Large Model Association Forum

Hi

Silly question,

What's the best way of sheeting complex curved areas?

Also to strengthen the lower and upper parts of the fuse centre crutch, instead of using balsa stringers would the use of Cyparis be a better choice?

Cheers mike

The strip method I have found to be the easiest. Don't make the strips too wide, start by gluing the first strip down,the next strip should be cut to match the first and so on, if you get to a difficult part, run a straight edge along the edge of the area already fixed and cut a straight line, remove the wood from the outer edge and start laying strips down again, easy in balsa. As for the crutch, Cyparis is much stronger than balsa and can be bent to extrme curves without breaking. It has a much greater strength to weight ratio than either balsa or spruce and absorbs any shocks extremely well. Hope this helps.
Cheers, Stuart.

Hi

Thanks for that. That clears it up.

Do you stock Cyparis? Will you be at Bradford on the 27th?

Mike

Hi Mike,
Yes I sell Cyparis and I will be at Bradford. Don't forget, because Cyparis is a good deal stronger and less liable to fracture than balsa, you can reduce the size of the stringers or spars whithout compromising strength.

Stuart

Mike

On the size model youre building, planking with 3/8 - 1/2" wide planks should only be necessary on very tight radii....the bulk of the job should be easily done with 3-4" wide sheets as long as the timber isn't too hard. I generally try and position stringers at 1.5 or 2" intervals around a former so I am always making a sheet to sheet joint over a stringer....makes it much easier as you have a surface to glue to, and when it's time to sand the join, the stringer adds stiffness so you avoid the starved horse look.

I personally hate planking & will avoid it at all costs........tight radii can easily be done with the use of ammonia. I have a 'neat' bottle which works amazingly well at softening the sheet, but any decent household cleaning product with an ammonia content can be used......the weaker it is, the longer it takes to work. I dab concentrated ammonia onto both sides of the sheet with a sponge (good ventilation required!!!), let if soak for a few minuted then tape the sheet in place around the structure until it's dry.....once dry, it will have retainied most of it's shape and can simple be cut to size and CA'd in place.

The photos below show a piece of 1/8" sheet formed with ammonia on the underside tail end of a 1/4 scale Sea Fury. This entire model was sheeted, not a 'plank' in sight. Stringers on this model (115") were 3mm x 6mm Cyparis.

Phil

Hi Stuart I will be visiting you at Bradford for some 6 x 6 mm Cyparis. 6ft long

Thanks for the advice on the sheeting chaps.

Phil where do you get your ammonia from?

Or what household products you suggest

Mike

I got a 1 ltr bottle of pure ammonia in a French hypermarket last time I was there (not easy to find in the UK anymore unless you have access to a school/college Science dept or something like that!!!). A lot of domestic cleaning products have an ammonia content.......just look at a few labels and pick one with the highest quantity.

Phil

Hi Phil,

Thats what I was thinking.

Ok will have a look at tesco lol

Cheers,
Mike.

After Phil told me about Amonia I had a look for some (without going across the channel) and coud only find this stuff
http://www.toolstation.com/shop/Plumbing/Consumables/Household+Ammonia+500ml/d20/sd2711/p96503
There are lot of similar ones in Tesco and boots and they vary form 5 to 10% Amonia.
Andy

I was just wondering if a different chemical would work and had a look around. Answer: urea and formaldehyde, but not as well as amonia. Here is the science..

"The scientists found that ammonia breaks down the hydrogen bonds within cell walls and within the lignin matrix. This allows molecular movement when subjected to tensile or compressive compresive forces. Once the ammonia evaporates from the wood, new bonds are made creating a permanent set; in simple terms, this can be considered similar to the process of adding a permanent wave to hair. "

So essentialy its the same as the wife using amonia on her hair

Now don't go pinching the hair products

Funny you should mention that as I have been reading on other forums for fish tank cleansing and some people were mentioning urine as it has ammonia in it.

Not the most feasable idea in the world. haha.

Mike.

I don't know, you could just pee on it and then bend it ....and then we will all stay well away

Haha. True. Think I will give that one a miss then.

Ordered some 10% ammonia fish tank cleaner. Seems to be the most you can get.

Can no other chemical be used for doing it?

Mike

Hi,
Have you tried this company?
93 / Litre of lab grade Ammonia Available in 1L or 2.5L bottles
http://www.abbey-chemicals.co.uk.

Regards
Alan

Hi Alan,

Thanks for that, just emailed them to see what the percentage is.

Cheers,

Mike.

HI,
I think GR 0.88 is its specific gravity (weight) which means that this will be about 35% ammonia and 65% water.
Andy

Cheers Andy.

Mike.

Hi Mike, i know this is quite a while since you asked your question.
I just put the balsa sheet to be bent in the bath with hot water, wait for about 10 minutes until its very wet then start to bend it by hand until it keeps some shape in it. put it in place on the desired part of the model, i then hold it in place with cable ties with blocks of wood in places to hold it tight.

I used to use Ammonia too, but couldn't stand the smell!

I also soak the wood in a hot bath tub for about 30mins to an hour and then hold into place on the model with medical bandages!

Thanks to Mr Rickett's advice i used Mr muscle which has a slight amount of ammonia too, this worked really well on the sheeting for the 12' fussy on the lanc.

Cheers Steve

PS test flight in a week :S