[NTCGRR]

Yea, its me again.
After reading all of Master Burl's writings I stepped out on my own.

I'm shaing the photos but its best to read the articals in GRYs he wrote.

I had to use one of his as my masters and filled in some spots to make it easier to remove from the mold.
I broke it but later glued it.

the "pour"

The little one is a 100 ton hopper brake wheel which failed. I was tring to make them for Leons project.

I tried to pour slow to let bubbles out but I am still missing a part.

 

[wildbill001]

I'm no expert by any stretch of the imagination so take this for what it is worth: Maybe add some "vent" holes.

When the big boys are casting alum and such they will add vent holes, small channels that lead from casting to the outside of the mold, to allow gases to escape. Don't see why the same principle wouldn't work here. I'd use some 1/16" wire to make the holes.

Bill

 

[rkapuaala]

Bill,
Venting is the best suggestion. In addition, don't clamp like that. I prefer something lighter like rubberbands. The heavy clamps tend to distort the part. When you use the rubber bands on the backer, they distribute the pressure better. Also, you don't need a lot of pressure to keep the mold together, so don't double wrap the bands unless the mold is too thin for them to add pressure. Too much pressure will also close smaller vents.

 

[NTCGRR]

Thanks
I did not have any rubber bands , will go to town tomorrow to get my "forgotten items"
my 3rd one I must have taken out too fast, its sad....
I even tried working on something else because I don't have patience. I don't like watching corn grow. hehehe
My first mold was a hard one. I'm tring two windows now. photos later.

I had to order more rubber just now. woow that stuff goes fast.

 

[Jerry Barnes]

I use Smooth-on products Marty, just ordered some more. What are you using? Got a 1/16" thick 4x8 through Syl's old sign supplier, came from Regal Plastics in Nebraska. $45 with shipping.

 

[Jerry Barnes]

Marty, use a syringe(I got one from my dentist) has a slightly curved plastic tip. That way you can jam it down inside and squirt the resin in the bottom some, so it wells back out the top. Then have a thin wire right there to poke down inside quickly to release any air bubbles. Works for me. I usually have carved an air vent also(the sprue on plastic kits is an air vent).

 

[ConrailRay]

Hey Marty,

Casting a brake wheel might be pretty hard without the correct vents and a pressure pot. You might be able to get away with a sort of open face mold of the brake wheel. Not really fully open face, but open enough where the rubber would still create the backside of the curved parts, but have a slight slit (as the open part) so that you can drag around a tooth pick to get the resin around and get bubbles out. Dont forget that the rubber is usually flexible enough to do tricks like this where the rubber mold slightly wraps around your part, but the part can still pop out ok.



-Ray

 

[ConrailRay]

Marty,

Here's a drawing of how you might be able to fix the other mold the the trailer part:

http://1stclass.mylargescale.com/conrailray/mold_pour.jpg You can use a sharp exacto knife to cut in some vents and such. In both phots, the blue line is a vent you must have. You can see the that part the trailer rests on, which is on the bottom of the mold, is already naturally slanted up and to the right, which is why you ended up with air trapped there as the air moved through the resin. So the left photo shows this cut, and you can pour the resin down only where the green arrow is. The air bubles should flow through the resin and up and out. Dont be afraid to use some vibration to get the b moving!

Ideally, you may want to try the right photo. Pouring the resin down this new path should force almost all the air out, so you dont have to rely on the air bubles going throught the resin as much. If that bottom part were level, this would also be the way to go as you would probably have trapped air on both sides.

-Ray

 

[cudak888]

Posted By ConrailRay on 12/21/2008 9:57 PM

Ideally, you may want to try the right photo.



Your image was coming up as a link. Here it is:

-Kurt

EDIT: That didn't work, did it...?

 

[NTCGRR]

This one is called an OPPSSSS

I think I took it out too soon and forgot to shake the darker colored stuff before I mixed it.

I use styrene as forms then cut it away.

 

[Jerry Barnes]

I think you are better off to STIR the resin than shake it. Don't be like James Bond! LEss air bubbles, I think.

 

[NTCGRR]

I thought that at first, I don't shake the thick clear stuff, I now shake the thin dark stuff and very little if any bubbles stay in. This last pour I poured it in the thinner other side and it worked great. I am taking notes as I go and amounts per each item so i don't waste so much.
I need to take a brake and get the end of my side dump car built so I can cast it. Hopefully many parts on it will be cast. I hope for 4 sidedumps to go with my section crew train.

 

[rkapuaala]

Do not shake, stir. Also, if you make a mold that is all wrong, reuse it as filler on your next mold. That saves on rubber (rtv). Cut the old mold into tiny pieces with a pair of scissors. put no more than 3/4 of it in the new mold and that way you only use a 1/4 of the material.
If you don't have a vacuum chamber to do this, you will have to do it slowly and in layers of cut material followed by the rtv.
By the way, what is the gel time on your resin?
Normally its 2 to 3 minutes.
I set a timer for my castings, and to keep myself from getting antsy and pulling the part out before it hardens, I do other tasks like, clean up, sitting up another mold or working on another model. I let my castings set for at a minimum of 20 minutes on a warm day and 45 when it gets 60 F in my garage.

 

[Jerry Barnes]

Larry Hergert sent me some pix of some cars he made. Molded each side and end piece and cast them. Then put them together. Worked out pretty good. Course he really knows his stuff!

 

[rkapuaala]

Thats a cab I did with 6 molds and 11 parts.

 

[NTCGRR]

good tip on RTV, I need to dig out the trash can now.

 

[Kovacjr]

Hey Rich...A resin cab huh, I guess its not for your Ruby your workign on?? Looks like it should fit a similar loco though....How did you make the master for that?

 

[rkapuaala]

Jason,
No, not for the Ruby, it was for my 2 electric 4-4-0s. The master was made from styrene and wood veneers, and even a little clay here and there

 

[NTCGRR]

JJ asked me to share more info and photos , so later I will up date some of the things I'm learning.
Here is what I bought,
http://www.alumilite.com/ProdDetail.cfm?Category=Starter%20Kits&Name=Super%20Casting%20Kit
Keep in mind alot of folks have given me ideas over the years.

I cut the bases off very carefully.


I bought a new drawer thingy to store my molds and some parts.
I'm now doing easy stuff .

the chunks in the cup is to push in around the edges to raise the level around the people.

I buy these after Christmas people and repaint them , very reasonable prices.

The wire holds them down and in the center.
I'm casting them in rubber so I can have half people for the seats of my passenger cars.
Tomorrow morning I will be casting people. And yes I still have to paint them.

 

[NTCGRR]

Last night I was working on my Duffus side dump car and today cast couple of the end panels. I'm waiting for more rubber to come in.

Also when I do a new pour and don't want to waste the extra have a small air tank or something to cast .