Molding the Entex Porsche - Printable Version

Molding the Entex Porsche - Printable Version

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Molding the Entex Porsche - Mr Scott - 02-03-2015

This post is going to be multi-part and long, but I want to tell the story, hopefully help others, and hear feedback. If you don’t like the wall of text just skip it and look at the pictures. [Image: cheeky.png]

A couple of months ago I got the opportunity to cut up an Entex Porsche body and make molds for the Slave I parts. It seemed simple enough, drop the parts in RTV, pour resin. Right? Let’s go!

Then I started studying the Entex parts and doing some math. Traditional block molds for the rear fenders would require 12+ pounds of RTV! The front fenders need 10 pounds more! The doors need 4 pounds and the bumper3. At this rate the molds would cost as much as the model! What had I gotten myself into? [Image: wacko.png]

I started to try and figure out a way to use less RTV, focusing on the rear fenders. My first idea was make a custom mold box that would follow the curves of the body instead of a cube shaped box. It turns out that did not help much because the rear wheel well sticks out so far and creates lots of negative space. Then I found a tutorial on the Smooth-On website about cavity pour molds. That would be the solution, but they used Plasti-Paste for the shell. It looked simple enough but looked like a mess. I had never used it and I did not want to learn on this job. Instead, I clayed up the part, put another layer of clay over the whole thing (cavity space) and then vac formed over that with .06 styrene.

[Image: DSC05127_zpssrxto269.jpg]

After the shell was created I removed the cavity clay. A pour hole was cut and several vents were drilled and extended with drinking straws. The shell was centered over the rear fender and bolted down through a sheet of scrap ABS that I had laying around. I used some old MoldStar-16 silicone to seal everything up. Lots of people use hot glue for the seal, but that stuff makes a mess. The old RTV worked great and was probably headed for the trash anyway.

The first part poured and curing.

[Image: DSC05134_zpsd6tu8z5r.jpg]

Clay removed.

[Image: DSC05142_zpseouawcaa.jpg]

Measuring how much silicone will be need for the second parts. I measured the first part the same way, but the pictures look like crap. The plastic beads are like what is inside beanie babies.

[Image: DSC05145_zpsv3bhag28.jpg]

Poured second part. Not pretty, but it works.

[Image: DSC05146_zpsvdlopjal.jpg]

I had planned on pressure casting these…uh oh.

I have a 2.5 gallon pressure pot. A pressure pot big enough would really bust the budget. Okay, I will try the part without pressure. It turned out pretty good. There are some bubbles on the top edges, but all of them can be easily filled, some of them will be trimmed off for the Slave part and others will be hidden so deep in the ship body they will never even be seen anyway.

Raw casting.

[Image: DSC05345_zpsqtmnusyu.jpg]

Other parts to follow

RE: Molding the Entex Porsche - bwayne64 - 02-04-2015

Those are some pretty parts. And great problem solving too. That's what I love about modeling, always new ideas and things to learn, Cheers,

Joe

RE: Molding the Entex Porsche - Mr Scott - 02-04-2015

The doors were done in traditional box molds, nothing too fancy.

[Image: DSC05160_zps5ftdikbs.jpg]

Here is a pet peeve of mine. I HATE punching vent holes in my molds. In the past I have tried using rubber cement to tack styrene rods to my master parts. It works about 50% of the time. The weight of the flowing rtv will knock over the rods. I know I could use a stronger glue/solvent but in most cases, especially this one, I don’t want to harm the master. This time I tacked down with rubber cement and then mixed up a few grams of rtv. I brushed it on to the rod base for extra support. When the small batch of rtv was reaching the end of its pot life I poured the mold. All my vents stayed in place and the RTV cured together as one. It seems to have worked nicely, but what a pain.

Does anybody have a better way?

[Image: DSC05170_zpsgfnr0jde.jpg]

Here are some castings. I have some minor bubble issues, especially with the strip on the back and the bottom of the door. I tried putting them in the pressure pot, but oddly enough I still had the same problem. So, why bother, the bubbles will be easy to fix.

[Image: DSC05386_zpsxbxgtxvf.jpg]

RE: Molding the Entex Porsche - JAWS - 02-04-2015

Good job. Good timing also.

RE: Molding the Entex Porsche - Mr Scott - 02-05-2015

(02-04-2015, 03:18 PM)JAWS Wrote: Good job. Good timing also.

Thanks.

That is one heck of a coincidence, isn't it? Wink

RE: Molding the Entex Porsche - dsp5500 - 02-05-2015

fix those damn smileys Angel

I can't figure out the tone of the posts Undecided

RE: Molding the Entex Porsche - Mr Scott - 02-05-2015

The front fenders created a whole new set of challenges. It was hard for me to get my mind around the negative space. I originally intended to do cavity pours like the rear fenders but the geometry of the part would require some fancy claying. Then I had a “duh” moment. I’m not making Entex front fenders, I making Slave I parts. The red line shows the approximate trim for Slave, the green is where I wanted my castings to go to ensure enough meat to trim down and align to the curve of the hull.

[Image: DSC05263_zpsugimufff.jpg]

Sometime ago beaz posted a method for molding the Saturn V cans and F-4 Phantom engines for the X-wing on the RPF. He used a brace system to support the silicone in the negative space. This creates natural pour space, great venting, and allows the second part of the mold to use much less RTV. Winner!

Here is what I came up with. If you look closely you will notice some mold features that show these did not turn out quite like I thought they would.

Clayed up master with styrene rod where support posts will go.

[Image: DSC05274_zpsrr3enwho.jpg]

First part poured and clay removed.

[Image: DSC05303_zpszpvgb1si.jpg]

It turns out one of my support posts was in a location that would not work (oops). Luckily I had intended to use three supports, I can make due with two. Here are the molds with supports.

[Image: DSC05308_zps7dqrhecl.jpg]

Second part poured.

[Image: DSC05330_zpsefgmnsox.jpg]

Here is what you do when your math goes bad and you mix up way too much silicone. Panic! Grab something, anything you can pour silicone over. Preferably something you want to make castings of. I grabbed the AMT C600 rails for the AT-ST. The pour time on the RTV after vac degassing and pouring the fenders was quickly running out. I didn’t even had time to figure out which was the correct rail needed for the AT-ST. Create a quick clay dam and stick in some styrene rod for keys. To be continued…

[Image: DSC05326_zpsjky0ridn.jpg]

Back to the Entex fenders, master part removed. The support structure keeps the second part of the mold where it should be.

[Image: DSC05338_zpsxiwkpixh.jpg]

Castings.

RE: Molding the Entex Porsche - bg_451 - 02-06-2015

Wow, great job on the casting Scott.
I'll have to bookmark this so that I can do the same to mine (Porsche that is!)

RE: Molding the Entex Porsche - Mr Scott - 02-07-2015

The bumper… At this point in the project I am running into several problems. I have a deadline of sorts, I am getting sick of the project, and I am running low on RTV. Curse that waste on the front fenders. [Image: sad.png]

Big parts of the ends get chopped away for the Slave part, but I don’t want to do that to the master.

[Image: DSC05255_zpsepgbp5rg.jpg]

I used clay to “chop” off the extra parts of the bumper in order to conserve silicone.

[Image: DSC05299_zpsjows1hwc.jpg]

Here is the finished mold.

[Image: DSC05340_zpsiy8zo5sc.jpg]

The edges need to be plugged up. I use a combination of hot glue and packing tape to plug up the sides. The hot glue make a pretty good seal if I glob it on thick and then press the tape into the still hot glue. Then I smear another layer of glue over the bottom edge of the tape.

[Image: DSC05375_zpsnocdz6v7.jpg]

This is the mold that is going to wear out the quickest. I made a mistake in my “negative” thinking and have a thin flap of rtv that is not going to hold up well. The castings will require some attention to remove extra resin.

Castings.

[Image: DSC05394_zpsysf7grrv.jpg]

RE: Molding the Entex Porsche - Mr Scott - 02-10-2015

After I finished with all of the body parts I still had enough RTV to finish up the C600 rail. After figuring out which rail I really need I cut away the other. The attempt at placing the styrene rod for keys was a waste so I cut some keys into the silicone.

[Image: DSC05334_zpsdg6pw1tw.jpg]

Mold box of foam core and clay.

[Image: DSC05336_zpspijtncp7.jpg]

Plug up the bottom with hot glue and tape.

[Image: DSC05402_zpsqdhortgw.jpg]

The castings come out good. Yeah, no need to buy another C600!

[Image: DSC05399_zpso3wvl4od.jpg]

RE: Molding the Entex Porsche - dsp5500 - 03-30-2015

Ive got a set of the casting's and to say i'm impressed is an understatement. Really well made.

Rob