F/G is flexing too much

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#1

I made a fiberglass seat cowl for my sport motorcycle. It has a latch on one end to keep it closed ( think of a truck bed tanuo cover made of F/G). The other end has a hinge bolted to it via some wood inserts I resined/glassed onto the bottom side of the part (seat cowl). The hinge has a spring that is kinda strong because it’s made to hold up a seat that weighs 3lbs. I was worried a little about the spring being too much pressure on the inserts… sure enough it is pulling one insert off on the side with the spring. All of this flexing and pulling has distorted the shape of the part a little and it now looks ugly. I used polyester resin and Bondo brand fiberglass cloth ( .008" thick)- 3 layers of cloth and a lot of resin rolled into the cloth, and on both sides after it dried i applied more resin. I waited two months before i mounted the part so it had plenty of time to dry.

Any ideas on how to make the next seat cowl so it doesn’t have this same failure occur again? I would like to use a spring to keep the cowl open on the hinge end when needed… but i can go to a lighter weight spring… just not a lot lighter weight.

Thanks :slight_smile:

#2

what was the ounce of the cloth that you used? Do you happen to have a pic of it installed to show where it is flexing with the spring?

#3

I’m not sure of the OZ…Bondo doesn’t say on the package.

I’ll go take a digital photo and be back… hopefully it will show what’s going on.

thanks

#4

if I can see where it is flexing I can hopefully help you :slight_smile:

#5

Ok…here is a link to the photos…they should be the top 4 on that page/s.

http://s210.photobucket.com/albums/bb186/Fastrr_photos/

#6

it is gonna be hard to make a part out of glass to use that oem spring, what are your other options in spring rate. The problem is that the spring was designed for a 3lb lid not your light lid.

#7

Well that is good news for me. I’m not concerned that this part is trash… I just wanted to know why. I can buy a lighter weight spring for the next ones i make.

Thanks a bunch, i appreciate your help :slight_smile:

#8

if its distorting why not make it a bit thicker? 3 layers of that thin bondo glass is not a lot. i’m sure you could ‘accidentally’ put your hand through it quite easily as well…looks like a nice part though. good work.

#9

3 layers of the pre-packaged Bondo fiberglass is definitely not enough. More layers, use core material, or layup with carbon. Or do all 3.

#10

Bonding in some 2mm aluminuim sheet in the area where the mountings are fixed, would spread the load, and very likely prevent the part distorting. This in combination with a lighter spring would very likely work fine.

#11

this is all true. I would suggest core material first. Also it is a pretty small part so you can try several different options and not kill the pocketbook. if you plan on selling a hundred or more you need to spend a little to do the R&D to perfect the product.

#12

Well considering that its a mid to late 90’s 900RR…I wouldnt worry about making a hundred of them. Targa has you beat to it and theirs is WAAAAAAY HEAVIER.

Three layers of glass for that part is way too thin. You could have made it about 8-10 layers thick and still been lighter than the seat.

Fortunately seat cowls are for looks.

Id just add layers to it and do a thin metal strap or a thicker wood strap to disperse the load.

It looks good though Im impressed for you being a newb.

Why dont you pop it off and put all your steps together on making a functioning seat cowl so the other newbs get an idea of how this works.

Im assuming you just ripped a mold off the seat and cheated in your mounts.

#13

I used an ancient Chinese secret :smiley:

Actually made a mold out of white styrofoam, shaped it accordingly, layed down a layer of aluminum foil tape, then a thin layer of green fiberglass bondo, sanded it all perfect to shape and smoothness. Then i primered and painted the mold. Waxed it then did the lay up. The top being so smooth was due to me laying on some Bondo about 1/16 thick and block sanding it smooth. I can work Bondo like nobodies business LOL. I want to get good enough with resin/glass/carbon fiber that i don’t use any fillers before the part is painted. If resin can be block sanded flat then that would work i think.

Next time i make the cowl i’ll add an aluminum piece that can be drilled and tapped for the hinge mount… just glass and resin it in place. That was a nice suggestion…thank you whomever mentioned it. I can even drill and tap the threads before i lay it in place.

Now onto making a better re- useable mold. I’d like to be able to make around 5 of these for my model year bike. Don’t want to make many as i’d end up being stuck with them.

Can resin be thinned and sprayed through an HVLP gun with a large tip … say 2.0 tip size?

#14

How did ya cheat in your mounts in one shot?

#15

The mounts i did last. I stuck modeling clay to the bottom of the seat cowl. lined it up with the body work then pressed it down onto the hinges to leave a circle pattern where the hinge mounting holes go. I then pulled it off the bike, modeling clay still on the cowl, stuck an awl through the circle pattern in the clay down to the fiberglass to make a small scratch mark. Removed the clay then glassed on the threaded mounts.

where do i buy this core material and what does it look like? Lay it just like the f/g?

#16

What ounce of f/g cloth would you guys suggest i use for these seat cowls, and how many layers? There are two corners that are rounded so the cloth would need to lay down in those corners once cut.

#17

I wonder are you intending to produce FG parts or carbon that has FG backing? If FG I cant honestly see there would be enough demand to make it worth while, certainly in regard to things like seat cowls, where the std plastic part works pretty well.

#18

Hey Classic…that particular bike didnt come with a seat cowl.

Fast, I use 6oz cloth for all of my parts.

#19

that is what I was thinking too. everyone wants carbon so you might want to look into that as well.

#20

I’d like to use carbon twill, but for now with my very limited skills and equipment i think i need to perfect the design and my lay up skills :slight_smile: If I can lick fiberglass then i will definately want to make some cf parts. I just hate to spend $120 on cf and have the part come out like junk.:o

I was thinking silver e-glass would look nice for a cowl, but i’m not sure if it will lay down in the corners of the mold.