Birch plywood for dob mount

[dark star]

Does anyone know a source of good birch plywood in London? I found a wood yard not far from me who sells it, but unfortunately they don't deliver on Saturdays, which is what I need.

Jewsons sell Marine plywood for £128 for an 8 foot by 4 foot 18mm sheet. This is rather expensive! This amount would be enough to make a dob mount, I hope! Also, is Marine plywood good quality? Is it very heavy? Is it worth the extra cost compared to, for example, MDF?

i don't know much about wood and am surprised it is quite difficult to find good quality.

David

[Bizibilder]

Marine ply is simply ply glued with waterproof glue (unless you get it from a reputable boatbuilder!). Good quality timber of any sort is hard to source these days - so much is just DIY grade junk. Can you not get round the delivery problem with your local woodyard? It seems that is your best option.

[sologuitarist61]

Follow this thread http://stargazerslounge.com/topic/155296-birch-plywood/

[JamesF]

You might also see if you can find hardwood WBP ply. It's not as high quality as marine or birch, but should be fine for dob construction if it's painted or varnished.

James

[pete_l]

Yes, there's little benefit to using birch ply. AFAIK the thing about birch ply is that it doesn't contain any voids - where one of the plys has a little hole in it. That shouldn't be too much of a problem for your application (if you get a hole in one of the surface layers either: ignore it, fill it, or cut your pieces around it. For outdoor use, WBP is generally good enough and maybe even interior grade - it's not as if you'll leave your dob outside in the rain, it'll only get a bit of dew on it, or pick up some moisture from standing on wet surfaces. Paint can deal with that. Just don't get talked into using MDF.

So far as weight goes, I was always told that a sheet (8x4 feet or 2400x1200 mm) weighs about 100lbs ('pollies for the old-fashioned units, it came from foreign parts ) per inch of thickness. So a 19mm (¾ inch) sheet would weigh 75lbs - 34kg.

[callump]

I would recommend avoiding MDF - its heavy, does not take screws well, and the dust created on cutting and drilling is not nice.

Unless you are a master wood-worker, then i'd suggest going with 'bog-standard' exterior ply from a diy shop, or somewhere like Wickes. If you buy it in person, you can choose the sheet you want, but if you buy online it will be a bit pot-luck. Wickes also sell exterior birch ply, but my local Wickes does not stock it, so i've not had a chance to compare against their standard exterior ply.

Wickes do deliver (and on a saturday), but pricey. If its a single sheet i need, i often get it from a local supplier, quite a lot more expensive per sheet, but they do free delivery, so cheaper overall.

Callum

[woodbob123]

DON'T use mdf if you have a cutting list even if it's just for the main parts go to somewhere which will saw it up for you if they make a mistake does not cost you anything so write it down and give it to them to cut, it will be square and with clean square cut's. Birch ply would be used for furniture and the like, just get exterior ply and as said you can pick out the best sheet. once cut will fit into vehicle. Hammerite smooth paint will make it waterproof.

[swamp thing]

1343168246[/url'>' post='1586018']

Yes, there's little benefit to using birch ply. AFAIK the thing about birch ply is that it doesn't contain any voids

There are a great many benefits of using a birch ply.

1/ it's a consistent plywood with the core being the same strength/type of wood as the veneer. This means it's less likely to bow.

2/ birch is a pretty tough wood on a scale of hardness of timber from 1- 5 with 5 being the hardest, birch comes in at 4.

3/ As you've already said. Less voids this not only gives it strength but helps greatly with the aesthetic appearance.

4/ There is no "junk" infill plys like you get on regular ply. Most of the inner cores on other plywoods are whatever rubbish the manufacturers could buy cheaply. Normally garbage hard or softwoods depending on the grade of ply.

5/ It has many more plys than other plywoods this is another way it gets strength. The more plys the more strength.

6/ it has a veneered finish. This looks nice. So it can have a varnished finish. Birch is a beautiful wood and any scope finished well in it will look lovely.

You don't have to use it. You can indeed use a cheaper ply, but make no mistake there are advantages to using it. My homemade 10" Dob is made of regular marine ply, but I was always going to paint it ( as the optical tube is concrete forming pipe and ugly as sin ). Plus I originally intended to build it and sell it straight away (but it kinda grew on me ).

The scope I'm building now I want to be a thing that not only works well but, looks good too, so birch ply and a varnished finish are the order of the day.

Whatever path you choose good luck with your project.

[Tinker1947]

I know nothing about a Dob base or whats required but last week i sorted out some timber that had been under the Car Port for maybe 5 or 6 years, i needed a worktop for my telescope room that's under construction, now if its sheets of ply then why not hardwood timber suitable planed thicknessed and with some biscuits joined together the follwoing picture are the timber in its raw state then when worked on a 53" long, 29" deep, 2" thick worktop a dob base i would use 1" thick Oak. The first picture shows 1 piece of Beech (on the left) and 4 pieces of Ash, so the Ash won and 2 pieces ended up in the second picture....

this is a work in progress and may take many more weeks to complete....but making a solid sheet of hardwood isn't that difficult......

[Moonshane]

I can say without any reservation that there's literally no comparison between birch plywood and good/average quality hardwood BWP plywood. everything Steve says is true and having seen some finished birch ply recently I'll never ise anything else again. as for suppliers in London I cannot help unfortunately.

[Tinker1947]

There are these people i used about 20 years back, so i can't say if there reliable or not, but they appear to do sheet material....

http://www.slhardwoods.co.uk/Search.aspx