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Re: Plywood And The ATM

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Posted by Dianne/">Dianne on May 4, 1999 12:24:36 UTC

: Hi Everybody,

: I am building a scope a la Kriege and Berry's, "The Dobsonian Telescope". In that book they are adamant about the use of hardwood veneer, hardwood core (HVHC) plywood over all other types. This is NOT the same animal as the various nominal hardwood plywoods that you can find at Home Depot, Minton's, OSH, etc. (which have only a thin hardwood veneer over softwood core layers, so-called HVSC). It turns out that HVHC plywood is something of a specialty item, requiring a ~50 mi road trip to a hardwood distributor and carrying a premium price.

: Now, this scope is going to be with me for a long time, and I am anxious to do it right. The price of the HVHC plywood that Kriege and Berry push is high, but not prohibitive. On the other hand, I feel no necessity to OVER do it. Case in point, for the past 10 years or so I have been using a 17.5" dobsonian that I home built using good ol' off-the-shelf softwood plywood (SVSC), and I have never had any complaint about its operation or stability.

: My question, for anyone that has an opinion (i.e. anyone who read this far), is this: Are Kriege and Berry right? Is the HVHC plywood sufficiently superior to the more commonly available HVSC and SVSC plywoods that it justifies the added expense and inconvenience? Or are they just being obsessive, and a scope made following their design and using a lower grade of plywood would be indistinguishable in terms of stability and ease of operation?

: TIA for your thoughts,

: Doug

Hi Doug!

I've done some instrument building (5-sring banjos) as well as some other non-conventional construction and if I am worried about strength, rigidity, and warping, I prefer to use a number of layers of thin (common) plywood laminated cross-grain with plastic rosin glue. It makes an incredibly rigid board and warp-free. If you are after a finished thickness of 3/4" and you use 3 layers of 1/8" ply, you end up with a 9-layer 3/4" sheet.

Side benefit - 1/8" ply is cheep and you can end up with "good both sides".

Good luck!!!

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