The ultimate objective of this exercise.

Shinobi | A Home-Grown Moulded Fuselage

Part V: We Glass and Reinforce the First Half of the Nose Cone Mould

Readers who have not already done so may want to read the previous parts of this series before continuing with the article below. — JH

Before the Kickoff

Here are a few things you will want to have organised prior to proceeding:

Gather Newspaper You can never have enough newspaper when doing glasswork, and you need to cover your working surfaces with at least two layers of it. Alternative bench protectors to the newspaper is rubbish disposal bags cut open to form large plastic membranes. Anything can be used, but I prefer newspaper because it’s generally free, easy to ball up and dispose of, and it’s absorbent.

Prepare the Tools You’ll need an accurate set of scales — preferably the digital electronic type — but unless you want to be awarded the marital pink slip — steer clear of SWMBO’s kitchen scales. For the epoxy mixing and application, ready some cheap 1in (25mm) and 2in (50mm) disposable brushes, some mixing spatulas — popsicle sticks or thin clean pieces of wood will do, and some paper picnic cups for the epoxy. For this small-sized mould, we will not be needing a roller as careful brush stippling should remove most of the bubbles. And last but not least, a good sharp pair of scissors. Kitchen scissors? No, don’t do it — your spouse will find out!

Prepare the Glass Cut enough 3oz glass fabric strips 2in (50 to 75mm) to 3in wide along the weave to cover your mould in both directions four times at 45º and place them ready. Then do the same with the thicker 6oz glass, again cutting enough strips to cover the mould four times at 45º. Lastly, cut a single piece of 6oz that is larger than the mould, cutting across the weave 45º to act as a finishing layer.

General Try to keep your work surfaces, and your weighing scale protected and protect yourself by wearing an apron and disposable surgical gloves at all times — and have more pairs handy. Preferably wear a mask too and conduct your work in a well-lit and well-ventilated space, with everything you will need readily to hand including a few dry rags to mop up any accidental drips or spills. You will have already decanted your epoxy resin and hardener into (separate!) handy-sized containers.

Glassing the Mould (At Last!)

Apply a generous coat of epoxy all over the gel-coated surfaces and then begin to apply the 3oz glass strips, placing them side by side while thoroughly stippling through the glass with the brush to make sure the resin is fully impregnated. Cut off the residual glass strip at the edges and use it for the next line. Spend time to make sure that all the bubbles are completely eliminated before applying the next layer of strips at 90º to the first layer. Again, make sure to completely impregnate the fabric and eliminate any voids or bubbles. Continue this procedure until all of the 3oz glass has been used up and the mould now has at least four layers.

The first strips of 3oz glass have been applied at 45º to the mould structure and the second layer will now be applied at 90º to the first layer — thus forming a crisscross layup so as to make very sure that the cloth complies with the plug shape and no air bubbles are trapped. Note the neatly trimmed glass overlap at the mould edges. Also, note the larger finishing ply of 6oz glass cut at a 45º angle to the weave, ‘standing by’ that will be the finishing layer.

Advice: Try to keep the glass overlap at the mould edges neat. It will help later when the mould needs to be separated from the parting board.

Advice: There are three important things to remember when stippling glass onto a mould: 1) Stipple out the bubbles, 2) Check that you have stippled out the bubbles, 3) Make sure that you have stippled out the bubbles.

After the First Layer Is Done

Clear Up, Prep Up Use little time to clear up any mess, dispose of the old paper cups, brush(es) and the sticky bench covering, and then apply some fresh newspaper or plastic membrane. Next prepare some more paper cups and a new brush ready for the next, heavier layers. Now it’s time to take a well-earned rest until the first 3oz layers of glass have hardened to the soft but not tacky ‘green’ state. This will be anything from a half-hour to a few hours depending on the room temperature and the type of epoxy and hardener.

First Layer Green? Give it a dig with a fingernail. OK? Now repeat the entire process using the heavier 6oz glass fabric, ending with the last single 45º ply finishing layer. Ideally, this should all have been done in the space of a single day, so now you know why it needs to be so carefully planned and prepared.

The second series of 6oz glass fabric has now been applied to the mould and allowed to cure until green.

Reinforcing the First Glassed Mould Half

Light composite structures can be flexible but are easily stiffened by the addition of more, or different types of fibre, and because of this make ideal structures for light and strong aviation applications. The ratios of strength and flexibility versus weight can be very well controlled.

Of course, we can add more layers and even use different types of fibre to make our structures, moulds or parts stiffer, but if the structure is a mould that will be exposed to heat/cool cycles then it needs to be externally reinforced to some degree. A mould must be an accurate copy of the plug and must stay accurate throughout its life, without distortion, or the parts we produce will be warped. Even on our small home project, it’s a good idea to reinforce the mating parts of the mould to make sure that they stay true. There are many ways to do this.

Large commercial moulds such as those used for boats, or maybe racing car parts will have a tubular section steel frame moulded into the mould during manufacture. But we don’t need to go to such lengths, so a couple of pieces of good stiff hardwood or good plywood will suffice. Cut the wood you need length — I use solid Meranti hardwood at about an inch-and-a-quarter (35mm) thickness as it’s easy to get here, but good plywood will also work well — as long as it’s thick enough.

Advice: Never, never — even in your wildest dreams think of using MDF as a reinforcing material.

Wood reinforcement is ready to glue to the mating surfaces of the mould — but note: It will be glued to the mating surfaces only and NOT to the exterior mould curves.

Advice: Epoxy shrinks. If you get the epoxy goop that you will use to glue the wood on the actual moulded shape and not just the mating faces then you may see dips or depressions form in the eventual mould as the epoxy goop shrinks and pulls the mould structure. Therefore, it’s important to glue the wood reinforcement to the mating surfaces only and not the exterior mould surfaces.

Once the wood is cut and shaped to fit so that it will not influence the exterior curved surfaces of the mould, the parts can be glued with epoxy/colloidal silica goop. It’s a good idea to add a couple of wood cross pieces while you are at it to provide more strength and rigidity, and also to place the mould a bit higher off the bench for eventual use.

In this picture, cross braces have been added to beef up the structure.

Proof of the Pudding

Now is the time to see if we have done a good job — especially with the mould seam. Remember my advice to keep the overlapped glass edges neat? Now you’ll see why as we need to separate the first half of the mould from the parting board. Take your seam knife — the same round-nosed one you used to trim the modelling clay around the plug, and insert it between the parting board and your layup — pry gently and not too far in. When the moulding begins to separate, ease the seam knife by wiggling it around the edges bit by bit until the mould separates from the parting board. Now using the same seam knife, gently remove the modelling clay from the mould seams and step back to take a look at your work.

The seam should be nice and tight to the parting board and the plug, no dips, no lumps, no bubbles. If it’s good, then you may now have my personal permission to reward yourself with one heavy tumbler of single malt apple juice — at least that’s what I tell SWMBO it is. If it’s not good you may turn off the lights, go into the living room with a really long face and proceed to sit and sulk and cuss that Hammond bugger who got it all wrong.

It’s parted, it’s nice and clean — good job! Time for a wee dram.

Now the surfaces — both the parting board and the exposed plug — will need to be cleaned with mild 75% alcohol to remove all traces of the modelling clay, and then re-waxed with mould release several times. As always — when you think it’s clean — do it one more time, and the same goes for the mould release. There’s no such thing as being too clean or having mating surfaces that are too easy to release.

All righty then…time to think about the second half of the nose cone mould, but before we get into that we also have to think about the mould location. How can we make sure that the left and right halves of the nose cone mould will always locate exactly? Well, there are several ways to do it, and many people have different preferences so as usual, I’m just going to show you my way, and I’ll tell you why I use that method.

Next time in Part VI, we make a balls-up!

©2022 James Hammond

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