Digitizing with rotary axis

[kdoney]

I am digitizing a saxophone mouthpiece by reading each Z at each X then rotating the y axis. This gives me a flattened surface in Rhino which I need to put back together by rotating around a center. Any suggestions?

[Dan B]

I don't get it. Could you describe your digitizing process with a little more detail.

Thanks

Dan

[HuFlungDung]

Kdoney, it sounds to me like you need to convert from radian measure, which is the inverse operation that a lot of CADCAM program use to create 4th axis.

If you are going to machine the parts using your 4th axis, I would think you do not need to convert it back to a conventional 3d surface unless you intend to change the offset (ie, your probe tip does not match the tool radius)

However if you want to, then you need to fool around with the degree to radian conversion factor which is 360/2*Pi.

For a rotation of 1 degree at a radial distance of 1" from your 4th axis centerline, the converted Y value would be .0174532", which I derived from 1/57.295778 using the above formula.

So, your Z distances (from centerline) determine the proportion of the above factor which you would use. For example, if the Z measurement indicates that you are .5" from your 4th axis centerline, then the Y value for 1 degree of rotation is proportional which would be .0174532/2

Clear?

[cnczane]

I think it's pretty simple. (Maybe because it's not my problem?)

Seriously, you're getting a flattened model because you misled Rhino.

You don't really have XYz, but R,PHI,z, where R is a RADIUS, and PHI is an ANGLE AROUND the z axis, and NOT a distance.

IF (and I can't afford to buy) Rhino can understand CYLINDRICAL coordinates, you need to tell it that each step in y, is really a step in phi.

How many "Y" points did you take? 360? That would mean instead of Y taking 360 values from 0 to whatever you said was the last one, PHI would take on 360 degree values, 0, 1, 2, 3, ..., 359.

If Rhino does NOT understand cylindrical coordinates, you can write a program to convert your r,phi,z data points to (real) xyz:
x = r cos(phi)
y = r sin(phi)
z = z
(I'd try it in a spreadsheet, although I admit I don't know what a points.dat file format looks like.)

[Graham S]

Assuming you had the rotary axis pointing in the x axis direction then x = x.

Then the Y and Z co-ordinates measured need to be converted to y and z for the model

However both the origional y and z values are required to find the proper y and z values in space as neither of them defines the position exactly. y only defines the angle and z the radius from the axis of rotation. Polar coordinates as mentioned before!

The angle will be given by theta = (Ry/360) X Yd

theta = angle
Ry = Range over which Y was moved that corresponds to a full rotation
Yd = Y value digitized.

Once the value of theta is known the final y coordinate can be found using the theta angle found.

y = Zd. cos(theta)

Where Zd is the digitized Z.

Now the z value for point cloud can also be found.

z = Zd. sin(theta)

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As an aside:

A point file is normally just a set of coordinates in a text type file

0.00 2.00 3.00
0.20 0.34 3.45

etc in the format Z, Y, Z. Turbo cnc outputs X0.00 Y0.34 Z0.45 etc and the letters have to be stripped out. Rhino allows simple point file input.

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kdoney, if this is all gibberish then send me a points file (or part of one) and I will knock you up a spreadsheet and check it in Rhino for you, if it is commercially sensitive feel free to digitize something daft.

Cheers,

Graham

www.indoor.flyer.co.uk/personnal.htm

[Carver]

If you are going to digitize "manually" in Rhino you need to rotate your construction plane a corresponding amount to the rotation of your original as you move it for digitizing. This will place the points in the proper place as you input them.
Also, do not try to build a set of massive construction points as though you were doing a fully digitized surface.
Aquire only the points that you need to dictate surface creation in Rhino. I.E. to create a circle you really only need three points on the circle, not 60. Use Rhino to Create the surfaces and your input to diminsion and place them.
Any method that "wraps" the flat surface will distort it and be inferior to your real needs.

Best of luck, Phill

[Graham S]

So how do you rotate the construction plane by the corresponding amount?