1001 Parcus Road, S.E. Huntsville, Alabama 35803
Fourteen years ago I made a decision to move up from ordinary
workshop puttering to the realm of building a highly detailed and
very challenging model of an Aultman and Taylor thresher where all
features were as detailed and as accurate as I could possibly make
them. This included having all operable elements work such as the
feeder, elevators and straw racks, etc. Little did I realize at the
time how much research and planning went into the building of such
a model. The fabrication of such elements as cranks, pulleys and
wheels each presented their own problems. In writing this article,
I propose to share some of the techniques I have developed in this
case, the construction of a model of a typical agricultural machine
spoked wheel.
A spoked wheel may seem at first to be a simple item, however,
rest assured, to make a small, strong spoked model wheel is not as
simple as it may seem. While other model makers may have their own
techniques, such as welding, casting or carving from solid stock, I
feel that my procedure is easier and has something to offer the
model maker.
In essence, my procedure is to cut and shape rims from an
appropriate sized steel pipe stock, make up spokes in the form of
long, slender screws, and shape, drill and tap hubs and assemble
the wheels on a jig and grind them to give final shape and
dimensions.
I admit that I have the benefit of a South Bend Model 10-K lathe
with accessories that facilitates the procedures I use, however, a
resourceful craftsman can improvise using jigs and simple tools
such as an electric drill to accomplish the same end. Where there
is a will there is a way.
The wheels that I needed were six inches in diameter, flat
rimmed, with two rows of eight straight spokes and a hub which is
illustrated by the accompanying photo and drawings.
The key feature of this procedure is that the spokes are screwed
into the hub somewhat like a bicycle wheel is made. No welding or
soldering is required.
The first step after research and planning is complete in the
machining of the hubs. I recommend avoiding the use of iron unless
you are extremely competent at tapping small diameter holes. Tap
breakage is very troublesome if iron is used. I used aluminum which
worked very well. Brass or bronze is quite good also.
I advise turning all four (or however many you need) hubs on the
same billet at the same time which makes holding the diameters and
shapes uniform by making it easier to generate the same contours on
each of them. Space should be left between the individual hubs to
allow for cut-off and final finishing of the ends.
After the hubs are shaped to one’s satisfaction, the next
step is to use a sharp-pointed tool bit mounted on the crossfeed to
scribe very fine lines around the hubs where the rows of spokes are
to be located. Then disconnect the power from the lathe and by
improvising an indexing setup using the headstock gears the scribed
circles can be divided off for the location of the individual spoke
holes. Bear in mind that most spoked wheels have two rows of spokes
with one row half offset from the other.
In my case I counted off a headstock gear that was divisible by
eight I needed two rows of eight half offset for each wheel. Do not
disturb the setting of the tool bit until all locations are
scribed. I used a small Phillips screwdriver with the bit placed in
the selected gear tooth notches, pulled back firmly but gently on
the chuck until movement was locked, held the chuck firm, and
worked the tool bit via the carriage adjustments across the
selected scribed circles and marked off the hole locations. This
was repeated until the circles were scribed all the way around with
light cross marks. An accurate set of scribe marks now exists ready
for center punching and drilling. No harm is done to the lathe and
the need for an expensive indexer is avoided.
Now the individual hubs can be cut apart and finished being
careful not to mess up the spoke hole scribe marks. I recommend
completing the axle bores and hub end fairings at this time so that
the hubs are completely finished before moving on to drilling and
tapping.
In most cases spoked wheels have the spokes set at an angle so
that the spokes are mounted much wider apart on the hub than on the
rim. This provides rigidity and strength to the wheel. Therefore,
when drilling the holes preparatory to tapping, the drilling should
be at an angle around five degrees from square. A drill press can
be set up by angling the table and using a V-block to do this
accurately and easily. The lathe can also be set up to do it. Drill
the holes all the way through into the axle hole. Doing this makes
tapping much easier.
Upon completion of drillng the next operation is tapping. This
requires a great deal of care and patience. A broken tap can take
much of the enjoyment out of the project. A typical model spoke
size will use a 4-40, 3-48 or 2-56 tap. These are more or less
common standards. If a model is based on a 1:6 ratio with the
full-sized machine using a inch spoke, the model spoke will use a
4-40 tap. The finer the threads, the better. The above taps can
also be had in 4-48, 3-56 and 2-64 respectively. If the model is
quite small other sizes such as 00-90, 0-80, 1-72, 1/16-64, 3/32-48
and British Association sizes 8 and 10 may be used. Small metric
sizes are also available. There should be no problem of getting the
proper scale size.
Be sure to use an appropriate lubricant when tapping aluminum
such as ‘Alumtap’® or some other solution to ease the
strain on the delicate taps and to prevent seizing which is a
problem in aluminum.
Now let’s direct our attention to the making of the rims. My
choice is to use either thin wall or regular pipe. If you use pipe
make sure that it is acceptably round. Not all pipe is. The thick
wall sizes work well when the face of the wheel needs shaping such
as the wheels on late model Huber threshers.
Chuck a short piece in the lathe and true up the roundness a bit
and cut off slices slightly wider1/16 inch than the finished width
of the rim. The lathe cut-off tool works well and is far more
accurate and easier than a hacksaw.
Now using the lathe chuck with the jaws set for inside gripping
I prefer the three jaw universal chuck for these operations since
its accuracy is good enough chuck the rings and lay out for the
spoke holes using the same general technique described earlier for
the hubs. Do not over tighten the chuck so as to distort the
rings.
Turn out a round piece of wood that can be inserted into the
rings to provide support during punching and drilling. With the
piece of wood in place center punch the hole locations and drill
the holes the size of the spokes so that a tight fit is assured.
Drill these holes also at a slight angle to allow for the angle of
the spokes.
Next use a larger drill and countersink the holes. Do not drill
all the way through this time. For example, if the spoke is 3/32
inch in diameter, a 3/16 inch drill is used to countersink, since a
3/16 inch rod will be used to form the spokes.
The spokes are turned from round stock. Cold rolled steel is
very good. In the example just given a 3/16 inch rod is carefully
turned down to the correct diameter and length of the spoke. On the
end opposite the threads turn a head to fit the countersunk holes
in the rims. Thread the other end and cut off the spoke leaving
about inch for a screwdriver head. Hacksaw a slot in the head to
receive a flat screwdriver bit. Also do not cut too much thread on
the thread end. Excess threads spoil the appearance of the finished
wheel. Make all the spokes.
Assembly of the wheel is, in my estimation, easiest and best
done on the lathe by using the universal chuck and the centers
simultaneously. The chuck holds the rim firmly and accurately
concentric with the hub which is carried between the two centers.
The degree of accuracy is approximately .003 inch. The rim must be
properly centered on the hub so the spokes line up properly. Now
insert the spokes and gently finger tighten only enough to take out
the slack. Inspect and make sure that all is well up to this
point.
Now, using a flat bit screwdriver, carefully tighten the spokes
a small amount at a time alternating from side to side and from row
to row. Do not tighten too much at once or in series or the wheel
will be distorted when it is removed from the chuck and centers.
The tension must be kept as uniform as possible around the wheel.
Mentally note or mark the spokes and tighten in a series such as
1,5,11,15,3,7,9,13,2,6,12,16,4,8,10, 14. Do not tighten all the way
the first time. Make at least three circuits and do not over
tighten so as to strip threads or break the spokes.
Remove the wheel and check for trueness. It should be excellent
if the tightening sequence was carried out properly. If it is not
true, loosen and do it again. Remember, the final 1/16 inch or less
will be ground off in the finishing operation.
When you are satisfied with the trueness remove the excess
screwdriver heads by jeweler’s saw, mini hacksaw or by
grinding. If you grind them off be careful not to heat up the
wheel. From now on, heat is your enemy!
After the screwdriver head nubs are all removed and all the
wheels are assembled, final truing (and if needed, shaping) is done
on the lathe. I set up a tool post grinder with a fine wheel and
mounted the wheel being trued on a mandrel chucked in the lathe.
The lathe was set for a slow rotational speed and the tool post
grinder was used to grind down the face of the wheel. The wheel
thus became nearly perfectly round and the traces of the spoke nubs
practically vanished. Finally the sides of the rim are ground to
size. Warning: The rim must not be allowed to heat up during
grinding. If it does the wheel will be ruined. A sponge soaked in
water held against the rim works quite well to suppress the
heat.
If all the above has been done carefully, you should now have a
beautiful, sturdy spoked model wheel.
If you elect to use aluminum for your hubs I recommend that when
the spokes are screwed in they be coated with Loctite or epoxy so
as to prevent electrolytic corrosion with the steel. My first
wheels are now ten years old and there is no evidence of corrosion.
If you use brass or bronze Loctite will help keep the spokes from
working loose.
Now inspect to assure that the spokes did not protrude into the
axle hole area. If so, grind or file them off. Do not attempt to
drill them out.
Lastly, the finished wheel should be thoroughly washed in dry
cleaning solvent to remove oils and films. Do not touch them with
your skin or oils will be deposited, causing poor paint bonding.
Undercoat the hub, if aluminum, with a very thin coat of zinc
chromate primer. Use iron oxide primer on the rest. After drying
they are now ready for painting.
