I spent most of last weekend in the machine shop. Progress has been slow but steady. Wheels have not been mounted yet, but hopefully they will be soon. We worked on preparing the rear wheel supports for welding. Our team welder, Jonathan, tacked those up and is working on them this week.
I tried to assemble the front suspension, but ran into a real world vs. virtual world discoveries. There was too much play where the tubes attach to the truss, making it very easy to pinch the thrust bearings at the knuckles. The knuckles (which support the front tires) need to spin freely or turning the sculpture will be impossible.
So we had to hold the attachment points at a specific distance and maintain the alignment between the top and bottom tubes.I was going to add tubular structure, but realized that the front axles run right through the area where the reinforcement would be located. We needed a brace that had a clearance hole in the middle of it. Jonathan suggested using plates instead of tubes. Great idea! Now, we just needed to make them. This sounded like a job for the Tormach!
I took some measurements, modeled the part in Fusion 360, and then created the CAM program to carve them out.
The fit up went well. Jonathan is also working to weld those pieces on this week. I also worked on the lawnmower differential.
This was the riskiest activity of the weekend. In order to get this to work with bike chain, I had to remove the large ring gear (the giant gear in the picture) and replace it with a sprocket. This would also remove some dead weight from the front. And I had to disassemble the differential in order to get measurements for mounting the sprocket.
I thought the mounting hole locations on the sprocket might be a problem, but they mated up perfectly with the holes in the differential housing. Awesome! Problem one solved. The next problem was that the hole at the center of the sprocket was much bigger than the diameter of the axle rod. However, it had to be a loose fit hole in order to keep the miter gear properly located inside the differential housing. Another job for the Tormach!
I measured up the dimensions on both the housing and the sprocket and modeled an adapter plate. I designed it with a hub to center the sprocket and a hole through it for the axle rod. I also added a matching bolt pattern so the adapter, sprocket, and housing could all be bolted together through the existing mounting holes.
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Then I wrote the CAM and made the part on the Tormach.
Upon inspection of the housing, I noticed that the mounting flange had tabs sticking out on its edges. The original ring gear had a relief milled out to accept the housing flange with slots where the tabs stick out. When the differential spins, the ring gear turns the housing by pushing from the tabs transfer the turning forces instead of the pins/bolts that hold everything together.
I decided I would also cut a relief out of the new sprocket to do the same. I measured and modeled again. Once I had the pocket I wanted, I wrote the CAM to make it. Since I only had one sprocket, I decided to do a test run on 1/4 inch aluminum plate.
Making a test piece was great. The housing didn't actually fit the first time.If I had run the job on the sprocket, I would've had issues. I adjusted all the dimensions to be slightly larger and tried again. This time it was a perfect fit!
Once I knew the relief would work, I then had to carve it into the aluminum sprocket. You might ask, "How did you hold the sprocket on the mill?" That was a question that perplexed me for a while. Then I realized I already had the solution.
The adapter I had just made had square sides and centered the sprocket. The only issue is that I couldn't use the existing bolt pattern to secure the sprocket because I was cutting through them to make the relief. So, I drilled and tapped a hole inside of that bolt pattern and used a shortened bolt (short enough to avoid the cutting head above it) to secure the sprocket to the adapter.
Milling out the relief was a lot harder than the test runs I did. The sprocket is black anodized, which gives it a tough surface finish that is apparently very, very hard. I had to slow down the feed to 2% (!) of the original, but I was able to cut the relief into the sprocket. The roughly 2 minute job on untreated aluminum plate took almost a half hour to complete on the sprocket.
I have to wait until at least Wednesday before I can work on the front/rear suspension. But in the meantime, I now have all the parts I need to mount the differential on the main truss! The parts all fit individually. Now we will see if it all goes together.
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