Thread: Shelf strength

You can check out the sagulator at The Sagulator – WoodBin for some guidance.

Originally Posted by mjwoodman

.....I'm building a bookcase (with) ... the shelf .. made from 38 mm thick saligna and spans 718 mm from cleat to cleat.....

You fooled me with the reference to saligna until I googles and found it is a fancy name for Sydney blue gum, and quite a tough timber if first growth, but I presume yours is plantation sourced, which will take its specifications back closer to those of Tasmanian oak or Victorian ash.

My wife was a university lecturer and I made her bookcases, lots of book cases.

Initially I made the bookcases from 19 mm radiata pine and eastern white pine (when in USA). All hopeless; pine sagged and spilled books.

Then I used two thickness of pine. This didn't spill books, but there was visible sagging and it looked horrible.

Then I switched to celery top pine 32mm thick and dovetailed the shelves into the stiles. This made assembly and disassembly easy and have had no problems of sagging. On later shelves I increased the spacing betwwn stiles up to 1500mm and have still had no sagging. Aesthetically the shelves still function well and look good after 30 years.

My wife was a university lecturer and I made her boobcases,

Worthless without pictures!

Originally Posted by AlexS

Worthless without pictures!

Touché

mjwoodman's situation is totally different to a bookshelf. The fish tank is 600mm wide and the shelf only 118mm wider. Most of the weight is carried fairly directly to the cleats. I can't see too many problems with what he is proposing as far as the shelfs adequacy of support goes.

Yes, thanks. I already had a look at the Sagulator but was unsure as to what wood was comparable to Saligna (Sydney Blue Gum) as it doesn't appear on its wood list. Would you have some suggestion?

Sorry. I thought that being an Australian site, members would be familiar with the name "saligna". Yes, it is plantation sourced. We have a lot of it over here in South Africa as it was originally use for pit props in the gold mines. So, do you think my idea will work?

Originally Posted by mjwoodman

Yes, thanks. I already had a look at the Sagulator but was unsure as to what wood was comparable to Saligna (Sydney Blue Gum) as it doesn't appear on its wood list. Would you have some suggestion?

Originally Posted by mjwoodman

Sorry. I thought that being an Australian site, members would be familiar with the name "saligna". Yes, it is plantation sourced.....

The standard reference for the specifications of timber in Australia is Keith Bootle book "Wood in Australia: Types, Properties and Uses."

The best online source that I know is "The Wood Database" which is better for international species but less complete for Australasian species.
The Wood Database

Neither reference differentiates the properties of old growth, regrowth or plantation timbers, although they may vary substantially.

You reference salingna - latin name eucalyptus salingna - which I know as Sydney blue gum, but I rarely use it as it is sourced some 800 kms from here. Bootle says its hardness measure or Janka is 9.0 kN, presumably for old growth timber.

I am much more familiar with Tasmanian blue gum - eucalyptus globulus - a different species - and it has the following Janka measures:

• Old growth - 12.0 kN,
• Regrowth - c.10.5 kN, and
• Plantation - c.7.0 kN.

The other specification measurements also vary substantially, but I do not have reliable data. Plantation Tas blue gum is much paler in colour, much less dense and much softer than old growth TBG as specified by Bootles. Very subjectively, I would assess its specifications as being closer to those of old growth messmate - eucalyptus obliqua - although the grain pattern is courser.

Very subjectively extrapolating from the above data and experiences, I would suggest that the specifications for plantation saligna might be much closer to the published properties for mountain ash and alpine ash than those of old growth saligna.

• Mountain ash - eucalyptus regnans,
• Alpine ash - eucalyptus delegatensis.

All eucalypt species mentioned are commercial species in Australia, sourced mainly from regrowth plus a small percentage of old growth.

My wife was a university lecturer and I made her boobcases,

Originally Posted by AlexS

Worthless without pictures!

Boobtube.jpg

Originally Posted by GraemeCook

Boobtube.jpg

Straight to the point!