Variable pitch and OD for flight (augers)

[hsfarm]

I'm hoping someone her can help me out, I am a drafter who does flat patterns for a company that makes augers, we have a customer who uses variable pitch and od for their flight. I have tried unsuccesfully to draw flat patterns for these, no one else here seems to have an answer, right now we're using a "fudge factor" to get these done. Does anyone know how to do this?

 

[JStephen]

First off, consider that some shapes can't be laid out into a flat shape without some stretching of the material. So you can lay a cone out flat, but not a dome. A helix shaped plate won't lay out perfectly into flat shapes. But if you cut it into short enough sections, you should be able to get close.

My approach would be to take the theoretical auger shape and divide it into narrow radial strips. Each strip is a 4-side section polygon. Calculate the diagonals of that polygon in place, and then layout out a flat figure with the same sides and same diagonals. Doing this repeatedly should generate a shape closely approximating the auger in question. It may be helpful to calculate the points in Excel and then import into AutoCAD. It will still be tedious.

(Note that due to the surface not being exactly developable, that both diagonals can't be transferred exactly to the flat surface.)

 

[unclesyd]

Checkout thread404-185768 there is a reference to following software. I have used it but it looks like it can handle anything you want to build.

http://www.advspiraltech.com/AST/index.asp

 

[PeterCharles]

A passable approximation can be achieved using SketchUp with a couple of plug-in scripts, drawhelix13.rb and JF_unfold.rb.

drawhelix13 creates an outer and inner profile which can be converted into a surface. JF_unfold then creates a flat pattern that can be exported as a DXF flat pattern.

Importantly, there's a free version of SketchUp and the scripts are free.