Hardwood exterior ply question and source

mental4astro (Alexander) · #1 24-04-2009, 11:12 AM

Hi all,

Finding a single species hardwood ply in Sydney, and without it costing a small mortgage, has been a 'Mission Impossible' thing.

I've come across a mob in Hoxton Park that sells 'Hardwood Exterior Ply', B-C face (I'm of the 'Look Through' brigade), A bonded, but using a mix of hardwood species throughout its laminate. And at $67 a 2400 by 1200, 15mm sheet, man it sounds very, very good.

The good book, 'The Dobsonian', dosen't mention mixed hardwood plys, but I don't see an issue flex wise if designed properly. I can see there being a certain element of the 'unknown', but everything I've read steers towards more the use of Hardwood, persay.

What are your thoughts, re 17.5" three pole scope?

Mental

acropolite (Phil) · #2 24-04-2009, 12:14 PM

If you're after better ply it may be worth doing a google search for suppliers of aircraft grade ply. The quality of aircraft grade should be very high as it's certified for use in aircraft construction.

tnott · #3 24-04-2009, 12:29 PM

Sounds OK. As long as it is HCHV then it should have the right stiffness.

Try to get a bit that has no voids, warps and has been properly seasoned.

Aircraft ply would be even more expensive then the marine grade Gaboon and Pacific Birch I have used in my scopes.

mental4astro (Alexander) · #4 24-04-2009, 12:42 PM

That was one thing I badgered this mob about, that of HCHV, and they said it was.

Voids, well, I guess they will be less than C-D construction ply, which is what I made my 10" with. I like the knoty appearance.

Aircraft ply would be an option if not so expensive.

And yes, the cost of the ply is zip next to the mirror, plus the quality, but I'm looking for less expensive, alternative materials with the same performance.

Rod · #5 24-04-2009, 02:48 PM

A cheap option I have used is formply. It is certainly hardwood exterior and has an outer coating of black phenolic resin. I don't know if the internal plys are hard or softwood. It is very flat and usually cheap. Formply is used for making moulds for concrete. It does not give you an attractive wood suface to varnish so it is definitely a 'look through' rather than 'look at' option.

Rod.

GrahamL · #6 24-04-2009, 05:45 PM

You could laminate some differant thicknesses useing a quality
AC or similar on your face sheets and the cheaper lower grades on the not seen bits

mental4astro (Alexander) · #7 24-04-2009, 08:58 PM

Formply I had thought about, however, with the design I'm looking at, the "cage" is just a single ring of ply taking all the stess. In this case, I'd rather a HCHV ply for the added firmness. Ta for the tips, TNOTT.

I too have thought of using CD ply for the not so critical areas to reduce cost. The rocker box would be such an element as all its loads are compressive, no tension or shear loads. And 30mm CD ply aint going nowhere supporting the alt bearings.

I can get CD ply for the same price in the eastern suburbs as this hardwood exterior ply, so might just stick to it for the rocker.

The design I'm looking at is similar to that of TNOTT's 10"er.

Cheers for the suggestions,

Mental