Shinobi | A Home-Grown Moulded Fuselage
Part III: We Prepare to Make The Slip-On Nose Cone
Readers who have not already done so may want to read the previous parts of this series before continuing with the article below. — JH
So how can we make a removable slip-on nosecone from solid plug that’s all in one piece? Because we carefully planned the operation well in the beginning.
The Parting Board and Frame
In the case of the Shinobi, we have four different components to make: Fuselage body, inner nose assembly, outer nosecone, and boom; so, although it’s maybe a little complicated for a first project, the various parts will serve to demonstrate slightly different methods of making the moulds. For the Fuselage body, and outer nose cone assemblies we will use the same parting board, so we’ll begin there.
The moulds will be made as two halves, left and right in this case, and so now we need to set the plug into a parting board, so first we need said parting board. I normally use a kind of vinyl coated plywood that is used for making kitchen furniture that’s available to me locally but if you can find any thin — ¼” to 3/8” — plywood with a nice smooth coating, you will be in business. If not, you will have to finish the surface of your own board somehow. I have seen many fast ways to do this, but the one I liked the most was using lines of clear 2” packing tape.
Mark the Outline but Add a Bit
Mark the centre line on your parting board then place the fuselage plug on it. You can hold the plug temporarily with a couple of blobs of modelling clay (Plasticine) and then mark around the outline. Ideally your line should be a bit larger than the plug, so I use a thin Sharpie-type marker pen taped to a square piece of wood to act as a guide. Using this way, you will end up with a profile line that’s larger than the plug by about half the width of the Sharpie pen — or about ⅛" (3mm) to 3/16” (5mm) which is just what we want.
Sawing Out the Plug Profile and Joining to a Support Frame
Using a saw — jigsaw, scroll saw, bandsaw — anything is OK, cut around the outline you have marked. Use a fine blade and try not to fray the edges too much when sawing. I usually put some masking tape around the outline to be cut so that the saw blade doesn’t tear the surface up too much. Normally the outline to be cut can still easily be seen through the tape.
Advice: Mark the outline larger than the plug all around by ⅛” to ¼”.
Advice: Use blobs of modelling clay to hold the fuselage plug in place when marking the outline.
Advice: Use tape around the marked line when sawing to protect the cut edges.
The Parting Board Frame
The next job is to make a simple support frame for the parting board and the plug. Basically, anything that will support the plug and the parting board above the work surface will be OK. Glue the parting board to the support frame at this point. The next thing to do is to add a couple of cross braces to the frame support in order to provide a place for the lower half of the plug to rest during the moulding process. These do not have to be accurate and are better left a little low so that blobs of modeling clay can be used to adjust the plug centre line height.
Setting the Plug into the Parting Board and Frame
This is the fun part — some would say the tricky part, but as with all things moulding, prior planning and preparation make all the difference. First set the plug into the frame/parting board. It should be slightly lower than the centre line. Don’t fix it in yet as we’ll need to move it a bit.
Preparing to Make the Nose Cone Component
From the beginning of this series I mentioned that its best to think this (or any) project through thoroughly before starting. Here’s the first example of where thinking things through saves a lot of time and effort. We wanted a cool slip on nose cone, but the problem is — it’s still attached to our fuselage plug. So how to separate from the plug for moulding? The answer is not to — we just use a mould fence to form the end of our nose cone mould at the place where it will join the finished fuselage.
As the nose cone will be a separate component and the first part of the fuselage assembly, we need to make the mould for it. This is the first moulding job, and to do it we need a mould fence to separate it from the rest of the plug. Make a fence to fit across the plug and as with the parting frame, make it a little larger where it will fit the surface. Make sure you know the position in which it will be placed. I normally make a couple of light pencil marks on the parting frame surface as a reference.
Preparing the Working Area and the Parting Frame
The first job is to thoroughly clean the work surface the parting frame, and the plug. Unwanted debris or hairs etc. can cause endless trouble when working with modelling clay. Now make a few clay rolls about 3/8” thick and keep them on the clean work surface. Then make a couple of small 1” (25mm) modelling clay blobs and stick them on your plug support pieces inside the parting frame. It’s a good idea to begin waxing the parting frame, the plug, and the mould fence with a good release wax. I don’t think it matters which release wax you use, but it might be a good idea to use only one type. Give everything at least four coats, following the manufacturer’s instructions. Then repeat the process with four more coats.
Setting the Plug into the Parting Frame
Working from one end, squeeze your clay roll on to the cut corner surfaces of the parting board, making sure some of the clay is above the centre line and some inside and below it, work along the profile using more of your modelling clay rolls until you have a nice 3/8” (10mm) clay bead all around the outline.
Next, gently push and set the plug down into the modelling clay on the parting frame. Try to the right depth to give you a centre line that is parallel with the parting frame surface. The blobs of modeling clay on the cross braces will help with the final positioning. If it’s not positioned right, either on the centre line or in the vertical plane, then do it again until you are certain its correct.
When you are sure the plug is in the right position or very close, squeeze the clay bead using your fingers simultaneously above and below the parting board to set it firmly around the plug/parting frame gap.
Advice: If you are not happy with the centering of the plug in the parting frame, do repeat the process until it’s all aligned properly.
Advice: The plug can be raised slightly and maneuvered inside the parting frame by squeezing the blobs or gently pushing or pulling the plug to centre it.
Next time we make the seam and begin the mould making process.
If you have any questions please don’t hesitate to post them to the Responses section below and I will do my best to answer them. Putting them here also means others will benefit from both your question and my answer.
©2022 James Hammond
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