Looking for info on engineering

I've bashed together a few things before and they've fallen apart or not been too stable. Now that I'm looking to get into woodworking proper I'm wanting to learn more about the structural engineering side of woodwork especially as my projects are either large (over 1½ metres high) or will be be load-bearing (bookshelves, equipment racks etc).

So rather than just over-engineering joins, using 150x150 hardwood beams) or sticking a billion screws and nails or applying kilograms of glue etc ("Russian" style engineering) I want to better understand forces and stress in timber and be better informed on when to design in struts and braces to distribute load and minimise risk of shearing, twist etc.

As an indicator of the use of wood engineering in wood work, have a look at the Wood Web Knowledge base. http://www.woodweb.com/KnowledgeBase/KBIndex.html
10,000 articles of various lengths on working with wood and about 4% of those articles come under "Wood engineering" - see http://www.woodweb.com/KnowledgeBase/KBWE.html
However, most of the wood engineering articles have little to do with structural/strength aspects, and most are about drying wood, moisture content, handling dimensional changes etc.
I'm not saying that structural aspects are not important but they are just one of a the many aspects about wood that most woodworkers need to worry about.

This is probably because unless you are talking buildings (where use of graded timber is a requirement) or designing furniture for Ikea, then using structural engineering to design furniture is of limited value.
Ikea furniture is "engineered" to use the minimum amount of wood for the average loads and they are able to do this by using materials like composites which have more or less constant properties.
I serious doubt whether top furniture designers work like that.
I guess furniture makers are expected to pick up the structural basics like their ancient counterparts did i.e. by experience.

One problem is that (unlike metals or composites) the properties of that piece of wood in your hand may not even be close to the average for that timber. The properties of wood vary significantly within a species, the same tree, the same piece of wood, the direction of the grain, the age of the wood, how it was dried, and over time etc etc - e.g. what about that small crack in the end , or that knot in the middle of the piece of wood in your hand? This is why experience is so important in working with wood.

Despite this you may find some very useful in the link above, there are short articles on limiting bookshelf span deflection, and basic engineering of table designs.

One of the most useful books I have come across regards a broad understanding of wood is
http://www.amazon.com/Understanding-.../dp/1561583588
Have a look at the table of contents and you will see there is a small section on wood engineering and far more on other aspects about wood.

Here's my random thoughts:

• The only really self-stable shape is the triangle; everything else will try to turn into a triangle at some time; most will fail and just become parallelograms.
• 16mm thick chipboard is quite ok as a support for bookcases and so on, to at least 2400mm high.
• No amount of precision joinery/glue/screws/nails will equal the anti-racking ability of a solid (even if only 6mm thick) back to a structure.
• 16mm chipboard is only good for about 600-800mm of shelf span, after that, talk to the sagulator - http://www.woodbin.com/calcs/sagulator.htm
• Adding metal (screws, brackets) to a wonky wooden joint is never a solution.
• Wood will never stop moving; so allow for cross grain expansion and contraction or your structure will try to pretzel.
• Steal ideas and designs from successful pieces.
• I've noticed that MDF sheets will shrink about 1-2mm lengthways after a few Canberra summers; just enough to reinforce the need for joins that can disguise movement.
• The above statement means that detailing to create shadow lines is quite useful.
• When all else fails, be prepared to take a saw to that wonky table and rejoint the whole top.
• Don't leave dressed timber lying around for too long; it may decide to warp. Dress it and then use it promptly, don't come back to it in six months time.

ISBN 978-1-60085-758-4

Bookcases Cabinets and Builtins by Taunton press. About $20 from Amazon.... http://www.amazon.com/Bookcases-Cabi...dp/1600857582/

Excellent collection of projects as per title and it discusses your queries at length.

Ev

Master S's random thoughts are probably the best summary you will find anywhere.

Master Splinter is right, everything shrinks a bit in this Canberra heat....even me. :)

NathanielBC, this is also another good book: http://www.amazon.com/How-Make-Kitch...dp/1565235061/

Both of these are available from the Canberra library.

If you get in touch with Delbs, he is The Library King. He has gone a tad overboard with his...ah obsession ... collecting, its impressive.

Thanks everyone for your advice and suggestions; have added some books to my wishlist although with my recent tool purchases I have no budget for books for a little while :B

See if you can find an old copy of Marks Handbook of Engineering by Lionel Marks. It is still being published but you don't want a newer edition because much of the old-time information has been dropped. I have a copy that is around 50 y.o. and has tables of many antiquated engineering considerations. For example, how many yards of earth can a donkey wagon pull etc. Another great source are the Audells guides. They cover practically everything from steam engineering through home construction and carpentry. Again, you want an old set to get the archaic information. If you look around these books can be found at flea markets, garage sales and sometimes in the used book shops.

Book learning is a good place to start, then if you want to get hands on do your own testing, for e.g. take a piece of wood machined to say 50x19 and support it at the ends (on bricks?) add weight to the middle and see how much weight it it can support with minimal deflection and continue to load until failure, you can do this on edge or on it's flat and from these two tests you will see which will hold the most, this is just one type of simple test that can be done to build up that knowledge of "how much will this support".
Google the woodgears bloke Mathias Wandell ? he has done some interesting testing of glued joins with basic gear.



Pete

Another good source of information is already available to you. Pull the chairs out from under the dining room table and look at how the table is built. Go around and study pieces that you would like to make and examine closely how the joints are made up and how the various structural elements go together. Construction methods and techniques are pretty stable through time.

As above, Mathias' website is excellent: http://woodgears.ca/

The dude is an engineer and he spends a LOT of time just noodling and experimenting. He has done quite a bit of experimentation to destruction... Joints, glues, spans, dominos vs dowels, that kind of thing.

He also seems quite prolific and builds things in a deceptively simple way....lots of pine.

There are a few contraptions that are amusing and good to know....marble machines!

E

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Originally Posted by Evanism

As above, Mathias' website is excellent: http://woodgears.ca/

The dude is an engineer and he spends a LOT of time just noodling and experimenting. He has done quite a bit of experimentation to destruction... Joints, glues, spans, dominos vs dowels, that kind of thing.

He also seems quite prolific and builds things in a deceptively simple way....lots of pine.

There are a few contraptions that are amusing and good to know....marble machines!

E

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E,

Thanks for the link, very unusual woodworking. I really like the experimental aspect.

Cheers,
Rob

Quote:

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Originally Posted by rob streeper

E,

Thanks for the link, very unusual woodworking. I really like the experimental aspect.

Cheers,
Rob

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Very welcome. He has an unusual way of speaking. Whenever I read his articles I hear them in his voice.

Almost like Morgan Freeman.....

Stumbled onto one of Matthias' videos this evening — didn't realise till I got to the end. Very cool, that pantorouter! :2tsup:

http://www.youtube.com/watch?v=MdH1DR-3ptQ

Last night the Fine Woodworking Association of WA held its monthly meeting.
The guest speaker was none other than Michael Fortune. (Google for more info) who spoke for 2 solid hours about furniture design and the way he goes about making stuff.
In case you don't want to Google, let me just summarise by saying he is one of the best furniture designer/makers in the world.

Did he mention engineering or doing a calculation? Nope not once. In fact he said he is terrible at maths.
His designs start with general sketches of the shapes and function he is chasing, then he goes onto a bit more detailed sketches, then he makes 1/4 scale models, then more drawings, then maybe more models and finally he might make an unfinished prototype to check things like stability and strength, and only then does he present his clients with a choice of 2 designs on paper on a take it or leave it basis. Given he does most of his work for just 6 very wealthy families in North America, most clients choose one without any argument. The design process takes anywhere from a few days to years. He carefully documents what he does so he can go back and use elements of previous designs that have worked. He reckons only about 3 out of 4 new designs go on to recover their design costs. He makes/uses a lot of jigs so that successful designs can be used over and over to makes a decent income. For reference his top dining chairs currently go for about $10k each, and his dining tables are about 5 times that.

Any way he gave us a most inspirational slide show, for the average Joe his stuff is way out there, but everyone walked away with at least a couple of useful ideas (and their jaws dragging on the pavement).

The photos of his workshop showed a complete package of goodies but the most used machine in his shop is his 14" bandsaw.

On top of that he donated his speaking fee to a prize for the next FWWA competition.