Front axle spindles; working with Dad

Working with Dad
Last weekend my Dad came up to help me do some planning on the ground; we laid out the steel I had and discussed some of the ideas I had for what I wanted to do.
I found that in designing it by myself I was tempted to consider too many things - since I'm a beginner at this scale of project I kept overwhelming myself with details so I found it really helpful to have a discussion with someone else who is mechanically inclined.

Just like the old days where I'd bond with Dad, each of us with a wrench in our hands :) He's going to be coming up every other weekend for a while so I expect progress to really pick up now! Love you Dad.

Buying additional steel
Initially I bought 20 feet of 1.5" square tube and 10 feet of 1.0" square tube, and some 1/4" plate for the motor mount. After talking with Dad and realizing how much steel this sucker is going to require, I have another 8 feet of 1.5" and 1.0" square, and 14 feet of 2" angle iron (for battery trays).
Probably 70 pounds of steel at this point, though since it's in a large pile it's hard to tell.

Front Spindles
To recap, my front tire assemblies are trailer tires connected to trailer stub axles (a bearing assembly with a 1 1/8" solid steel bar which will be welded to the spindle)
This spindle will be connected to a fork welded to the frame via a kingpin bolt - in my case, 5/8" dia. and 6" long.

It will look something like this. Of course to turn, the stub axle has to turn relative to the fork - it pivots on the kingpin. To provide easy rotation, I'm using two brass bushings for each spindle.
Thus the kingpin and fork remain stationary; the spindle holding the bushings rotates around the kingpin.

If you're wondering why the kingpin is at an angle, that angle is called the KPI (kingpin inclination). It should generally be set such that the kingpin points to the ground where the bottom of the tire is sitting. If this is not the case, it is difficult if not impossible to turn the tires!

Now I need a spindle that will hold the bushings, and is simple to weld to the stub axle. Of course no standard pipe sizes will fit the bushings 1" O.D., so I'll have to fabricate it myself.


What I saw on other go karts was always round spindle, because they use a different bearing assembly than I'm using (more purpose-made for go karts). Welding a round pipe to the round stub axle at this angle will require a lot of angle-grinding and even more patience. (Try and picture the intersection of these cylinders)

My friend Ron looked at me funny and asked why I didn't make square spindles - d'oh! The light came on, and I went to buy two 4" long sections of 1.5"x1.5" solid square bar. Of course this is after I spent $8 on 4" long sections of 1.5"x1.5" solid round bar. Sigh.

$10 for the pair. Cold rolled steel unfortunately - precision I don't need at a cost I'd rather not pay. Luckily the guy at the metal store cut me a break, should have been $20 but he knocked it down because he didn't have hot-rolled to sell me.


So here's the idea (without the angle)

To get the required angle, I will have to grind the stub axle so that it ends in an angle. Thankfully it now only requires a flat surface for the angle, which will be simple to accomplish compared to the complex curve of two intersecting cylinders. Huzzah!



Of course turning a square bar along its axis in a lathe is an interesting proposition for a novice. After a bunch of reading, I changed to a four-jawed chuck and spent several minutes with a dial indicator to manually adjust each jaw - getting the square bar centered within about 2 thou (0.002").


First I faced one side so the cut ends became square to the length of the bar. Turned it around, aligned it again, and faced the other side.
Next a center drill in the drill holder to get a perfect center for the hole. Followed by several very long and boring drilling operations - proceeding through 1/4", 9/32", 3/8", and 1/2"  - drilling through the entire bar in each operation.

Here's what the result of about two hours of setting up and drilling looks like - you can see the circular lines around the hole which are the tool marks from 'facing' the bar to be flat.

Boy that's an awfully small hole - it's only 1/2" and it needs to be 1" to fit the bushing inside!
Now I have to bore the hole larger using a 'boring bar' on the carriage instead of in the drill chuck.
It's a single-tooth cutter that you push inside the hole, taking off at most 0.08" each time (at least 7 passes, each pass is 3 minutes at the feed speed I'm using - and that's only one side!)

Not as early as I could have, but before I'd finished the boring operation, I realized that the hole through the spindle does not have to be 1" all the way through. In fact, it's best if the bushings sit in cutouts that are just deep enough to contain them, and between the two bushings the spindle is just slightly larger than the 5/8" kingpin. This way the bushings are not free to move about the spindle - it would cause serious problems if they moved.

Here's my poorly drawn explanation. It's rotated like 70° from what it should be (on that funny angle) but bear with me.

• The blue area is the forks, and the connection to the go kart frame at the bottom of the image.

• The green area is the kingpin bolt, with head and nut at opposite ends of the fork holding everything together.

• The grey area with black boarder is the spindle I'm machining.

• The brown areas are the two bushings I'm machining the spindle to make room for.

As you see the hole in the spindle does not need to be equally wide along its length!

Here's the first side machined to a hair over 1.00"; small enough that the bushing can't be pushed in by hand.

Perfect!
Note the kingpin doesn't go through since the hole on the other side is still only 1/2" in diameter, the boring bar is too short to do the entire spindle in one shot.

See where I'm going with this?

Now, repeat this process for the other side of the spindle.
Once you do, toss the bushings in the freezer (I happen to have access to one at -40°C) and push them in with an arbor press.

Unfortunately something happened with one of the bushings - it refuses to seat completely. You can see it sticking up here 3/16". However I've realized this could actually be beneficial.
Remember - this square spindle is held up by the wheel, while the fork is pushing down from the top. Thus the top fork will turn on the brass part, rather than scraping on the top of the spindle.
Of course this means what I did unintentionally with this side I must accurately replicate on the other.

Right - this is only one spindle of two I have to fabricate. Total time was probably 5 hours for this part, though I expect the second round will go much more quickly now that I know what I'm doing!

I'm pretty happy with how this spindle turned out, I think it will work well.


Final notes: 
1. I realize the kingpings I have are too short for the spindles I made - there needs to be room for the fork on either end of the spindle, and two nuts to double-nut the kingpin and keep it from vibrating loose. This is good because I should have purchased a better grade of bolt (which I learned *after* I bought these bolts).
That's how it seems to go, buy, learn, buy again.
2. Grease fittings - you need to grease something like this. I have some zerk (grease) fittings that I plan on installing, one per spindle. It's a matter of drilling a hole into the side of the spindle, tapping it and threading the zerk in. The grease will stay in the area between the two bushings and keep everything lubricated in there.