This job was a lot more than I expected. I ordered 5052 1/8" aluminum plate and, in retrospect, I should have gone with 0.080 aluminum. 5052 is cold formable but is NOT heat formable--as I discovered in this process--even after reading up on its properties (it was supposed to). Heat changes the properties of the 5052 and it gets brittle fast. More on that...
In a previous post, I showed the wooden bucks I made for both the clutch and chain guards. These came in handy. I laid out the pattern on the sheet and used my ancient scroll saw to cut the flats out. Below is the second cut after the band has been slotted.
After the cut.
Layout for the frustum hole (covers the clutch).
The two blanks cut. My thought was, with a little heat, I could bend the sheet pretty easily. But that was not going to be the case. The chain guard required far more heat and did not soften. What happened is that it became really brittle and literally fell apart when I started to bend it.
So, I made a tactical decision today: I cut slots along the fold line and bent the metal cold. More welding, but it worked. I used the buck to form the curved edge. All of this was by hand with some help from a few clamps.
The frustum was remeasured to make sure I had the right dimensions and, glad I did...made up a new template this morning and transferred it to the sheet. This was cut with the scroll saw about 4" at a time.
To form the cone, I used a 2" tube mounted in the vise and slowly began bending the cone to shape. This was all done with a lot of grunt and time. Periodically, I'd have to pull the curve back and reshape it to close the two ends. The hardest part was getting the curve on the end...I used a clamp and gently nudged it along.
The key to getting the cone correct is to constantly check and adjust against the buck (upper and lower radius). I screwed the buck into the work bench so could tweak a little here and a little there.
Below is the nearly finished product. The circle on the guard needed to be adjusted some (I kept it smaller just to be safe).
I left a tail on the piece in case the welder needs a grounding point. It seems to me that it'll be best to tack it together on the buck and then weld it all up.