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1/4 Scale ASK21

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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

After a couple of coats of pattern coat primer, initial sanding with 120 grit, then working through the wet & dry grades (used wet) to 800 grit, followed by a polishing paste, I think I have a fuselage plug about ready for the mould making process.
A photo below shows the fuselage complete with its 2 small canopy aperture blanks which will be hot glued in position after a few more coats of wax polish, then the joints sealed with wax.

Next job is to prepare the parting board.
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7B97B0B5-30FA-4E24-AF90-9F4B57397C02.jpeg

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Peter Balcombe
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Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

With whole plug prepared with 6 coats of beeswax, it’s time to prepare for making the 2 part mould.
After measuring the fuselage width and getting some 3mm parting board material, I made up a box (screwed only, so easier to dismantle once 1st side of mould made) which allowed the split line to be on the upper parting board level when the fuselage is sat with one wing root on the bottom of the box. The fin is also supported to be at the correct height.
Previously positioned marks on nose, rudder post and top of fin show the splitting line.
Once the fuselage outline is cut out of the parting board (and edges also supported at correct height), the fuselage can be sat into place, the gap filled with wax (carefully cut back to give a flat surface into fuselage) prior to adding mould registration features.
The photos below show the mould box before & after fuselage plug is sat in place.
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Mould box
Mould box
Plug in position
Plug in position

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Peter Balcombe
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Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

First side of mould now laid up.
A bit of a learning curve, but hopefully it will come out ok in due course.
Need to get more resin for 2nd side as it used a lot more than I expected ;)
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Simon WS
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Location: Kent, UK

Re: 1/4 Scale ASK21

Post by Simon WS »

Looking good Peter. Was making a mould something you fancied trying or are planning on making more than one for your mates?!

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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Thanks Simon,
Although initially thinking of going down Roo’s one-off route, I somehow decided that I would have a go at making a mould as a project!
This was partly because at the time, I wanted to try the process to make another fuselage off of an unused DG100 fuselage I have & partly because I thought it might be useful to be able to make a spare if needed.
I haven’t seen 1/4 scale ASK21 models about, so thought it a good subject.

There is a looong way to go yet though ;)

MarkDev
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Location: Dorset

Re: 1/4 Scale ASK21

Post by MarkDev »

Peter, Are you going to make a heavy moulding, a 'just in case' so you can make another mould if anything goes wrong with the first or it gets worn out by all the requests for one?

M

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Peter Balcombe
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Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Mark,
What is a ‘heavy’ moulding?
As far as I know, I am making the mould as a kit manufacturer would - layers as recommended by John Hall.
There is a gel coat plus the equivalent of 1 layer of 300gsm + 2 layers of 450gsm on the fuselage part of the mould, with twice that on the flanges.

Mark Erwood
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Joined: 22 Mar 2018, 19:02
Location: Saltash, Cornwall

Re: 1/4 Scale ASK21

Post by Mark Erwood »

Normal industry practice is to make moulds at least twice the lay-up weight of the mouldings that you expect to produce. Seems to give a good life to moulds.

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Peter Balcombe
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Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

Mould layup is probably triple the expected fuselage content, so seems to fit the bill in that respect.
However, lessons learnt for next time:
1. Take more care to ensure parting board gap fill is perfectly level with parting board at all points.
2. Fit fence to rear of fin (for open rear of fin).
3. Limit mould to within about 3” of plug to reduce layup materials needed and weight.
4. Add lots of registration features along intended mould half bolt line.

1st side now carefully removed from parting board (together with plug) and turned over once the overall mould outline had been slimmed down to within 3” of the plug. Mould half bolting hole line marked approx 30mm from plug outline & new registration countersinks added every 12”or so, as the original features were nearly all removed when the mould flange was slimmed down. Bolts will be fitted every 6” or so.
Vertical fence fitted at rear of fin for 2nd side (1st side mould rear will be cut off later).
Nearly ready for making a start on the 2nd side of the mould when I have restocked with resin ;)
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D036E060-0864-4B14-A7C1-872544E13772.jpeg

Mark Erwood
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Joined: 22 Mar 2018, 19:02
Location: Saltash, Cornwall

Re: 1/4 Scale ASK21

Post by Mark Erwood »

Hi Peter,

Sounds as though your mould will be more than adequate. The last mould that I made I trimmed the flanges to about 1". For registration I drilled a 1/8" hole every few inches in the first flange and superglued a 1/8" snap head rivet in each hole. it worked a treat. Good luck with the rest of the build.

Mark

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