Saturday, November 5, 2011

Part 16 - Seat Pan

There's no off-the-shelf seat for the War Eagle frame so you get to make your own. To start making the seat pan, mask off the area of the seat using masking tape and then cover the taped off area with aluminum tape. The aluminum tape will prevent the resin from being absorbed into the masking tape and also present a smoother surface that makes removal of the molded seat pan easier. It also makes the job take twice as long. I have seen it done without the layer of aluminum tape but it would make a mess if you missed a spot with the masking tape and had resin leak through onto your motorcycle.

Use blocks of wood, foam or anything else you have handy to make clearance underneath the seat for things like the battery, electrical relays and such. The picture shows the spacers I used to create extra clearance for the battery, electrical control module, bolt heads for the fender and the fender gussets. The finished seat pan is going to sit a little higher off the frame than when you mold it due to the seat covering. Providing extra clearance for things like bolts and gussets is not strictly necessary but if you move your fender mounting points slightly to realign your fender in future, it is nice to know you have extra clearance under the seat to accommodate this. Now is a good time to make sure the rear wheel and fender are aligned properly! I allowed for at least 1/8 clearance above and to each side of the gussets and bolts.  Just make sure you don’t have undercuts since you will be pulling the completed pan upward to remove it from the bike. With undercuts you will need a grinder to cut your pan free and start all over again….

I extended the seatpan area to the rear of the fender so that I could make a detachable pillion pad for a passenger. I used a piece of Styrofoam to make the backrest (more like a butt rest actually). I used 3/8" vinyl tubing to provide a form for strengthening ribs between the horizontal and vertical pieces to reinforce the back rest.

A plastic drop cloth was draped over the motorcycle and a hole cut where the seat will go. The edges of the drop cloth were sealed with masking tape. You don’t want resin on the bike anywhere other than the seat pan.  The resin makes a real mess.

I marked the the outline of the seatpan with a permanent Sharpie. This line will magically transfer to the fiberglass when you lay on the wet layers of fiberglass and resin, permanently embedding the lines in the fiberglass which is a useful trick for when you need to trim the seatpan to size. I went about 3/8 down each of the side support rails so that the seatpan would have built in side to side stability. It doesn’t just sit on top of the side rails, it fits over them. You don’t want to go too far down. If you pass the midpoint of the curvature you may not be able to get your seatpan off.

Cover the seat pan area with a mold release agent. This will make it easier to remove the seatpan after it has cured. I used Leather Boot Conditioner…. Car wax will probably also work or you can buy special mold release products. If you don’t use mold release it is going to be tough to remove the seatpan.

Use a dust mask and appropriate gloves to protect your hands and lungs from the fiberglass.  I used double layer nitrile gloves and 3M 95 sanding mask.

Prepare the fiberglass. I used both fiberglass mat and fiberglass cloth. The cloth is stronger than the mat or so I’ve read. Why use both I’m not entirely sure but the result is very strong.

A large piece of cloth is roughly cut to the shape of the seat pan area with some overlap on all sides. Cut slits into the cloth in areas where it is difficult to conform to the contours by hand and cut smaller pieces to fill these in later. Do a rough trial fitting to see where your problem areas are. Then the mat is cut into 5” by 2” pieces (no need to measure….) and some is shredded by hand. The smaller pieces make it easier to work into the tighter curves and corners.

Make sure your work area is well ventilated. The resin creates a lot of fumes that may not be good for your health. Remember the dust mask for protection against airborne glass fibers. If you are making seats everyday you may want to invest in more sophisticated safety equipment. Mix the resin to the manufacturer’s specification and work fast. Too much hardening agent and the resin will set before you can use all of it. Too little and it will take days to cure or never really cure properly. For your first time out, I recommend using the manufacturer’s recommendation plus an extra drop or 3. People with fiberglass experience use up to double the amount of hardener and work fast since they know what they are doing. I don’t and therefore didn't. The chemical reaction gives off heat so adding more hardener increases the speed of the reaction which increases the heat output.

To start, paint a layer of resin onto the seatpan area (quickly) directly over the aluminum taped area and then lay on the first pre-cut large layer of cloth and position it as smoothly as possible. Working quickly, paint another layer of resin on top of the cloth and make sure the entire cloth is saturated. I found it useful to dab the paint brush up and down instead of making painting strokes to stop the cloth from moving around. Add another complete layer of the shredded/2x5 mat pieces and cover with resin. Keep adding layers of the mat until you have your desired number of layers of mat - at least 4 (total layering is 1 x cloth layer + 4 x mat layer). You may need to make more batches of resin if you work a little too slowly and the resin in the cup starts to gel. I mixed 6 ounces at a time and made at least 3 batches – lost count. Add 2 final layers of cloth to the top and cover with resin (1 cloth – 4 mat – 2 cloth). This arrangement ended up being very strong. Not sure why you cant just use the cloth for all layers but that is an experiment for next time.

How much resin to add? Just enough to saturate the cloth or mat. When the cloth/mat changes from white to yellow resin color, that’s enough. No harm done adding more but it will not make the seat any stronger.

Clean up and leave the seat pan to cure overnight. If it doesn’t cure properly overnight and is tacky to the touch the next day, mix up another batch of resin and add twice the recommended amount of hardener. Working fast, paint a thin layer over the seat. This will set up hard and help cure the tacky layer underneath at the same time. Leave the seat to cure another night. A heatgun or hairdryer will accelerate the curing process but be careful not to accidently burn the seatpan doing this.

The resin in the mixing bowl gets pretty warm when it starts going from syrup, to gel to solid.

When the pan is dry, pull upward to release from the motorcycle. Depending on how well your mold release agent worked, your pan will come up without a fight or stay stuck to the masking or aluminum tape. Use industrial leather gloves to grip the seat as the edges can be very sharp and the fiberglass will cut you.

Using adequate dust and eye protection, use a cut-off wheel or other appropriate tool to trim the seat pan to shape. If you don’t have a dust extraction system, do this outside or your garage will be covered in white powder that takes forever to clean up and gets in everywhere.… Don’t ask me how I know this….

A dry fit to make final adjustments before prep for upholstering the seat.

Sand the edges smooth. Mark a line all the way around the seat about 1.25 inches in from the edge. Make sure this line clears your frame or you will have rivets grinding the hell out of your expensive paint.
Mark points about an inch apart all the way round.
Drill holes through the marks with a 3/16 drill bit or whatever size is needed based on your rivet diameter.

Cover the edges with Edge Banding. I got mine from AutoZone. The edge banding will prevent the fiberglass seat edge from cutting through the leather.

We are now ready for phase 2 – padding, shaping and covering the seat
While researching the method for building the fiberglass seat pan, I found a number of useful sites that I used as a basis for making my own:

No comments:

Post a Comment