The old seat pan I had made no longer works with the new subframe, plus I was not entirely satisfied with the way the old one turned out, so I decided to make up a new one. I started with a model made from thin cardboard that I thought looked good on the bike, and then transfered that pattern to some 3/32" aluminum sheet I had been saving.
I used a squaring shear
to trim out the blank.
And used this sheet metal brake
to bend the sides to the angle I had decided on with the cardboard model. To get the large radius bend from the brake I set the brake fingers back about 20 mm from the hinge joint, the setup of which can just be seen in this view.
Here's the formed pan compared to my cardboard model. I rounded down the sharp corners with a file.
To space the pan from the frame and to add some stiffness I cut these sections from aluminum rectangle stock. As can be seen, in preparation for welding I cleaned up the area around the stiffeners with a flapper disk
on an electric angle grinder
I had planned to make a slip-in front mount to make it easy to access under the seat, but decided for now to simplify the mount and just have it bolt together. I'll add the slip-in mount when I make an under seat storage box. For the frame side of the mount I attached this section of aluminum angle stock to the rear seat mount and drilled a single hole in its top.
I found I needed to do some rework on the pan's front mount once I got it fitted on the bike. It was too wide to fit within the subframe mounting bolts. With the pan centered on the bike I drilled up through the hole in the frame mount and into the pan mount and pan.
To hold the blind side of the front mount bolt which will be covered by the seat foam and cover I welded a tab to the head of a bolt and fixed the tab to the pan with a pop rivet
. I ground the bolt head down to a lower profile.
For the rear mount I made these tabs to weld to the subframe.
On the seat pan I welded two tabs cut from 1" x 1/8" aluminum stock.
I used these clip-on nuts for the rear mount bolts. I may weld some nuts on the bottom of the frame tabs the next time I have the subframe off, or better, make a locking quick release mechanism to work with the slip-in front mount.
Here's the seat pan ready for foam and a cover. The side panels really aren't necessary, but I didn't want to just have square block of a seat there so I put on some sides with angles that looked interesting when viewed together with the tank and subframe.