Variable Pitch Auger Creation

Recently one of our customers asked for a workflow to create a variable pitch Auger. Here is one process.

1.             Create cylinder or shaft for auger.
Name parameter for diameter as “D”
2.             Create
workplane tangential to outside surface of cylinder.

3.             Open
“Parameters” and create a new unitless numeric parameter called
“Num_revolutions” and give           it
a value of say, “6ul”.
4.             Create
sketch on newly created plane and constrain endpoint to the centreline of the
auger shaft.                Draw a
horizontal line extending outwards from this point and dimension it with the
value        PI*D*Num_revolutions. Draw a curve or series of lines and arcs to
represent the change in pitch. In     this
example I have used a spline. The other sketch lines are just construction geometry
and the                 dimensions on the
left hand side are just to show the various pitches for each of the
revolutions. This           geometry can
be contructed and dimensioned however you like. Finish the sketch.

5.             Create a new 3d sketch and select
“Project to Surface.” Pick the outer face of the cylinder as the
face, the curve in the 2d sketch as the curve, and depress the “Wrap to
Surface” button. Click OK.

6.             Create a workplane through the
central axis of the cylinder, normal to the tangential plane you      created earlier. Create a new sketch on
this plane and project the endpoint of the wrapped 3d sketch               into it. Draw a line to represent
the height of the flighting.

 7.             Using the “Sweep”
command, select the “Path and Guide Surface” option from the dropdown
list. Pick          the vertical line you
drew as the profile, the 3d helix as the path, and the outer surface of the
cylinder              as the guide
surface. This will create a surface that represents the flighting.
8.             Using the thicken command, thicken
the surface you just created to create the flighting. If this thicken          fails, chances are it is because the
flighting pitch is too small in some area.

The next step could be to split it up into segments to make it manufacturable. If you need ideas on this, give us a call. 

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