King
Pins
I started building the trikes by salvaging
the headsets from old bikes. While this was cheap, and the bearings
provided smooth steering and pretty reliable service, it also took a
fair amount of time and effort to salvage, modify and weld them back
up to a trike. After seeing a friend's trikes, and some "commercial"
ones on the net, I switched to using bushings and bolts. This
method is inexpensive, and very fast to implement, but the durability
might be an issue for sintered bushings compared to roller bearings.
All the steel used, except for actual bicycle tubes and parts,
are made of plain mild steel.
I'll describe both methods that I
used to produce both kinds of kingpins. Pardon the blurry pictures.
Bike Headsets Bushings
& Bolts
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I started with a set of forks
and cut the legs off the steerer tube (the top threaded part). You
can either use a grinder to smooth off and round out the bottom
section where the forks used to be, or you can use a lathe. I
used both methods as determined by what tools I had available
at the time.
I also cut out a 1 1/4"
x 3/4" piece of steel tube, with 1/8" walls. This
will be the axle tube. I make it 1 1/4" long for a
few reasons. First, I want to keep it as short as possible,
but not so short that it is too weak to be able to handle supporting
the wheel axle and 1 1/4" is the shortest that I feel comfortable
with. Also, most BMX wheels with 14mm axles can accommodate
shifting the axle far enough to one side so that it can go through
that length of axle tube and still have enough thread left over
for a wheel nut. This length of axle tube has supported
the axles on 6 of the trikes for well over 7,000 km with riders
up to 260lbs. I also used two small pieces of 1/8"
thick steel plate. They were 1 1/4" long, and the low
end was 3/4" high. The height of the taller end was
determined by using an angle of 15 degrees (or 75, depending on
how you look at it) and cutting along the line. The 15 degree
angle was arrived at by taking some measurements of my front wheels
to determine the king pin inclination.
The three pieces of steel will be welded on the bottom to
form both the proper kingpin incination and the axle tube.
If you are welding, try to stay
away from old 10 speed steerer tubes because their fork assemblies
and head tubes generally have a lot of brazing. The welding
heat weakens the brazing bond and you can have weld failures later
on. Use the forks from kids' bikes or mountain bikes.
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After cleaning the paint off
the steerer tubes with the wire wheel on my pedestal grinder, I
decided how long I wanted my kingpin housings (bike head tubes)
to be, and cut them to size. Then, I briefly re-assembled
the whole assembly by installing the cups and bearings, and reinserting
the steerer tube to determine how much I had to shorten it. The
picture to the right show the head tubes after I machined the
bottom portion round on the lathe. The bottom steerer tube
has also been shortened and the pieces welded back together. Depending
on the weld, you may have to grind the outside of the bead a little
to fit back inside both the lower bearing cup and the head tube
itself. The jig I used to line up the two pieces of steerer
tube was simply to clamp them in a short piece of 1" angle
iron.
When machining the bottom of
the steerer tubes, make sure that you do not remove the small
shoulder that the bottom bearing race presses onto. If you
do, you'll have to weld the race on (not a good option) or weld
small beads on the steerer tube base for the race to sit on instead.
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| Here,
the axle tube pieces are cut and ready to be welded together. Again,
the steel tube is 3/4"OD x 1/2"ID x 1 1/4" long.
The pieces of 1/8" plate are 1 1/4" long, with the
low side being 3/4" and the high side length being determined
by using a 15 degree angle from the low side. |
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In this picture, the axle tubes
and their side plates have been welded together. The one
on the left is sitting right side up, the one on the left, is
upside down to show the bottom. On the left one, the top
edges of the two angled sides will be welded to the flat bottom
of the steerer tubes and will form the proper kingpin inclination.
As a side note, I drilled out
the hole in the axle tube to 14mm at this point so that the axle
tube would accept the BMX axle. Sometimes the welding would
harden the steel and make it more difficult to enlarge the 1/2"
ID. If you plan to use the BMX wheels, it might be advisable
to drill out the tubes first, then weld the side plates to them.
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Next step was to weld the axle
housings to the bottom of the steerer tubes. No fancy jigging
was used as the axle tube was clamped flat, and the bottom of
the steerer tube was held flat against the top of the side plates.
The one on the left has had the axle tube's side plates
welded to the bottom of the axle tube. The one on the right
shows the axle tube in general alignment with the steerer tube's
base, ready to be welded. Nice thing about this method is
that alignment issues are pretty much non-existent.
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| I
build my trikes with direct steering and rim brakes. After
the steerer tubes are welded to the axle tubes, I now get ready
to add the steering and brake arms. The long pieces of 1"
x .064" box tube are where the brake mounts, handle bars and
tie rod will be connected. The short pieces of tube are where
the brakes will be mounted. |
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| To
the right, the long section of box tube (about 14" long in
this example) has been welded against the flat face of the axle
tube's side plate. A bead was run all the way around all 4
sides of the square tube. The side of the box tube is about
1/8" back from the end of the axle tube. |
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| This
picture shows the steerer tube assemblies welded to the long pieces
of box tube. A pinch bolt will be added to the end of these,
and the handle bars will be slid into them. The short pieces
welded to the end of the handle bar mounts are where the brake calipers
will be installed. I used 1" square chair feet to close
off the end of the tubes when I am all done. |
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This is the left hand kingpin
fully assembled. The small tab half way up the arm is where
the tie rod end will be mounted and produces the Ackerman compensation.
The small hole near the end of the short piece of box tube
is where the mounting bolt for the rim brakes is attached. This
design can use an adapter to mount V and U brakes, or it can use
side pull brakes. A 1/4" connector nut is welded near
the inside end of the long box tube, and slit in half. This
is the pinch bolt that will secure the handle bars.
Two notes:
- disc brakes can be used with this design by simply adding
the mounting points for the caliper, and omitting the short brake
tube mount
- the Ackerman compensation is about 11 degrees, which is
pretty much the standard angle I use on all my trikes. I
found that the Ackerman compensation isn't that critical to the
trike's handling because even at low speed, the weight shift to
the outside wheel on a corner is enough to all but render the
need for Ackermann compensation a moot point. What IS more
important is proper toe-in alignment, center point steering, and
enough rake or trail. While lack of proper Ackerman compensation
can make the steering heavy at low speed, and cause increased
tire wear at low speed, it's effect is minimal, IMO. YMMV
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| Here
is a front view of the left hand king pin with the wheel stuck in
it. With the BMX wheels, I loosen the axle nuts and shift
the axle as far to one side as I can. This usually produces
about 2" or more axle sticking out one side of the hub, with
a small stub sticking out the other side. The long-side axle
slides all the way through the axle tube, and you then can spin
a wheel nut on to the axle end to tighten the axle into the axle
tube. The way the steerer tube angles up and to the left is
how the king pin inclination is maintained. |
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| A
side view of the left hand king pin assembly. The steering/brake
tubes are welded basically at right angles to the steerer tube in
this example, but I've also used 45 and 60 degrees. |
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This method can also be used with
the new threadless headsets as in the examples of trike like Catrike,
and many others.
Bushings & Bolts
I switched to using bolts and bushings
because once the little jig is made, it takes about 4 minutes to make
a kingpin and axle tube assembly vs more than an hour using bike head
tube assemblies. Instead of using sintered brass bushings, you
could also use high molecular density plastic bushings, either home
made or commercially bought. These are much longer lasting than
the sintered bushings, but they can make the steering feel a little
"sticky" or heavy.
| First thing,
was I made a small jig out of a few scrap pieces of angle iron.
The cardboard it is sitting on (along with the rest of the
pictures) is just to give a little contrast so it's easier to see.
The angle the two pieces are welded together at is 15 degrees,
which produces center point steering based on the way I built the
kingpins and the dimensions of my front wheels. |
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| The main kingpin
ingredients are a grade 5, 1/2" dia bolt, about 3 1/2"
to 4" long, and the familiar piece of 3/4" steel tube,
with a 1/2" ID. I cut these axle tubes about 1 1/4"
long as well. Prior to welding the bolt to the axle tube,
I use the wire wheel on the bolt head to take a little of the coating
off. |
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| I place the bolt and the steel
tube on the jig. I use a nut on the end of the bolt to help
keep the bolt parallel to the jig in the vertical and horizontal
planes. A small piece of angle iron is welded to the top of
the jig to act as a stop for the axle housing. This little
"stop" ensures that all the kingpins made with this jig
have exactly the same orientation of the 1/2" bolt to the axle
tube. Once the bolt and tube are in place, I clamp them down
using C-clamps and vise grips. |
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| Here are the parts, clamped in
the jig, and ready to be welded. Nothing more than this is
required to make essentially identical pieces, every time. |
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| Less than a minute later, the
bolt is welded to the axle tube at the desired angle (15 degrees
in this case). The bolt head is welded all the way around
to maximize the strength of the bolt-to-axle tube joint. I
use grade 5 bolts because I'm sure the welding process weakens the
bolt a little, and the grade 5 rating is massive strength over-kill,
even if it is a little weaker. The kingpin is done. |
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| Two kingpins, one before welding
and one after. |
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New kingpin with all the parts.
The numbered parts are as follows:
- 1/2" NC nut, Nyloc preferred
- 12 mm SS flat washer (better fit on a 1/2" bolt than
a 1/2" washer)
- 3/4"OD x 1/2"ID x 1"L sintered brass bushing
- 1"OD x 3/4"ID steel tube. Length to fit
bolt used.
- Same as #3
- Same as #2
- Grade 5, 1/2" NC bolt. I use 3 1/2" to
4 1/2" long.
- 3/4"OD x 1/2"ID x 1 1/4"L steel tube. Drill
out to match axle size.
In the 3D drawing, part of the
cross member is installed on the side of the kingpin tube. I
leave a 1/2" space between the bottom of the steerer tube
and the cross member.
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| New kingpin with washers, bushings
and nut installed in 1"OD x 3/4"ID steel tube. |
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Here, the new kingpin assembly
is fastened to the axle end of a 20" wheel. While it
may not necessarily be required, I also drill and tap a small
hole in the back of the kingpin tube and install a grease nipple
so I can charge the kingpin tube with grease to help lubricate
the assembly. All that is required now, is to weld it to
the crossmember and attach the brake hardware and mounts.
This style of kingpin is very
fast, inexpensive and easy to build, and because it is relatively
compact, it can also be used inverted without having to worry
about the kingpin tubes hitting the spokes.
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Top
King
Pin Inclination
Under construction . . .
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