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1/4 Scale ASK21

Let us all watch your new project progress.
roo Hawkins
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Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 1/4 Scale ASK21

Post by roo Hawkins »

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

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Peter Balcombe
Posts: 1247
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

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.

Pete Marsden
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Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: 1/4 Scale ASK21

Post by Pete Marsden »

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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Joined: 21 Mar 2015, 18:23
Location: Pukekohe NZ

Re: 1/4 Scale ASK21

Post by Stuart Ward »

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

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

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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Andrew Ray
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Joined: 19 Mar 2015, 19:15
Location: Staffordshire

Re: 1/4 Scale ASK21

Post by Andrew Ray »

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

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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 »

Epoxy glass fuselage laid up last Saturday in a marathon 6hr stint.
After discussion with John Hall it had been decided to lay up each half with matching join line overlaps using slow cure epoxy resin. The 2 halves were put together whilst the resin was still wet & the overlaps smoothed down onto the other side to form the complete part in one sitting.
After the normal cure period, the part was post-cured for 8hrs or so at 30+. I finally managed to release it from the mould this afternoon after a bit of a struggle (as anticipated due to the less than perfect nature of the mould surfaces)
However, it is now out and should be useable after tidying up some surface blemishes.

I still have ply wing root & tail fin top to epoxy into place as these were left out at the lay up stage to reduce work.
An idea of the result is shown below.
Attachments
5ED15AEB-E002-4291-8D99-5312E53A4C2E.jpeg
C3102C5B-53E2-4F4B-8FA8-4FE66A77F130.jpeg

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VinceC
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Re: 1/4 Scale ASK21

Post by VinceC »

Excellent work Peter. When does production start?

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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 guys.
Still a long way to go to get a flying model, but at least I now have something to attach things to!

The mould needs some repairs & surface polishing before I can even think about re-use, and probably isn’t good enough for serious ‘production’ use - at least with my fibreglassing skill level. We will see where we go once the design is proven.

Once I have added the internal ply wing roots/tailplane mount and checked that my planned wheels will fit, I can progress the built-up wing and tailplane designs ready for part cutting.

roo Hawkins
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Joined: 18 Mar 2015, 20:12
Location: Northamptonshire

Re: 1/4 Scale ASK21

Post by roo Hawkins »

Well done Peter. A lot of hard work I think I will keep with my lost foam method. But it is some great work you have done look forward to seeing how the rest of the model comes together. .Roo :D

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