Seeking advice on gauge of aluminum for fabricating rear fender

B

BubbaMcCranky

New Member
Seeking advice from dotheton gurus of aluminum fabrication. I'm partway through a cafe mod / resto of a 79 Suzuki 425GS. I'm planning to fabricate a minimal rear fender from aluminum to run roughly from the rear of the seat to just above the point where the top of the swing arm reaches its fully compressed point (i.e. so the swing arm won't hit the fender when the bike hits a bump). The fender should basically be just enough to protect the carbs and filters from rocks / dirt / water / etc. thrown up while riding, and big enough to pass the PA inspection, which requires a rear fender. It will be fastened at the top to a frame crossmember below the seat and to side supports of the frame near the bottom of the fender (engine side). It should be a bit less than 90 degrees of total arc and will not extend past the seat in the rear.

My question: what gauge and alloy of aluminum sheet would you recommend for the fender? I'm a noob with metal fabrication, though getting better at it with some practice and the tools at our local Techshop. I'm thinking 16 gauge (~0.05") 5052 aluminum sheet. I'll need to be able to roll it to get a compound curve, want it to be as light and inconspicuous as possible (planning to paint it black), but still have enough structure to not get destroyed by kicked up rocks.

I'm planning to order the stock aluminum from onlinemetals.com unless somebody has a better suggestion on where to get the stock aluminum.

Thanks in advance for any advice provided.

-- Bubba
 
Do you have a local supply house? I would get it there. You need such a small amount for a fender, you may find it in a cut-off bin for a better deal.
 
Why not buy one from http://7metalwest.com/motorcycle_parts.html I have bought 4 fenders from him, all are amazing, made of 1/8 aluminum, you can stand on them without any distortion.
 
roll it to get a compound curve? by compound curve you're meaning, the shape of a fender, right? if so, you're not getting that done with a roller, you need to stretch and shrink metal to get a compound curve
 
Thanks for all the good advice.

@RocCityCafe -- yes, I realize that I'll need to do more than roll it. I over-simplified things. I haven't done this complex an aluminum fabrication before but I'm planning to use this and an under-seat electronics box as not-so-visible pieces to learn with before I try to do the much more visible cowl.

@TheJester -- Thanks for the link to 7metalwest. That looks like a great option and probably cheaper than doing it myself.

By the time I'm done, buying it for $85 would almost certainly be cheaper than doing it myself, but I'm also trying to get better at metalworking as part of this project.

Most of the aluminum fenders I've seen seem to use ⅛" stock, which seems much thicker than what I need, and correspondingly probably harder to work with. Am I off the mark in thinking that I could successfully use something thinner if I support it on the frame and don't try to keep a close tolerance with the wheel (perhaps a few inches clearance most of the time? Or would you suggest I stick with something thick (~⅛") and plan deal with the challenge of working with the thick stock?

Greatly appreciate your guys help.

-- Bubba
 
deviant said:
Do you have a local supply house? I would get it there. You need such a small amount for a fender, you may find it in a cut-off bin for a better deal.
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Good idea. Unfortunately, I haven't found a local supply house that I like for metal stock (though I should probably look harder). The material amount looks to be small enough (~$20) that it's not worth driving around vs. just buying the cut stock online, if I'm able to find the right thing.

Greatly appreciate your advice.

-- Bubba
 
16 ga aluminum will be too flimsy. It will crack and break where it's mounted. That's the gauge of steel that we use for fenders.

Save yourself some drama, and buy a pre-made fender, then fit it. Unless you already have bossing mallets, shot bag, planishing hammer, and English wheel, you are just jerkin' off in a whore house.
 
if you want to make one, you need a dolly, piece of oak or maple, shotbag and mallet, if you've got an english wheel then you can probably polish it, if you don't, you'll be better off painting it. there's a step by step in my blog on making one, it's not all that hard
 
Anything done with an English wheel can be done with a planishing hammer, and vice versa. Also, a good set of hand planishing hammers works well without having to go out and buy a pneumatic one. A set of planishing hammers, a bossing hammer or two, and a couple dolly shapes go a long way. You can be creative and come up with alternatives for shot bags and planishing stakes- like a collection of carved wood shapes. A planishing hammer and the edge of a dolly will even compensate for not having a break. Hand forming takes patience and practice, but you can make anything by hand.
 
Roc City Cafe said:
if you want to make one, you need a dolly, piece of oak or maple, shotbag and mallet, if you've got an english wheel then you can probably polish it, if you don't, you'll be better off painting it. there's a step by step in my blog on making one, it's not all that hard
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Thanks! The link to your blog has exactly the info I was looking for, and does a great show-and-tell. Really helpful. I'll give it a try myself, and if I can't make it work, send you an order for one of your basic alloy fenders and go from there with fitting to my bike. I really like your blog, btw, especially the videos -- all sorts of good info.

deviant said:
Anything done with an English wheel can be done with a planishing hammer, and vice versa. Also, a good set of hand planishing hammers works well without having to go out and buy a pneumatic one. A set of planishing hammers, a bossing hammer or two, and a couple dolly shapes go a long way. You can be creative and come up with alternatives for shot bags and planishing stakes- like a collection of carved wood shapes. A planishing hammer and the edge of a dolly will even compensate for not having a break. Hand forming takes patience and practice, but you can make anything by hand.
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Thanks deviant. I have a membership at the local Techshop, which has an amazingly well-stocked metalshop. I've been taking some classes there and I'm looking for a more complex challenge than the basic items I've been making. They have an English wheel available, so it will be a combo of hand tools and English wheel for this project.
 
AlphaDogChoppers said:
Do you have a link to info about this shop?
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Sure -- http://www.techshop.ws They have about seven sites around the US. There are other shared-workshop spaces as well (Google for one in your area). Great place overall, though it's frustrating how they charge you for classes to learn how to use the big tools before you're allowed to use them on your own projects (class costs are above and beyond the monthly membership). Makes sense for things that I don't know how to use (like the big CNC machines), more frustrating for things like basic wood working machines, that I've been using in my own shop for decades.
 
AlphaDogChoppers said:
Thanks. That is useful info. I am working on a business plan for a motorcycle shop cooperative, and seeing how other people are putting together this kind of shared space is helpful.

http://cyclehackerspace.com
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That looks great. I'd sign up if it were within about 10 miles of my house (I'm guessing it's in Philly, though). Not sure how easy it is to make a go of it as a business, but it would be great as somebody looking for shared tools, space, and expertise.

Good luck with it!
 
Thanks, I don't have the lease finalized yet, but the location I am expecting to move into is just outside of Philadelphia. (Oreland, PA.)
 
AlphaDogChoppers said:
Thanks, I don't have the lease finalized yet, but the location I am expecting to move into is just outside of Philadelphia. (Oreland, PA.)
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I hope it works out. I could have used a place like that. I had to work out of my little Tacony row home garage. For what you're charging, it's competitive with the cheap garages in the hood. And to have access to equipment I couldn't necessarily afford- that's killer.
 
deviant said:
to have access to equipment I couldn't necessarily afford- that's killer.
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It's pretty much the whole point. I think the social club aspect of it is really important, too.
 
AlphaDogChoppers said:
It's pretty much the whole point. I think the social club aspect of it is really important, too.
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Yeah, one of the things I like best about the Techshop membership is hanging out with other people tinkering on all sorts of weird things. Not all bikes, but definitely a maker kind of attitude. Sometimes I prefer to work on my own in my barn but it's nice to get out and work with other people as well.

Best of luck with it.

-- Bubba
 
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