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by:
Glenn McBride
photos: Bert Klassen
illustration: Len Churchill |
MARBLE RACER |
| Get
your bearings with this clever children's toy |
There's no better way to bump into a little adventure than the
road trip. A few times each year, my mother and stepfather would
get in their car for a week of touring Pennsylvania's Amish
country. They always had a starting point and a few favourite
destinations, but freedom of the road means getting off-track
and stopping on a whim, as they once did at an Amish market
in the village of Bird-in-Hand. As an auctioneer, unusual objects
are my stepfather's stock-in-trade, and one such object caught
his eye at this market.
It was
one of those ingenious mechanical toys that's simple but mesmerizing.
Load a handful of ball bearings in the top trough, tip the lever,
and watch as one ball after another zips down the ramps and
spins the pinwheels. My stepfather picked up one for his own
amusement and since then I've built several replicas of this
clever toy contraption.
My plans are fine-tuned
for oak so I recommend using this wood. Other woods can work,
but different densities mean you'll have to adjust angles and
sizes to get a smooth reliable action. And though this is a
toy, the mechanics demand precision—measure, cut and drill
carefully and keep your assembly square. Use 5/8" steel bearings—they
have enough weight to keep the moving parts moving; glass marbles
are too light. I got my bearings at Atlantic
Bearing (905-876-1105) for 65 cents each for a minimum of
20. Remember that small parts, like bearings, make this toy
unsafe for very young children.
Begin by
milling the troughs according to the sequence shown on the plans.
Cut the uprights, box parts and cover plates. Assemble the mitred
box, then cut 1/4" grooves in the box and the base. Glue uprights
to the box and base, making sure everything stands square and
parallel.
Next, attach the side rails,
which are ready-made cove moulding. While they make the machine
easier to load, especially for children, they are optional.
Fasten the upper trough
to the base and box uprights using #4 brass screws. Be sure
to predrill and countersink generous holes since these screws
are small and break easily. Don't use glue. Add the middle and
lower troughs followed by the middle uprights.
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| click
on the image above to see detailed plan |
|
The
project has three sleeve-covered axles: one for each pinwheel
and one for the lever. Drill 5/32" dia. holes for the axles,
preferably using a drill press so they're accurate. This is
especially important for the lever, the most mechanically sensitive
piece.
Install the pinwheels and lever on their axles and sleeves.
If the action isn't smooth enough, you can make fine adjustments
by filing the sleeves a bit, adding a small washer as a spacer,
etc. Cut the brass cover plates for the trough ends and fasten
them with #2 brass screws in predrilled screw holes. A fine
hacksaw blade works well for rough-cutting the brass parts before
final shaping with a bench sander.
All the
brass parts should be easy to find—I bought them at my
local hardware store. The shape of the metering rods is crucial,
so use the bending jig shown on the plans. Install the little
brass guides that hold the rods, and plug the rods into the
lever. Test the action and adjust if necessary.
Then take everything apart
for finishing—I used urethane. Remove any dried finish
from the holes and reassemble. Use screws to hold the structure
and epoxy to hold the axles and sleeves in place. Now there's
nothing left to do but load up the machine with bearings and
get rolling. |
|
Glenn McBride has fun building bearing machines
and other ingenious toys in his Milton, Ont. workshop.
|
| Materials List |
| PART |
SIZE |
QTY. |
| Upper
trough |
3/4"
x 1 1/2" x 18" |
1 |
| Middle
trough |
3/4"
x 1 1/2" x 20" |
1 |
| Lower
trough |
3/4"
x 1 1/2" x 17 1/2" |
1 |
| Lever
|
3/4"
X 1 3/8" X 11 1/4" |
1 |
| Box
sides |
1/2"
x 2" x 5" |
4 |
| Box
bottom |
1/2"
x 4" x 4" |
1 |
| Box
uprights |
1/4"
x 1/2" x 14 1/4" |
2 |
| Long
middle uprights |
1/4"
x 1/2" x 11 9/16" |
2 |
| Short
middle uprights |
1/4"
x 1/2" x 10 3/16" |
2 |
| Base
uprights |
1/4"
x 1/2" x 15 15/32" |
2 |
| Pinwheel
|
1/2"
x 3 1/2" dia. |
2 |
| Side
rails |
1/2"
X 4 1/2" cove moulding |
2 |
| Base
|
3/4"
x 2" x 7" |
1 |
| Guides-brass
|
5/32"
dia. x 1/2"-long |
4 |
| Brass
upper cover plate |
1/32"
x 2" x 2 1/2" |
1 |
| Brass
end cover plate |
1/32"
x 2" x 2" |
1 |
| Brass
small cover plates |
1/32"
X 3/4" X 1 1/2" |
2 |
| Brass
axles |
5/32"
dia. x 2"-long |
3 |
| Brass
sleeves |
3/16"
i.d. x 7/32" o.d. x 7/16" |
4 |
| Brass
metering rod |
0.081"
dia. x 12"-long |
2 |
| Brass
screws |
#4
x 1/2" flat head |
24 |
| Brass
screws |
#2 x 3/8" |
20 |
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