the Miniature Turbojet Engine Rendered in 3D

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Closeup of where we are now ...

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If we extrude these cross-sections about the shaft axis,
one obtains the upper and lower bearing races. In my soft-
ware, this is known as 'lathing'.



NOTE: If these cross-sections were circular, one would obtain con-
centric 'hoops'.

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Adding a little color and returning the single ball bearing
back into the picture.

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Duplicating the ball a multiplicity of times about the shaft axis
gives:

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adding these to the picture ...

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While working on a set screw, I inadvertently selected everything else,
deleted them, and saved 'over top of' my last revision. All my work
since my last (saved) revision is gone.

I lost my glow plug, my bearings, my ubc, and my fuel nozzle.

Needless to say, I was a bit frantic when I realized what I had done. This
about 'sums up' how I felt when I realized what had happened.

(c.t.)

Fortunately, due to post processing, I saved 2 parts separately; the
bearings and glow plug. So, I only have 1/2 the work to redo. In the
above pic, you can see I already successfully restored the bearings
without having to redraw them. I did have to scale and translate them
back into their proper positions, though.

Hints and Kinks

Do the following or be sorry someday that you didn't.

1. save each completed part individually when finished and
2. start a new assembly revision after each part has been
   completely drawn and saved.

Live and learn ...

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Glow plug and both 'for' and 'aft' bearings restored.

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I had to redraw the 'ubc', and here is the screw that
caused me all my grief.



Since I am in 'redraw mode', I have changed its head
to an internal hex socket type.

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'ubc' is shown in position.

There are threads in the 'ubc' sleeve and also in the
compressor impellor. The set screw 'threads'
through these and 'butts' up against the engine's
shaft. In the drawing, there is no 'flat' at this shaft
location, but it may be a good idea to add one.



One can barely pick out the blue speck here, which is
the set screw.

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Notice the reflection of the 'ubc' and pin on the inner
surface of the compressor housing 'horn'.

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I've been using a simple piece of software as a 'sketchpad' for some
of my notes. It can do quite of few things, is simple to learn, but doesn't
have a 'snap to endpoint' or 'snap to center of circle', etc., and some other
'high powered' tools that I am used to using.

The plans give a dimension 'across flats' for a nut.

I was thinking,

Pretend you have only a straight edge and compass (neither protractor,
nor triangles).

How would you draw the required hexagon?

PS You can use a piece of software for this, but can only use
functions that a straight edge and compass can perform.

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1. draw a horizontal line and mark off the 'across flats' dimension

2. draw a circle of some radius at each end of the horizontal line. The
radius must be 'large' enough that the circles will intersect (cross) at two
points. Connecting them, one obtains a line that is perpendicular to the
horizontal one and also 'splits' it in half (or subdivides it into two pieces).
The midpoint is naturally, point c.

NOTE: technically, the 2 end lines are perpendicular also to the
horizontal one and can be 'erected' in a fashion similar to that just
described.

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We know the width 'across the flats', but we do not know the
width of the flat. That is why I drew the vertical (red)
lines of arbitrary length. We will now determine this.

Draw a circle, centered at c of some radius whose length is larger
than d/2. Where this circle crosses the horizontal, label point, a.

At point a, draw another circle of radius, rac. Note where it
crosses the previously drawn circle and label it point, b. Now
draw the line segment, ab.

Triangle, abc is an equilateral one; all sides are of equal length
(prove it to yourself). It is also equiangular; each interior angle is 60°.
We now need to 'bisect' angle acb in order to get 30°.

As before, draw circles of the arbitrary (but equal) radii at points,
a and b. Draw a segment through the two points where they
intersect. This segment not only subdivides line segment, ab,
in two, but also 'bisects' angle acb! Furthermore, when this segment
is extended, 'lo and behold', it 'includes' point, c.

We now need to extend the left vertical line (shown in red),
up so that it intersects the 30° line through c. This determines
the radius for which we seek.