Scratch-Built Seat Noob

[MisterCinders]

Thus begins the latest of my lengthy and terrible "Noob" threads.

I have two extra tanks and a spare set of side panels already. With a second seat I can have two bikes (at least cosmetically).

To complete the alternative outfit, I need another seat. Instead of just buying one, I've been looking at the scratch-built seat threads. I picked up a nice board to start laying out the seat pan. I may end up using a nice piece of hardwood coated with spar varnish for a lot of the pan, since it will be covered with upholstery, etc.

Here is the first part of the puzzle. I still have the old "duck-bill" tail piece and want to incorporate it into a cafe style seat. Beergood's bike has this, but alas, he did not show his work on the seat part. The front of tail piece has sort of a rabbitted lip where the original seat meets the tail when you close the hinges. I want to level that out for a smooth frontal transition to the rest of the pan.

Similarly, the back face of the tail is recessed to fit that monster stock tail light. I'd like to level this face or the tail piece and use a flush-mount tail-light instead.

What should I use to modify the tail-piece? Is there any abs sheeting that I can meld on with the acetone slurry? Is this a fiberglass project (which I have no experience with? Something else?

Will try to illustrate with pictures later.

 

[MisterCinders]

Dug into this more. Looks like it's going to be a fiberglass adventure to either make a pan that marries up with the tail piece or a full on pan.

I'll start mocking up one or both with some foam insulation board. Guess I'll dig up the old foam cutter. Hope the filament is still good.

This should be fun.

 

[TheCafeKid]

Dug into this more. Looks like it's going to be a fiberglass adventure to either make a pan that marries up with the tail piece or a full on pan.

I'll start mocking up one or both with some foam insulation board. Guess I'll dig up the old foam cutter. Hope the filament is still good.

This should be fun.

Yanno, something I may try with my next attempt at a 'glass seat will be making a pan out of 'glass using the stock on as a mould. That way it still attaches like stock, but then you can do whatever you want to the top. Make a shorter actual seat, and a bum stop attached or whatever..
Don't think it'd be too hard just remove the hardware from the pan, run a layer of tape over it, and use some wax as a release agent. Do one side at a time, then resin the two halves together, install the hardware...

 

[wally]

Love to see how it turns out - i need to make one in a few months.

 

[MisterCinders]

Yanno, something I may try with my next attempt at a 'glass seat will be making a pan out of 'glass using the stock on as a mould. That way it still attaches like stock, but then you can do whatever you want to the top. Make a shorter actual seat, and a bum stop attached or whatever..
Don't think it'd be too hard just remove the hardware from the pan, run a layer of tape over it, and use some wax as a release agent. Do one side at a time, then resin the two halves together, install the hardware...

I have been studying your massive seat build thread from awhile back. At this point, my plan will be to pick up some insulation board and start playing with shapes that either incorporate the tail piece or stand alone as a seat pan. My preference for this one leans toward a Dunstall style of seat. For example:

[Edit: huge pic would not resize] PIC

etc.

 

[MisterCinders]

I picked up a sheet of 2" pink foam board yesterday and started roughing out the shape.

We aren't even close yet, but here is what I've got for a rough shape so far:

Need to do a ton of sanding and shaping still, but that bottom layer is pretty close, and lines up with the frame pretty well. The other two layers are glued together, but they are not yet glued to the bottom part yet.

So far, I have been shaping with a box cutter and a hot foam cutter, followed by sanding with a medium/rough sanding sponge. The sponge removes material pretty quickly, sometimes too quickly. Of course, a full sheet of 2" foam is way more than I'll need, so there's plenty of back up material for when I screw up the shaping.

What grit is best for sanding foam?

When I finally get it to a shape that works, I have another pretty basic question.

Where do you get the fiberglass materials?

I've seen some fiberglass stuff at AutoZone, but are those just for patching and small repairs? Can you get the different cloth types and other components there for a project this size? Let me know if there are other, better sources.

 

[Toasty]

http://www.eagerplastics.com/

This place in Chicago sells fiberglass stuff.

 

[EvilEnfield]

ebay, best buying it all seperately, matting, polyester resin and hardener, release wax, & gel coat. I use heavy glass matting for stiffness and a finer woven matting for the finishing layer. Are you making a fibreglass mold? If so you'll need probably four layers of heavy matting, and for the actual piece two layers of heavy and one woven. I've probably forgotten something, I'll check again later.

 

[ChicagoBob]

I used epoxied plywood, Liquid Nails glue, and a scooter fender (pre-finish photo)

 

[MisterCinders]

Thanks for all the info.

Of course, more questions arise.

Various guides suggest using the shape to make a mold before fabricating the seat. It looks like this makes sense if you plan to make multiple pans. For a one-off seat, other guides call for laying the cloth over the foam form and then smoothing it out with filler and sanding.

So - mold or no mold?

Also, any tips on sanding grits for this pink foam? I have a bunch of different paper in various grits, but haven't worked much with foam. It seems to clog a lot, but I doubt that wet-sanding would work on this stuff. I can just get a stack of cheap sandpaper if clogging is unavoidable. If someone can save me some trial and error on this . . .

 

[musicman]

What about that mesh stuff you use for sanding dry wall? Seems like it wouldn't clog as easy, maybe even a rasp or something.

 

[MisterCinders]

What about that mesh stuff you use for sanding dry wall? Seems like it wouldn't clog as easy, maybe even a rasp or something.

I might try that for shaping, but those are going to remove a lot of material, and leave a pretty rough surface.

Not sure how granular this foam board really is. Seems fairly dense, but once the grit gets finer than the foam grain, I'd think that you lose any sanding benefits.

 

[musicman]

Well if you're going to not make a mold and end up doing bondo and everything on the seat anyway, why worry too much about a rough surface? The bottom of the seat can be ugly, haha

 

[EvilEnfield]

Well if you're going to not make a mold and end up doing bondo and everything on the seat anyway, why worry too much about a rough surface? The bottom of the seat can be ugly, haha

I agree, but I think a mold is the best way, it gives the best finish and bondoing and sanding fibreglass is a real pain in the arse, every time I've gone for the lay it over the top method I've ended up with loads of lumps and thin bits. Also, just get the foam in the basic rough shape, I don't know what that foam is, is it like our Celotex over here? just use a rasp to get the rough shape, then coat it in loads of PVA, then cover it in decorators powder filler, getting it as close to perfect as you can when spreading it, don't go too thick as it will crack, do thinner layers to build up any really low spots, then sand it perfect. I use that filler because if you have trouble getting the mold off then you can just soak it in water and the plug will dissolve.

 

[wally]

Have you seen this video?

http://www.youtube.com/watch?v=AT6P7qaUPLw

 

[MisterCinders]

Made a lot of progress on the foam stage. Here are a bunch of pics:

Smoothed out the rough shape. Initially, I wanted to go with a boxy Dunstall shape, but the harder edges contrasted with the lines of the tank -- even though the tank for this seat may not have knee-dents, but will probably just be a standard shape, sans the fuel door and badges.

Then I shortened the back of the form and added a bit of a flair to the tail angle. Still a bit too boxy for the lines.

From there, I decided to sharpen the vertical angles and bring more of a "Coke-bottle" curve to the tail shape. This is where I ended up.

Now the curves actually pick up the knee dent lines, maybe I will hammer in the second tank after all.

Although the foam version sits a bit high, the actual seat will be a bit lower. The board I am working with is 2", but I plan to reduce the base thickness to about 1" - 1.5" when I trim the fiberglass.

I now see that the slight curve at the bottom of the back end will make glassing this a little more difficult, since I may not be able to simply lift the glass off the foam. Looks like there are a few ways to navigate that issue.

1. Cut the form just past the mid-point and a few inches into the hump, so the front drops out of the glass allowing the back to shift forward and down.

2. Glass the main pan to drop out and then glass the bottom of the tail afterwards.

3. Just glass the thing and use acetone to get rid of the foam in the back.

Thoughts?

 

[MisterCinders]

First attempt at glassing was a catastrophe. As soon as I started laying glass, I knew my pieces were too big. Tried too work through it, but the results were horrid.

Will start over, since the form cannot be salvaged. Going to stick with that coke bottle shape though. It's pretty sexy.

One question, the ratio of hardener to resin on the package is unclear. Any good rule of thumb to tell when you have the right mix?

 

[EvilEnfield]

I think it is 2-5%, I weigh the resin in kg, work out 2-5% then translate that into ml. So 500g needs 10ml of hardener, put more hardener depending on how low the the temperature is where you are doing it. Did it melt that foam or did you just bust it up getting it out? after watching that video I may well start using that method.

 

[MisterCinders]

I think it is 2-5%, I weigh the resin in kg, work out 2-5% then translate that into ml. So 500g needs 10ml of hardener, put more hardener depending on how low the the temperature is where you are doing it. Did it melt that foam or did you just bust it up getting it out? after watching that video I may well start using that method.

Didn't melt foam, but the shape and extra glass make it impossible to retrieve the form.

 

[Reaper0001]

show us a picture of what you have come up with so we can help you
fix this problem!