2 part mold without embedding in clay

So I had a problem. I needed to cast this in a 2 part mold, but I wouldn't have been able to clean the clay off it (I tried).


So I used small baked clay balls to suspend the object above the floor of the mold.


For keyholes I did this, but next time I will just erect pens of something. That will be more efficient as this was quite a mess.


Poured the first half:


So far, so good. Built up the mold wall:


But oops, I screwed up! Once I poured my second half, I realized that I forgot to spray mold release! I tried to remove the freshly poured silicone, but to no avail. I poured it back on top. I had to use a cutter to separate the two halves, so this really sucked.

Then I cut out an air vent, sprayed release and closed the mold with cardboard and rubber bands. I looked for my air vent, but couldn't find it.

I measured how much resin I would need by placing the object in water and then measuring the amount of water displaced. I used exactly that amount.

But once I poured the resin, I realized mistake number 2! I stupidly had the air vent pointing down, not up! Resin started linking out! I plugged the hole, but lost a good deal of resin.

So here it is, the clayless 2 part mold. Besides the 2 screw-ups, the idea of making a mold without clay worked pretty well. I don't like how messy it gets and how it sticks to objects.

 

Nice trial and error work! Looks like you got the results you wanted in the end. I also hate the idea of embedding in clay, I tried doing that with Play-Doh and discovered that it sticks to primer... Awful experience.

 

Try Magic Mold Putty!!!!

 

Magic mold putty is pretty cool, but it doesn't produce clear resin according to the demo video.

 

I'm hoping I just didn't screw up $200 worth of silicone.

 

Don't be lazy! Make a 3 part mold! Use clay!

 

Play Doh would have worked with that. I've used it on masters made with Sculpy, Styrene plastic, Wood, Aluminum, as well as Castelline and Azbro wax, bare and painted (not the wax). Just make sure your paint and primers have fully cured as per manufacturer specs. Also when designing/sculpting your toy try to make it in separate pieces, you actually save on mold materials that way.

 

Just gave this pic a good look, You might have a hell of a time pulling your castings out seeing atleast two of the legs locked in that half of the mold. I hope that silicone has a high tear strength rating cause it looks like you'll have to slice part of the mold to release the legs.

 

Thanks for the look. Yeah, I realized that after pouring. So stupid. I thought I would just slice thorough, but that's not an easy task and already cut into a leg. I actually used clay to make a 3 part mold for the top. But I really screwed up and this silicone was unbelievably expensive. I can't afford to get a new batch right now.

 

What kind of silicone are you using? Smooth-on's Oomoo is pretty nice price-wise and the tear strength isn't bad. Mold Max 30 is tougher but the 1:10 mix ratio can be a pain in the butt.

 

Mold Star 30. I ran out, actually, a whole $200 (after shipping) gallon. So I got some amazing putty to put on the bottom (haven't done so yet).




The silicone is really tough. I have to cut through it, but it doesn't cut so easily. I already cut a chunk out of one of the legs (will be fixed by pouring resin on top of the finished figure to make a slime effect).

 

Wow, I guess a YouTube search for 3 part molds was too much of a hassle.

I'm sorry that was such a waste, but the best way to prevent all of this is to do proper research. That figure was not going to fit in a 2 part from what it looks like. Unless you mold the legs and build the half there crosswise

I would suggest using clay to mold it with release vents and then clean up after casting, if you are too worried about the clay damaging, use brush on silicone for the first 1/2 inch or so, build a rig and mold the rest with a higher shore silicone and make a sleeve for it after it cures, way more work but it's almost fool proof and it will keep the mold from warping when it's in the library.

Finally, if you are worried about the cost, use fillers. Anything you don't really care about can fill the silicone; extra Legos, clay, even pieces of tin foil made into little balls. just make sure there's at least 3/4 in. Distance between the filler and the master and walls you don't want it to rip.

 

The fillers is a great idea and I feel like an idiot for not thinking of that.

The brush on is a good suggestion as well, thank you.

I did watch videos, but I have a kind of one-tracked mind and I really wanted to bypass the clay entirely. That was the point of this thread, to try to experiment with a different method. I was so focused on that that I was hoping the silicone would just stretch out of the figure's legs. But unlike the oomoo and alumilite silicones I previously used, the Mold Star is super firm. The reason I tried to go clayless was the first clay I bought (I forget the brand) couldn't be removed from the piece. It made me hate clay. This blue stuff, craftsmart clay, works pretty well.

I cut out the silicone (along with chunks of the legs that will be patched up with clay, stupid irony)


So back to topic, while the initial piece was mildly successful with a clayless mold, it was really, really stupid to try to apply it the larger piece.

 

I think the problem lies in the toy design itself. It doesnt lend well to making simple two part molds unless you make your figure separate into multiple peices. I would have made the leg cluster separate. A two part mold can be made for that but you will def need to imbed it. I highly suggest using play-doh cause imbedding clay is too firm.
If you're using soft high tear strength silicone, you would want to establish your gates and vents using wax. Cutting it in after the mold is cured would be a pain. The head and that lower bulbus part can be cast using a one part mold. Use Alumilite High Strength-3, its super flexible and works great on masters with extreme undercuts. Its a 10 to one mix ratio and its not really a hassle to figure out as mentioned. If I can do it anyone can.

Basic tip= If you're planning to use pressure pots when casting in resin, make sure your molds have been cured under pressure as well. Those bubbles in the mold will collapse under pressure and you'll have bumps all over your castings.

 

Thank you for the tips. No pressure pot.

I totally agree with the design problem. Having no experience, it was quite a challenge to think how I should mold this. Originally I wanted the top to be the pour hole, but I decided to have the legs be the pour holes. Next I'm concerned about messing up the air vents.

If this fails, I'll separate the pieces. It has a tin foil wrapped around wire armature skeleton, though.

I'm the kind of person who learns through the experience of mistakes. I could watch youtube videos all day, but unless I get my hands dirty and really try things, it's difficult to really understand what I need to do. So I really appreciate all these comments, suggestions and criticisms because they are helping me out.

 

Just cut it. Use a fine toothed saw like a hack saw or a cut off wheel if you have a dremel, either one will work. Then just repair/modify each ends so it keys into each other. I would add some sort of design element to hide the joints if it bother you like a skin fold or something.

 

Thank you so much for these suggestions. The final piece will be covered in clear resin to give it a slimy extracellular fluid effect. It did a good job on hiding flaws of some test pieces.

 

One little tip I should mention, when pouring silicone into the box or legos or what ever you're using for boundaries, you want to pour slowly from a high place into a corner of the box. It definitely minimizes bubbles in the silicone when molding.

 

I don't think cutting will be necessary.

 

That sucks but its not beyond fixing. This is one of the reasons I switched to wax.

 

If the mold doesn't work, it could be a blessing in disguise.

 

If you dont mind me asking what type of wax are you using?

 

Back to the topic, the clayless mold gave me a perfectly flat seam-line. But only 3 of the key holes succeeded.



The bottom is a total mess. But at least it's the bottom (and the pour holes).


Now to do some research as to where to cut the air vents. That's my weakest part of mold making.

 

I requested that both my threads be merged because they both have converged to the same topic.

Getting closure:

 

Casteline in medium and hard compounds. Below is an old post I did on the subject. Still hoping the mods will make it into a sticky one day.

viewtopic.php?f=19&t=34221&hilit=casteline