Front axles, Frame, Welds

Front Axle Spindles

Here are the two finished spindle/fork assemblies which allow the front tires to turn. The spindle is 4" long and rotates in the fork, on a 5/8" Grade 8 bolt called the Kingpin. The kingpins will have a cotter pin installed at final assembly to keep the front wheels from falling off :)

Assembled spindles and forks - click to enlarge

The issue becomes - how do you mount the spindle/fork onto the frame and the wheel?

My initial assumption is reflected in Option 1, where the fork is welded to the frame and the spindle to the wheel. Somehow this option feels more natural for me.

Mounting option 1

 However there is another alternative, actually inverted - the fork is welded to the stub axle and the spindle to the frame. The reason I am considering this option is because I will actually get more travel out of the steering this way.
With Option 1, with the Steering Arm welded to the spindle (on the face towards the rear of the kart) pushing outwards (turning wheel towards center of kart) is no problem, but when pulling inwards (turning wheel out) the Steering Arm will hit the fork, limiting steering travel.

Mounting option 2

 I will need to so some soul-searching before welding these on 'backwards' but it may well be the best way to go.
Of course in both these images, the stub axle needs to be cut, and is shown with a KPI of zero (just for demonstration). On that note, however - my machinist friend (who has worked on race cars) tells me a zero KPI is perfectly okay - since this goes against everything I've read about go kart steering I will have to do further research, but am fairly sure I will still be including a healthy KPI in the final design.

So this is kind of what I'm thinking in terms of mounting. Again, just a mockup, it will be very different.

Top view

Steering mockup. Includes threaded rod with Heim joint, does not include Steering Arm from fork to Heim joint. 

Frame design and welding

Skipping past all sorts of design, measurements, ensuring everything is square and level (about 12 hours worth) here's the basic frame finished up. It includes the rear axle, motor mount, and narrowed section for the front tires to pivot into (See Top view, above)  

 

  

Now I'm sure some are wondering why the motor mount plate is behind the rear axle. It's a straightforward answer - as with lots of things on the kart, it's a compromise. 

At a #50 chain you need about 19 inches (center to center) between the rear axle and the motor's axle. Putting the motor in front of the rear axle means the the kart has to have a stupidly long wheelbase - motor & driver - which would cause a poor turning radius. The benefit would be that the top of the chain is tight (optimal) compared to the situation we chose where the bottom of the chain is tight (not quite as optimal but better than vertical or on an angle)

So we keep the kart a more reasonable length for steering and have less issues with chain tensioning as in a vertical mount system (engine above rear axle, which we seriously considered)

In the end I think it'll look a bit funny, but that is okay with me.

Sample welds

Admittedly I cherry-picked the welds to show here, but the others aren't bad either. No porosity or cracking which I can see. In some cases I burned holes through the 0.100" tubing, which I welded shut again - I'm not happy about it but it should be okay.

Motor mount plate welds:

The motor mount is 1/4" plate welded to 0.100" tubing. The thickness difference made welding interesting - I turned my welder up one setting higher for current and turned the wire feed up a bit. I carefully spend most of the time pouring heat into the plate before quickly detouring onto the tubing to make the joint, and repeat. I think they turned out really well.

I think this is the weld I'm most proud of.

 Not sure if I got good penetration? Check out the heat colouration on the opposite side of the welds above - I'd say I got the plate hot enough! (except the upper-left weld I suppose)
I'm not expert but I don't think I have anything to worry about here. It's possible I should complete all the weld beads, but I get the feeling that the current amounts are strong enough; this plate is not coming off.

Heat-coloured motor mount plate

Frame front section:

0.125" wall (all fully visible pieces) welded to 0.100" remainder of frame. 

1/4" bar welded as a fillet inside the front section to help resist lateral forces.
Welds appear disjoint because I did them in three sections to try to reduce heat warping (even with tack-welding)

Frame height offset:

Not so obvious from the above pictures is the offset I have designed into the frame. It's goal is to ensure the center of the rear axle lines up with the center of the front axles. 

Now I'm not sure exactly why that's important but I was informed that it is, and it sounds reasonable.

As you can see the rear axle sits about 1.5" from the top of the frame, so 2.25" from the center of the frame. If we extended this frame forwards the front tires would be 2.25" off the height of the rear tires.

Offsetting the forward section of the frame by one frame-width (1.5") gets us close to our goal without any complicated setup. The remainder 3/4" we plan to account for when welding the front spindles.

Frame offset - note the kart is unfortunately upside-down in this image

Another view of frame offset

As you can perhaps see the front tire (shown adjacent to rear tire only for this explanation) basically lines up with the height of the frame in the forward section.

 

Same image as above with a different perspective. See how the axles can both be mounted in a reasonable fashion?

Naturally the fork/spindle will be installed between the front tire and the frame, these pictures are for illustration of the purpose of the frame offset only.



Here's one last mockup of what she will look like, including the seat I purchased.
Please note that this mockup sucks, I hope she will be much more attractive in the end.

This week
-buying steel for seat mounting
-looking for a steering wheel and any additional steel for mounting it
-researching KPI further
-buy 0.045" tips for the 0.045" flux-core wire I purchased - neither my local Lowes or Rona carry them. In fact, Rona carries no welding supplies of any kind - a fact three of four Rona agents were unaware of. [Sigh, no, welding tips are not dangerous 'like bullets' Rona employees. No, I do not want soldering supplies. No, trust me, it's not in the "hardware" aisle, stop asking me to look there]

Steering wheel spindles

So I was on the lathe again. The idea is to make a bushing that I can weld to my frame that will hold the steering wheel shaft in two places along the shaft, allowing it to rotate but holding it steady otherwise.

The shaft will have two 'washers' welded on either side of each bushing to keep the shaft from sliding through the bushings.

I started with 1.25" dia by 2" long solid bar. Faced and drilled out progressively to 1/2" as with the front axle spindles - mainly because 1/2" is the largest bit I happen to have.

Then I bored the hole larger, to around 0.65" all the way through. Finally I bored 1/2" deep holes into each end that are wide enough to house the 5/8" bushings.


Here you can see the progression from stock to finished product.
I will be cutting the bronze bushing (on the right) in half, putting half at the top and half at the bottom. Also you can see the zerk (grease nipple) and the hole which I drilled and tapped which will deliver grease to the volume around the shaft.

The zerk is threaded in, and the bushing halves were driven into the spindle.

The bushings are a little loose, as I am still finding it difficult to get precision results with the boring bar - it seems to flex in varying amounts which depends on how much material I try to take off, making all of my cuts inconsistent. e.g. 60 thou movements take off about 60 thou, but 40 thou movements only take off about 25 thou. Need to talk to a machinist about this issue.

Lastly here's the bushing with the steering column through it. Spins like a dream. As you can see I turned down the steering column to nicely fit the bushings - a most unpleasant task of which I have no pictures.