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Casting a Resin stockcar
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 Posted: Sun May 15th, 2011 11:51 pm
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ON30Carl
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A while back a built a jig to make a stockcar,the jig works great but stockcars have lots of parts and are not an easy thing to build even with a jig.I thought this is a great candidate for casting and I'm glad I tried it out. I've never cast anything before so this was all trial and error (emphesis on error)I built up the skeleton of the stockcar and the end pieces and glued them to cardstock

I added NBW castings to the frame and boxed it all in for the rubber.I used Alumalite silicone rubber to make the mold and found it very easy to work with. I had no bubbles in my mold and I didn't degass or vibrate the mold. I did run a .025wire around the master after I poured the rubber to insure no bubbles.

The mold:



The resin is a much different animal to work with You get 90 seconds to mix and pour the resin before it begins to set up.It took me 2 tries before I got a satisfactory casting. The first try I poured too much resin into the mold and got too much flash, infact it was more then flash it was a solid wall of resin.



the plastic you see in the above photo is thick and hard and would be too much work to cut and sand down.



 



The pictures above show what I was after and I got that by mixing small amounts of resin at a time and scraping the back of the mold after the pour and before it began to set. By doing this I found you get more working time by mixing small amounts of resin at a time, if you mix a large batch the resin heats up too fast and cures quickly. I next built and cast the roof wich was a bit tricky because of an undercut.





this is the casting of the roof




The roof has some flaws in it, i'm not sure if I'm not getting the resin all the way to the ends or if there is a flaw in the rubber mold. I will keep trying to use it and see whats up.:bang:
Well this is whaI have so far. I will cast the underbody frame but I'm not sure I will cast the floor planks.
Please comment and make suggestions. It will be a while before I get back to this, I'm all out of rubber and resin.

Carl

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 Posted: Sat May 21st, 2011 08:34 am
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sledhead
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I've heard casting is not an easy skill to master, but once you get down pat the techniques that work for you building multiple models becomes a breeze. Those last two photos really look great! Keep posting updates and what you learn, I really want to try my hand at this when I have time. Right now I'm still trying to master brass etching. Thanks for showing your work!



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 Posted: Sat May 21st, 2011 12:39 pm
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Herb Kephart
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To make perfect castings, you need a way to draw a serious vacuum on the rubber and the resin each step of the way. This ensures that there are no air bubbles in either the rubber, the resin, the rubber filling the pattern, or the resin filling the mold.

If you have an air compressor, try connecting the air INTAKE to a container large enough to contain any of the above. Try to get at least 20 inches of Hg. Vacuum, and what ever you use has to be quick enough to get to that point without taking too much time, as it will cut down on some of the time that you have before the resin goes off.

Another tip-- instead of scraping the top of the mold, try laying a piece of glass over it with a weight on top to get a flat back on the casting.

You are doing very good so far, keep going!

Herb  :old dude:



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 Posted: Mon May 23rd, 2011 02:48 am
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ON30Carl
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Thanks for the interest guys,

Herb I will try the glass next pour,

at the moment I am fabricating a master

for the undercarriage of the stock car.

I may not get to it for a bit as I am

building bedroom closet in 1:1 scale.

Carl

 

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 Posted: Tue May 24th, 2011 03:33 am
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pipopak
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Why on earth are you wasting perfectly good layout money and space in a .... CLOSET???. Show who's boss, throw the clothes away!!!.



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 Posted: Tue May 24th, 2011 08:07 pm
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Herb Kephart
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If you get away with the above, try keeping the resin and catalyst in the freezer, to get more time before it starts to set. Ninety seconds seems awfully quick--what brand of resin are you using? there are lost of varieties out there that will give you a lot more time to work.

Take a look at    http://www.smooth-on.com/


Herb  :old dude:



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 Posted: Tue May 24th, 2011 09:45 pm
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pipopak
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Also make sure you are mixing the proper quantities and proportions.



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 Posted: Wed May 25th, 2011 03:41 am
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ON30Carl
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Good one Pipopak,

I'm asking myself the same question!

A mormon friend of mine has a good quote,

"you don't have to be a bigamist to

have one wife too many".

I have to admit, the wife is very

suportive of my hobby, so hunnydo's

are part of the give and take.

Besides it would cost alot more

if she contracts it out!:doh:

Carl

 

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 Posted: Thu May 26th, 2011 11:52 am
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dave1905
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I have found that putting the castings in a pressure chamber minimizes bubbles.

Pressure makes the bubbles smaller so they aren't noticeable. 40 psi ought to minimize most bubbles, 80 psi will make them so small you won't be able to see them.

Shop other places for resin. I like at least a 3 minute set time. I have used Hobby Silicone resin and RTV before.

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 Posted: Thu May 26th, 2011 04:00 pm
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Herb Kephart
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Pressure will indeed make the bubbles smaller--however, you have to keep the pressure on during the whole cure time. Then, if you have a bubble near the surface of the rubber, you will have a bulge in the rubber surface once the pressure is removed.

Once  you pull a good vacuum for a couple SECONDS --ALL IT TAKES--- the bubbles come to the surface and burst--end of bubbles.

Even the amount of suction provided by a shop vac is better than nothing.

Ya pays yer money and ya takes yer choice---


Herb  :old dude:



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