Motorcycle Saddlebags

General Composites Discussions Composites Talk
#1

I’m new here and new to fiberglass. My project is a pair of custom fiberglass saddlebags. To give you a rough idea of the size, they are about 24" long, 15" tall, and 10" deep. They will be bolted through the back wall of the bags to a steel frame on the bike. After looking at how much they would cost to buy (over $1200) I decided to try and make them myself. I figure I’m mechanically inclined with a structural engineering background. So I’m smart enough to pull this off…I would think…lol!! I’ve done a bunch of reading on the net and have learned alot about the process of laying fg, the types of resins and reinforcements, etc. However, I still don’t have a feel for how thick the products end up.

Anyways, from what I have learned, I have created some foam plugs from blue insulating foam from Home Depot, which are almost ready to make my forms. I intend to use polyester resin, so I know I need to protect the foam. I am thinking about taking a thin plastic bag (like a garbage bag), placing the plug into the bag, and then sucking the air out of it with a vaccuum. Will this work? I am aware that I’ll end up with some crease lines from the bag in the form, but since this is a one-time project (hopefully), I’m not too worried about the extra finish work. I’ve also read that using latex house paint would also protect the foam. Would this be a better method? And finally I read that covering the foam in clear plastic packing tape works too. What would you recommend?

Anyways I’ll then create a 2-piece form using 1.5oz fiberglass mat. My question is How many layers should I use? I’ve been told it should be at least 1/4" thick. But I have no idea how many layers it takes to get that thickness. I want to order my materials this week, and have no idea how much to order.

After the form is done, I’ll lay up the bags in the forms with pe resin and cloth (probably in the 6 or 8oz range) for strength, with mat to build up thickness. My question here is How many layers of cloth and mat? And what order do I lay them down? I was told at one time that 3 layers of 6oz cloth alone would be good, but then was later told by someone else that that would not be nearly enough. So I am confused.:confused:

And finally, my last question is about the gel-coat. Is it really necessary? I am already expecting a fair amount of finish work. And since this is hopefully a one-time project and not for any type of production runs, I am trying to keep the costs down. But if it is necessary, I definitely want to do it.

Thanks for any help. And I am sure I’ll have more questions as I progress along through this project.

#2

my opinion, if you are set on using the blue foam coat it with several coats of latex paint over a few days. the bag wrinkles will be too much to deal with and garbage bags leak. A better choice would have been some urethane foam, you can still buy it at the home center, it is much more expensive, but it doesn’t disolve. You do not absolutly need gelcoat, it is there for the final finish layer, since you plan on lots of post lay up sanding and finishing you can skip it. I would not use any woven cloth for this project. just 3 to 4 layers of 1.5 oz chop strand mat. it is plenty strong for sadlle bags, (unless you are planning on carring 500 lbs of gold in each one). mat conforms easily and can be torn and placed at just about any angle remember Mat is weighed by the square foot as weave is weighed by the square yard so 1.5 oz mat has the same amount of material as 13.5 oz weave. if you use 6 oz weave you will probably need 5-8 layers minimum for the parts.

#3

Thanks Bricklin. Yeah, I know I kind of screwed up on the foam selection. I had just picked it and jumped into this project with both feet prior to reading and learning all of the subtle details and such. And it is really too late to change now…unless I want to start all over again because the foam plugs are just about ready for finish sanding. And I hate to do that because of all of the work/time I have in them. Also, I wasn’t too concerned because my original recommendation from a friend in the boat business told me to use epoxy, so it really didn’t matter. And I wasn’t originally going to even make a form, but just glass over the foam, then melt/carve it out. But then another friend in the auto-body business told me I should use polyester resin and matt to make a mold because of the “growth” of the original part if I just glass over the foam. But then I found out about the pe resin and foam thing, so I was back to epoxy. But then I found out that mat is not compatible with epoxy, so I am back to pe resin and the foam problem.

So as you can see, I’ve kind of been learning as I go…and I feel like I’ve been going in circles. But I am getting close now. And again, I really appreciate your input. Thanks!:slight_smile:

#4

You could also paint a layer of epoxy on the foam to use as a barrier then sand, polish and wax the epoxy before using the PE resin and mat. There are tons of ways to skin the cat, they all work it’s just a matter of what you have available to you and your preferences. If you are going to use the pulg to generate a mold you should use gelcoat as the first coat to help with the finish, if you are just going to lay up over the foam then don’t bother.

#5

Thanks again. In fact, I have been debating whether I really want to generate a mold or not. I am a little concerned about the growth of the bags. But really, I could probably live with it. I’ll have plenty of clearance. And as it stands, I am looking at 3-piece molds for each bag, plus a 1 or 2 piece mold for each of the lids. At this point, I am thinking that making the molds would be more trouble than re-producing the foam plugs if I ever wanted or needed to produce another set. And I had made a jig and templates for the bags, so I know I could re-produce another set pretty accurately. Plus, this being a first try “prototype”, I can already see some things I’d do differently if I ever was to make another set. So I guess I am leaning towards NOT making molds at this point.

My question would then be…after I removed the foam from the inside either by dissolving with acetone or just carving/grinding it out, would it still be possible to then go back and add some matt to the insides of the bags, say to add some stiffener ribs (if necessary) or to build up some thickened “bosses” around where the mounting points will be? How would I prepare the inside surface for good bonding?

#6

no problem just hit the area you want to bond to with a coarse grinder disc and you are good to go.

#7

Thanks again! You’ve been a big help.:slight_smile:

#8

Thanks Bricklin for filling in as I had been away on a 2 day that turned in to 3 days business / vacation trip from hel-,…I’ll post that later!

If you are doing a one off, then do use the PS foam and epoxy resin for the lay up but mat does not work with epoxy resins as the mat is held together with a Styrene binding agant, which PER breaks down. So you will need to use cloth.

Then crave, cut, grab or melt the PS foam away. Then sand and then you can add more reinforcements on the inside (if needed but PER will not stick too well to Epoxy resin parts…

After you finish (sand and paint) them, make the top, mount them and test them out and if they work / look the way you want them, then remove them and make your molds from them!

Good luck and if you can or want to, take digital pictures and post your step by step process for us to help you along and others too!

#9

what I was getting at is that he wanted to use PER, so if he painted a coat of epoxy on thef oam and let it set up, the epoxy would be a barrier and he could then do a polyester lay up with mat. then he could desovle the foam with laquer thinner or acetone. he would have a more finshed inside of the bag (where it is hard to sand) and he could sand and paint the outside. I still prefer to work with PER despite the smell when doing layups like this. I personally find epoxy harder to work with doing stuff like this (covering, overlay) unless you bag it to hold it all in place, PER sets up faster and for me holds the reinforcements in place better. It could just be that I have much more experience with PER and am more comfortable with it.

#10

Thanks guys. I think I’ll stick with the PE Resin since that is what is most readily available to me. And also, since this is a first time project, I’ll have less $$ at risk if I screw it up. Using PE Resin and Mat, I can lay these up for under $60 with 4 layers of 1.5oz mat. Using epoxy and 4 layers of 6oz cloth, I’m almost 3 times that amount. I’ll just take care to protect the foam one way or another. I was actually thinking of spraying the foam with adhesive, then stretching saran wrap (plastic wrap) over the plugs. I figure since the plastic wrap is rather stretchy, I can get it quite smooth without too many wrinkles. And the adhesive will hold it in place. I’ll just end up with a few edge lines where the wrap overlaps itself. And since this would be the inside of the bag, the finish isn’t all that important as I’ll be lining the bags with some sort of carpeting. What do you think about that?

And I’ll see what I can do about some digital pics.

#11

Well, I finally started this saddlebag project and it is going well. However, I do have one question.

On one of my bags, I got only 1 layer of mat laid down, and then ran out of resin and had to stop. So it has now fully cured. I still have 3 more layers to put down this weekend. So how do I prep the surface of the single layer to ensure a good bond with the next layer? Should I hit it with a sander to remove the shiny surface? Or is it ok to just proceed as it is? By the way, I am using Polyester Resin.

Thanks!
Bob E.

#12

ALWAYS rough up the surface again when this occurs.( mechanical and chemical bond this way)You’ll even want to do this before you do any final body work to them prior to painting ,of course.
Good luck !

#13

Thanks! That’s what I figured. But I figured I’d run it by the “experts” here first.:slight_smile:

#14

If you used a “waxed” resin, one that drys hard with no sticky film, You may want to wash it with household ammmonia before you sand it to remove any wax that has migrated to the surface.