Two part mold

TazMan2000 · Post by **TazMan2000** » Wed May 29, 2013 8:00 am

In making a two part RTV mold, I accidentally de-molded the master while removing the clay. Since the master part is very light, I'm afraid that just sticking back the master and pouring RTV over top will result in the RTV making its way into part 1 of the mold. Is there any way to re-secure the master without wrecking the first part of my mold?

TazMan2000

Rocketeer · Post by **Rocketeer** » Wed May 29, 2013 9:26 am

How about a light coating of thinned white glue? Ought to hold long enough to get the mold done.

modelnutz · Post by **modelnutz** » Wed May 29, 2013 11:18 am

A solution dicovered through trial and error....lots of error...

But, I know from experience....it works !

Step 1... apply a light coating of vaseline cut with Mineral Spirits to both the mold cavity as well as the master.

Step 2 .... insert the master back into the mold cavity. ( wipe away excess vaseline )

Step 3 ( The tricky part ) create a "bridge" of foam core board over the mold/master/mold box....I use 3 layers hot melted together ( think..plywood effect ) I use opposing top edges of the mold box and just hot melt the "bridge in place. [ you want the bridge to be as close to the master but far away enough so you can pour the second side of RTV without coming in contact with the "bridge" ]

Step 4... using long pins passed through the "bridge"...you want to slightly press the master into the cavity ( obviously, you need a flat surface on the first mold half for this to work well ) Hot melt the pins to the upper surface of the "bridge" so they stay put.

Once you are happy with the seating of the master in the mold cavity and have wiped away any extra vaseline....coat the first half of the mold as you would normally and pour the second side of RTV

Step 5... pray that all goes according to plan.

If any RTV slips past the master and comes in contact with the first half of the mold...the light coating of vaseling will keep it from sticking.

Hope this process is clear enough....any question...feel free to ask away !

Good Luck !

modelnutz · Post by **modelnutz** » Wed May 29, 2013 11:19 am

Ooops...double post

TazMan2000 · Post by **TazMan2000** » Thu May 30, 2013 2:14 pm

For so much effort that Modelnutz has put into his post, I feel bad for not trying it out first, but I think I'll try out Rocketeer's white glue trick because it seems easier. But first I will see if the glue that I'm using will detach easily from the RTV.

TazMan2000

Ziz · Post by **Ziz** » Thu May 30, 2013 2:59 pm

I hate doing two part molds. That's why all my parts have that T sprue on them. It allows me to do everything as one part envelope molds.

Stu Pidasso · Post by **Stu Pidasso** » Thu May 30, 2013 3:08 pm

Ziz wrote:I hate doing two part molds. That's why all my parts have that T sprue on them. It allows me to do everything as one part envelope molds.

Wait until you get into 3 and 4 part molds...

Rocketeer · Post by **Rocketeer** » Thu May 30, 2013 4:57 pm

My record is a four-parter that I used to cast wooden chairs in 1/25th scale.

Ziz · Post by **Ziz** » Thu May 30, 2013 6:22 pm

Stu Pidasso wrote:
Ziz wrote:I hate doing two part molds. That's why all my parts have that T sprue on them. It allows me to do everything as one part envelope molds.
Wait until you get into 3 and 4 part molds...

If I refuse to do 2 part, why would I even attempt something more complicated?

Stu Pidasso · Post by **Stu Pidasso** » Thu May 30, 2013 6:31 pm

[used car salesman commercial voice]'Cause you're CRAAAZY!!!! [/used car salesman commercial voice]

naoto · Post by **naoto** » Thu May 30, 2013 6:43 pm

Stu Pidasso wrote:[used car salesman commercial voice]'Cause you're CRAAAZY!!!! [/used car salesman commercial voice]

https://www.youtube.com/watch?v=5ODs4nxNnWM
https://www.youtube.com/watch?v=jc-Mhynh_pg

speaking of car dealerships... Cal Worthington and his dog Spot!
https://www.youtube.com/watch?v=QOsLdT4slsk

TazMan2000 · Post by **TazMan2000** » Thu Jun 06, 2013 1:59 pm

Rocketeer's idea worked like a charm.

I will use Modelnutz idea when the master is less dense than the RTV.

Thanks to all who provided ideas.

I've done a 4 part mold myself. Well... it didn't start out as 4 parts. While trying to de-mold the first casting in a two part mold, one of my halves ripped into 3 pieces. I still used it to cast several more pieces, just with a bit more clean-up to do afterwards.

TazMan2000

Rocketeer · Post by **Rocketeer** » Thu Jun 06, 2013 5:16 pm

TazMan2000 wrote:Rocketeer's idea worked like a charm...

There's a first time for everything!