Wednesday, November 17, 2010

A Near Death Experience

I came home from work.  I wanted to hurry up and get some casts made.  I went into the basement where unfortuneatley I have to keep Sable as she has been ripping the house to shreds when alone.  There is the crawl space and the laundry room.  The crawl space goes under half the house and opens up in to the laundry/furnace room and on the other side of the basement under the stairs.  There is a wooden baby gate to block it off.  There is a little hallway from under the stairs to the door leading upstairs and beside it the door to the laundry room and another straight ahead into the finished basement where I am doing my casting.  I keep this door closed AT ALL TIMES as do I my collection room.

THANKFULLY!!!  Sable destroyed the baby gate, chewed the wood to splinters, pulled all the clothes off the dryer and some that were hanging up.  She pulled up and destroyed the carpet to the point I couldnt open the main door into the basement hallway.  She destroyed home 45mm reel movies and worst of all...

In the basement hallway is my grandmothers old Singer Sewing machine from 1912 I believe...could be as late as 1917.  Its on there I just forgot.  But when its down it makes a nice little table.  And its the perfect size for my Chess Set.  While all the doors were closed, Sable went around under the stairs destroyed the baby gate and now had complete access to the basement hallway.  But thats as far as she could go.  And as far as she needed to go in order to get to My Custom Micronaut Chess Set. 

Black Membros (Bishop) and The Black Defender (King) were totalled beyond repair.  The bases will have to be repolished to see if I can get all the marks out.  If not, I will have to make two more.  The figures will have to be replaced.  I still havent found Membros head.  The Galactic Defender can probably be salvaged for a few parts.

Yup...It was a near death experience.  She doesnt know how close she came.  I have never owned such a stubborn and destructive dog such as this in my life.  Never let anyone else pick out your dog or give you one as a gift.  Picking a dog is just as important as picking a partner.  Now to see what I can do about the carpet.  Shit.

One More Reason To LOVE Sprue Molds

As if my love affair for sprue molds needed more reasons to keep me happy.

Here is one more reason to use a sprue mold if you have the choice.  Smush Mold...resin in 1/2 of the mold and resin in the other half of the mold.  Smush em together, pressurize if possible and cure. 

How many things can go wrong here?  You can trap air in the mold.  You inadvertently orient the mold wrong and in your panic, all the resin runs out.  You wait too long to put the 2 halves together and the resin has already started curing and now you cant get the 2 halves of the mold tightly together giving you an oversize and distorted cast.  Once cast, if there is an air bubble somewhere, its very hard to fix.

Those are the most common things to go wrong.  Here's is how a Sprue Mold overcomes these issues.

The mold is already together when you pour the resin.  Guaranteeing you a close to accurate cast size.  So your biggest worry here is The Shrinkage Rate.  Expect 3%-5% of total size lost.  Since the Mold is preassembled prior to pour, there is no chance of improperly orienting the cast halves. 

But here is my favorite.  A sprue mold relies on the basic concepts of physics.  Gravity.  gravity pulls things down.  So when you pour a cast, gravity pulls the fluid resin down.  It will follow the channels pushing the air out in front of it.  IF something does go wrong, its usually at the end of a pour. 

Recently after I poured a sprue mold, when I took it out of the pressure pot, the air pressure had pushed the resin deep into the mold forcing the air out via the channel.  I had thought the mold full when I put it in the pot only to find that because of the air pocket the cast was no incomplete.  There wasnt enough resin poured into the mold now.

Because of the expereince I have had curing 2 separate colors together, I simply made a little bit more resin.  Carefully put the mold back together with the cast still in it and poured the resin into the mold ontop of the previous cast.  It filled it in beautifully.  You wouldnt know if I didnt tell you.  And if I didnt know, I wouldnt be able to tell.  Its a PERFECT fix.  Try doing that with a smush mold.  Most likely you would scrap the piece and try to make a new one.

Also, in areas that might trap air in the cast, you simply create (cut) a small air pocket where the problem is.  It pushes the air up into the pocket so that the resin can fill in the mold.

Yup, there are so many plusses to sprue molds.  But Smush molds are still easier and involve less trimming and are VERY goos for hi detail parts.  But you will have more scrap if you arent careful.

Sunday, November 7, 2010

Resin Mixing Ratios

Every resin has a mixing ratio.  The ratio is how much of Part A to mix with how much of part B.

And then there is the fine print.  The wuh?  Yes...the Fine Print.  Fine Print is what we dont see because we think we know it all.  And then all of a sudden everything goes kerfluey and we dont know why.  Because we didnt see and read the Fine Print.

The Fine Print says...Mixing Ratio "X amount" of A: "X amount" of B......and this is the important part...By Volume "X amount A: "X amount" B by  Weight. 

And some resins, MOST in fact have 2 ratios.  1 ratio is for WEIGHT and 1 ratio is for VOLUME.  The weight ratio is the one that is usually the weird ratio.  100:80 or 100:90.  The volume ratio is usually closer to a 50/50 or 1:1 ratio.  Last week or so when I first made the Roboid molds I was having issues with my urethane resin.  Why?  because I was confusing the volume and weight ratios.  I was trying to measure the weight and instead adjusted the volume and it impacted the resin in a negative way. 

You cant measure weight with measuring spoons.  Measuring spoons measure volume.  And thats exactly what I did...or attempted to do. 

Since I dont have a scale, I have been measuring by volume.  When you get the volume ratio right, the weight ratio will be correct and visa versa.