Casting resin bodies. Filling the body with clay help.

[Len Woodruff]

I always seem to have a problem filling the body with clay. If you do this kind of casting do you have any suggestions to make this an easier process?

Any suggestions would be greatly appreciated.

Thanks in advance.

 

[mrm]

Ceram wrap 

Edited February 14, 2022 by mrm

[Len Woodruff]

1 hour ago, mrm said:

Ceram wrap 

I don't know what that means.

[Khils]

29 minutes ago, Len Woodruff said:

I don't know what that means.

I think he means the clear clingy plastic used in covering food & containers..Saran wrap.

[Len Woodruff]

Ok Saran Wrap. But how does that help.

I am just looking for an easier way of filling the inside of the body with clay.

I use the microwave to soften the clay.

 

[mrm]

49 minutes ago, Len Woodruff said:

Ok Saran Wrap. But how does that help.

I am just looking for an easier way of filling the inside of the body with clay.

I use the microwave to soften the clay.

 

It would make it really easy to remove the clay cleanly. I thought that’s what you needed. 

[Len Woodruff]

1 hour ago, mrm said:

It would make it really easy to remove the clay cleanly. I thought that’s what you needed. 

I am sorry I should have been more specific. To me it is a PITA to to put the clay in the body and try no to have it push out. I just thought there would be some ideas about how to mold the clay to make it easy to put in.

[Shark]

The resin caster I know tapes the window and good openings from the inside with good quality tape, a couple layers crossing each other. He has no clay inside the body.

[Len Woodruff]

28 minutes ago, Shark said:

The resin caster I know tapes the window and good openings from the inside with good quality tape, a couple layers crossing each other. He has no clay inside the body.

Thanks I like to know how he does that. The amount of rubber would bust trough most tape. I would like to know how he seals the bottom to keep it from seeping in. 

[Lunajammer]

Are you using Play-Doh? At least that's a little easier to wash out the tailings with water and detergent (not perfect, but a little easier).

[Len Woodruff]

11 minutes ago, Lunajammer said:

Are you using Play-Doh? At least that's a little easier to wash out the tailings with water and detergent (not perfect, but a little easier).

That's a good idea. I used the clay from Reynolds Materials which I heated in the microwave to soften it.

Do you have any trouble with the PlayDoh letting the liquid rubber seep in around the body?

 

[Mark]

I didn't fill the whole body with clay.  I cut foam blocks to take up most of the space inside the body, glued those together (and to the base), covered that with cling wrap, then used clay to fill the rest of the space. 

The foam block MUST be glued securely to the base, as if it breaks loose it will want to float to the top of the uncured RTV.

[Lunajammer]

1 hour ago, Len Woodruff said:

Do you have any trouble with the PlayDoh letting the liquid rubber seep in around the body?

Not really, if you're careful to pack it in good. It behaves like any other clay. If there are any minor air pockets within the layers, it doesn't seem to be disruptive. Mold release helps when getting it back out, but you'll still need to get in there with a toothpick.

Fresh is key, if it looks like this, don't use it, air will get in. Pic was taken before a failed attempt of this mold, thinking I could get away with it.

 

Result of the successful cast.

Edited February 25, 2022 by Lunajammer

[Mark]

If you change the clay that will be used, be certain that it is compatible with the RTV being used to make the mold.  Incompatible materials could result in the RTV not curing in areas directly adjacent to the clay.  A little time in checking can save a lot of time and money potentially wasted on an unusable mold.

[Len Woodruff]

15 minutes ago, Mark said:

If you change the clay that will be used, be certain that it is compatible with the RTV being used to make the mold.  Incompatible materials could result in the RTV not curing in areas directly adjacent to the clay.  A little time in checking can save a lot of time and money potentially wasted on an unusable mold.

Good point. That is why I stayed with the clay from RM.

[NOBLNG]

I also taped the inside of the windows with masking tape. Then I put a slab of modelling clay up against the tape to protect it and then packed the rest of the cavity with clay. Sorry, no in progress pictures.

Edited February 25, 2022 by NOBLNG

[robdebie]

I've always wondered about the following. The clay-filling of a body is quite a bit of work, the clay removal before casting the second mold half is quite a bit of work, and all this needs to be repeated every time a mold wears out, after (say) 30 castings. Isn't it better to create a permanent (but removable) plug for the interior? I haven't found a perfect method yet, but maybe the clay plug can be baked, or you cast the plug from plaster and seal it, whatever. What do you think of this approach?

Rob

[NOBLNG]

46 minutes ago, robdebie said:

I've always wondered about the following. The clay-filling of a body is quite a bit of work, the clay removal before casting the second mold half is quite a bit of work, and all this needs to be repeated every time a mold wears out, after (say) 30 castings. Isn't it better to create a permanent (but removable) plug for the interior? I haven't found a perfect method yet, but maybe the clay plug can be baked, or you cast the plug from plaster and seal it, whatever. What do you think of this approach?

Rob

Well if you’re going into production, it might be better to make two sets of molds. Use one set for casting, and keep the other set and the master for making new casting molds when needed?

[Lunajammer]

3 hours ago, robdebie said:

Isn't it better to create a permanent (but removable) plug for the interior? I haven't found a perfect method yet...

There are many kinds of RTV rubber mold material of different firmnesses. When I did modeling for a pewter miniatures company, we experimented with harder rubber. Didn't like it. It's more difficult to work with; harder to get the resin pieces out, less flexible, breaks/tears easier, etc. However we did not try making part one soft rubber and part two hard rubber. Regardless, a firm plug is not very forgiving.

[Rick L]

20 hours ago, Mark said:

If you change the clay that will be used, be certain that it is compatible with the RTV being used to make the mold.  Incompatible materials could result in the RTV not curing in areas directly adjacent to the clay.  A little time in checking can save a lot of time and money potentially wasted on an unusable mold.

Incompatible materials would be clay with sulfur in it or using latex gloves. When mixing the rubber. 
  Unfortunately it’s a trade secret how this molds diking was made but I can show you this photo and tell you that plexiglass was involved.

[Len Woodruff]

Wow. What is it?

Thanks for the reminder about the Latex gloves.

[Rick L]

It’s a short run casting of a housing. I build the master in 4 sections on a 3 axis mill from model board.

[robdebie]

On 2/26/2022 at 5:15 AM, NOBLNG said:

Well if you’re going into production, it might be better to make two sets of molds. Use one set for casting, and keep the other set and the master for making new casting molds when needed?

Interesting thinking! If one would cast two copies of the 'second' (lower, body interior) mold half, and save one of those, my goal would be roughly achieved. The claying would still have to be done once though, but not for making subsequent mold sets.

Rob

[robdebie]

On 2/26/2022 at 2:39 PM, Len Woodruff said:

Thanks for the reminder about the Latex gloves.

An important drawback of addition type silicone (platinum type) silicone rubber is that the curing reaction can be inhibited by a number of materials. This is called inhibition or poisoning. The following materials are listed by various manufacturers:

- condensation type silicone rubber (especially its tin-soap catalyst)
- unsaturated hydrocarbon solvents
- sulphur (in vulcanized natural and synthetic rubbers)
- phospor
- epoxies containing strong amine catalysts
- isocyanates of urethane resins
- tape adhesives
- metallo-organic salt-containing compounds (especially tin salts and heavy metals)
- plasticizers in plastics (especially vinyl)
- some epoxy and polyester resins
- nitrogen containing materials
- some modelling clays
- solder flux
- wood
- leather
- chlorinated products (such as neoprene rubber)

It's a scary list for sure. Better do a test when in doubt.

Rob

[Rick L]

On 2/25/2022 at 11:15 PM, NOBLNG said:

Well if you’re going into production, it might be better to make two sets of molds. Use one set for casting, and keep the other set and the master for making new casting molds when needed?

Why two sets of molds, why not save the male half of the old mold as your diking for the next mold if your running production. 
Spray the mold half with release agent.

Slide master onto mold half.

Build box around mold half with master.

Pour rubber into box.

Remove old male half.

Pour rubber to create new male half.

PRESTO! New mold.