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I'm planning ahead for when I start needing knees. Finding enough natural crooks that small is unlikely so I have to saw them out. In order to make them reasonably strong how do you deal with the grain? Do you laminate them, lap the corners. miter them or just cut them willy nilly in any direction and hope they don't split?

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33 minutes ago, wefalck said:

What wood are you using, that you are worried about splitting ?

Hazel. It seems pretty solid. One of the first things that my father taught me was don't use wood with the grain across the wood. Don't want another "Ajax" here😃

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35 minutes ago, druxey said:

Run the grain diagonally so that neither arm is cross-grained.

I'll give that a try, it's still going to be a little cross grained though, isn't it. I guess it doesn't have to be that strong. I've got some Hazel heartwood that was too dark for matching my framing. It seems denser.

Thanks

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As posted above, depends a lot on the wood.  Castello and Buxus are fantastic for this purpose but there are no doubt others.    There is no need to make laminated pieces.

 

If you want to truly aggravate yourself consider the following.   I was going to make knees from crooks as was done in full scale and collected hundreds of pruned pieces from an apple orchard near our home and debarked them and let them dry.  As they were so small they were ready in a few months.  They were the best way to go for strength but took so much work that in the end it was just not worth it as this is a model after all and the stresses are not such a big deal.  

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From my experience:

For dense woods like pear, going a bit across the grain makes no difference, for the loads they ll carry on the model they will be fine. You can laminate two thinner sheets of wood with the grain at 90 degrees so that you can cut in any direction but do not use PVA, the whole sheets will twist horribly due to the water in the glue-use epoxy. Or you can laminate half circles with 0.5 mm strips using epoxy to cut the knees but it is labour intensive, messy and the laminate will be very hard to cut and sand.

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3 hours ago, wefalck said:

Some people also mill or plane the rough shape from a square billet and then slice it up to get the individual knees.

When I imagine mass production of knees, truck sides, deck beams by milling a billet and then using a table saw to slice off the finals, I obsess about the amount of wood lost to kerf.

 

There was a recent thread (gun trucks?) that reminded me of an efficient way to increase the productivity when using this method.

Make the billet up using slices that already the desired thickness that are held together using a reversible glue.

Spot bonding using PVA and immersion into 2-propanol.  A tissue paper spacer between each segment may speed the reversal.

 

I just made up a batch of small sponge stick glue applicators using bamboo toothpicks and Duco - and Duco would be an alternative, but I think I would like PVA better.

 

 

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    I think it is important to note that a knee is essentially a triangle with 2 sides affixed to a solid location.  Given that (as noted by several above) a model knee is under much less stress than an actual knee,  grain direction is not as important.  Plan accordingly.

knee.thumb.jpg.bc074ea2a0874fb92ec997c588a1c2ba.jpg

 

  I recently made a couple knees from Alaskan Yellow Cedar for my cog.  They turned out quite well.  Grain ran parallel  to one edge, making it easy to manufacture.

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Posted (edited)

On this photo the grain doesn't seem to be all that critical since these all just seem to have the grain running vertically.

elbows-frames_tryworks-charles-morgan-aug2013.thumb.jpg.5af7ad3693687d34770e2a7e611c3dd8.jpg

   

      As far as mass production goes, they can just be shaped with overly thick legs and the angle could be easily modified  with a belt or disc sander for the ones that didn't match.  If you look at posting #39 and #41 in my Wanderer build log, you can see how mine were made.  In my build the angle was 90 degrees, but as I said they could have been just as easily modified with the sander. 

Edited by BETAQDAVE
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