Draw Enigma rotor

kurtzweber · Postby **kurtzweber** » Thu Jan 08, 2015 11:02 pm

Hi!

I need to reproduce in InkScape an Enigma rotor to have it laser-cut by a service.
I'm working on it using old photos as reference but I'm stuck drawing the following elements:

http://users.telenet.be/d.rijmenants/pi ... rotor2.jpg

I need to draw both the external disk and the internal ratchet... I considered the use of plugins but I wasn't able to find a suitable one so I'm trying to combine simple forms (circles...) to get the result. Which is in your opinion the best way to draw the two elements? For example for the external one, I tried this way:

but I can't correcly combine the circles...
Thanks a lot!

tylerdurden · Postby **tylerdurden** » Thu Jan 08, 2015 11:59 pm

You might also consider some of the free cad programs found online, but for now...

Using tile clones, you can make a repeated pattern in a circle. See Tile Clones, Tricks in the manual.
Using a bit of simple math, you can make guides to assure precision for the primary segment. See the manual on guides, and the release notes on the latest version for improvements on guides.

Lazur · Postby **Lazur** » Fri Jan 09, 2015 12:43 am

Hi.

There should be 26 repeats on the disk pattern?
360°/26 can only be replicated as 13,846°, which in the end would produce 359,996° if tiled clones is used.

This case instead of using a tile construction, I would suggest using a pattern along path live path effect if possible. Meaning, if you know the shape of that "toooth profile" unbent.
Or are those supposed to be constructed by circle arcs?

For the inner 26 circles, because of that angle rounding problem I would probably use translation instead of rotation.
You can draw a polygon with 26 nodes with the * tool, which you can snap to the small circles.

Or use the extrude extension in combination with pattern along path lpe/extension, to place them at once.

-By meaning circles, I would use the * tool again, to draw polygons; 26gons would be the best, because they would also represent rotation by the node's placement after the translation. After drawing the polygon, converting it to path (Ctrl+Shift+C) and setting its nodes to smooth it will be more accurate than if drawn with the ellipse tool.-

tylerdurden · Postby **tylerdurden** » Fri Jan 09, 2015 1:33 am

Also simple using the star tool:

: Erotor1.jpg (145.86 KiB) Viewed 3053 times

Another 26 point star could be used to snap the small circles in the pattern.

hulf2012 · Postby **hulf2012** » Fri Jan 09, 2015 1:44 am

Hello,
I wonder if it's somehow critic the shape of the teeth, also.

The star tool can make a very good aproxiamtion of what you want, around the gear.
There is an extension to make gears, in the render menu. And I remember to see a live path effect to make gears too, maybe in Ponyscape, Inkscape 0.91 or an special version.
The array of circular holes seems to be mis aligned with the teeths. For that you can use the clone tool, but follow the instructions that appear here:
If you have problems:
1.- Post a sample (or samples) of your file please.
2.- Please check here:
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/index.html
3.- If you manage to solve your problem, please post here your solution.

Lazur · Postby **Lazur** » Fri Jan 09, 2015 1:50 am

^--- That gear lpe is in the stabile, as far as I know it was one of the first.
Though it doesn't represent a shape in function.

ragstian · Postby **ragstian** » Fri Jan 09, 2015 3:08 am

Hi.

A lot of good suggestions here!
My method; use parametric curves and plot the function as seen here;

(Click Image for larger version.)

Here the profile is just a sine wave - as I am "mathematically challenged" I'll let
others work out the function for the teeth profile on the "real thing".
Plotting the curve on top of a photo - the curve might be "good enough"?

Chime back if any interest in the function to plot the inner "cog" wheel (here in green).
The green curve can be "smoothed" by increasing the number of terms in the
fourier series or - strangely enough - lower the number of samples to be plotted.

Use this to cut and paste to the parametric curves dialog box:
for the X-Function;

Code: Select all

cos(t)+cos(t)*(1.0/25)*sin(t*26.0)

for the Y-Function;

Code: Select all

sin(t)+sin(t)*(1.0/25)*sin(t*26.0)

Good Luck
RGDS
Ragnar

kurtzweber · Postby **kurtzweber** » Fri Jan 09, 2015 5:19 pm

Guys,

thanks a lot for your good suggestions! You helped me a lot!

Lazur · Postby **Lazur** » Sun Jan 11, 2015 2:38 am

Lazur URH wrote:Hi.

There should be 26 repeats on the disk pattern?

Oh I overlooked enigma and thought of a regular mechanical part.

Couldn't take use of the pattern along path, but the translational positioning did work with circles.

ragstian · Postby **ragstian** » Fri Jan 16, 2015 4:22 am

Hi.

My original post updated as the formula in original screen-dump contained an error.
Added code to enable cut and paste from the page to the Inkscape Parametric Curves dialog as well.

RGDS
Ragnar

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