modeling a iaito.....

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modeling a iaito.....

bboett
Hello!
since confinement added more daily training as usual, my old iaito got more used too, and since i use it quite intensively anyway, and its now 27 years old, yesterday the saya broke down in a lot of splinters, a fair number of them inside my hand... :'(
so i looked for a new one, directly from Japan, atm, i was told, its very complicated.... translated form japanese: impossible.....

so i turned to a local woodworker, who has a CNC machine, and he told me, do the model, and i feed it the machine....

well..... how do you model a curved blade???

i have measured the thickness and transversal shape of the blade, which slowly decreases over the length, and the arcing is not fix wither, the blade curving more at the tip than at the handle.....

if you have any tip, on how to start on this and how to handle it?

BTW:
iaito Iaido training blade, dull, made of some aluminium alloy
Iaido: japanese martial art of fast drawing a sword
saya: sheath for a japanese sword

thanks in advance

ciao

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Re: modeling a iaito.....

Parkinbot
It is not so difficult to model. In principle you need a function that
parametrically describes the iaito's cross-section as a polygon, with N
points (i.e. a 2D-shape) and another one that describes the curve along
which this parametrized shape will be extruded (by sweep). If you further
employ an interpolation scheme like nSpline or Bezier, it is enough to feed
just a couple (4 or 5) of polygons into the scheme ...

But to be honest, I doubt that your woodworker will be able create a steel
knife with a CNC. The art of black smithing has a very long tradition.



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Re: modeling a iaito.....

bboett
hmmm....
so in the function i need to compute the crossesction at each point of the sword?
i have no idea on how to use bezier in openscad??
rotate_extrude will want to extrude along a circle? and linear_extrude along a line..... neiter will do the job?

and the work worker only has to engrave the shape of the sword into wood, no need to work on steel?
ciao
Bruno

Am Mi., 15. Apr. 2020 um 10:42 Uhr schrieb Parkinbot <[hidden email]>:
It is not so difficult to model. In principle you need a function that
parametrically describes the iaito's cross-section as a polygon, with N
points (i.e. a 2D-shape) and another one that describes the curve along
which this parametrized shape will be extruded (by sweep). If you further
employ an interpolation scheme like nSpline or Bezier, it is enough to feed
just a couple (4 or 5) of polygons into the scheme ...

But to be honest, I doubt that your woodworker will be able create a steel
knife with a CNC. The art of black smithing has a very long tradition.



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Re: modeling a iaito.....

Parkinbot
linear_extrude() and rotate_extrude() will not be very helpful for your
"specific" use case.

I can guide you for further steps. The following code is an example for a
parametrized shape function:

function swordCS(D=100, d = 10, f=.8) =
[[-D, 0], [-D/2, f*d], [0, d], [D/2,  f*d], [D, 0],  [D/2, -f*d], [0,-d],
[-D/2,-f*d]];

you can use it (in principle) to describe a sceleton to be skinned by a
sweep()-function:

for(i=[0:4])
  rotate([0, i*i, 0])
  translate([0, 0, i*200])
polygon(swordCS(-i*15+100, 7-i));

<http://forum.openscad.org/file/t887/swordCS.png>


the sweep function expects a list of polygons. You need a second function
that builds this list. It calls the parametrized shape function and places
the shapes into 3D by applying a translation and and a rotation (note: all
"unknown" functions like Ry, Tz and vec3 are provided by a libary like
Naca_sweep.scad)


function sword() =
[for(i=[0:.1:4.001])
  Ry(-i*i,   // rotate function
  Tz(i*200,  // translate function
    vec3(swordCS(-i*15+100, 7-i))))
];

finally you call the the sweep-function (also provided by the library)

sweep(sword());

and you get:

<http://forum.openscad.org/file/t887/sword.png>


Thus your full code will be (in principle) as simple as the following:

use <Naca_sweep.scad>  // download from
https://www.thingiverse.com/thing:900137

sweep(sword());   // skin the sceleton

function sword() =
[for(i=[0:.1:4.001])
  Ry(-i*i,  // rotate
  Tz(i*200, // translate
    vec3(swordCS(-i*15+100, 7-i)))) // parametric call
];

function swordCS(D=100, d = 10, f=.8) =
[[-D, 0], [-D/2, f*d], [0, d], [D/2,  f*d],
 [D, 0],  [D/2, -f*d], [0,-d], [-D/2,-f*d]];












 



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Re: modeling a iaito.....

rew
In reply to this post by bboett
On Wed, Apr 15, 2020 at 11:05:08AM +0200, Bruno Boettcher wrote:
> hmmm....
> so in the function i need to compute the crossesction at each point of the
> sword?
> i have no idea on how to use bezier in openscad??
> rotate_extrude will want to extrude along a circle? and linear_extrude
> along a line..... neiter will do the job?

Correct! But... Just yesterday I asked about a specific shape
(parabola) that needed to be extruded (with a circular cross
section). The replies included two different ways to "extrude along a
path"! Check out the replies to my "parabolic tube" question!

        Roger.

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Re: modeling a iaito.....

DanS
In reply to this post by Parkinbot
"But to be honest, I doubt that your woodworker will be able create a steel
knife with a CNC. The art of black smithing has a very long tradition."

If he wants a blade as good as the old style ones (outer part hard steel, inner part soft steel) it isn't going to happen.

But he was saying he is ok with a dull Aluminium blade.  I think if one made that from wood (or wax, or whatever) one could make a mold and do "lost wax" technique at a foundry.  A dull Al blade doesn't require a blacksmiths skill.

On Wed, Apr 15, 2020 at 4:42 AM Parkinbot <[hidden email]> wrote:
It is not so difficult to model. In principle you need a function that
parametrically describes the iaito's cross-section as a polygon, with N
points (i.e. a 2D-shape) and another one that describes the curve along
which this parametrized shape will be extruded (by sweep). If you further
employ an interpolation scheme like nSpline or Bezier, it is enough to feed
just a couple (4 or 5) of polygons into the scheme ...

But to be honest, I doubt that your woodworker will be able create a steel
knife with a CNC. The art of black smithing has a very long tradition.



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Re: modeling a iaito.....

OpenSCAD mailing list-2
In reply to this post by bboett
Most knives are made on CNC machines these days, and while I appreciate and respect the craft of blacksmith (and will never forgive my father for selling my grandfather's anvil), iron, steel, alloys, and heat-treating are very well understood these days, and one can make a quite nice knife, even with just a desktop CNC:

https://www.youtube.com/watch?v=2_DnkEnhZPM

(see the balance of that video series for the actual process of manufacture)

William


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Re: modeling a iaito.....

bboett
In reply to this post by DanS
Hello
Still trying to understand what parkinbot send me :)

I am sorry if i was not clear enough...

I have the blade.... its a training blade in an aluminium zink alloy, and that one is still ok.....
Even after more than 25 years of service ! 
BTW i fear the moment it breaks down too, not having a typical japanese physique a replacement will cost a little fortune.....

What is not ok, and broke down is the wooden thing around the blade....
Saya in japanese, Schwertscheide in german, i thought sheath in english but obviously i am wrong?

But for my iaido training i need that thing.....
So i need to draw my sword in openscad, make a diff with a sort of tube....
But it has to be quite precise.... once the sword is completely inside, the air pressure is thought to keep the sword inside.... so holding the sword upside down, the sword won't fall out (not the only trick in that respect) 
But having the sword rattling inside a wrong saya is, especially at exam time, a no go....
(At least at my level.....)

It takes a learned woodworker 3-4 days fulltime to do such a thing, imagine the price :'(

My woodworker proposed to do it for 30€ if i do all the work :D so i am going for CNC after i manage to model it, and wil learn how to laquer afterwards.....

Ciao

Bruno Böttcher
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Dan Shriver <[hidden email]> schrieb am Do., 16. Apr. 2020, 19:34:
"But to be honest, I doubt that your woodworker will be able create a steel
knife with a CNC. The art of black smithing has a very long tradition."

If he wants a blade as good as the old style ones (outer part hard steel, inner part soft steel) it isn't going to happen.

But he was saying he is ok with a dull Aluminium blade.  I think if one made that from wood (or wax, or whatever) one could make a mold and do "lost wax" technique at a foundry.  A dull Al blade doesn't require a blacksmiths skill.

On Wed, Apr 15, 2020 at 4:42 AM Parkinbot <[hidden email]> wrote:
It is not so difficult to model. In principle you need a function that
parametrically describes the iaito's cross-section as a polygon, with N
points (i.e. a 2D-shape) and another one that describes the curve along
which this parametrized shape will be extruded (by sweep). If you further
employ an interpolation scheme like nSpline or Bezier, it is enough to feed
just a couple (4 or 5) of polygons into the scheme ...

But to be honest, I doubt that your woodworker will be able create a steel
knife with a CNC. The art of black smithing has a very long tradition.



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Re: modeling a iaito.....

Parkinbot


bboett wrote
> how do you model a curved blade???

Wasn't this your question?

In order to model a sheath for a sword you won't get around to model the
sword first. And this is what my code shows.




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Re: modeling a iaito.....

bboett
indeed it was, that's why i wanted to model the sword, even if it is not the purpose to build one?
and yes still measuring my sword and trying to digest your example :D


Am Fr., 17. Apr. 2020 um 00:48 Uhr schrieb Parkinbot <[hidden email]>:


bboett wrote
> how do you model a curved blade???

Wasn't this your question?

In order to model a sheath for a sword you won't get around to model the
sword first. And this is what my code shows.




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