1/4 Scale ASK21

Let us all watch your new project progress.
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Peter Balcombe
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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 03 Jun 2018, 19:41

Mark,
I now understand what you mean by a ‘heavy’ mould :)

roo Hawkins
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Re: 1/4 Scale ASK21

Post by roo Hawkins » 04 Jun 2018, 06:45

Well done Peter. Will have to do a mould some time myself.

MarkDev
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Re: 1/4 Scale ASK21

Post by MarkDev » 04 Jun 2018, 09:31

Peter,
I was taught by a RN Marine Engineer, amongst others, most navy stuff is 'built for the job'!!! My son was sponsored by a custom board manufacturer who helped me as well, they would do anything to get the weight out of their products, important lessons.

If you use filler in the damaged areas, it will work but not for long before work is needed, depends how many fuses you want out of the mould? A 'heavy' fuse would allow further work at a later date.

M

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Peter Balcombe
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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 04 Jun 2018, 10:09

I see what you mean Mark.
Although looking reasonable from a distance, my moulds look as if they need a good deal of attention upon close inspection.
I think I I’ll get John Hall to have a good look & advise when he calls by in a week or so.

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Cliff Evans
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Re: 1/4 Scale ASK21

Post by Cliff Evans » 04 Jun 2018, 10:27

Good Idea Peter.

Pete Marsden
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Re: 1/4 Scale ASK21

Post by Pete Marsden » 10 Jun 2018, 10:49

This is a great effort! Having made epoxy one-offs for years I know just about everything that can go wrong! (and in my case still does!)
Just for info I enclose a pickie of a fuselage mould I recently made.
Without wishing to tread on toes the following may be of use:
I finish the pattern with two pack paint polished to a mirror, 7 coats of release wax, and then take an epoxy mould from this.
Never mix epoxy lay-ups with polyester ones. i.e. if you finish the pattern in epoxy or two-pack, don't try and take a polyester mould from it. It will invariably stick solid.
Make the mould symetrical: i.e: - one coat of gel (very thinly applied), an epoxy/microfibre fillet along all tight corners, one layer of 100gsm glass To prevent the weave showing through), 2 to 3 layers of 200gsm, one layer of 100gsm and another coat of gel. This should prevent the mould warping with age.
Put a fence around the whole lot - this too gives rigidity.
Use locating pegs - this can be done simply by drilling dimples into the first half of the mould, re-waxing and then make the second half.
Regarding the dividing plate: - I don't get too hung up about the initial fit of this (I use 9 mm MDF with a lower fence to hold this the correct height above the workbench to allow the plug to fit centrally). I taper the hole in which the plug fits and with everything firmly held, I apply a fillet of filler into this notch. Once set I remove the plug and sand this fillet flush with the surface of the dividing plate. The plug should now fit perfectly.
Hope this helps a bit.
Attachments
Fuselage mould.jpg

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Stuart Ward
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Re: 1/4 Scale ASK21

Post by Stuart Ward » 14 Jun 2018, 20:42

Peter
Thanks for the explanation
But for someone that has only built woodies and would like to try to build a glass fuse, most of the paragraph above was gobbledygook. Maybe someone could start a new thread with step by step instructions on making moulds. Even small mould like control horn fairings.
Stu

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Peter Balcombe
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Re: 1/4 Scale ASK21

Post by Peter Balcombe » 26 Jul 2018, 10:40

Not able to find space to take the ASK21 mould to the Shrivenham aerotow, so a couple of pics to show current progress.
The excess mould flange material has been removed and the inner mould surface voids filled. Just needs a final surface polish now prior to making the first part.

I have decided to make an epoxy part (rather than polyester resin) as with a slow hardener this will give me a lot more time to get the various glass cloth & roving layers in properly before the resin gels.
The downside is that I will need to make both sides and then join them in one hit - using glass overlaps from each side to form the central joining bond. The upside is that I hopefully get a complete part in one go.

However, before all that, I will be having a practice on some much smaller moulds that John Hall has kindly lent me.
Attachments
Mould_side.JPG
Mould_top.JPG

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Cliff Evans
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Re: 1/4 Scale ASK21

Post by Cliff Evans » 26 Jul 2018, 10:49

If you can get it to me Peter, I can put it in the van!

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Andrew Ray
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Re: 1/4 Scale ASK21

Post by Andrew Ray » 01 Aug 2018, 06:29

Superb work there Peter. I have always liked the K21, lovely lines for a 2 seat training glider.

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