Which plywood

[petersull]

Hi, I am new to this forum and not very experienced in woodworking, but can do a reasonable job if I take my time.

I have a project to build that requires mainly 18mm thick plywood, and will take two 8ft x 4ft sheets to complete.

The properties I require from the plywood are rigidity and stiffness, lightweight and the ability to be finished to a high quality on the faces and edges to take yacht varnish. I understand that these properties depend a lot on my own designing and finishing skills, but I would like your advice on the best plywood to use if cost was no object. The weight aspect is probably the least important, just that I will be moving this around regularly by myself and it will be approaching my limits in weight and bulk.

So far I have been trying to weigh up the pros and cons between Finnish Birch, Baltic Birch and Marine ply.

Any help and ideas would be appreciated.

Thank you,
Pete.

 

[Grayo]

I suppose it depends on what your using it for really. If it's for outside use or near water then I would use marine ply every time, not the cheapest by far but will last a lot longer than ordinary ply.

 

[petersull]

I'm building a telescope something similar to the attached image.

It will regularly get wet with dew, but will mostly be stored in a garage.

 

[deema]

Welcome to the forum.

Looking at what you are building you should be OK with WBP ply, which stands for Water and Boil proof. I would look for very good quality puppy ply. You would be best avoiding Chinese ply, it tends in my opinion to be low on wood content and high on glue, which is not again in my opinion good for stability. The other to watch out for is ply with voids within it. It does occur, but the better the quality the fewer you will get.

 

[Shrubby]

I would look at Delignit ply for a mchine like this. Quality of Baltic birch seems to be slipping downwards.
Also yacht varnish is an elastic finish so it might be too soft for where you have components adjusting and clamping against it (from looking at the pics - I haven't built a telescope ,but lots of machines,tools and jigs)
Matt

 

[custard]

I'm building a telescope something similar to the attached image.[/quote


What a brilliant project!


=D> =D> =D>

 

[hanser]

Welcome to the forum.

'................ I would look for very good quality puppy ply.................'

New one on me :mrgreen:

I'd be wary of WPB. The quality of WPB I've used in the last 12 months leaves a lot to be desired - voids and loose plies.

 

[MMUK]

3/4" ply lightweight? :lol:

 

[petersull]

Thanks very much for that info everyone.

I googled the Delignit ply, and it does look like the ultimate material for my project. LT Lewis in London seem to be the UK supplier. They don't have any prices online so I will have to phone them unless anyone has another link.

Regarding the comment about the yacht varnish above, does anyone have any suggestions for a high quality, tough and durable wood finish/multicoat system, possibly spray applied and not necessarily clear.

Cheers,
Pete.

 

[wallace]

How about trying one of those two part floor varnishes Rustin's. I have used it to seal turned goblets and it is very durable

 

[Mar_mite]

I'd love to make a big dobsonian like that. Please keep us up to date with your build. In my opinion any birch ply will be fine. Will yours be as big as that picture?

 

[petersull]

The one in the photo has a 25" mirror. I'd need a lottery win just to buy the mirror and a big van to transport it.

I'm still at the design stage and will need to plan carefully how I will build it to dismantle enough to fit in the car, since I want to use it at dark sky sites to get the best out of it. A 20" will be the absolute maximum size for affordability and transport. I may have to settle for a 16" or 18", but the general design will be something similar to the photo. A 16" version won't even fit through your average house doorway