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Thursday, November 01, 2007

JART

For all the JART fans busy building out there, here is the next part of my build thread. Part 4 and 5. (For more posting on my Jart Build, click on the "Jart" label at the bottom of this post)This is quite detailed and lengthy as I know there are others going the moulded route .

The photos are from my cellphone so not the best but if you have any questions please ask on the TAG board















The final coat of 2k was good (sanded and sprayed 4 times in total).
This was water papered with 800 grit wet paper on my fingers not a block.
The fuselage was surported on two blocks of foam sponge and polished with a sponge mop shown left, water and premier P1 polishing cream. (Not rubbing or burnishing compound. It is white in colour). Use plenty of water and keep it on the move so as not allow heat build up (very important if you have a foam plug.)













It must gleam as the finish will be reproduced in your mould. (I wear gloves so no fingerprints)















The Jart outline is marked onto a suitable piece of chipboard (this piece was part of a previous mould). I drill holes where the jigsaw blade needs to change direction and then cut it out (select a jigsaw blade that cuts on the down stroke. It gives a smoother edge.)




The Jart plug is test fitted. It must fit in to the centre line. The chipboard may need to be spaced on some blocks, be carefull not to touch the finish of the plug which protrudes underneath.
The gaps are now carefully filled with fast setting body filler. I use a product called featherlite. The type that uses a blue or red paste as a catalyst, not MEK liquid catalyst.
Tip: Mix small amounts (teaspoon) at a time and scrape it into the gap with a mixing stick and flatten it as you go. The filler soon becomes rubbery and then it is scraped flush with the splitter board and 90 degress to the plug.

It is easier to do than to descibe. Promise!
Once the plug is seated in the splitter board and gaps sealed and flush, you wax. Plenty of release wax. An hour or so later you buff off the plug, but not the splitter board. I have also made two little rounded bumps which will help locate the two halves later.















The gelcoat is painted on with a soft brush and allowed to go tacky but not cured. At this point I lay on the glass cloth and resin.


I lay carbon tows into the edges as shown. (A little extravegant but it makes this mould a little stiffer) You can also use a mix of flox and resin. The first layer of cloth is the finest, 49 gr then 86 gr then, 104gr and finally some realy thick bi-axial cloth to give thickness. Finish off with some fine cloth as this is easier on your hands later when working on the moulds.















The layup was allowed to cure properly and now the splitter board comes off. The mould is trimmed using a grinder with a thin cutting disc (Inox stainless steel 1.6 mm or thinner if you can). A Dremal cutting disc also works but is small and tedious.













The splitter is carefully cut in two weak points. Not right through as you don't want to scar the mould. Then it is easily broken away. The plug and face of mould are cleaned of any debris and waxed. Again only the plug is buffed off. Gel coat and glass layup as before. After this has cured I should have one JART fuselage mould.











The next post will probably show the final product getting ready to fly. I am not doing a build thread of the wings as we have done bagged wings on this blog before.


So far so good one side off.


Some of the paint has stayed behind. This happens from time to time. I will waterpaper with 1000 grit and polish the moulds with polishing cream. (The gel-coat is polishable)
Should I make it hot red, or clean white , or vibrant yellow, or evil black hmmmmm.

2 comments:

Piet Rheeders said...

Hi Mike,

It is really amazing how fast you can make molds. Some times I wonder if you swallowed a CNC machine, a windows XP computer and HP7082 scientific calculator all at the same time. In the end you will have to guard that mould with your very life.
Hope to see the first one flying on the next slope outing.

Regards,
Piet.

Ps. You are not just my Hero but also my Roll model.:)

mike may said...

Piet,
Thanks for the patronage I am sure the new Jart will be my "ROLL MODEL" if set up correctly.
Mike
GFOGB go fast or go big