The differential support took some time and needed to be accurately located. Here are the related drawings.
Here are the location coordinates for the support. The axes origin is located at the rear, bottom, center of the bottom cross member of the rear seat assembly.
Basically the sequence of assembly is:
- Build the two bucket supports. For strength, I added a top to the bucket supports.
- Use the differential to position the bucket supports and add a cross member between the supports.
- Use a jig to position the supports in the frame.
- Cut the tubes that connect the supports to the frame.
- Weld everything together.
Here are some pictures. First I did some practice welds. This showed me that I would get better penetration if I beveled the circular tube. Note that the bottom disc has a larger diameter than the tube.
First I welded the bolt to the lower bucket plate. Since I live in the United States, I used a 1/2 inch bolt. This is close to the 12 mm bolt on the Miata. There is plenty of slop in the Miata bushing to accommodate the slightly larger diameter.
Next I welded the bolt and plate to the bucket cylinder. I used a machinist vice to hold things aligned. Again, the diameter of the plate is larger than the tube. Notice the bevels on the tube.
After welding.
The right bucket shows how things looked after adding the top plate and cleaning up the welds. The one on the left still needs to be cleaned up. After adding the top plate they are not really bucket supports, but we will call them that.
Then adding the cross member connecting the two bucket supports, using the differential to position the supports.
The Miata subassembly that supports the differential has a circular area the contacts the bushing (see above). I added a plate to accomplish the same thing. This is a test fit.
I made a wood jig to position the supports in the frame. The wood is planed and is 25 mm thick, so it puts the top of the cross member at the top of the frame tube.
Making sure the support is correctly positioned.
Now I cut and fit the support tubes.
Ready to weld.
Partially finished welding. The view is from below.
Adding the bushing plates. Note that allowance is made for the steel tube in the bushing. View from below.
Everything welded. A detail of the support. View from above.
I added a vertical support also, since the torque on the differential is reacted vertically at the supports. This ties into the tube where it is supported by the triangle coming down from the roll bar boxes.
And everything is finished.
Happy with the progress.
