.

Would you be so enticed as to see what results if you try to reduce an HO truck (or expand an "N" scale truck) say like an archbar or an Andrews truck frame? This is something that I have been thinking about doing for time, but since you have seemed to have
mastered this procedure...? What do :problem: you think?
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Re: exspanding cast resin kit.

Postby Rob M » Tue Feb 28, 2012 5:28 pm

I haven't had luck shrinking HO parts. I do have some of the Smooth-on Mold Max 30 and Fast Cat 30 on order which is suppossed to setup quicker. Originally I tried the Micromark rtv with Coleman fuel added to it but it doesn't setup fast enough so the Coleman fuel settles to the bottom. That makes the mold distort when the solvent evaporates.

Soaking a normal rtv mold in solvent to expand it seems to work pretty good, but then you need the fast setting resin which I received today and was able to do the side frame above.

Anyway, I will see if I have any of the archbar or andrews frames in N scale and give it a try. I don't know if I can do a whole truck or just the sides.
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