How to fix down a fiberglass seat pan?

[enterlance]

Hi, DTT, I'm new here. Just finished my first fiberglass seat pan and I think it turns out to be pretty neat!
Just one question: how do I fix it down onto the frame to avoid impacts from road surface? I was thinking to put some foam in between the seat pan and the frame but that would make the seat pan slightly above the frame hence losing the curve I desired. Please share me your wisdom!

 

[2_DONE_THE_TON]

Nice seatpan!

I would recommend to build a metal steel base for the seatpan.You dont want youre bodyweight, especially on the impacts of roadbumps and higher speed to go trough that fiberglass it will break.
Make sure that the steel base is well connected to the frame, in a manner that you can remove the seat easily.A friend of mine finished his CX500 build just a few weeks back and he needs approx 1 hour to remove his seat and tank combo!!

MAKE SURE TO DISSCONNECT YOURE BODYWEIGHT FROM THE FIBERGLASS SEAT PAN.

A good way is to weld on straps or tabs onto the frame rails (in between the rail),tap a thread into them.
Then fiberglass metal strips with a certain thickness (I would take at least 5MM) into the bottom of the seat pan and use a screw from the bottom to connect the seat pan to the strips or tabs welded onto the frame.
Make sure the fiberglass has a good strength, not the resin but the fiberglass material gives strenth keep that in mind.
Alwyas use as little resin as possible.

Use a thin layer of foam between the seat pan and the frame.An voila youre finished!

 

[enterlance]

TranceMachineVienna, thanks a lot! I think your advice is extremely helpful and it really guides me the way to go!
Unfortunately I am unable to work on the seat pan until this weekend but here's my plan:

I bought a "Universal Cafe Seat" on eBay and obviously Universal is the word that we should all be warned considering a cafe racer project. Anyway, it did not fit due to my DOHC cb750 has a upward frame and that's why I decided to make one. But here's the good news: it comes with 3 pieces of mounting hardware (one for under the gas rail, two for the frame). My plan is to:

1. Drill holes to corresponding mounting hardware on the seat pan.
2. Mount the hardware onto the seat pan and fiberglass them on.
3. Screw them in, these hardware would give me enough clearance. If not, I will put some rubber spacer or foam in between the seat pan and the frame.
4. Weld nuts onto the frame once everything in place.

How do you think of that? I will take your advice seriously!

 

[enterlance]

Went to garage to take a quick measurement:

The brackets (hardware) do fit the seat pan pretty well, though some modification will be required to make them angle right, I think this is very doable!

 

[2_DONE_THE_TON]

Make sure the seat is easily removed,since I assume you willbe hiding your electrics under the seat are you?
Imagine having a non starting bike and you need to do some maintainance roadside wise.

Do you have enough clearance for the rear tire on the back?

 

[enterlance]

I think I have enough clearance.

Update: I put the brackets on and it loos perfect. Easy to remove. After painting the seat pan I will send it to upholstery and let them to warp over the edges and put a thin layer of form in between the frame and the seat pan to give it some extra protection. To fix it down, I will drill two holes on the frame to bolt it on.

Here are some pictures, let me know how you think!

 

[2_DONE_THE_TON]

Looks good, If I were you I would lay some fibergglass over the foam side of the (the shiny golden side)construction in order to fuse it together with the seat base.would be really bad if once upholstered this setup would crack out of the pan.

Put some big metal discs between the screws and the seat pan to widen the impact on the fiberglass.you dont want such a small "impact" area.