TARDIS II: Altitude Axis Housing

Bill Volna's Retirement Sandbox

This is the housing for the altitude axis bearings and spindle asssembly. The aluminum casting was designed using Shark FX software.

Make Core Box

Make Pattern

MAKE CORE BOX

A significant difference between this core box and the earlier Tee Casting core box was its lack of main axis symmetry. This made it necessary to fabricate a complete, two-sided box, because two half-sided cores could not be cemented together for the casting, as was done for the Tee Casting.

The following pictures show this feature with its several fabrication challenges. Replacement 12 x 24 inch jaws for the mill vice proved very helpful to produce similitude in the two halves. Fabrication took eleven months of spare time.

Fig. 1 Sawing half-circle pieces.

Fig. 2 Sawing half-circle piece completed.

Fig. 3 Fixture for sawing half-circles.

Fig. 4 Fixture for cutting inside radius.

Fig. 5 Completed cut.

Fig. 6 Attaching driver plate to glued stack.

Fig. 7 Fixture plate lag bolts.

Fig. 8 Fixture plate and glue-up ready for lathe.

Fig. 9 Tightening the chuck.

Fig. 10 Initial cutting on the stack.

Fig. 11 First internal cut on the stack.

Fig. 12 Custom-made radius tool boring bar.

Fig. 13 Indicating for a perpendicular cut.

Fig. 14

Fig. 15

Fig. 16

Fig. 17

Fig. 18 Side arm grain pattern.

Fig. 19 Fly cut for match.

Fig. 20 Super structure start.

Fig. 21

Fig. 22 Bottom view details.

Fig. 23 Setup for fly cutting core box edges.

Fig. 24 Alternating grain structure and layer alignment key.

Fig. 25 Finished core box.

MAKE PATTERN

A total of about 500 pie-shaped pieces of pine (aged for 3 years) were cut for this pattern. Then they were glued together to create semicircular polygons, as shown in previous pattern work. After gluing, they were joined and planed flat, parallel, and of constant thickness. The glues, used interchangeably, were Elmer's Professional and Titebond Two. There was no significant difference between the two brands.

Separate stacks with changing diameters (by design) were first glued together and turned on a lathe. To achieve overall coaxial registry, a 1/4-inch pilot on one piece engages a mating cavity on the adjacent piece.

Fig. 1 Stacks of glued polygons next to patternmaker, Bill Volna.

Fig. 2 Stack of layers ready for review, with CAD drawing.

Fig. 3 Both halves with trimming completed.

Fig. 4 Note: The radial, rather
than the tangential, wood grain
on this layer of the pattern
enhances resistance to
breakage during handling in the foundry.

Fig. 5 Layers glued together in
four sub groups to minimize
excessive overhang during
lathe work.

Fig. 6 First subgroup in lathe
with custom face plate to be
attached for added support.

Fig. 7 Face plate nested in a
concentric cavity ready for
lag bolts.

Fig. 8 Tail stock live center
bearing on face plate center
for added support.

Fig. 9 Lathe work finished
on this sub group.

Fig. 10 Face plate removed.

Fig. 11 Turning the large
center section sub group.

Fig. 12 Note the radial wood
grain on the rim and tangential
grain on the body (see Fig.4).

Fig. 13 The use of custom-made
face plates proved very
successful.

Fig. 14 A steel hose clamp was used for lathe work on this longest sub group, instead of gluing two halves together with a layer of Kraft paper in the joint as described in the "tee" casting build.