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Author Previous Topic: Intro.- the Holt house- the White house. 11-23-20 Topic Next Topic: In-ko-pah RR: New project
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Guff
Fireman

Premium Member


Posted - 11/03/2020 :  5:02:47 PM  Show Profile  Send Guff an AOL message  Reply with Quote
Thanks Bob, the tutorials help me to understand the process, however, it looks very challenging to me!


David Guffey

Country: USA | Posts: 1966 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/05/2020 :  05:24:18 AM  Show Profile  Reply with Quote
Thanks Dave. Maybe someday you will find the need to reproduce a number of your details.

I started to take some photos for the next step but developed a problem with my camera
(it is real old), the fitting for the USB cord seems to have broken off inside the
camera, that may delay my postings.

Anyway, the next process is to start resin casting and there are some things you should
have on hand beside the liquid resin. Lets deal with the one piece mold first.

Guys who want to go full steam will need such things as a pressure pot and a source for
pressure/vacuum but this is not intended for them, it is for the guy who just needs to
make a few parts. IT IS MESSY AND IT IS CALLED THE SQUASH METHOD.

I recommend that you wear gloves and you will need a lot of newspapers to protect your
working area. Cut something FLAT to just over the size of your mold, I use Gatorboard but
flat plywood would be OK too. Next you will need a sheet of something that resin will not
stick to, I have heard that some plastic wraps work ok but I always use the paper that
is left from a sheet of labels or stamps, that non-stick side works great. You will
also need some sort of weight to press the flat board down to seal the casting while it
sets. Machine shop weights, wheel balancing weights, or bottles or bags of lead shot, or
anything that's heavy.

We will pour resin on the next post.

Bob


http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=30102
http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=51837

Edited by - sgtbob on 11/05/2020 05:25:45 AM

Country: USA | Posts: 4113 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/07/2020 :  05:03:52 AM  Show Profile  Reply with Quote
Now is the time to start casting, we will deal with the one piece mold first.

Some folks apply mold release to the mold and let it dry, I normally do not require this
step, it's up to you. Your mold should last longer of you do so.

With the mold face up on your newspapers, slowly pour you resin mix into the parts
until it SLIGHTLY overflows. Then take the non-stick paper and starting at one side lay
it over the mold and sort of roll it over the rest of the mold pushing excess resin along
with it. That helps to push any air bubbles along instead of trapping them in the mold as
would happen with simply laying this down without rolling. Then quickly lay the flat
board over all and apply the weights to hold it down and force out any remaining liquid
resin. Let it set for whatever time your resin instructions say, I usually wait about a half hour.

Then remove the weights, the board, and the paper and pick up your mold and carefully
remove the new resin part. There will be a thin film of resin around the parts but it is
usually thin and easily removable with a hobby knife and sanding sticks after breaking
it away by hand. I did not get a photo but will posting one with the two piece mold
write-up. If this film is too thick and hard to remove you can usually fix that by adding
more weights to press down on the mold.

Here are the first two castings on this project. Any little air bubbles that might
remain can be filled with hobby putty.



Bob


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Edited by - sgtbob on 11/07/2020 05:05:46 AM

Country: USA | Posts: 4113 Go to Top of Page

Ensign
Fireman

Posted - 11/07/2020 :  08:24:41 AM  Show Profile  Reply with Quote
Bob, your first castings came out looking just perfect, but that's what we've come to expect from you now isn't it.

Greg Shinnie



Country: Canada | Posts: 8849 Go to Top of Page

Michael Hohn
Fireman



Posted - 11/07/2020 :  09:16:25 AM  Show Profile  Visit Michael Hohn's Homepage  Reply with Quote
Bob,

The castings came out beautifully. Your description of the squash method is going to be very useful to me when I get back to resin casting.

I was given a sheet of glass with rounded edges a couple decades ago which makes a great work surface. Residual resin can be removed with a razor blade.

Thanks again.

Mike



Country: USA | Posts: 6751 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/07/2020 :  10:57:18 AM  Show Profile  Reply with Quote
Greg and Mike,thanks, I appreciate your posts.

There is a little step that I do without thinking so I forgot to mention it.

Right after you pour the resin into the mold I take a toothpick and just dab it into spots that
could hide an air bubble. That includes closed protuberances such as the hub of a wheel, or
small thin sections such as the bracket arm at the front. That will release any small
trapped bubbles.

Bob


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Country: USA | Posts: 4113 Go to Top of Page

Guff
Fireman

Premium Member


Posted - 11/07/2020 :  4:00:07 PM  Show Profile  Send Guff an AOL message  Reply with Quote
Splendid casting results Bob! How long have you been doing casting with resin? If you want to make multiple castings, like your meter boxes, do you cast one at a time or make many masters to cast?

David Guffey

Country: USA | Posts: 1966 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/08/2020 :  04:22:15 AM  Show Profile  Reply with Quote
Good morning Dave, I have been doing resin casting for about as long as I can remember.
What has changed is the fact that RTV rubber and resins have improved many times over.

I'm not sure I understand your question about multiple castings. If you just need several of the
same casting I simply pour one, work on something else for about a half hour, pop the
casting out and pour another. etc. etc.

If you need MANY castings you can make multiple molds from the same master or cast a few and
then use them to make a mold with several mold cavities. In either case pouring many castings
at the same time.

Bob


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Country: USA | Posts: 4113 Go to Top of Page

TRAINS1941
Engineer

Premium Member


Posted - 11/08/2020 :  11:10:13 AM  Show Profile  Reply with Quote
Bob that came out perfect!! A master at mold making for sure!

Jerry

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

Country: USA | Posts: 12867 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/08/2020 :  12:41:05 PM  Show Profile  Reply with Quote
Thanks Jerry.

Here's the first casting from the two piece mold. Scary isn't it?? Not too bad, perhaps a
little more weight will make that web even thinner.




Here are the same wheels with the web quickly removed. Now all that is needed is a clean-up with
the #11 hobby knife and sanding sticks. A little work but nowhere near the work of making another
set of wheels from scratch.



I had a reason for making the sides and the wheels first. I have a lot of other parts I want
to make masters for but in most cases I needed these parts to measure against so further parts will fit properly.

Bob


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Edited by - sgtbob on 11/08/2020 12:41:45 PM

Country: USA | Posts: 4113 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/08/2020 :  1:29:56 PM  Show Profile  Reply with Quote
In a traditional two piece mold you cut a gate into the molds so that while holding the
two parts together you pour the resin into it. However, without the pressure/vacuum
equipment there is always a problem with getting the resin to fill the mold completely. In the
squash method you lay the two mold pieces side by side face up and pour resin into both
molds then pick up one of them, quickly turn it over and place it on the other mold, the
keys will line it up OK. On top of this you place the board and weights to hold then
together until the resin hardens.

Bob


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Country: USA | Posts: 4113 Go to Top of Page

Guff
Fireman

Premium Member


Posted - 11/08/2020 :  2:59:34 PM  Show Profile  Send Guff an AOL message  Reply with Quote
Hi Bob,
You answered my question. Since drying time is fast, the one at a time method would be a good choice for this novice.
Thanks,


David Guffey

Country: USA | Posts: 1966 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/09/2020 :  07:18:45 AM  Show Profile  Reply with Quote

I cut a floor and the divider at the back of the cab area from .060 styrene and assembled the
wagon so far. Again, this was so I could measure and judge the sizes of additional pieces and
know that they will fit (hopefully!).

This switching back and forth between making masters for parts and making molds, and
casting parts, all keeps you from becomming bored and removes the idle time waiting for resin to set.



Bob


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Edited by - sgtbob on 11/09/2020 07:42:55 AM

Country: USA | Posts: 4113 Go to Top of Page

sgtbob
Fireman

Premium Member


Posted - 11/09/2020 :  07:31:57 AM  Show Profile  Reply with Quote
I guess this is as good a place as any to tell you my philosophy on moving parts for
models that are to be part of a static display on a model railroad. I am against it. If you want
to make all the wheels turn and the duflinkies move back and forth and either
never show it off or pick the model off the layout to show visitors how everything moves,
that's up to you. I do not like to do that and I also think that it encourages visitors
to see which parts move and which break off. You are the model builder and the railroad
boss so do as you please but I wanted you to know why nothing is made to be movable on
this wagon.

Bob


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Country: USA | Posts: 4113 Go to Top of Page

BurleyJim
Fireman

Premium Member


Posted - 11/09/2020 :  08:42:56 AM  Show Profile  Reply with Quote
Bob,

My long winded post on your casting tutorial went to internet heaven! 

VERY NICE JOB!!!

Jim


Take the red pill

Country: USA | Posts: 5833 Go to Top of Page
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