Design principles

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I had to read this 3 or 4 times to work out why this version was correct. Thanks for the update :)
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On 5/10/2013 10:14 AM, Alexander Lamaison wrote:

The basic problem I see with your design is angular bracing. As I see your design, it would seem that over time the unit would wobble and the joints loosen up, with ultimate collapse.
There would be two ways to prevent this. The simplest would be to add pieces in the corners 45 degrees to the up rights. This could be plywood triangles or short piece cut at 45 degrees so they would fit into the corners.
If you want to keep the openness of the structure I would half lap all of the joints. Half laps are quick and easy to cut and are very strong joints. They may not take any more time that cutting and installing all of the 45 degree braces above.
It you really want to get fancy you could make mortise and tennon joints, but I think that is over kill, unless you want the practice for a future project.
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Thanks for the advice. So that's bracing _or_ half-lap joints?
Alex
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On 5/10/2013 2:27 PM, Alexander Lamaison wrote:

This is shows how half laps are cut
http://en.wikipedia.org/wiki/Lap_joint
The strength come from the fact that the weight of the cross member is borne by half of the up right. The sides of the cut prevents the joint from twisting, and keeps it square.
http://www.gazebodepot.com/gazebos/corner.asp
These are a lot fancier that what you need but gives you an idea of what I am talking about. A brace is a piece of wood placed in the corner to create a triangle.
I suspect our problem is I am speaking English in America and you are speaking in English in the UK.
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Actually, we call them the same thing. It's nice to have explained for once what lap joints are good fore. The books tend to skip that bit.
I'm familiar with braces, but I've never know when they are necessary and when they aren't. Once you start adding braces in one place, its tempting to add a few in others and hard to know when to stop.
Alex
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Alexander Lamaison wrote:

This is a very, very, very old problem. Trees didn't come with directions. Indeed, all trees are different and many of them are probably not very happy about what you have in mind! : )
More specifically with regard to your question, I'm reminded of the words "form" and "function". Ignoring "basic rules" there are entire cultures of ideas of how to transform the flesh of a tree into something more noble.
I like this web site--after numerous visits, I still haven't seen eveything on it. http://www.museumfurniture.com/
Bill

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Being such an old problem, I don't know why there seems to be little advice. All woodworking books I've got my hands on spend the their time describing the million-and-one ways of making a joint. None give advice on how to structure the pieces you are joining. Most don't even explain when to choose one joint over another.

I guess I'm interested in function more than form. How you design something with to use minimal effort/material but still be confident it will do the job. Up till now I either hope or overengineer it. I'd like a better method.

I'll trawl that this evening.
Thanks,
Alex
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On 5/10/2013 1:36 PM, Alexander Lamaison wrote: ...

...
You're looking in wrong places...
<http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id 0&header_id=p>
What you seem to ask is more to do w/ engineering and is what architects and structural engineers do. It's not common in the recreational woodworking literature because there's such a widespread conventional set of dimensions used for virtually all such pieces that amateurs or semi- to moderately-advanced woodworkers tend to build that there's little real need for actual stress or sizing calculations. Really experienced will have enough through their experience to be able to extrapolate or will consult w/ knowledgeable folks who can do that. Otherwise, it's really all about the design for appearance.
OTOH, the other place where there's real engineering for wood products is w/ the manufacturers who design for production and efficiency and cost.
As for the complaint of joint selection for purpose and the like, I would recommend Tage Frid's series of books published by Taunton Press probably 30 yr ago. While somewhat dated in their appearance by today's standards of publishing, they're very well done and not much better than I know of yet.
And, of course, for structural design, there are building codes that provide minimum requirements for structures that include things like live/dead loads, deflection limits, wind and snow loads and such things as hurricane/tornado/earthquake enhancements for locations affected. Don't know the UK equivalent, in the US it's known as the Uniform Building Code.
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<http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id 0&header_id=p>

I'm not trying to build anything as engineering-critical as a building ... yet. Just every day items: log store, yard gate, kitchen cabinet, TV table, wash stand, window frame etc.
I'm not aware of a "conventional set of dimensions" so maybe that's where I'm struggling. I didn't even realise there was such a thing. Perhaps you could enlighten me. Let's say I wanted to build a simple table to hold a small television; how would you size the pieces that make this up?

It must be good. Even old versions are still expensive on Amazon :P
Scanning the contents list it still reads like the others: let's go through a load of tools, let's go through a load of joints. Hopefully its interspersed with higher-level information about good structure as well.
Thanks,
Alex
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On 5/10/2013 3:07 PM, Alexander Lamaison wrote: ...

Well, it's been experienced carpenters and the like that take the kinds of work for the more and scale it down to the lesser...I've certainly seen a number of DIY'er type books on racks at the places like the BORGS and all in the States--I'd presume they're there, too.

...
Well, virtually everything in the US for face frames, rails, things like table aprons, shelf uprights and shelves, etc., etc., etc., are nominal 3/4" stock w/ widths generally adjusted for appearance on most small stuff. Larger spans/heavier loads means wider aprons to provide additional bending moment/load capability. That's about it for structural design.
After that for joints, furniture is generally a combination of M&T and possibly some dowels for traditional craftsmanship; commercial stuff uses many shortcuts or machine-cut joints for efficiency and cost-savings. OTOH, fences and the like generally are just nailed/screwed together w/ perhaps a lap or slip tenon or something again pretty simple.
Again in the US standard lumber sizes are nominal 1x, 2x, 4x and occasionally 6x timbers for structural members like deck legs and the like. These are, as said, nominal rough/green dimensions whereas the actual stock as sold is 3/4, 1-1/2, 3-1/2, etc., ... Also, widths of construction lumber in the use are nominal less 1/2" pretty consistent.
Ply used to be all english units as well but now has unfortunately succumbed to the metric of being 19 mm (I believe it is otomh) which is just under 3/4" enough to be a real pita in thickness compared to actual lumber. It's still 4x8 sheet size, however, owing to the universal stud spacings of 16" for 2x4 or 24" on much 2x6 now so that at least sheet lengths and stud spacings still work.
I am sure there are standards similar in dimension but w/ metric numbers over there as well. It doesn't take much thought to realize that when one can by 1x4 or 1x6 off the shelf that 99%+ of projects will use one or the other but only a very pricey custom piece of work will actually specify 1x5 because it is exactly what a load calc says is need or the aesthetics are pleasing since it would require buying the 1x6 anyway and then onsite cut to fit.
Hardwoods or clear pine/fir/etc. for cabinet work or furniture are _not_ sold in prefinished sizes like construction lumber, however, but as roughsawn thickness (in 1/4" increments generally) and random width/length and priced on a board-ft basis. Some retail outlets will sell dimensioned stock but it will come at a very premium price markup as compared to market prices.
As for the Frid books, indeed Tage does talk a lot about using what when altho it's _not_ home repair or yard projects or fencing he's talking about--he was a furniture maker/highly skilled cabinet maker and that's the audience he's after, not the DIY'er homeowner.
If that's your target, you might look at the Taunton site again, but at the Fine Homebuilding site instead of Fine Woodworking. I can't make recommendations; I've not had interest in the genre so don't know about the selection.
There are also the trade journals and such like Journal of Light Construction (or very similar title) and there are, of course, trade school and college design texts altho my collection there is so dated that I'm sure none are still in print so won't name any even though the content is still valid for the most part for what an individual would find useful. What's missing in them are all the new engineered materials such as glulam, engineered trusses, joining systems, etc., etc., etc., ...
I can't help much on that front other than the generalities--I'm another who just picked it up from having grown up w/ such things so it just seems second nature. Doesn't hurt I suppose that am also engineer by training so structural and mechanics are sorta' routine even though I was a NucE/Physics guy primarily still had to have the rudiments of statics/dynamics/strength of materials, etc., ...
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snip
Thanks. All very useful information.
Alex
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There is no one path to learning "design", but there is one sure fire method to get you started on your own designs for just about anything you want to build out of wood:
Stand on the shoulders of those who came before by carefully researching the item you wish to build, then incorporate appealing elements and combinations of form and function, gleaned from your research, into your own design.
This can be as simple as clipping ideas from magazines, or using technology like Google searches using the "image" feature and/or websites like Houzz.
Then either sketch, or use a 3D modeling program like SketchUp (with which you already appear to have some proficiency), to finalize your design, paying particular attention to incorporating appropriate, traditional joinery methods that have stood the test of time
The more research you do, the larger your store of design ideas becomes, for both current and future projects.
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