Answered With a Picture(s)

[He Who Shall Not Be Named]

While laid up with the bum knee I've been planted at the computer. I've collated most of my digital pictures. Over 10,000 of 'em. And this does not include the pre-2004 slides and negatives I have yet to scan into the hard-drive. I can now pull the digitized stuff out of the computer with ease.

So, I've started this new thread -- to use this vast visual resource on model building -- as a means of conveying how I apply my methods and use different mediums as I practice the Craft of model building.

You posit specific model building questions here and I will answer them with pictures. You have follow-up questions, I hit you with more pictures.

M

[vital.spark]

Great to hear! A picture is worth a thousand words!

[trout]

David,
An area I want to learn about is creating molds of a sub. I would like to build a sub from scratch, a 1/48th scale Israeli Dolphin Submarine. The biggest (not the only) fear is working with fiber glass. Have not worked with that medium. So, from start to finish, can you show the plug to pull sequence? Safety precautions? Cutting the pulled casting (is it called that)?

[He Who Shall Not Be Named]

David,
An area I want to learn about is creating molds of a sub. I would like to build a sub from scratch, a 1/48th scale Israeli Dolphin Submarine. The biggest (not the only) fear is working with fiber glass. Have not worked with that medium. So, from start to finish, can you show the plug to pull sequence? Safety precautions? Cutting the pulled casting (is it called that)?

In this demonstration I'm employing a hybrid type tool (mold). One that employs two elements: an inner flexible, high-detail capturing rubber 'glove' that captures the contours of the master; and an outer shell, a stiff strong-back 'mother' element that holds the inner glove portion stiff during the part lay-up operation.




I'm applying some mold-release wax prior to placing the first layer of RTV mold making rubber over the master and face of the mold board. A specialized RTV is needed here, called a 'brushable' rubber in some circles.

The first layer of RTV down and cured. Further layers are built up till I have an approximate glove wall thickness of about 3/8". As you mix each batch of rubber you subject the mix to a high vacuum to de-air the mix of air introduced as you combined the catalyst and rubber. Don't have a vacuum table? Get One!

By time you get the glove to the desired thickness, it's formed some ripples -- this is a good thing: this will insure that the removable glove mold will key with the outer mother mold when the two are re-assembled for use. here I'm cutting away excess rubber from the flange area of the tool.


The surface of the glove is waxed to keep the mother-mold element from sticking as its laid up.

The mother mold can be built up of just about any re-enforcement-resin combination. I chose the Freeman tooling urethane, strengthened with glass fiber shards. Shoot for a 1/4" wall thickness.

Before popping the mother mold away from the glove-mold I built up a stiffening 'egg-crate' structure. This keeps the tool from warping over time, It also provides a stable base that permits the open cavity to face upright during part lay-up.

With the tool completed. it is flipped, cavity-side-up, and a PVA part-release is sprayed into the cavity of the glove. Then a thickened resin is brushed in. This to radius the sharp edges within. It's a good idea to color this gel-coat with a distinctive tint. I like blue. Coats of gel-coat are laid on till you have a surface within the tool that will permit 6-ounce cloth to conform without wrinkling.

smaller structures should have a GRP wall thickness of between 1/16" - 3/32". I first establish the glass-resin lay-up methodology by making a test patch of GRP employing an estimated number of layers of varying weights of GRP, each saturated with the minimum amount of catalyzed resin. Once I establish the methodology, I mark it down and follow it as I cut out the glass blanks needed for a complete laminate.

A typical laminate for a model this size goes: 2 layers of gel-coat, 2 layers of 2-ounce glass cloth, 2-layer of mat cloth. The resulting GRP part has a nominal wall thickness of just a bit over 1/16".

Card-board templates to set the shape of the glass cloth and mat are prepared and used to guide the circular cutting tool as the glass blanks are cut out.

Once the last coat of gel-coat is tacky, the first layer of 2-ounce cloth is laid in and wet down with catalyzed resin. Excess resin is wicked out and you wait till it is tack, then lay in the second layer of 2-ounce. Then the mat.

Once the GRP has cured hard (at least 12-hours in a hot environment), the part, still clinging to the glove-mold, is pulled out of the mother-mold. It is then easy to strip the glove off of the part. Hence, the name, 'glove-mold'. The glove is re-inserted into the mother-mold and the tool prepped for the next cycle.

Wa-la!

[trout]

Thank you! What are some of the areas that need special attention? Or what are some of the gotcha pointers you learned?

[He Who Shall Not Be Named]

Thank you! What are some of the areas that need special attention? Or what are some of the gotcha pointers you learned?

Getting the gel-coat down right. Not just a light dabbing. No -- you lay it down thick and nasty, brushing out all the bubbles and filleting all the tight corners within the cavity of the tool. Next important thing is to work out the weight and number of laminates of cloth and/or mat.

Experiment! And keep a log of your methodology.

[Subculture]

I would start off with something very small and inconsequential. Making a 1/48th scale boat which is going to require a split mould is advanced for a beginner. Perhaps make a simple little hard chine boat hull from plastic sheet and pull a tool from that.

Practice applying release agents and your lay-up techniques, if you make a mess of it and I can guarantee you will make many mistakes, you haven't lost much.

You didn't mention the resin system you want to use. Polyester resin is much cheaper, but you will have a slightly heavier hull as it's not as strong as epoxy. It also stinks to high heaven, so unless you're working well away from the house, you should avoid that. Polyester resin isn't such a good adhesive as epoxy, so if you use cloth with the former, you need to lay an intermediate layer of chopped matt in between layers to avoid delamination.

In practice I use chopped matt exclusively with polyester resin. With epoxy I use cloth, if you want to use chopped matt, be aware there are two types, powder bound and styrene bound. Powder bound is the one to use with epoxy, but can also be used with other resin systems. Styrene bound is much cheaper, but should only be used with polyester resin. A snag with chopped matt is that it has about double the resin to glass content than cloth. This gives stiffer castings but they are more brittle. However still much stronger than thermoplastic items.

A few other caveats with polyester resin. If laying up into a rubber tool, don't use gelcoat as it won't cure. Polyester resins use a different type of resin for gelcoat which is air inhibited. Mix some fumed silica in with normal lay-up resin to make a gelcoat from that.

A few snags with epoxy-

About four times the cost of polyester resin. Not a massive deal if you're only making one or two, but the cost can ratchet up on larger hulls.

Mould/tool prep has to be spot-on with epoxy. Being a much better adhesive than polyester, any missed areas will make the chance of lock-in or damage to the tool or master much more likely. Also epoxy has a much lower shrinkage rate than polyester, which makes it more stable, but also doesn't help when trying to get a release. It's not surprising that rubber tools are popular when laying up with this resin system.

Fairly long cure times. Dave mentions 12 hours. I'd say that is an absolute minimum, and if you can bear to wait that long 24 hours should see a more thorough cure.

I would recommend having a look at the videos on easy composites channel. Also the Fibreglast tutorials are first class.

https://www.youtube.com/user/easycompositestv

If you want to go with polyester resins, then i would get the Glassfibre handbook by R H Warring. This will only be of minimal assistance if you use epoxy however. West systems also have many booklets with useful information.

http://www.ebay.co.uk/itm/like/191383183047?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=108&chn=ps&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0-L&ff12=67&ff13=80&ff14=108

[He Who Shall Not Be Named]

Excellent stuff, Andy. I learned a few things about mat types and an alternate thickening agent for the gel-coat. And the line of videos you recommend are top-drawer training aids.

M