The last subassemblies that can be made separately are the front and rear wheels. The front wheels pivot on a block called the "uprights" which has the steering's idler link built in. We'll be putting that together now.Parts Required:
The 0.25" panel of steering upright components
The square upright retainer plate from the 0.125" brake parts panel
Colson Performa 4" x 1.25" with ball bearing hubs, QTY 2
1/2" diameter x 1.75" length shoulder screw, McMaster p/n 91259A718 QTY 2.
3/8"-16 x 2.5" standard hex head bolt
3/8"-16 nut and lockwashers
#4-40 x 1" socket head cap screw
Step 9.1 thru 9.4: Identify the parts needed and separate & clean the tabs
3/32" hex wrench
Flat file or sander
#4-40 hand tap with tap wrench
1/2" drill bit or reamer and a drill to put it in
You know the drill by now. You might elect to hacksaw off another one of the 3.5" long rear axle bolts and turn it into a 2.5" one - I did this just because I would have to go out and get two random bolts otherwise.Step 9.5: Tap 4-40 threads into the bottom upright plate
Oh, dear. Tapping threads is something many people dread, and I'm having you do it as the first major fab exercise!
If you have never tapped threads before, I would recommend taking a piece of aluminum and drilling & tapping some practice holes before trying a "production" part! There are some helpful videos on YouTube about how to use a hand tap and tap wrench - one of them is this one by iHeartRobotics
which gets the point across fairly well. If you aren't confident in your hand-alignment skills, you can start the tap in a drill press
(unpowered - just turning the chuck by hand).
I strongly recommend buying a "gun tap
", also called a "spiral point" tap. These clear their own swarf (cut up bits of metal) much better than a straight-flute generic tap you might find at the hardware store, resulting in less breakage. They cost a few bucks more, but they're well worth it. A 4-40 gun tap from McMaster is p/n 2523A444.
Use a legitimate tapping fluid or cutting fluid if you can - I prefer Tap Magic, which comes in a thinner aluminum-specialized formulation. In a pinch, you can use WD-40 too.
Proceed slowly! Or else....Step 9.6: Oops, I accidentally..
It happens to everyone. I was just going too fast here, like driving in a screw fast. Taps break because of applied sideways forces which your wrist has to be trained to eliminate. Flute clogging may also suddenly head to a blockage of the rotational motion, then the inertia if your hand is enough to break the tap.
A general rule for tapping is "two turns in, half a turn out". The half-turn back breaks off any long strings of chips which may have formed, and it helps the tap spread the chips out along the flute.
It's better to be extra slow and conservative than to keep breaking taps into your part! This assembly will work fine with only 2 screws holding it together, but that's alot of broken taps...Step 9.7: Prepare the upright plates for assembly
Find the bottom, middle, and top plates shown in the picture and the retainer plate. There are two large "T-slotted" plates that go in the middle, and the top and bottom plates have smaller square cutouts.
The hex head of a standard 3/8"-16 hex bolt fits into this approximately rectangular area once the plates are stacked together.
First, test the fit of the bolt into the middle plates' T-slots. Many bolts have a manufacturer's stamp on their heads which creates a raised area that will not pass the T-slots. You may need to file off these markings.
Next, insert four 4-40 x 1" socket cap screws through the top plate. These will pass through the two middle plates and then thread into the 4-40 threads you made earlier.Step 9.8: Stack the upright plates around the hex head bolt
Starting with the bottom plate, lay the hex head bolt with hex flats
parallel to the table onto the rectangular divot ( the points do not go into the divot). The width of the T-slot in the middle plates is the point-to-point width of the hex. Stack two middle plates, then stack on the top plate.
Make sure the square nubs that are on one side of the top and bottom plates are aligned. Slide the retainer plate along the bolt until it seats into the stack, upon the square nubs. Depending on how tightly your bolt fits, you might need to wiggle or mallet things into place.Step 9.9: Tighten down the 4-40 cap screws to secure the stack of plates
The retaining plate does not have fasteners - it is kept in purely by bolting the front wheel in, so make sure it doesn't fall off as you do this. Tighten fully
the 4-40 socket cap screws to turn this stack of plates into a solid block.Step 9.10: Verify that the steering kingpin shoulder bolt clears the holes in the plates
Take the shoulder bolt that will be the kingpin and slide it through the stack of plates. It should either slide loosely through, or require at most thumb pressure. If it doesn't clear, it will generally just get caught on something and will not move.
If this happens, you will need to use a 1/2" drill bit or reamer to clean out the hole.Step 9.11 and 9.12: Clean out the 1/2" bore, if necessary, but don't try to Superman-grip the upright as you do so!
Even though there looks like a tiny amount of material in the way, your drill bit will likely catch and dig in very quickly because it is all at the periphery. Then the entire upright will suddenly rip itself away from your Superman-grip and may or may not mill out a small portion of your hand in the process.Put the upright in a vise or clamp it to a bench
before drilling out the hole. Proceed slowly with the drill and don't let it catch and chip around!Step 9.13: Bolt the front wheel on
Take a 4" Colson and slide it right onto the 3/8" axle. Secure with a nut and lockwasher, or locknut. Tighten this well, because this is your front wheels. At least 3/8 turn past flush-tight is recommended.Step 9.14: Make a mirrored assembly
As with many things on Chibikart, there is another side to the problem. Make a mirrored assembly - this should be identical save for flipping the bottom upright plate around!
After these are done, put them aside and clean off your work area. The rear wheels are the single most complex fabrication step and you will be using quite a few tools.