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Plainsman 01-18-08 11:40 AM

Custom aerobars...
 
I'm looking to have some custom aerobar extensions made, and I'm hoping someone here can give me some help. (Note: I am not a machinist or mechanic, just a rider). I've looked on the websites, and both Profile Design and Oval concepts seem to use a 6061 T-6 Alloy with a 22.2mm OD. I've looked online and I can buy 6061 T-6 very reasonably (2 - 2ft pieces for <$10). Here are my questions:

1. Is 7/8" OD close enough to 22.2mm? The brackets I'm using (Profile Design) are designed for 22.2mm

2. Does anyone know the typical Inside Diameter or wall thickness of the standard PD or Oval concept extensions? I don't think I own the calipers neccessary to take those measurements.

3. Who could I find to bend these bars, say a single or double bend at 30 degrees (machine shop, plumber? electrician? )? I'm doing this to save a litte $$, and get a little longer aero extension than you could buy stock, so if I can get the bars for cheap, but then it costs $40 to bend them, I'm not gaining anything. Any idea what that service would cost?

Thanks for the help in advance!

cujet 01-19-08 06:30 AM

Smooth bends in tubing are done on a mandrel bending maching. There is an internal mandrel to prevent the tube from collapse. You might have a hard time finding someone to bend the tubing without kinking it.

The wall thickness of aluminum tubing is all over the map. The more expensive parts are thinner, and better aluminum alloys. I have a set of bars with tapered wall thickness, thicker at the mount than at the end. Just guessing, the wall thickness is about 0.050 inches.

Believe it or not, I have bent aluminum tubing quite nicely using a propane torch, and heating it to above 700 deg F (the point at which it becomes plastic). But, I work with metal every day, and I understand where to put the heat to get a good bend. Also, this destroys any heat treating the metal has. So, the end result is a part with unknown properties, never as good as the original. You could experiment with some cheap tubing and a propane torch. It takes a while to heat it, as aluminum transfers heat quickly away from the spot the flame hits.

Once it is up to temp, it bends easily, it becomes soft. But, the melting point is very close!

Chris

Plainsman 01-19-08 02:42 PM

Thanks for the feedback. Through my day job, I sometimes have contact with a metal fab shop (mostly does steel stairs, handrails, struct. alum, etc. One of their employees has offered to bend the tubes for me for free. Think they would have the capability you are talking about?

cujet 01-19-08 05:08 PM

I would not even be able to guess at the capability of the shop. Never hurts to ask.

Believe it or not, you want to do something that is so simple, but can end up very complex and difficult to accomplish.

If it were me, I would try a few different methods. Cutting and welding 6061 tubing is no problem, so I might try that first. The next might be to bend it using heat.

Also, there are companies that will do this for you. But the cost will be quite high.

Chris

NoReg 01-20-08 11:41 AM

I would doubt they would have a mandrel bender, since that is more typical of places like muffler shops. Steel fabrication that does stuff like Office furniture or chassis, tends to be mild steel oriented in structural dimentions. You might be able to bend the al anyway. Most of my bending has been steel, but the need for a mandrel is roughly proportional to the thickness of wall to tube diameter ratio. Most Al tubes are fatter walled than similar steel tubes so you probably are ok. You can also pack tubes with everythign from frozen water to sand, to produce an effective mandrel.

You would be pretty lucky though to find your metal a perfect fit on diameters. I haven't calced your project, but most tubes are not sized to easily interfit because the people doing the fabricating want the option of machining to a perfect final fit.

I bet you could probabluy home make something you need, but makign it out of metal is pretty easy when you know how and have the gear, but not easy to wing. You can do your own carbon fabrication with popscicle sticks and scissors, metal really gets tool intense.

I you are after a smooth U-bent here, you may be in for a surprise. If you just bend a piece of wire, by grabing it at either end, you will notice you do not get a smooth curve (well it is smooth, but parabolic not U shaped). You get a bend that is tighter at the begining than the end. There are various ways around this, but it is just one example of how even a grand of bender won't solve all your problems.

cujet 01-20-08 07:16 PM

Most muffler shops do not have a mandrel bender. They have hydraulic benders that support the pipe externally, but crush it a bit during the bend. The result is about a 25% reduction in diameter, right in the middle of the bend.

Only OEM exhaust systems and very high performance exhausts are made on a computerized mandrel bender.

Plainsman 01-27-08 07:02 PM

Yikes! Sounds like what I though would be a really simple task is not that simple at all! Well to be honest, I'm not sure if a smooth bend is really a neccessity, or any bend at all for that matter. I wonder if I should just go for a cut and weld then. Can't see that aerodynamically it would be radically different.

NoReg 01-27-08 07:56 PM

You can make some decent bends by making repeated half way cut every inch or so and welding them shut. If I have the aero bar design right, the bends aren't where the load is? Not to say good welds would break.

I don't think this is a difficult project, except that there seems to be a money saving aspect to it. If you are doing it solely for the experience or desire to make a particular unavailable thing, then people will spend the dough required to do it. But when you have to nail everything on the very first try, possibly using expedient methods in a situation where a welding, machine, and railing shop equipment are the minimum...


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