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08-15-2008, 05:18 PM #1
Help with ring roller for motorcycle fenders
Is there anyone here with roll form experience? I restore vintage motorcycles as a hobby and I took on the challenge of making a ring roll with roller dies the shape of a aluminum fender used on the motorcycle. When the aluminum is rolled the inside radius of the fender has to shrink or it creates ripples.
How do I eliminate these ripples during rolling. Some people mentioned heating to aneal or something.
I also am not sure of the exact specs for aluminum I should use. 5052 ?
There are also soft grades of 5052. No clue which I should use.
08-15-2008, 05:33 PM #2
08-15-2008, 05:52 PM #3
Motorcycle fenders are typically spun or stamped, and not rolled, for the exact reasons/problems you're finding. Cheap utility trailer fenders are sometimes rolled, and even on a production basis they exhibit the wrinkling effect of the material being longer than it needs to be on the smaller radius areas.
Not sure, but I'd guess most people who form one-off items like this probably use 3003-H14 aluminum sheet.
08-15-2008, 06:02 PM #4
Must be 40 years ago I watched a guy making ally mudguards, IIRC he used a combination of forming rolls, English wheel and dressing with a bossing mallet & stick over hardwood formers. The deeper types were made in sections and welded up.
08-16-2008, 03:20 PM #5
I had a bad feeling they were stamped and someone did mention spinning. I can't imagine spinning a 24 inch diameter piece of aluminum.
Maybe I can form the fender on rollers and some how spin the ripples out. Where is MacGyver when you need him.
So much for my ring roller investment. I should have done more research.
08-16-2008, 08:42 PM #6
Actually, somebody did post a link to a fender rolling process here, a couple of years ago.
In industry, in large quantities, they stamp them, but I think a few boutique manufacturers might have rolled them over the years.
However, they would use a multiple station, rollforming setup, where the sheet metal went thru a series of rolls, each one taking it a big farther- kinda like one of these-
This eliminates the wrinkles, by doing it in baby steps, rather than all at once.
A ring roller for pipe or solid bar is not the right tool to do this with- you need to support the rolls on both sides, not just on one end. You would roll an oversized blank, then trim it to actual fender shape at the end.
Here is a free book online that discusses the general process-
"Roll Forming Handbook " at Google Book Search
You certainly CAN roll motorcycle fenders- but it will take big, heavy, rigid machines, special tooling, and some trial and error.
08-17-2008, 05:33 AM #7
I designed a mudguard rollformer for mass production of aluminium mudguards (bicycle, not motorcycle) a few decades ago, with the help of my genius of a boss.
Worked a treat, more thanks to his input than my talents at the time.
However the dick-head client shafted us out of a happy handover, but telling us when the design was finished and the geometry of the rolls optimised (and they'd been sent away for hardening), that 'by the way', they would also be using it on steel guards, of 20% thinner sheet. Sheesh !
The key to getting the curve ripple free is to "iron" the midpoint material thickness to a suitably thinner dimension, so that the circumference of the resulting ring grows in correct proportion relative to a theoretical unmodified thickness at the rims. (in practice, the latter will grow very slightly thicker but this can be ignored: you don't want much or you'll be back into ripple territory)
The thinning needs to be pro-rated to the rest of the section, in proportion to the radius (ie distance from the axle).
Naturally this means much higher roll loadings than straight rollforming. It can be done with cantilevered rolls, but much easier if they're supported both sides, especially since for "ironing" (think rolling out pastry) the roll diameter should be as small as feasible, to keep the force down.
PM me if you want a fuller explanation, especially if you were thinking of making one for production: there are some clever tricks we learned.
08-17-2008, 10:56 AM #8
Slightly off the roll forming topic, there's an article in the July Metal Forming magazine about making Harley rear fenders.
It's the cover story. I couldn't get the direct link to the story to work.
The fender shown is 304 stainless, you can only imagine how difficult that was to design stamping dies around that material.
In another forum several years ago a die maker showed a bit about dies he had made for 16ga steel rear fenders for Harley, I recall he said the dies were $490K.
08-17-2008, 11:42 AM #9
Wow, you all been a great help. Thanks
08-17-2008, 11:54 AM #10
Yes, I found that reference here in this forum some place. That was why I went a head and built my own. Unfortunately there was no reference to the ripple problem. After close examination of the photos supplied you could see the ripples in the fender. Hard lesson learned for a person with no roll form experience.
The dirt bike fenders I am making a more extreme in arc so the ripples are more pronounced.
Thanks for your input.