Saturday, March 28, 2009

aft mounting bracket

The forward mounting brackets worked out okay so I reinforced them and sanded them down a bit. Now it is time to get the rear bracket sorted out.

I wanted to use the OEM rubber damper that fit the original tank to it's mounting post that we left intact here, so I'm going to fabricate a tab that attempts to use it. The layup here was as quick as possible: build up a cardboard form with some thickness at the bottom to accommodate the offset of the rubber. I'd then prep it and rest the tank on the glass/epoxy layup while it was still curing so that everything dried in place.


I folded up some newspaper to support the cardboard form right where it would make contact with the tank.


Here you see everything prepped and draped with paper to prevent drips from sticking to the bike. In the upper left you see a wooden block that the tank will rest on during the cure.


Here it now sits. We'll see how it looks tomorrow morning!

Monday, March 23, 2009

forward mounting brackets

Had the hardest time trying to figure out how to place the forward mounting tabs for the tank. The tabs are nothing more than a "C" cross section that I molded around a foam block. Well I eventually cut the tabs to size and then press fit that foam block in where the mounting posts would be, and then tacking the "C" tabs into place. It sort of works, but It was hard to transfer the mounting points exactly onto the tank when it was in position.

I'll lightly test fitment tonight and if it looks okay, reinforce the attachment with more glass and epoxy.

Saturday, March 21, 2009

more work on airbox

OK took some time while the tank glue-up dried to finish and test out the fit of the air intake adapter. Worked pretty good but I am going to have to put a slight "elbow" for the inlet flange to orient the air filter a little upwards and a little inwards for better tire clearance. I'm wondering if 6,1/2" long filter is really necessary but If I can get it to fit, then no worries.


tank assembled

OK, mixed another slury of the milled glass fibers with the slow cure epoxy and laid a bead along the interfaces. Got a lot of squeeze-out once the thing was taped down (especially along the inside when I peered in with a flashlight through the cap hole). Hopefully it'll be alright.


Friday, March 20, 2009

one last check before closing up the tank

OK, I talked to the tank sealer guys at Caswell and they said I ought to scuff up the insides of the tank since I can and it'd help adherence. They said go ahead and glue everything up before dumping their sealer into the tank to coat the interior. So that's what I'll do.

It's been a long process so I'll take a sec to make sure everything's wiped down clean with acetone after sanding and vacuuming all the dust. Nothing but rubber gloves at this point; you don't want any of your finger grime/oil getting onto joint surfaces.

Monday, March 16, 2009

losing the foam

OK! a few CC of acetone into the inlet duct and it just sort of devours the foam:



A few minutes of clawing away at the inside with a long screw driver and I've got most of the guts barfed out the intake orifice. The PVA melts with the acetone as well, so the tape that sealed the foam inside peeled from the walls pretty easily. any remainder will come off in a hot water bath...here's my new shower toy:

Sunday, March 15, 2009

airbox layup

OK, wrapped the foam mold up in packing tape and treated with PVA. Also remembered to glue a stick into one of the entry points so that I have something to hold onto while carrying on with the goopy mess:



petcock fitment

looks like they'll bolt right on no probs. You can see on the right side how the positioning plates formed the epoxy/paste mixture into a flat surface that the petcocks can interface with all nicey-nice.

Saturday, March 14, 2009

intake intake intake

While all that was going on I was spending time on a new airbox assembly using a 6x3.5" K&N Pod filter attaching to a much smaller "plenum" than my original design. I did this because the older airbox I had fabbed was taking up too much room for the battery and the exhaust pipe.

Here's the profile, that glowing white thing is a polystyrene foam plug for the mold. I used some sticks to locate the angle of where the intake rubbers mate to the airbox because they have some protrusions which would make it difficult to orient the airbox plug once the final assembly is insatlled. (the rubber is resting atop the frame in this picture). This will be a male mold. I'll do the final layup around this foam piece and then pour a little acetone into the intake hole to melt away the foam like butter! It's known as the "lost foam" method:


Here's a view of how all the big pieces will be oriented, filter on left, batt on right. I'll fabricate another fiberglass assembly to house the battery and electricals once the airbox plenum is situated.

more fitting glue-up

OK, Milled glass fibers came in the mail and so now onto mixing into a thick slurry with epoxy to finish off the T-nuts that mount the petcocks, and then the gas cap assembly.

I pressed some PVA-released positioning plates into the mixture as it'll make a flat surface interface to the petcocks.


I took the outer surface of the tank down to 600grit sandpaper to clean up the flash and a few boogers on the outer surface; It'll look okay once I get a coat of wax on there, kind of satin hopefully.




Thursday, March 12, 2009

mounting petcock nuts.

OK, managed to epoxy on a few "T" nuts to the bottom piece which will attach the petcock valves. I've positioned them with a few jigs I cut from some old fiberglass layup done on a previous project; just cut some holes the correct distance apart to fit the petcock valves. Once this glue sets, I'll lay down a slurry of epoxy and milled glass fibers to really solidify the assembly. I actually would have done this all in one step but ran out of the milled fibers to make the reinforcement with. Figure it's okay to "tack" the nuts down right now and then reinforce them later.

Monday, March 2, 2009

demolding the top part

I probably should have let the thing cure a bit longer in the mold but it looked solid enough and I just couldn't wait. I'm that way with scabs, too. And like a scab unready for the picking, it took plenty of encouragement to bust the mold loose. First some prying between the flanges, then a bit of drumming on the hull to pop free along the surface, more prying, more pounding, you get the idea. These things stick together quite a bit because of the PVA. It's weird stuff: a thin membrane that starts off applied to the mold but when you take everything apart, it ends up on as a coating on the final part that you just rinse off with water.

This is how it looked immediately out of the mold, so a lot of boogers and some flash to clean up, but the part seems pretty sound!



I ran it out to the garage to confirm fitment with the bottom, and after roughing out the edges a bit they look to be mating pretty well.



Next step will be to double up a few more layers on the top part from the inside where it looks a little thin, then it's on to fitting up the petcocks and gas cap.

An opera in 3 pots.

Never made a gas tank before. It's obvious I'm way over my head here. Anyway, let's begin making the top part.

I chose to use four facets of glass per layer. As luck would have it the tank is reasonably symmetrical, so the pattern consisted of 2 facets, roughly looking like this:



Keep that mildly pissed off woman's expression in mind, because by 8:00pm yesterday, I was right with her, maybe even several lengths past that, ready for a bucket of plonk and a flintlock to point at strangers.

Making the patterns is pretty easy, just hanging some news print off of the plug, and cutting notches around the compound contours. Kind of like so:


(I like how her picture ended up upside down...perhaps that's why she's giving me that scorning look of disapproval -- as if my shenanigans have no purpose to her discussion on philanthropy for the Arts in the post-Bush, pre-economic apocalypse).

Layup for the top was a complex affair. I knew I'd take too long to get it all in one pot of resin before it started to gel. Even with the slow hardener, after 30 minutes resin begins to cure really fast when it's amassed together in the mixing dish. I carried forth the layup in these overtures:

  • First a topcoat of black tinted resin right on the mold that I'd let cure to the point of tackiness. This from an idea taken directly out of Tygaboy's advice on Bay Area Riders Forum to achieve a smooth outer surface and facilitate adhesion with the first layer of glass.
  • Then mix some milled glass fibers with more black resin to fill in the cracks/crannies around the fuel cap recess, as well as the dimples around the shoulder of the tank that are there to: a) clear the fork triple clamp bolts, and b) make it harder for the glass to lay down smoothly.
  • While the topcoat dried to a tacky consistency, I cut the glass for the main facets. Once cut, I mixed the first pot of tinted resin and went at it. After a couple layers the resin started to get kind of snotty, so I found a stopping point, ran inside and took the turkey thighs I had roasting out of the oven, and mixed a pot of clear resin to finish out the layup.
  • Vacuum bagging. This exercise was fail from the get-go. First, I didn't cut the peel-ply big enough to extend past the overhang in the tank -- crucial because I wanted to tape it down to the outside of the mold. I then had a few wads of breather cloth jammed into the interior, some bunched up into the shoulder and under the overhang to help apply pressure from the bag. I then stuffed all this into the bag and began pulling air with my bicycle pump. After not long, it was apparent that there was not enough surface area of the bag to reach into the overhangs of the tank *and* all the way into the depths of the shoulder of the tank, even with all the extra wadding I had used to take up these areas. I decided to quickly pull the layup from the bag, remove the wadding, peel-ply and just let it cure on its own.


Six pairs of rubber gloves later, and this is what the place looked like last night. Note the brush right in front of the mold, I sawed off the handle for easier maneuverability within the mold:



Yeah, vacuum bagging is a nice to have thing, and a lot of composites geeks use it to consolidate a layup and get the optimal ratio of resin to reinforcement for the lightest possible construction. I've never been as interested in that factor as much as the way vacuum bagging helps the fiberglass to wrap around complex edges. Since I'm laying glass on the interior of the mold, it actually seems to have laid down pretty well. I'll leave it and see how it comes out of the mold in a day or two.