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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 »

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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0236641C-9004-4AD4-A083-FCBC3AD7ADC9.jpeg

MarkDev
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Joined: 19 Mar 2015, 10:41
Location: Dorset

Re: 1/4 Scale ASK21

Post by MarkDev »

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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Joined: 19 Mar 2015, 10:41
Location: Dorset

Re: 1/4 Scale ASK21

Post by MarkDev »

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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Location: Clevedon, North Somerset, U.K.

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

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

Re: 1/4 Scale ASK21

Post by Peter Balcombe »

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

roo Hawkins
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Location: Northamptonshire

Re: 1/4 Scale ASK21

Post by roo Hawkins »

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

MarkDev
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Joined: 19 Mar 2015, 10:41
Location: Dorset

Re: 1/4 Scale ASK21

Post by MarkDev »

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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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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