15mm plywood

[Astralstroll]

Well, Ive spent too long thinking about building a dob so now its time for something more constructive so to speak. Im planning to use 15mm ply, but I cant find anywhere that both stocks such a thickness and has the ability to cut it into more manageable sections. Does anybody know of such a supplier of 15mm ply in and around the Bristol area?

Dave.

[JamesF]

Why 15mm particularly?

James

[swamp thing]

15mm birch ply is not usually a stocked item.

What size Dob are you going for Dave? I would use 3/4" (18mm) on large scopes. The faffing about involved in ordering 15mm is not really worth it.

[Astralstroll]

Yes, Im beginning to find that 15mm is a bit esoteric. I was tryimg to opt for a compromise between 12mm (possibly a tad too thin), and 18mm (possibly a tad on the over engineered side). Might need to reconsider though, as 15mm really does seem to be as rare as the proverbial. The design is currently for a 16" based upon a purchased mirror.

Dave.

[JamesF]

I'd go for 18mm for a 16" mirror I think. Better a little over-engineered than too flexible.

James

[swamp thing]

I agree with you James.

[ronin]

Alloway Timber do 15mm, says WBP I had it listed for marine ply so may cost more.

DHH Timber also have 15mm, birch ply.

[LeeB]

I agree with 18mm I'd aim to over engineer everything, example my 8.5 dob f7.5 is on a 35mm base , yes its heavy and yes its solid. (no tuning fork)

[Horwig]

If I might share with you my motto In building astro kit, which is, If in any doubt, OVER ENGINEER.

As long as you are not attempting portable kit, mass and stiffness are your friends.

Huw

[skybadger]

15mm isn't that hard to find. My local builders even has it. Not in Birch though, marine.

I always tend to underengineer and let the 'sum of the whole' provide the required stiffness through proper joints, shaping and local reinforcement if necessary.

There's always time to do it again, but better.

Mike

[swamp thing]

You are right Mike, proper joints are indeed the best way to keep a job good and strong.

Any job is only as strong as its weakest joint.

[Astrobits]

It depends on the design you plan to follow. Very rigid structures can be made from relatively small amounts of material provided the right design is chosen. A Serrurier truss is a case in point. Rigidity does not necessarily come from mass.

You've seen my 16" Dob which is made from 16mm MDF. I have not had any problems arising from the that and I think that good quality Ply should be somewhat stiffer than MDF.

Nigel

[Digz]

I would also consider the price point of 15mm ply, if you find some. Additional delivery charges or fuel etc required to get the timber to your door may make it cheaper to go with 18mm ply from the local timber merchants....just my thoughts.

[Moonshane]

my local supplier buys in all birch ply and 15mm is strangely cheaper than 9mm, 12mm or 18mm. it's very robust indeed and is what K&B suggest for the mirror boxes on their dobs to about 18-20" from memory.

[Astralstroll]

Well I finally managed to pull my finger out and get an 8ft x 4ft piece of 18mm plywood from Travis Perkins in Yate. Also got it cut into some useful sized licences free of charge too. A total bargain and a good find as other places were making getting a piece of ply cut a really painful experience.

[JamesF]

Excellent news

James

[Tinker1947]

Just to get it right from the Off 3/4" = 19mm

[8kids]

Just to get it right from the Off 3/4" = 19mm

I think you'll find it's 19.05mm.