Monday, September 2

Mold Rubber Monday - AMAZING 1:27 Scale Model
R/C Crawler Body by Lonnie Sexton

1:27 Scale Model R/C Body by Lonnie Sexton

This project is for a company in the oil and gas field and is once again made possible with Amazing Crafting Products. This tutorial covers the new Amazing Mold Rubber, creating a 2 part mold using the brush on/back fill method.

Normally I would create my own primary and I never promote copying other designs or products. However the Die Cast body weights aprox 225 grams and is too heavy for the R/C chassis suspension to hold. A light weight plastic version is in order and I had to purchase 2 of the original die cast kits to pull the bumpers and windows from.  Even if I make tons of bodies, I would still have to purchase die cast kits to complete the plastic versions. As a custom crafter and a part of my creed (P), integrity is everything. Please do not copy other artist/crafter designs and always credit your inspiration when applicable. 
This is a lengthy method for using Amazing Mold Rubber. If you have never used this product before, it’s advised you test it out on less involved projects to learn the nature/attitude and familiarize yourself with its characteristics.
Part Prep
It’s very important you spend the time to properly prepare your part.

First cut a piece of foam board big enough to hold your primary with at least a 3/4” margin around the outside. Using polymer Modeling clay fill in the inside of the primary and smooth the edges. Add Clay bumps around the edge, this will create key marks the 2nd half of the mold will fit too.

Be sure to fill all major undercuts with clay. You want minimal to no under cuts when building the top surface mold.
Amazing Mold Rubber Layer’s
The run off from this method may seem wasteful, but every bit of cured silicone is just as good as none cured. Cut pieces of cured rubber can be added to your next project to fill in volume, using less new product. It’s also important to let the excess run off naturally to create the first super thin detailed layer.
Measure and mix the first batch of Amazing Mold Rubber. I used 80/8grams (10:1 by Volume by weight: 80 grams rubber, 8 grams catalyst) for the first layer. Brush it on thick at the top edges and let it naturally run down. 

Wait 3 hours until the first layer becomes tacky and no longer runny.

Mix the second batch of Amazing Mold Rubber (10:1 ratio) and brush on the 2nd layer.

Wait 3 hours until the first layer becomes tacky and no longer runny.
Mix the third batch of Amazing Mold Rubber (10:1 ratio) and this time let it stand for 10-14 minutes until the rubber starts to thicken. Brush on the 3rd layer as thick as possible, scooping up the run off and brushing it back to the top of the primary part, applying as much as possible to the vertical sides. Around 20 minutes the Rubber begins to set. By that time, let it naturally run down.

Layer 4-6 are down the same way as layer 3. Each time waiting for a tacky cure and letting the rubber pre-set a short time.

By layer 6, I was satisfied with the thickness of the bladder layer and let it cure for 24 hours before proceeding to the next step.
Mold Box/Back Fill, 2-part
Now the extra run off can be trimmed away from the edge of the Foam Board. DO NOT throw away any excess cured Amazing Mold Rubber. It can be used as filler on other projects. I used it for the 2nd half of this mold. Cut and Hot glue foam board around the outside to create a mold box. At this point you can use whatever back filler compound you wish; Plaster, Expandable foam, etc. I choose to use expandable foam, Alumilte 610.

Mix and pour around the lowest point of the mold box and let it naturally expand around the bladder mold and out the top of the mold box. Mix and add any spots that didn’t completely expand above the mold box edge. After the foam is cured, trim the excess that sticks out above the box rim.
Molding the 2nd Half

Flip the Top ½ over and remove the clay filler.
Create a mold box around the top half.

Hot glue Inlet and Outlet dowels to key points of the primary object. I used ¼” diameter dowels, 1 on either side of the part. The flash will be trimmed off later.
Apply 3 layers of Mold Release to the cured Rubber. Brush on, let dry 10 min and apply again.
Be sure the edges of the mold box are tight and will not leak. Mix and pour the back side of the mold. I used 150 grams of new Amazing Mold Rubber and about 56 grams of already cured pieces to fill in the entire back side.

Place in Vacuum Chamber for 20 sec. Let cure for 24 hours.
The Bladder Mold
The first attempt at this project I used 5lbs of Amazing Mold Rubber to create a block top and bottom 2 part all rubber mold. Due to the total volume my vacuum chamber didn't pull out all the air bubles and the surface quality in the casting zone was compromised. Leaving behind a ton of dimples in the casted part. Using the brush on method I used 1/5th the amount of Amazing Mold Rubber to create the bladder layer. It also makes de-molding simple. 

Casting a New Part

Figuring out the required casting volume to mix can be complicated. To make it fast and easy I always place my primary part in a beaker filled with a pre-measured amount of water. The beaker needs to have measuring marks. Place the part in the beaker and note the water level increase. The increased amount is the volume of the part... Always mix a little more than required to fill the mold.

Preheat both side of the mold to 150 degrees. You don't need a laser temp meter, but it sure makes it easy.

Laser temp reading 153.2f

Mix the Amazing Casting Resin and pour into the mold.
Place the bottom "buck" into the mold and work the edges to ensure it's sealed.
Re-apply heat to the mold to keep it warm for 60 sec. Do not over heat the foam.

Let cure for 20+ minutes before pulling out of the mold. I always leave them longer for thinner casting.

Remove the Foam Block.
Remove the Amazing Mold Rubber bladder top.

Remove the flash from the edges and remove the part from the mold.
Trim all the extra flash.

peeling away the flash

A pre-paint pose...

Pre-paint pose

The end result was a much lighter version of the die cast body, from 225.5 grams down to 45.5 grams (with rack). The micro crawler R/C has no problem operating as expected.

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  1. Fantastic project! Thank you for sharing so many good techniques!

  2. A wonderful and highly detailed tutorial Lonnie. Awesome work! :)

  3. Thanks for the kind words everyone. These R/C projects are so much fun!


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