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Bernd
Fireman

USA
3947 Posts

Posted - 11/24/2020 :  9:30:15 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
A little update on the chipboard material. A forum member helped me find where I first heard the term "chipboard". Thanks Pennman (Rich). It was Tony Burgess's scratchbuild Sewall's Foundry. It's about 3/4 of the way down the post on page 2. I then saw Carl B use that material on his Chesapeake and Ohio Combination Office and Depot in HO scale. Thanks to Tony (RIP) and Carl B for putting me onto a new modeling medium. This reminds me of a material I first worked with back a number of years. It was called Strathmore board and came in a verity of thickness's.

LINK:http://www.railroad-line.com/forum/topic.asp?TOPIC_ID=47927&whichpage=2

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/26/2020 :  1:56:09 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
Todayís project was to pour the silicone rubber for the first mold. I use Smooth-On OO-M-OO 30 for my molds. This will be for the roundhouse project.

The first picture shows a Ĺ gallon of water. I use that to fill the mold to see how much silicone rubber Iíll need to fill the mold. Two plastic containers, one each for the part A and part B of the silicone. And a mixing container which was to small to hold both plastic containers of part A and B.



A piece of wood was used to mark the first container on how full to fill one of the containers and then transferred to the second container.



Next comes the messy part of pouring a mold, getting the plastic container filled to the marked off distance.



Once both containers are filled to their mark itís time to mix the two together.





I measured the height of the mixing container and took half of that distance and made a mark for filling up one part of the liquid rubber.



Next I added the other part of the liquid rubber to be mixed. I should have stirred it while pouring into the mixing container.



Next a lot of stirring to get a good mix while trying not to make too many bubbles.



Getting there. The color should be almost a very light purple when done.



Next I used a mold release spray to help release the rubber from the master mold.



Pouring from a bit of height helps with eliminating bubbles.



When I was pouring the liquid rubber I noticed that it wasnít quite the purple I was used to seeing. As you can see from the red arrows on the containers holding the rest of the liquid unmixed rubber that itís at different levels from each other.



It was to late to do anything but keep pouring and hope for the best.



After I mixed the rest of the liquid rubber and poured it in the mold you can see the more purplish color. Thatís what it should look like.



This is what happens when youíre in a hurry to get something done. I hope it doesnít turn into a total disaster. Iíll find out tomorrow. It takes about 6 hours for a cure and a total of 24 hours for a full cure.
One thing I needed was a better way of dipping out the liquid rubber from the original containers and a larger mixing container. Perhaps tomorrow Iíll go to the dollar store and see what I can find in the appliance department for better equipment before I pour the next mold.

Check back tomorrow and see how the mold turned out. Right now I donít have much confidence of it being any good. It sure will be a mess to clean up that master mold.

Till next post.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds

Edited by - Bernd on 11/26/2020 1:57:06 PM
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thayer
Engine Wiper

327 Posts

Posted - 11/27/2020 :  02:53:25 AM  Show Profile  Visit thayer's Homepage  Reply with Quote
Bernd,

Best of luck with the silicone cure. I hope it works out for you.

As you discovered, a larger mixing container is key. I recommend graduated containers from the paint department of your local hardware, or big box store. Having demarkations is a great second check that you've got a proper ratio, and mixing in a container that is twice the volume of your mold will make life a lot easier. The high pour is a good call for helping to eliminate bubbles, as is pouring off to the side of your part, and letting the silicone flood the tool like a rising tide.

While using the water might have been "more fun" than a ruler to measure the volume, I recommend using rice next time. It is a standard in many model shops, and much easier than water for this purpose. You do need to be thinking ahead to source it though, unless you have a better kitchen pass than I do! If you want to eat it afterwards, line the mold box with saran wrap first.

FWIW, I don't mean to beat you up on your process, as you've done it essentially the same way I would. My goal is simply to offer up some ideas that might help on the next round, or will encourage others to give it a try. My initial molding knowledge came 25 years ago (really?!) while working on a feature film with a very busy model shop, and was the most valuable skill I took away from that job.

Great job so far, and I look forward to seeing your roundhouse come together. It looks like a fantastic project.

Thayer
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  08:48:09 AM  Show Profile  Visit Bernd's Homepage  Reply with Quote
Thayer,

Thank you for your comments. I started with Micro Mark casting rubber several years ago. All those projects were small. I know better to have larger mixing containers. Problem is I was in a hurry to get the first mold poured and now have to suffer the consequences. Watch the next pour.

All comments are welcomed. Everybody can learn from them. I can take critical comments so don't worry.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Carl B
Fireman

USA
4147 Posts

Posted - 11/27/2020 :  08:50:44 AM  Show Profile  Reply with Quote
Watching closely Bernd. Thanks for the HUGE pix. Very helpful.

Are those gallon containers of Smooth On? Yikes
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  1:00:07 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Carl B

Watching closely Bernd. Thanks for the HUGE pix. Very helpful.

Are those gallon containers of Smooth On? Yikes



Hi Carl. Thanks for following along. Be careful though this stuff is sticky.

I like huge pix. They show what's going on. They are 1024 x 786. I reduce them down from 4000 x 3000 so they come out just about screen width here on the forum.

Don't know if they are one gallon or not. They are marked 9.00lbs. But they do look like about a gallon. Right now I'm wondering if that's enough with making six large molds.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  1:06:29 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
A quick run to the bank and then the Dollar Store for some supplies to cast the next set of molds. After a win on E-bay I decided it was time to see how the mold turned out.
It was nice and firm, meaning the rubber had set up. Note the two different colors.



Hereís a good view of the bottom. I used silicone caulking to hold the mold down. I figured that is would leave a slight cavity around the outer edge. As you can see some of the liquid rubber seeped under the mold. No harm done as it can be cut off later.



After removing two sides of the mold wall, I was easily able to lift the rubber mold off the master part. The mold release compound helped that out very nicely.



It turned out better than I had thought it would. Goes to show that if you donít quite get the mixture perfect you are still rewarded with a mold that will work.



This is what I purchased at the Dollar Store all for a total sum of $11.02. Four measuring cups, three mixing bowls and two ladles. The mixer I remembered saving a very long time ago. See saving something you might need in the future holds true.



So with that much success today Iím going to start on a second mold in the afternoon. Pictures will be coming to show the making of the second mold. Stay tuned.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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George D
Moderator

USA
16776 Posts

Posted - 11/27/2020 :  1:42:20 PM  Show Profile  Reply with Quote
I've never done any casting, Bernd, so I'm following your latest work with interest.

George

Fly Army
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Michael Hohn
Fireman

USA
7202 Posts

Posted - 11/27/2020 :  2:17:17 PM  Show Profile  Visit Michael Hohn's Homepage  Reply with Quote
Bernd,

Looking good. My impression from mold-making is that the rtv rubber is fairly tolerant with regard to proportion. Iíve used both Bragdon and Micro-Mark products.

Also, I think you could save significantly in use of materials if your box was not so deep and the walls of the mold not so thick. The rubber has a lot of integrity.

Mike
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Philip
Fireman

USA
3468 Posts

Posted - 11/27/2020 :  2:17:28 PM  Show Profile  Visit Philip's Homepage  Reply with Quote
Lookin good Bernd! Are you going to use hydrocal or resin?

Philip
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Carl B
Fireman

USA
4147 Posts

Posted - 11/27/2020 :  2:17:56 PM  Show Profile  Reply with Quote
Looks great to me!
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  2:54:53 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by George D

I've never done any casting, Bernd, so I'm following your latest work with interest.

George



I'm no expert. I learn by making mistakes and try not to repeat them a second time around. I'm still in the learning phase.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  2:59:29 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Michael Hohn

Bernd,

Looking good. My impression from mold-making is that the rtv rubber is fairly tolerant with regard to proportion. Iíve used both Bragdon and Micro-Mark products.

Also, I think you could save significantly in use of materials if your box was not so deep and the walls of the mold not so thick. The rubber has a lot of integrity.

Mike



Yes the RTV is quite tolerant in regards to proportion. If you get to far off you get very gummy RTV mold.

The reason I made the boxes so deep is that the mold is quite large and will benefit from the extra thickness by being much stiffer making for a more leveled pour.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  3:00:46 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Philip

Lookin good Bernd! Are you going to use hydrocal or resin?

Philip



First attempt will hydrocl or casting plaster. Might try resin later.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  3:01:28 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Carl B

Looks great to me!



Thanks Carl. Glad to have you along for the ride.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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