Casting

I started out with a kit probably between fifteen and twenty years ago, so forget the brand. It was fine.  Since then I have just bought the mold materials and the casting materials.  The kit gave me the confidence to continue casting just using the raw materials.

Some tips- design of the mold is critical.  Through the years I have learned tricks.  Wrote an article for FSM several years ago.  Mold should NOT be open with the part cavity exposed to the air.  The longer the pouring sprue the better.  The pouring sprue should be J-shaped, with resin entering mold cavity from bottom, NOT TOP.  Every local high spot in the mold cavity should have a vent riser tube to let air escape.

I've used Alumilite but I like the kit from MicroMark better. I believe it is made by Smooth-On.

Woody

I've used Alumilite but I like the kit from MicroMark better. I believe it is made by Smooth-On.

That matches-up with what I've heard about the Micromark product.   

Go to the Smooth-On site for their free download of how-to information,   http://www.smooth-on.com/howto.php  then surf around their site for their starter sets and local distributors.

I use Smooth-On and am satisfied with the results.   I've tried Alumilite and have found the resulting resin was coarser .   YMMV

One of or own here on FSM has a great book for about $15.  I have and it is worth it.

http://www.vairhead.net/modelshack/products_book.html

THis is the site where I learned to make molds from.
http://www.castlemolds.com/moldmake/moldmaking.html
It is a good general How to tutorial.  Bruce explains pro's and con's of some common silicone.

His sites is a great site for diamora how to ideas.  Not just for his probducts but pretty good out of the box ideas. http://www.castlemolds.com/tipsmain/tipsmain.html
They are well worth a quick read.

Hope this helps,

I just remembered who I bought that first casting kit from- a place called Ace Resin(s).  Don't know if they are still in business but I was really satisfied with their beginner kit.

EdGrune

Woody:

I've used Alumilite but I like the kit from MicroMark better. I believe it is made by Smooth-On.

 

That matches-up with what I've heard about the Micromark product.   

Go to the Smooth-On site for their free download of how-to information,   http://www.smooth-on.com/howto.php  then surf around their site for their starter sets and local distributors.

I use Smooth-On and am satisfied with the results.   I've tried Alumilite and have found the resulting resin was coarser .   YMMV

Your remark about Alumilite being courser is right on with my experience.

I started with an Alumilite kit, and like Don, it gave me the confidence to continue.  I had to replace some parts that were missing from a glue-bomb I was rebuilding.  Alumilite sets too quickly to be poured in a mold like Don describes.  I did my pieces in halves, then tightly clamped the halves together before the resin set.  It resulted in good parts, but there was some flash to cut off. 

Something that takes longer than a minute to set would be much better for working with when trying to get a bubble-free part. But definitely go for it.  It's great fun, albeit a bit messy.

Gene Beaird,
Pearland, Texas

wing_nut

One of or own here on FSM has a great book for about $15.  I have and it is worth it.

http://www.vairhead.net/modelshack/products_book.html

Is the book only available through Lulu?  I only ask because I'm uneasy about that site for some reason.

Any good videos out there on the basics of resin casting?  I need to do some pretty small parts and feel a little overwhelmed. It seems to me that the mold is so soft that you can just pull the parts out when cured? Is that correct? I want to make copies of some 1/144 helo miniguns from A Revell kit.

http://www.smooth-on.com/media.php

Their Basics of Mold Making has a number of good demonstrations

So I ordered the book and it covers the basics of mold making but what about selections of the mold material and resin?  There is a large variety of the two out there.

Do I need a vacuum or pressure pot?

68GT

So I ordered the book and it covers the basics of mold making but what about selections of the mold material and resin?  There is a large variety of the two out there.

Do I need a vacuum or pressure pot?

No.  If you were doing the castings for sale it would help, but with proper mold design you can eliminate most bubbles.  Two important tips.  The pour sprue should be J-shaped, so the resin enters the mold cavity from the bottom.  That way it pushes air in the mold upward rather than trapping it in the cavity.  Then, you must have an adequate number of vent tubes- at least one for every local high spot.

Smooth-On has Mold Max 10-40, XLS II and OOMOO.  which would be best for starters?

I've used Mold-Max and OOMOO.   I checked the product specs at the Smooth-On site for the XLS.  It is for "hot" resins which are large and intricate.   Stay away from the platinum-cure urethane rubbers (pricy and not as suitable for modeling applications).

The 10 to 40 indicate the Shore Hardness of the finished rubber.    The lower the number the more jelly-like.  The higher the number the more firm.    40 and above may be too stiff to easily remove the master on a one-piece mold resulting in tear-out.   But 40 may be good for a two-piee mold.

Mold-max and XLS are 100:10 (10:1) mixes.   They are a little more work to get the proportions right -- you need a scale or good measuring cups.   Not as forgiving if you dont have the tools.  Vacuum degassing is recommended for XLS and MoldMax

OOMOO is a 1:1 mix by volume.   It can also take a bit of too much of one or the other in the ratio, by as much as 10% I've been told.    More forgiving.  I use 1 ounce condiment cups from the restaurant supply store.  Measure, pour, scrape and discard.   I mix in a plastic cup.   Mix, pour scrape, and discard.  Degassing is not necessary  (be careful to limit entraining bubbles when mixing).

I switched from Mold-Max to OOMOO because of the 1:1 mix and degassing.  I found that I had better results on my molds getting the ratios right.   I've used both OOMOO-25 and OOMOO-30.    Even though the demold time is longer for the -30, the molds  using -25 were not as robust.    My preference is -30

I don't have a vacuum pump, so I pressurize both the rubber and the resin.   The molds seem to give better results when pressurized than when not.   But as pointed out, pressure is not required if your mold is well thought out with minimal undercuts.

Check the distributor list at the Smooth-On site,   or call the Smooth-On help line.  Tell the hlep line or rep at the disrtibutor what you want to do and ask for product recommendations.    There is a distributor just over in Dallas from where I am and they've been helpful answering questions.  Get on their mailing list.   Smooth-On runs some local seminars which allow you a hands-on opportunity to try their products.   Also having a distributor handy allows you to make an over the counter purchase when you need the stuff now - not wait on shipping. 

Thank you so much!

This is exactly the stuff I wanted to know.

I just made my first mold with the Oomoo 30. I can't see any issues with air bubbles. Made a 2 piece and it looks good so far. The local shop did not have the resin I wanted (smooth cast 321) so it is on order. Gonna try without pressure and see how it works. I found a paint pressure pot at harbor freight that looks like it could be adapted to perform pressure and vacuum duties if I need to go that route. There are lots of good video clips on you tube and the smooth on site.

hi,

I saw in the last FSM issue that there was an article on casting parts.  Hope that helps

James

I guess I shouldn't have let my subscription run out since I can't find a March issue.  Everyone has sent it back to the distributor.  Last I checked it was still March and this ranks up there with bathing suits being in store during winter and not in summer in my area.

Yes I can but I'm not sure if the article is worth $10.  If the magazine was still on the rack then I could check it out but everyone has sent their March issues back already.

You know,  many  cities in North America have this thing called a public library where they keep books and magazines for people to look at or take home for a while

Been to four city public libraries and one county and they don't have FineScale Modeler on the shelf.  I asked one Librarian (are they still called that?) if they could get me a copy and after 15 minutes of searching she said that she was sorry but couldn't find anything.

We use to have an indoor flea market here were the guy would get back issues from a distributor and sell them.  You could get issues going back 6 months to a year easily.  I'll have to keep looking.

68GT

Been to four city public libraries and one county and they don't have FineScale Modeler on the shelf.  I asked one Librarian (are they still called that?) if they could get me a copy and after 15 minutes of searching she said that she was sorry but couldn't find anything.

 

We use to have an indoor flea market here were the guy would get back issues from a distributor and sell them.  You could get issues going back 6 months to a year easily.  I'll have to keep looking.

Many (if not most) libraries today belong to some sort of regional association from whom they can borrow books through Interlibrary Loan, or obtain electrographic copies, if you know the exact issue and page numbers of the article you want. In some cases you do have to pay a nominal copy fee.