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Question to Master Blade Maker Hipnotic

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    Posted: 11/09/2020 at 8:44pm
Hello Hipnotic,

Thank you for the continuous update of your work, I am sure to be on top of the news with here and Facebook and it's always a treat to wait for the big pics to load before enlightenment takes me again.

I have learned to accept the multi pieces core because 1st you say it's ok (glue is stronger than wood) and I trust you and 2nd, if the process is ALWAYS the same, it's got to be fine, especially if we can't make a difference in a blind test.

I asked a question to Ross Leidy back in the days and I received a mitigated answer, I was wondering what you think about the idea:

What if we have the core as you do it (1 piece, multi pieces or not) but all other plies are just the paddle minus anything under the handle, the playing surface only: the core  is one 257mm (10cm handle + the typical 157mm head) but all other plies are just 157mm tall and are glued above the handle.

I would expect more flex and catapult yet the carbon plies and all other will still kick in even if tamed a bit. I never tried that and I am wondering what you think on top of your head. Is it an idea we can discard right away or is it worth testing? I can't imagine a strong stroke bending the core enough to break it, where the handle ends, there is enough width to make sure it's not going to happen. Of course it will be easier to break it when snapping it on our lap out of anger but that should not be a factor in the decision to try or not.

There is so much room to play now since we can imagine harder cores than can be thin or thicker ones as the chosen material softens.

Of course it would be legal since the playing surface is the same all over.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hipnotic Quote  Post ReplyReply Direct Link To This Post Posted: 11/10/2020 at 6:35am
Hi!

You can call me Sérgio, Hipnotic was the unfortunate nickname I chose about 10 years ago when I registered on TTD, I just stuck with it when I signed up here just for the sake of continuity.

Don't want to get in an argument again about the multi core pieces but the other days I was holding a recent Xiom blade and clearly saw a multi piece core. I have been using a single piece core for Ayous for a long time, and if you look closely to some of my recent builds you will also see a single piece Kiri core. You will still see the 2 piece core from time to time because they are actually 2 different species, the "old" is lighter while the "new" one is a bit denser and closer to Ayous. But the good news is that I can get this wood in boards wide enough to make a one piece core.

Regarding your question, I suggest you take a look at this post I made on my Instagram account: https://www.instagram.com/p/B_wwcDGHOOS/

It talks about the difference between stiffness and hardness, which is basically what your question is all about. By discarding the medial and top plies beneath the handle you are drastically reducing the stiffness of the blade, while the hardness is the same. This will feel very weird, it will feel flimsy but hard at the same time, like swinging those hammers with flexible handles, so the control will be very compromised. Also, the medial ply is responsible for a lot of the tactile information you receive on your fingers and hand, because of the orientation of the wood plies. Without it you would get less feedback. Not a very good idea in my opinion. 

But the opposite can actually work and there are a few examples out there with this concept like the Butterfly Defence 2. They increase the number of plies beginning just above the handle, which increases the stiffness but retains the hardness.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stiltt Quote  Post ReplyReply Direct Link To This Post Posted: 11/18/2020 at 3:49pm
Hello Sergio, thank you so much, I enjoyed the analysis and the Instagram document.

I might have to rename the thread "Ask The Pro Blade Developers" so more people can pound on your knowledge; and more pros could join you ?

My question today is about cross grain gluing: we know it increases stiffness. What if we rotate each successive plies by less than 90 deg? why not 30 or 45?  Would the stiffness still increase, only less? if that's true, we could play with various degrees of stiffness (?)

Example:
core (vertical grain direction) - 2nd ply +45deg - 3rd ply +45 deg  (so 90 total, the grain direction of the outer ply points to the right, horizontal grain direction)



Edited by stiltt - 11/18/2020 at 4:43pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hipnotic Quote  Post ReplyReply Direct Link To This Post Posted: 11/19/2020 at 3:50pm
Well, your premise is wrong, or incomplete at least.

Wood is an orthotropic material,  meaning it has unique and independent properties in different directions. So, mechanical properties will be high along the direction of the grain, but smaller in comparison in the other directions. That’s why most blades use a crossed grain pattern, in order to achieve stability in all directions and make the plywood more homogeneous. The medial ply adds very little stiffness along the longitudinal direction of the blade, but will add stiffness in the perpendicular direction because the grain is at 90º. It does also add longitudinal stiffness indirectly by increasing the distance between the outer plies and the center axis. 

This stability is what we usually call sweetspot, it basically means that the mechanical properties are more homogeneous along all directions of the blade face. This is why 7 ply blades usually have a bigger sweetspot than 5 ply blades. By increasing the amount of layers placed horizontally we are creating an even more dense crossed pattern, thus increasing the sweet spot.

Now to answer your question. Putting the plies at an angle wouldn't work, or wouldn't be beneficial. It's very important that the blade is symmetrical along it's longitudinal axis, otherwise the risk of warping is very big, and with that configuration you will never be able to achieve symmetry. You may have sufficient stiffness in all directions to avoid warping if you use enough layers, but you'd end up with a unsymmetrical blade.
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