Thin Plywood

[Tony Harrison 2]

With my first build I can already see how useful thin ply is, as an addition to balsa. In fact I'm thinking of beefing up this fairly lightly built electric glider by skinning over the fuselage with thin ply - and I want to strengthen the internal floor between the servo and battery compartments.

I've had good advice about "liteply" which sounds useful and I'll get some. But as a not wholly inexperienced DIY type & hobbyist, I wondered about commercial alternatives. For example, I see lots of thin ply being offered by model shops and on Ebay - but at prices that seem steep to me...

Already found I can buy a large (1.5m square) sheet of 1.5mm (approx 1/16" birch ply from my local builders merchant for very much less per square metre than smaller sizes/packs from modelling sources or Ebay.

I wonder which thicknesses of ply people find most useful? And where do you buy your plywood?

rgds Tony

[Dave Hopkin]

Balsamart in Blackburn usually, I seem to find I use more 1/16th (I dont "do" mm) ply (both Lite and Birch) more than any other size, but I dont really use that much, as I tend to laminate 1/32nd Balsa more often than not - its as light as liteply (if your sparing with the glue) and stronger

[Chris Barlow]

Whatever ply you get you need to compare price, finish, density and defects in the core i.e below the top skins. A builders merchant 1/16 ply usually has quite a rough finish, open grained and quite a few internal voids/defects compared to liteply or "marine" grade ply.

But if it does the job you need it for...

Have a look at Slec and Balsa Cabin for prices too.

[Barrie Dav 2]

1/32" - 1/16" - and rarely 1/64" . As Chris says above, builders merchants and in my experience timber yards, are cheaper for ply but for our pastime we need good quality stuff. Also the surface finish of the ply is likely to be rougher than that purchased by SLEC or Balsa Cabin. I usually buy 12" x 48" Sheets.

[Dave Hopkin]

The stuff I have seen in Builders Merchants seems to have two very very thin veneers of outer skin and one thick much darker looking wood inside, and doesnt seem bonded together especially well

[Ernie]

Hi Tony I'd be careful about skinning a fuselage, Even thin ply wont cope with double curvature, and you'll add quite a bit of weight...ply +glue

I find the very thin stuff (that you can easily cut with scissors) really useful; Especially good for laminating on either side of a balsa core. I wouldn't touch the B&Q stuff, it isnt as strong as marine ply, and splinters when you cut it

ernie

[Ben B]

I panelled out my shed with cheap builders merchant ply so got to "examine" quite a lot of the stuff.. I wouldn't use it on my planes- delaminates very easily, not straight to begin with and the inner core is horribly spongey stuff. Does the job for building purposes but on a plane I'd go for something better.

[John F]

Adding ply to the fuselage will increase wing loading by a large margin and make it much more heavy than it needs to be. For a glider the risk is either snapping of the wings in flight or make it fly like a brick.

Some fuselages even have huge cut outs from the panels to save weight so proves a light build fuselage is perfectly fine.

I doubt you'll need to add the ply to a glider, it won't need beefing up.

[Stuphedd]

I buy mine 1/16 from a wood yard ! not a builder's merchant 8x4 ft , ( cabinet maker )

quality is very good !

cheers

anybody remember MIRRALIGHT?? used to skin my foam wings with it instead of veneer

[Erfolg]

Tony

I take a similar strategy as yourself.

For a lot of what I do, I use any old and often salvaged ply. For electric models, this is often good enough for fire walls. But then again the extra weight of a good quality plywood is often no problem up at the front.

In other instances I use the type of ply as sold by Blackburn model supplies, as Birch ply. This is for high duty work such as wing joiners.

I increasingly use light ply, because it is light! Stronger than equivalent balsa, yet not prohibitively heavy. It also cuts nicely, seems easier to cut than balsa of the same size.

Then again I find i can no longer afford 1/32 ply, and substitute 1/16. The weight penalty is often not worth worrying about, the glue often being more significant in weight. It also cuts easily with scissors. Yet for rolling into tubes etc. 1/32 does it much better.

Yes, I believe in horses for courses.

Although I use imperial, fractional sizing, the trades us mm, thickness. Why, because this is how the vast majority is made. The problem then is sizes quoted are often such as 1,1.5, 2, 4 mm thick, which never quite match my system. In reality, rely on how it looks, relative to typical applications and the cost per sheet.

I do agree that in the North of England, Blackburn Model Supplies are the best, worth going to, although not open on all days, particularly when Football matches are on.

[Tony Harrison 2]

Gentlemen, many thanks, too many useful contributions for me to respond individually but I appreciate your input. Re quality, I've been in contact with Travis Perkins, and my local branch can get me this stuff at a couple of days' notice:

Birch Aircraft Plywood A/B Grade 1525 x 1525 x 1.5mm – "Ideal when a quality thin panel is needed for joinery"

Which suggests it's reasonably good quality and not the rough 'n' ready stuff some of you rightly warn against.

Thanks too for the input re skinning my glider's fuselage: it's flat sided so curvature would be no problem, but I take the point about unnecessary weight. I was thinking that this is an old design and built very lightly for the relatively inefficient motors (and heavy batteries) that would have been used a few years ago, so with a modern 3S battery and reasonably pokey brushless outrunner it might handle the added weight of 0.8mm or 1.5mm ply quite well. However, perhaps since this is (after all) my first build I should follow your advice and not get too ambitious. I just find it hard to resist the urge to tinker, whether it's with modelmaking, or cookery recipes, whatever...

Glad to hear it confirmed that very thin ply can be very useful

rgds Tony

[jrman]

The only thing to add to an aircraft is "lightness".

[kc]

1525 x 1525 is a strange size for ply as it's usually only 1220 wide in one direction, interested to know what it costs and if it's any good though.

I suppose if you can find any trade that use this type of ply then what they throw out as offcuts would probably be large enough for what we need!

Edited By kc on 03/12/2014 16:16:09

[Tony Harrison 2]

Posted by kc on 03/12/2014 16:08:54:

1525 x 1525 is a strange size for ply as it's usually only 1220 wide in one direction, interested to know what it costs and if it's any good though.

£29.52 incl VAT, = around £13 per sq meter - which sounds good to me when I've seen it from modelling sources at around £15 for a third of a square meter...

rgds Tony

[ceejay]

I have used ply from this supplier for work and play, it is very good quality and the do 18mm down to 0.8 mm (in roundish numbers 3/4" to 1/32nd

 

**LINK**

page 14

chris

Edited By ceejay on 04/12/2014 08:33:43

[kc]

The link to Brooks seems to give 2010 prices which may be out of date, and they are dearer.

Travis Perkins seems cheaper than balsa suppliers like SLEC if you need large quantities, but SLEC supply in handy small sheets such as 300mmx1220mm at £7.38.

[ceejay]

last order I did the prices were the same, but that was 2013 I think!! did not claim they were cheap just that the quality is very very good,its birch throughout not just birch faced, the price is comparable to slecs (6x7.38 equates to £44.28 for a 1525x1525 sheet), and yes if you only want small quantities SLEC,s the very place, or your LMS, if you have one,

chris

[Toni Reynaud]

I hate to lower the tone of the discussion, but I have been known to go to the vege stall on the market and get an old tomato box. This gives me several pieces of softwood ply, abour 1/10", 2.7mm to 3mm thick, which is quite light, reasonably flat, and great for formers. Also useable for U/C supports and motor mounts on smaller electrics.

[Erfolg]

Brook Brothers do apparently have an outstanding range of timbers. Far better than anything I am aware of  in the NW of England.

It does seem there are two approaches to purchase. For some it is a practical and cost effective option to go to a supplier. In my case (Brooks) this is not a sensible option for me, although itis quite different for others. For me it is Blackburn MS, on my way to, or, on return from Lytham and St Annes.

In the case of postal purchases, Plywood is not such a good proposition (in my opinion), as sheets are invariably reduced to convenient sizes with respect to the postal charges. Although for thin sheets this may work, now, given the very high cost, in my case limiting the sheet size I could afford to buy. This seems more so when the Post Office is the carrier, being very expensive, and in my opinion no better than the others. Although some are rubbished by the BBC, yet they never bother high lighting the PO, where I have had bad experiences.

My own experiences do suggest that the building trade, and most wood yards do not stock the thicknesses i am after, which are invariably in the 3mm and less. Where I want ay 4mm, again the quality of the ply is not great often being just 3 ply. I much prefer 5 ply or greater. Often salvaged ply have suitable numbers of ply. Will not be the sort of stuff some demand, in being guaranteed waterproof, Marine etc. grades. For my models more than good enough. I sometimes wonder what some people are actually building, certainly not the size of model i do, wheree it will not be the failure of even standard commercial grades of ply. that will be the issue.

Edited By Erfolg on 04/12/2014 15:25:53

[Dave Hopkin]

Well put Erflog - Regards to your last point, I and a suspect quite a few other have very fickle grasp on structural engineering and hence the actual balance between the strength our models actually need and the strength we build into them - I suspect mine are far too strong for their operating environment - but the fear of a structural failure in flight keeps us doing it!