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 Structures on th LP&N RR, vol.4
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Author Previous Topic: Inspired by CarlB Topic Next Topic: structures on the LP&N RR vol. 5
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sgtbob
Fireman

Premium Member


Posted - 10/24/2020 :  07:59:15 AM  Show Profile  Reply with Quote
Thanks guys for all the welcome comments.

I am still working on a set of wagon wheels. Work has been slow because of the outside
work around the house getting ready for winter. It happens every year and I get
slower every year too.

Looking back on my previous explanation of making wagon wheels I see that I do step
that I forgot to mention back then. After the parts have all been glued together but before
adding the tires, I clamp a flat piece of wood to the table of my disc sander. I then
lay each wheel on the wood surface and move it into the sander until it just cleans the
wheel off at the pencil line marking the outside diameter. I then use a strong pin
pushed down into the wood at the center of the wheel and by turning the wheel 360 degrees I get a
perfect circle ready for the tires.

Bob


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sgtbob
Fireman

Premium Member


Posted - 10/29/2020 :  05:41:30 AM  Show Profile  Reply with Quote
Here are the styrene masters for the wheels and the two sides. After a bit more clean-up
I will try today to get the first rubber mold material in place on these parts. It's kind
of important to get these done because the fit of other parts is dependent on having
these to fit to.

The sides will have flat backs so that mold can be a simple one piece mold but the wheels have
detail on both sides so that will have to be a two part mold.

Bob








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Ensign
Fireman

Posted - 10/29/2020 :  10:00:13 AM  Show Profile  Reply with Quote
The master makes his masters, masterfully.
They look great Bob!

Greg Shinnie



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sgtbob
Fireman

Premium Member


Posted - 10/31/2020 :  10:34:01 AM  Show Profile  Reply with Quote
Thanks Greg.

I know most of you guys already make your own molds and castings but I know some do not and
would like to know how to. I was almost ready to pour some rubber and just by chance I
realized that this would be a great place to show the difference between a one and a two
parts molds. THERE ARE MANY WAYS TO DO THIS BUT THIS WORKS WELL FOR ME.

Here is the master for the sides. The back side of each finished piece is completely
flat so this is what is needed for the one part mold. The parts are glued down to the
flat sheet, in fact they were built on that sheet.



All you need to do is make a wall around it to contain the liquid rubber until it sets.

Now the wheels have detail on both sides so it requires a two part mold. You can see that
the masters are set into some modeling clay about half way deep. I pushed the end of the
handle of a paint brush into the clay in several places to make what will be "keys",
they will keep the two parts of the mold aligned when the resin is poured. Where you
see blue clay in this photo will eventually be the second part of the mold. Again, it
needs the wall to contain the rubber.



Bob


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Carl B
Fireman

Premium Member

Posted - 10/31/2020 :  10:42:58 AM  Show Profile  Reply with Quote
Thanks for the individual steps Bob.
I guess I'm one of the few who doesn't do any molds or castings.

Appreciate your extra effort to explain your techniques. Perhaps I'll give it a try sometime.



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Anna-Carin
New Hire



Posted - 10/31/2020 :  12:50:16 PM  Show Profile  Visit Anna-Carin's Homepage  Reply with Quote
In the past weeks I've skimmed through all four volumes of your thread, and it's been very inspiring to see everything you build, and the techniques you use. Thanks for explaining everything so clearly! It even made me pick up a resin kit on sale recently, thinking that I must try it sometime.

Learning to use styrene is also on my list now, thanks to you. I'm especially curious to try scratch building wheels using your method, and to see if they would hold up in 1/48 scale too (I'm thinking of wooden artillery-style car wheels, so the spokes would be fairly short).



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sgtbob
Fireman

Premium Member


Posted - 11/01/2020 :  11:57:31 AM  Show Profile  Reply with Quote
Carl and Anna-Carin, thanks for your posts.

Here are the two mold boxes with RTV rubber poured into them. When I sold castings I had a
pressure pot in which I could apply vacuum or pressure to the uncured rubber or resin but I
sold all that equipment years ago. This will be done the quick and dirty home made resin parts
that every model maker can easily do.

Just follow the instructions on your rubber, mine requires simply one part rubber, one
part hardener and it is very forgiving if you are a bit off. Slowly pour it into you mold
box and if you have any deep parts you can use a toothpick to make sure it fills all the
details of the master.

You will see some little air bubble rising to the surface and you can tap the mold box to
help those bubble come up. Most modern RTV rubber products de-air themselves quite well.
Make sure your work surface is level and let them cure, generally about 4 hours.

the sides




the wheels



Bob


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Bernd
Fireman



Posted - 11/01/2020 :  2:46:09 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
Hey Bob,

Been following along here. I've done several molds and it's quite fun to see the finished product. I've tried both vacuum and pressure casting. And as you said doing it the way your are now brings fine results. I'll have some casting projects coming this winter.

Who's product are you using for your rubber molds? From the color I'd say you are using Smooth-On.

Good luck on those molds.

Bernd


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sgtbob
Fireman

Premium Member


Posted - 11/02/2020 :  05:29:56 AM  Show Profile  Reply with Quote
Bernd, thanks for your post. Over the years I have tried just about every brand of RTV rubber
and resin that's out there and in most cases I have not found much difference. Some are more
picky in how accurately you measure the mix and a few I did not like (I forget the names).
However, for the past several years I have used nothing but the items sold by Micro Mark, 1-to-1
/ RAPID RTV rubber #82083 and 1-to-1 EXPRESS resin #86226.

Bob



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sgtbob
Fireman

Premium Member


Posted - 11/02/2020 :  05:41:33 AM  Show Profile  Reply with Quote
The next step is to pull the rubber molds from the mold boxes. These need a bit of cleaning up
yet. You can see small bits of thin rubber around some edges. These are caused by areas on
the masters where you thought was solid glued sheets of styrene but a few voids let the rubber
ooze between them. No problem, they are easily removed with a scalpel or fine scissors.



That is all that's needed for the one piece mold, it is ready to cast resin.




That's also it for the first half of a two piece mold too but you must be really careful
not to remove the masters from the rubber, you will most likely never be able to get
them back in place if you do. Now you must construct mold box walls around the rubber of
the first half of the mold and I will post that next.

Bob


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sgtbob
Fireman

Premium Member


Posted - 11/03/2020 :  06:10:40 AM  Show Profile  Reply with Quote
Here are the mold box walls around the first part of the two piece mold.

VERY IMPORTANT!!

Do not pour fresh RTV rubber on top of the old rubber of the first part of the mold. If
you do it will bond together trapping your master in a solid block of rubber. The two
solutions of which are to throw it away and make a new master or destroy the mold by
cutting it away from the master.

What you have to do is paint a good coat of mold release over all parts of the surface of
the rubber part one. I use #80475 rubber-to-rubber mold release but there are many
others, in fact Vaseline desolved in paint thinner works well too.

Once that drys you can pour the rubber to make the part 2. You can see how those
impression from the paint brush handle will make the two mold halves align every time
they are brought together,




Here are the two parts of the mold for the wheels. The next step will be to make some
resin castings to see how they turn out.



Bob


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Carl B
Fireman

Premium Member

Posted - 11/03/2020 :  07:42:02 AM  Show Profile  Reply with Quote
Great tutorial Bob!

However, I was a bit surprised at the cost of the Micro Mark materials. I imagine many copies of your originals makes it justifiable.



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Michael Hohn
Fireman



Posted - 11/03/2020 :  07:48:22 AM  Show Profile  Visit Michael Hohn's Homepage  Reply with Quote
Excellent course in two-part molds and casting. Thank you.


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TRAINS1941
Engineer

Premium Member


Posted - 11/03/2020 :  08:22:01 AM  Show Profile  Reply with Quote
Thanks for all that info Bob.

Jerry

"And in the end, itís not the years in your life that count. It's the life in your years." A. Lincoln

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sgtbob
Fireman

Premium Member


Posted - 11/03/2020 :  2:17:06 PM  Show Profile  Reply with Quote
Carl, Mike, and Jerry, thanks for your posts, much appreciated.

Carl, you have a point, they are expensive. However, I have checked around on sites to order
parts and wow, they are really expensive, especially 1/24 scale parts. Not only am I
casting parts that are of my own design and requirement, not available for purchase, but
when I divide the cost of resin by the number of parts I get per bottle it turns out they
are quite cheap in comparison.

Bob


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