Rubber for molds

Got a question about techniques, materials or other aspects of physically building a model? This is the place to ask.

Moderators: DasPhule, Moderators

User avatar
Ziz
Posts: 9374
Joined: Fri Jul 12, 2002 9:24 pm
Location: Long Island, NY
Contact:

Post by Ziz »

homyakchik wrote:I really can't afford Alumilite prices for the stuff (the Smooth-On stuff certainly seems a better bargain), but the only dealer for the SO is down in Norfolk, and I'm betting they're not open on Saturday. Dangnation and blastoderms, anyway. Another week to wait for a UPS delivery.
www.reynoldsam.com

Reynolds Advanced Materials. I get my stuff in a couple of days, shipping is cheaper than direct from SO AND Reynolds doesn't charge me sales tax, SO does.
Modular
Models

Build your fleet
YOUR way.

http://www.modular-models.com
----------------------------------------------------------
"I know you think you understand what you thought I said, but I'm not sure you realize that what you heard is not what I meant." - Alan Greenspan
____________________________________
"The customer that spends the least complains the most."
homyakchik
Posts: 81
Joined: Thu Feb 26, 2004 2:25 pm
Location: North Little Rock, Arkansas

Post by homyakchik »

Thanks, Ziz. I went there to look. Interestingly enough, although their website appears to be wholly different from Smooth-On, both have the same base setup for their buttons, and right now both are having exactly the same DB access errors in serving up information on the rubbers they sell! *bwah-hah-hah*

Still, I shall check them out as soon as they're back on-line. Thanks for the heads-up.

Dj (still frustrated, but now a little less so)
User avatar
saiyagohan
Posts: 350
Joined: Wed Sep 26, 2007 1:03 pm
Location: Tiffin,Ohio
Contact:

Post by saiyagohan »

I have a question, is there any way to make a mold without pressure casting? That will turn out without bubbles or defect to the mold or to what your trying to make? That is affordable, and if so what kind of product is it? I'm sure this question has been asked before. But I've got a 1/1000 scale Jupiter Station Klingon D-7 variation kit I built that I need to redo the neck on because it warped after many years and when I used hot water and tried a blow dryer it snapped into. Any help is appreciated, thanks
What do the USS Enterprise and toilet paper have in common? They both circle Uranus looking for Klingons.
User avatar
chiver
Posts: 645
Joined: Wed Feb 08, 2012 5:25 pm
Location: Trenton

Post by chiver »

I got alumilite quick set, how long should I wait to remove it from the mold. Box? It's not very big only 4oz and is it important to heat the mold?
KEEP CALM AND CHIVE ON!!!
homyakchik
Posts: 81
Joined: Thu Feb 26, 2004 2:25 pm
Location: North Little Rock, Arkansas

Re: Rubber for molds

Post by homyakchik »

I think this might be where I could ask this question; thread owner, if it's not, feel free to dump it wherever it might be more appropriate.

I know about using the rubber to make a mold for casting resin parts; need to get back to doing that. But I had a thought the other day, while working on an older Zoid.

Zoids were in general held together by 'Gyro Caps,' little caps of what honestly feels like the rubber we make molds of; you push them onto the axles of the joints (in the main) and they keep the arms and legs (and necks and heads and tails) from rattling apart as the Zoid moves. Each Zoid came with a sprue or two (or three) of Gyro Caps sized for it; there were three or four different sizes, usually interchangeable to a small degree between some Zoids and others.

I have one project that I'd like to work on, a Zoid Centaur (combining a Gojulas and an Ultrasaur, possibly with other parts tacked on to make it even more fearsome), that are going to require an influx of Gyro Caps from somewhere as the leftover Gojulas I have hasn't any of his original Gyro Caps. Argh. And they aren't making those Zoids any more and my sources for trading classic Zoids have all dried up and I don't want to have to pay inflated 'collector' prices just for a handful of rubber pieces (assuming I can even find any on eBuy).

So the thought occurred to me: would it be possible to make a cast of a sprue of such rubber parts (my as-yet-unassembled Mad Thunder uses the right-size Gyro Caps) and then cast the parts out of more casting rubber? Slather everything in lots of Don't Stick To This Mold Release 'cause I can't afford to lose my last sprue of these things and do it?

Or is that a futile hope? IF so, is there any way to make a casting of such things, and/or to make a mold and cast such soft rubber? What might I cast the part in? If not the same rubber as the mold, then what could I cast the stuff in? Is making a cast of soft rubber even possible (at my level of hobbyisting)?

Sorry about the length. Wanted to be clear what I was after.

Many thanks!

Davey
User avatar
Rocketeer
Posts: 1592
Joined: Fri Jan 18, 2008 4:48 pm
Location: The outskirts of Hobart, WA

Re: Rubber for molds

Post by Rocketeer »

That ought to be very do-able. It'd have to be a two-piece mold, because the caps have holes in their backs and detail on their fronts.

I just did a quick search, and found these:

https://www.polytek.com/product-type/po ... ng-rubbers

They say that their rubbers can be cast in either silicone (no release agent required) or polyurethane (release agent required) molds.
homyakchik
Posts: 81
Joined: Thu Feb 26, 2004 2:25 pm
Location: North Little Rock, Arkansas

Re: Rubber for molds

Post by homyakchik »

Looks like that's probably what I need to look into, 'cause knowing me, as soon as I start this, I'll have to officially notice that a lot of the other sizes of Gyro Caps--still on the sprues--are starting to rot from sheer age. *sigh* "Modeling is fun." I keep telling myself that.

Many thanks!

Davey
User avatar
Tesral
Posts: 3449
Joined: Mon Nov 18, 2002 2:54 am
Contact:

Re: Rubber for molds

Post by Tesral »

Having seen a few of the caps so mentioned I would use 10:1 rubber as it is firmer than the usual 1:1 mix.
Garry AKA --Phoenix-- Rising above the Flames
The Mighty Ten-12 lives.
Star Trek mort. Viva la Star Trek admiraetur.
Olde Phoenix Inn http://www.oldephoenixinn.net
OdysseySlipways
Posts: 7966
Joined: Thu Sep 19, 2002 9:26 am
Location: Altoona, Pa
Contact:

Re: Rubber for molds

Post by OdysseySlipways »

gyro-caps?
Chris,
Odyssey Slipways

Odyssey Slipways on Facebook

Now accepting Pay Pal, I'll be taking your money now ........... (waves hand in the air, using Jedi Mind trick)
jpolacchi
Posts: 999
Joined: Sat Oct 16, 2004 8:08 pm
Location: West Coast

Re: Rubber for molds

Post by jpolacchi »

You can't go wrong with RTV silicone,just be sure you get the parts "A" and "B" measured in correct ratios be it by weight or volume.
OdysseySlipways
Posts: 7966
Joined: Thu Sep 19, 2002 9:26 am
Location: Altoona, Pa
Contact:

Re: Rubber for molds

Post by OdysseySlipways »

nothing wrong with adding an extra splash of the catalyst to the mix, specially in the winter
Chris,
Odyssey Slipways

Odyssey Slipways on Facebook

Now accepting Pay Pal, I'll be taking your money now ........... (waves hand in the air, using Jedi Mind trick)
User avatar
Kylwell
Moderator
Posts: 29643
Joined: Sun Nov 02, 2003 9:25 pm
Location: Lakewood, CO
Contact:

Re: Rubber for molds

Post by Kylwell »

OdysseySlipways wrote: Tue Apr 24, 2018 11:55 pm gyro-caps?
Also known as "poly-caps".
Abolish Alliteration
OdysseySlipways
Posts: 7966
Joined: Thu Sep 19, 2002 9:26 am
Location: Altoona, Pa
Contact:

Re: Rubber for molds

Post by OdysseySlipways »

and they are?
Chris,
Odyssey Slipways

Odyssey Slipways on Facebook

Now accepting Pay Pal, I'll be taking your money now ........... (waves hand in the air, using Jedi Mind trick)
User avatar
Kylwell
Moderator
Posts: 29643
Joined: Sun Nov 02, 2003 9:25 pm
Location: Lakewood, CO
Contact:

Re: Rubber for molds

Post by Kylwell »

OdysseySlipways wrote: Sat Apr 28, 2018 10:25 pm and they are?
https://en.wikipedia.org/wiki/Poly-cap
Abolish Alliteration
User avatar
MillenniumFalsehood
Posts: 16974
Joined: Tue Nov 16, 2004 5:23 pm
Location: Wichita, KS, USA
Contact:

Re: Rubber for molds

Post by MillenniumFalsehood »

I bought some silicone spray to coat masters with before molding them as I've been having tearing issues even with baby powder. Being the cheap-skate that I am, I was trying to get away with something inexpensive so I picked up a can of this for $12: https://www.amazon.com/Sprayway-SW946-S ... 924&sr=8-6

But then I wondered if it would work on the master to help it release from the mold since the mold and the spray are both silicone-based. Is this going to have any sort of reaction if I use this spray on a part that is then being covered in uncured RTV, or am I going to have to get something else for a release agent?
If a redhead works at a bakery, does that make him a gingerbread man?

Ponies defeat a Star Trek villain? Give them a Star Wars award ceremony!
seam-filler
Posts: 3889
Joined: Thu Apr 17, 2003 11:05 am
Location: Aberdeen, Scotland

Re: Rubber for molds

Post by seam-filler »

RTV rubbers are so susceptible to contamination that can affect curing time (including whether or not it cures at all), strength, flexibility, durability, etc. and each brand, type and sub-type seems to have a different sensitivity to different contaminants.

I would suggest experiment on a small scale to see how this particular mould release spray works with the particular rubber you have. You may also want to consider the reaction it will have with the resin you are going to use.

Most problems with casting are due to poor mixing ratios, compatibility of components (rubber, release, resin & filler), and contamination.
"I'd just like to say that building large smooth-skinned models should be avoided at all costs. I now see why people want to stick kit-parts all over their designs as it covers up a lot of problems." - David Sisson
jpolacchi
Posts: 999
Joined: Sat Oct 16, 2004 8:08 pm
Location: West Coast

Re: Rubber for molds

Post by jpolacchi »

RTV silicone for mold making is just "expensive" there's no way around that.You gotta bite the bullet if you are going to cast parts.Stick with the manufacturer(don't combine others) and do your homework.Know what you are casting in the mold,know if your silicone is tin or platinum based and if that will have issues with what resin you are using?Most times there shouldn't be,but urethane resin is a funny animal...different manufacturers etc...so you need to know some basics.Otherwise its not too terrible to wrap your head around.
publiusr
Posts: 18641
Joined: Fri Jul 12, 2002 1:47 pm
Location: Alabama

Re: Rubber for molds

Post by publiusr »

A new material
https://phys.org/news/2021-12-rubber-ma ... asses.html

This study by Nagoya University and the Zeon Corporation is the first to evaluate the impact resistance of the new elastomeric materials based on i-SIS

For glow in the darks
https://phys.org/news/2021-12-gelatin-f ... cence.html
Strong, lightweight and biocompatible foams glow in the dark when ultraviolet light is shone on them, RIKEN chemists have discovered.
jpolacchi
Posts: 999
Joined: Sat Oct 16, 2004 8:08 pm
Location: West Coast

Re: Rubber for molds

Post by jpolacchi »

I don't know if anyone answered this, but in answer to the question can you cast an RTV mold without a vacuum chamber, "YES you can". Its a little bit longer of a process. The best way to go about it is to brush on a thin layer onto the part(s) being molded in silicone. The next thing is to (after thoroughly mixed, and there will be loads of bubbles in the mix) is to hold your silicone mix a good distance above the mold/mold box. At least a good foot or so. You want the silicone to pour it into a very thin strand. This will burst/break most all of the bubbles in the silicone mix. Pour it into the corner of the mold box, not directly on the part being molded. You don't want any surface bubbles on or near it if possible. It is not 100% full proof, but I have made good RTV molds this way with few(if any) bubbles that might show on the surface. You still might get some, but hopefully in spots where they are easily filled later on or in an area you wont see. casting the resin is the next headache, but you can get bubble free castings for the most part, but there are some things you have to contend with.
Post Reply