1/4 Scale ASK21

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MarkDev
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Re: 1/4 Scale ASK21

Post by MarkDev » 24 May 2018, 14:12

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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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 24 May 2018, 16:46

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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Re: 1/4 Scale ASK21

Post by Mark Erwood » 24 May 2018, 20:53

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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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 26 May 2018, 14:50

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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Mark Erwood
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Re: 1/4 Scale ASK21

Post by Mark Erwood » 26 May 2018, 20:17

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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Peter Balcombe
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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 03 Jun 2018, 12:39

Completed the mould layup yesterday & have just split the mould.
After a bit of a struggle getting the 2nd side off, the plug came out reasonably intact.
A bit of remedial work is needed where the plug stuck/ or where there are small voids, but I hopefully now have the basis of a useable mould.
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Cliff Evans
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Re: 1/4 Scale ASK21

Post by Cliff Evans » 03 Jun 2018, 13:07

Well done Peter, you should be justifiably pleased with yourself!

MarkDev
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Re: 1/4 Scale ASK21

Post by MarkDev » 03 Jun 2018, 17:18

I've dealt with mainly boats, the first thing you do when you take out the plug is polish the mould down to 1500 w&d, then polish with a non colour paste which opens up the pores of the mould and lets you get more wax or pva in for non-stick. Then the first thing you make is a heavy hull or fuse in your case, essentially a non flexible moulding to use if you should damage or wear out your mould, you can use it to make another mould. The last ones I made were normal layup then a couple of layers of 600+gsm mat vacummed down.

Its a 'just in case' senario, after all the work you've put in, I made a 2.5m yacht then a heavy hull, just in case, a mould won't last forever!

MarkDev
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Re: 1/4 Scale ASK21

Post by MarkDev » 03 Jun 2018, 17:24

Did I mention teddy bear eyes? Put them on the first side of the flange then mould round them so the two sides go back together correctly when you start to join the two sides.

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Peter Balcombe
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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 03 Jun 2018, 17:40

Mark,
Good tip with ‘just in case’ scenario.
I have a number of registration points included in the mould halves (added when original ones were going to be cut off!).
Will clean various stuck plug areas off tomorrow & then attack the other damaged areas.

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