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Aluminium Casting Parts for Foils

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faklord
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Re: Aluminium Casting Parts for Foils

Postby faklord » Sat Dec 03, 2016 11:59 am

Agree with kitexpert here.
I would only add: 1st wrap strut in carbon (or glass or whatever), then drill & fit barrel nuts (so they engage on this 1st wrap layer), then wrap a covering layer.
If you really want to go to town, to fit the barrel nuts, you could drill oversize holes, fill with epoxy chopped glass mix, drill to size then cover with the final wrap.
You need a decent skin thickness (>3mm ?) cut off square to butt onto the fuse.

But...it's a bit late for all this now!

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Re: Aluminium Casting Parts for Foils

Postby DartBoard » Sat Dec 03, 2016 11:54 pm

kitexpert wrote:Good work with aluminium casting.

But I think joining aluminium fuse to wood core mast can be done with screws and barrel nuts. I would slide into fuse some hardwood block and then drill through holes and countersink. Super glue/epoxy to the holes to not let water do it damage. The ends of the fuse can be filled with PU foam. Barrel nuts should be located reasonably far from the end of the mast, for the strenght. Wrapping some layers carbon at the end of the mast should prevent any possibility for splitting and increase a bit area against the fuse. The end of the mast should be cut precisely straight.

This is the method I will use my in next builds. Goal is to have a bit more transportable hf and to make the fuse easier to build.
Yep, that would be another way to do it. That is similar to how I made inserts for twin tips and never had one fail. In that case I set ss locking nuts into resin. The resin seals off the wood as well. Many ways to skin a cat!

I think your point about a precise square cut is an important because you only have 1/2 the width of the foil involved in counteracting the twisting of the fuselage. I always try to find ways to overcome the lack of precision I have in my workshop set up and so if I was trying this, my 2 cents worth, I'd probably use a few layers of glass on the end of the mast and let it cure against a piece of the fuselage to get it flat. This is also a chance to get it really square relative to the mast by making sure the mast is spot on vertical while it cures. Using a bit of fibre glass sheet or c-plate might also work.

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Re: Aluminium Casting Parts for Foils

Postby NYKiter » Sun Dec 04, 2016 1:53 pm

This guy does a pretty good cast...
https://www.youtube.com/watch?v=qPnSb3yzytE

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Re: Aluminium Casting Parts for Foils

Postby skyte » Mon Dec 05, 2016 9:57 pm

Good DIY skills!

I think you need to be careful with using damp sand when casting aluminium... I think if there is too much moisture in the sand it can get superheated and turn to steam when you pour in the aluminium... The rapid production of steam can be explosive. Just from memory of googling aluminium casting a while back... hopefully you know more than I do :)

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Re: Aluminium Casting Parts for Foils

Postby DartBoard » Tue Dec 06, 2016 2:05 pm

skyte wrote:Good DIY skills!

I think you need to be careful with using damp sand when casting aluminium... I think if there is too much moisture in the sand it can get superheated and turn to steam when you pour in the aluminium... The rapid production of steam can be explosive. Just from memory of googling aluminium casting a while back... hopefully you know more than I do :)
Thanks Skyte! Even though it doesn't take much to be safe with Al casting I treat it like its a ticking bomb. What you're saying about moisture is spot on if the moisture can't escape. The internal pressure builds up and crack! Fortunately, even tightly packed play sand or 'green sand' bound together with clay or, like in NYKiter's clip, water glass has large enough pore spaces that the steam can escape. It may be a different story if your using plaster of paris molds that haven't been properly dried (apparently baking them for many hours is the only way to drive out the moister that is created and trapped as a normal part of it setting).

I'm finishing off the plug of my next attempt where I'll cast the top and bottom sections of the mast. The office shuts for 3 weeks over xmas so hoping to have some dedicated time to finish it off. :jump:

Image

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Re: Aluminium Casting Parts for Foils

Postby DartBoard » Tue Dec 06, 2016 2:20 pm

NYKiter wrote:This guy does a pretty good cast...
https://www.youtube.com/watch?v=qPnSb3yzytE
Pretty impressive large pieces!

The binder they're using in the sand is very cool stuff and most important its DIY'able too. Its called Water Glass or sodium silicate and you can make it from drain cleaner (caustic soda) and silica gel (which again is sold as cat crystals / kitty litter) and water. I made a couple of small molds with it and it really sets like a rock (sandstone :lol: :lol: ) Unfortunately I was using vinegar and baking power to generate the CO2 gas that you need to set it and I wasn't able to build up enough pressure to get the gas deep into larger molds so they didn't set up properly. Probably need to buy C02 gas cylinder to use it on larger parts like these guys do. The other things is that you can't re-use the sand - better casting but more waste.

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Re: Aluminium Casting Parts for Foils

Postby NYKiter » Tue Dec 06, 2016 5:18 pm

Dartboard, looking forward to seeing more of your casting.
Can you tell us why you didnt cast the mast and fuselage together in one shot??

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Re: Aluminium Casting Parts for Foils

Postby DartBoard » Wed Dec 07, 2016 6:18 am

NYKiter wrote:Dartboard, looking forward to seeing more of your casting.
Can you tell us why you didnt cast the mast and fuselage together in one shot??
Other than making mini-muffin ingots this was my first attempt as casting so I wanted to keep is small and simple and work my way up as I ironed out the bugs. Some of the things I had going around in my head were:
+For the larger pieces would the cooling metal getting in the way of it flowing through the whole cavity or create voids?
+There is a comment on kitehydrofil.com about a solid aluminium mast he made that was along the lines of 'great rigidity but not very strong'?
+Weight - I think it would take some experimenting to see how thin a mast could be if it were solid and if making a hollow version I think that extruded, tempered, off the shelf sections would have better weight and strength. Tempering seems pretty tough to do at home because of the high temperatures you need to maintain for long periods of time?

Also, with the original all wood core build I found that I spent almost no time laying up the main section of the mast but the base plate and fuselage and reinforcing the high stress areas seemed to take forever and needed lots of sanding and filling because of all the pleats in the vac bag I needed to get around the 90 degree bends. If the cast parts work out okay then it will reduce the resin work to cutting equal size, rectangular layers of laminate which is quick and easy and shouldn't require much sanding afterwards.

Have you got some plans to have a go ? You've probably seen these already but just in case there are some really good videos on Makersize (he's making a Dave Gingery lathe, casting everything and hand milling everything to get it all square) and MyFordBoy's casting series is great as well.

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Re: Aluminium Casting Parts for Foils

Postby skyte » Sat Dec 10, 2016 3:50 pm

DartBoard wrote: What you're saying about moisture is spot on if the moisture can't escape. The internal pressure builds up and crack!
I think it's more that if there is too much moisture and it is suddenly heated to 600degC when you pour in the moulten aluminium then it can turn to steam so quickly and expand violently so even if the mold is porous the steam can't escape fast enough and it explodes.

You're probably fine though... just wear some safety goggles! :o

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Re: Aluminium Casting Parts for Foils

Postby NYKiter » Sun Dec 11, 2016 11:58 pm



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