LumberJocks

Shop Tips & Tricks #26: Naturally Grown Wooden Crooks and Knees

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Blog entry by GnarlyErik posted 09-11-2019 08:33 PM 625 reads 0 times favorited 1 comment Add to Favorites Watch
« Part 25: SHOP AIDS and PICK-ME-UPS Part 26 of Shop Tips & Tricks series no next part

The subject of wooden ‘crooks’ (naturally grown ‘knees’) seems esoteric today, but some people may be interested. After all, when we allow all the ‘old school’ crafts and skills to be forgotten, they will need to be re-learned if they’re ever needed again, won’t they?

Old School boatbuilders usually called grown crooks either ‘crooks’ or ‘knees’, and used them extensively as knee brackets and bracing to strengthen and reinforce ‘joins’ of two components which meet a right angles, or near right angles. Examples would be where a ship’s deck beam joins a hull frame – and gets a ‘hanging knee’ to tie the two parts together and provide bracing. When the knee is horizontal as in joining deck beams to the hull to resist racking, or the transom of a boat to the side members it is called a ‘lodging knee’. Some knees are massive, as in the knees used in vessels like the US Constitution, and the Mayflower II).

Wooden crooks were also used in large wooden building construction in the past too, as in barns, mills and factories. In building construction they are usually called ‘brackets’. Today large wooden buildings depend on bolted bracing installed at 45 degree angles as in post and beam construction – but they are not nearly so attractive to my eye – but then, I may be prejudiced on the subject of crooks. Crooks are sometimes seen today as brackets for holding up robust mantelpieces and the like. When used for mantels, they are often called ‘corbels’, but corbels can also be made from stone, metal and other materials too. Go figure.

Crooks come in two major flavors, i.e., hardwood crooks and softwood crooks. Perversely, the best and strongest softwood crooks are obtained from root crooks below the ground, while the best hardwood crooks come from limb crooks well above the ground. Neither softwood limb crooks nor hardwood root crooks will last in a marine environment and will quickly rot. Odd, eh? As you might guess, some wood species provide better crooks than others. For example, the best softwood crooks come from larch (hackmatack) and spruce. Here are softwood species which are relatively soft and weak as building materials, yet their roots below the ground are exceptionally strong. And, there are no better hardwood crooks than those from live oak trees, although other oak species and hardwoods are also used. Generally speaking, most larger crooks are from hardwood species, and smaller ones are from softwoods.

A century ago and earlier, there actually used to be ‘crook merchants’ who gathered, bought and stockpiled crooks for resale to ship, and boat builders and anyone else requiring them, but I don’t know of any today. Not that I’m a century old, but I ain’t that far off! The point is, if you need a crook today, as in say, building a fine wooden dinghy, or hanging a beautiful new mantelpiece, you will very likely need to gather your own.

Crooks should be gotten out wherever you find them and cut off several inches longer than you expect your need to be. Ideally, you would dry them before sawing them, but that takes up to a year or more. Usually I wind up sawing them, then air drying them for a shorter period. One inch thickness will be moderately dry after two or three months or so. I sometimes speed things up by running a small fan at low speed through the stickered sawn crook slabs for just a few days, although then you run the risk of splitting the ends. If I can get them down to about 12% moisture content in the hot weather and high humidity in my region I am quite happy. I use a small pin type moisture content reader for the readings.

As to gathering crooks, hardwood crooks are easier to get simply because they occur above the ground, and they will usually come in the form of two branches or limbs forking. Sounds more than a little pornographic that way, doesn’t it? Anyway, You will normally have a three-pronged piece. (will the porn never stop?). Softwood crooks must be dug out, and are usually found in the roots near where the vertical tree trunk begins to send out horizontal roots. If you are searching for softwood crooks, a good source would be where there is land clearing in process, and the trees are being uprooted. (Be sure to ask permission first!)

With limb crooks, first, cut off the lessor fork. Then take a look at your resulting raw crook, and pick the best side, or the side where it seems most flat in the transverse (long) view. You will want to flatten this side as best as you can. I use a drawknife, then a power jack plane. The flattened side also needs to be straight, so as you cut away and plane, you should keep a straightedge handy to keep checking. A flattened part two or more inches wide is usually sufficient. And, it doesn’t need to be absolutely totally straight, but ‘near enough’. Know what I mean?

This flattened side goes up against your saw guide/slide. (‘Slide’ – see below)

After you are happy with the flat siding go to the larger end and strike a centerline parallel with the flat side. At the small end, make another parallel line, but at the same distance from the flat side as your centerline on the large end. This is important, and it should become obvious why as you make your cuts. Now, as carefully as you can, you should use something like a Sharpy pen to make a nice bold ‘centerline’ down the length. It’s not actually a centerline since it is not centered at the smaller end. However, if your crook is big enough, you can lay out the centerline so that it is actually centered on both ends. In that case you will need to work out a way to mount your crook to your slide so your saw lines are parallel with the face of the slide. The big advantage is that your resulting sawn crooks will be near perfect matches (as you work out from the center in pairs).

The backside of a bendy broken bandsaw blade is helpful in connecting the dots so to speak. This will be the line for your first and most important cut.

One big exception to the centerline rule is when your crook is too small to provide more than one sawn crook. Then, you should lay out your saw cuts to either side of the centerline.

I have a shop-made guide ‘slide’ which consists of two pieces of wood about 6” wide by about 16” long and carefully screwed together at a strict 90 degree angle. The flat side of your crook is tightly clamped to this guide. Depending on which side of the crook you have chosen to flatten, you will end up with either the small end towards your saw blade, or the larger. It doesn’t matter, except it’s a little easier if the small end is forward.Two clamps are used. I use a bandsaw, but you could use a table saw for at least a partial cut and then finish the off with a bandsaw or “Redneck Resaw”. I believe you probably have access to a bandsaw though, so I will go ahead with that description.

You must be careful to maintain very good control as you saw, and be sure to keep the foot portion of your slide tightly down on the saw table. Since you have double clamped your knee, the saw blade will be approaching one of the clamps as you saw. When near, simply stop the saw and transfer the clamp beyond the blade. Same thing with the second clamp. Once you are through that first cut you are in high cotton and sipping sweet duck soup. Simply re-clamp the resulting two pieces, flat side against your slide, and repeat the process. Depending on the overall size of your crook, and the depth of cut of your saw, you will also likely need to stop the saw once or twice to rotate your crook vertically enough so the ends clear the upper guides of the saw. Always allow at least at least an extra 3/8” or so in the thickness of your pieces for planing since you are bound to end up with a little waviness in your slabs. You will be planing your knees to their desired thickness later.

Just in case someone might misunderstand, the ‘centerline’ and saw lines for the crook should be on the INSIDE of the curve of the crook. If laid out on the outside, there’s a good possibility that you will not be able to pass your crook through the saw if the throat depth of the saw is very limited.

The thicker your raw stock is, the more sawn crooks you can get out of them. Anything under about 5” diameter will give you only two 1” crooks if that. The two best crooks will come from either side of your first centerline cut. If you look at your stock carefully you can decide if you can get three (if so, move your ‘centerline’ accordingly). The best I can do is about four. The sweet thing about the pair of centerline crooks, is that they end up ‘booked’ (almost duplicate) which is very attractive in things like quarter knees or things which occur in pairs.

Another note – make a thin wooden pattern for the knee(s) you need, to lay on your stock, especially when doing them in pairs. You will use this to adjust around for your best advantage, both as to looks and for function. It probably doesn’t need saying, but pay attention to the grain direction in your crook, since from a strength perspective, it should run as near as possible to a 45 degree angle to the joined parts.

(I’m including a few pictures below showing sawn crooks gotten out of a mid-sized pecan limb. These should be self-explanatory)

Happy bracketing!

-- "Never let your dogma be run over by your karma!"



1 comment so far

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Wintergreen78

29 posts in 220 days


#1 posted 09-12-2019 06:03 AM

Nice write-up! Now you’ve got me thinking about tracking down some crooks…

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