Building Hidden Wheel Retainers
In Scale Modeling, the wheels often have hub caps. All too often, the common wheels we normally use don't
allow adequate clearance for the "store bought" hardware available we use to mount the wheels. So, the
solution is actually a simple one, but requires a bit of soldering and tube cutting. But don't worry, it's really
not hard, and after all, we're modelers, and making things is what modelers do, right? Here's how the whole
process works.....

For the smaller Park Flyer type airplanes I fly, 1/16" and 3/32" wire landing gear axles are typically sufficient,
but the common light foam wheel sizes come with holes drilled in the hubs for 1/8" or 5/32" wire axles. To
make the wheels work on the smaller axles, one or more spacers will be required to re-size the hole.
Typically, if you have 3/32", 1/8", and 5/32" O. D. brass tubing on hand you'll be in good shape. And
typically, only 2 sizes of washers will be needed; a #2 washer fits the 3/32" O. D. tube, and a #4 washer will fit
the 1/8" O. D. tube. The spacers are cut from various sizes of brass tube to the proper length using either a
small tubing cutter, or by rolling the tube under an X-Acto knife blade to score it, then break it off.

The way the system works is to retain the wheel on the axle by way of a washer soldered to a brass tube,
then the keeper is retained on the axle by way of a single wheel collar on the inboard side of the wheel. This
way, after the hub cap is glued in place, it won't have to be removed should the wheel need to come off for
any reason.
Here are the tools you'll need to get the parts made up.
Cut the appropriate sizes of  brass tube to length to fit the
axle to the hole size of the wheel. The bearing tubes should
be cut to the width of the wheel hub. The smallest tube
should be cut approximately 5/16" longer then the width of
the wheel hub to accommodate the washer being soldered to
the out-board end, and the width of the wheel collar on the
in-board end.
 
Make up a drilling jig by drilling the appropriate size hole in
a piece of scrap wood and slip the axle tube into the hole,
leaving about 1/32" protruding. Slip the washer over the
tube and solder in place using a lead free solder such as
Stay-Brite.
 
Remove the tube from the jig. Then using a Dremel rotary
tool with a Cut-off wheel, grind a slot in the other end of the
tube to receive the set screw in the wheel collar that will
hold the whole thing in place. Clamp the tube lightly in a
vice to cut the slot. Don't over-tighten the vice or it'll crush
the tube and it won't fit over the axle.
Now that the axle assemblies are prepared, slip the
bearing tubes over the keeper tube, fit all that into the
wheel and slip the collar over the inboard end. Tighten the
set screw just enough to prevent the collar from falling off
the tube. And with that, the wheels are ready to mount on
the axles.
To mount the wheels onto the model, cut the axle to length, just enough so that it won't
protrude past the outside wheel hub. Slip the wheel assembly back onto the axle and
snug the wheel collar.
Now you can make up your hub caps from whatever items you
find work best. I like to use those little plastic seals from
Orange Juice cartons, or for an even more versatile item to fit
those less common sizes, the domed bottom of an aluminum
beverage can can be cut to any size using a drafting Circle
Template to mark the proper size on the aluminum, then
trimmed to size using a scissors.
The caps are glued in place with Pacer Canopy 560 glue, so that in the event that the
cap does need to be removed, the glue can be softened with plain water and the cap
removed without damage to either itself or the wheel.