Matrix Sentinel Studio Mold - UPDATE - CASTS FOUND!

[Cameron]

Hey my casting experts.
I recently picked up a studio used mold that was used to make the claws of the full sized Matrix Sentinel. It is a 3 part mold. I want to cast one up for myself and I've had requests from some other Matrix collectors for a copy. If all goes well on the first cast I may offer some up. The mold is in ok shape but has a few minor issues.

I've cast plenty of things in resin but this will be different so I have a few questions for the molding experts.

1. Can you recommend a product for casting. I believe the originals were a self skimming rigid foam product.
2. There is residue and probably mold release present. Do I clean these a bit first?
3. It looks like there were 14 attachment points for the mold. Will these be enough?
4. There are 3 long claws deep in the mold. Any advice on getting a good fill down there?

Thanks in advance!

 

[Duncanator]

Thats a cool prop to have!

Correct me if I'm wrong, but it looks like the mold has a silicone inner surface with a fiberglass mother mold, Yes?

That sucker looks like it will eat up a lot of resin if you try to pour it up solid - not to mention the heat it could build up which could cause shrinking or distortion.
If you want to do it solid, you'll want to use a slow setting resin. Like, overnight...

If not cast solid, then either using a self skinning foam (like you mentioned) or do a slush cast with resin, and then fill that with foam. The slush cast should be more durable since you can build up a thicker skin for the part. I like Smooth-On's Smooth Cast 300 for the skin coat, but you can use whatever you are comfortable with. There are other urethanes that set up more progressively, which give you more time to build up the skin.

Once you've skinned it, then you can fill it with a rigid urethane foam like Smooth-On's Foam-it. The foams come in different densities which corresponds to how much it expands - a denser foam won't expand as much as a less dense foam. It's all about the air bubbles!
I'd probably go with the 4lb Foam-it. Be aware that it expands 14 times the volume of its liquid form, so don't mix up too much. You can do it in multiple pours, since the stuff sticks like glue to everything it touches.

I hope that helps! Let me know if you need clarification.

 

[Cameron]

Yes to the mold questions.
That is some great advice. There is some mold damage that will cause some large "pimples" so to speak and they will need to be trimmed off so Im thinking maybe no skin coat? What do you do when something needs to be trimmed?

 

[Duncanator]

Yes to the mold questions.
That is some great advice. There is some mold damage that will cause some large "pimples" so to speak and they will need to be trimmed off so Im thinking maybe no skin coat? What do you do when something needs to be trimmed?

If you slush a thick (1/4") skin coat, then you should be able to sand, cut or grind any surface imperfections off of the finished part without cutting through to the underlying foam. That's why I'd prefer that method for casting for this piece.

 

[Duncanator]

Self skinning foam only gives you a thin skin, which doesn't allow for sanding without hitting the foam.

 

[Cameron]

The arms are very deep and separate so would you suggest I slush cast each arm to about 1/4 separately first?

and/or

Do I slush the open mold or do it closed up?

 

[Mr Mold Maker]

The silicone in there looks well past it’s library life so I would advise caution.. When silicone starts to get discolored and tear like that, it’s a good sign it’s on the way out.

The first thing you may want to do is make a master copy. That looks like a huge pain in the butt to cast, but doing a good resin skin and foam filling as advised above is probably your best bet so you can address the surface damage. You could alternatively lay up fiberglass and put a butter coat on the seam before closing, and foam fill that. Just be aware that any pull from that mold could be the last.

Something to note, urethane foam is incredibly tenacious. It can and will stick to silicone, as well as the fiberglass shell, so a generous release is recommended anywhere it may touch. You want a wax based release like Ease Release 2831 or Stoner Rocket Release.

 

[Cameron]

How about a complete resin pour for the master copy?

 

[Mr Mold Maker]

If casting solid is ideal for you, have you considered stone? Hydrocal comes to mind.. It will be heavy, but it is cheap and easy to clean up the surface.

As mentioned by another poster above, solid resin? You’re looking at an awful lot of material. Exotherm, shrinkage, distortion, bad deal.
I suppose you could do it in very thin layers, but the risk there is delamination. If you put one layer down, let it mostly cure and pour the next layer too thick for example? That thicker layer will delaminate and shift.

Just my thoughts. Hope it helps somewhat.

 

[Cameron]

It does help, thanks. Ive never slush cast a mold this big but that with foam backfill seems like the way to go from what you are both saying. Do I slush the legs first separately?

 

[Mr Mold Maker]

Yeah, if I was casting from that mold I think I would give each leg two or three coats just to make sure you’ve got it covered, then slush cast the body.

When you cast your foam I would quickly and evenly fill each leg. I would then use a well released board clamped to the opening to apply back pressure on the foam. It will reduce the chance of airbubbles and give you a more dense foam. If you are worried about the foam applying too much pressure to the mold, you can put a few bleeders (holes for the foam to escape) in the board.

 

[Cameron]

What products would you recommend for the foam? Duncan like Smooth-On Foam It.

 

[Mr Mold Maker]

I think Foam-It 5 with back pressure would do the job just fine. It’s a great medium between density and expansion, and it mixes 1:1 by volume.
For what it’s worth, I’ll add this info as well. My resin of choice is Onyx Fast for rotocasting.

 

[Cameron]

Is Ease Release 2831 good for resin as well as foam? Since I will be using a resin skin and foam may hit some parts is it good for either?

 

[Mr Mold Maker]

Yes, 2831 works just fine for releasing resin from silicone.

 

[Cameron]

Thanks you sir. Seems like 2831 is a lot more expensive than Rocket release. Any big differences?

 

[Mr Mold Maker]

Application will be different since 2831 is a liquid and Rocket Release is a spray.

I prefer 2831 myself, it goes further and gives you more control, in my experience. You apply a layer with a brush or spritzer and once dry, gently buff it into the surface. Follow up with a second thin coat and you’re ready to go.

You can use Rocket Release and follow similar steps and I’m sure it would release just fine. I just have a preference towards the 2831.

 

[Matsuo]

Lots of good advice!
I'd personally solid cast it in resin. If you use a slow set resin it has a lot less exotherm and if you use a lot of filler like 3M micro spheres you can cut down the weight and the resin use. Use enough filler and the resin expands to some degree.

My fear in this whole thing is damaging the mold and destroying any possibility of further casting. As Mr Mold Maker noted, that the silicone looks degraded. One tough pull out of that silicone might destroy the mold. I'd definitely go liberal with the mold release to mitigate any mold brittleness. If you start pulling chunks of silicone out of it on your first pull you can kiss any further castings goodbye.

Another thing that occurred to me is that if you got a couple viable solid pulls I'd cut one up and re-articulate the claws as originally intended.

 

[Cameron]

Lots of good advice!
I'd personally solid cast it in resin. If you use a slow set resin it has a lot less exotherm and if you use a lot of filler like 3M micro spheres you can cut down the weight and the resin use. Use enough filler and the resin expands to some degree.

My fear in this whole thing is damaging the mold and destroying any possibility of further casting. As Mr Mold Maker noted, that the silicone looks degraded. One tough pull out of that silicone might destroy the mold. I'd definitely go liberal with the mold release to mitigate any mold brittleness. If you start pulling chunks of silicone out of it on your first pull you can kiss any further castings goodbye.

Another thing that occurred to me is that if you got a couple viable solid pulls I'd cut one up and re-articulate the claws as originally intended.

Everyone has been very helpful and I am indebted.

What slow set would you use?

 

[Matsuo]

Smooth-on Smooth-cast 305 is good. With a listed pot life of 7Min and 30 min demold time.
Alumilite sells a virtually identical formula called Slow Set 7 with the same specs.
Also of note, slow cure resins have a lower shrink rate.