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Old 02-16-2013, 10:37 PM   #226
Roadracer_Al
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Agreed -- you ***really*** want to radius the edges, because the weld will crack if you just put a bead on a 90* corner.

You can easily whip up a set of T-Dollies for this job. They're designed so the stake rests on the cross-bar of your vise -- make sure that the stake is long enough so the round dolly part sticks up 3~4 inches above the vise jaws.



Use the T-Dolly to form the half-round-over on each side of the edge ( the intersection of 2 planes). Corners (intersection of 3 planes) are a bit tricky, but a little practice and you'll get the hang of it -- basically, leave the corners long, and file them back to about 45* after you've rounded the corner over.

I suggest that you fit everything first, just taping the pieces together so you can weld it all at once, preferably with back-gassing.

Also, I strongly suggest investing in some aluminum files - you'll never know how you got on without them if you do much aluminum fab. They cut fast and don't clog. You'll like'em, I promise.

Regarding your bends, make sure that you use a generous radius -- aluminum doesn't like to be bent sharp or crisp -- it will break along a sharp bend. The minimum recommneded radius depends on the thickness of the material, but a wider radius is always better b/c it won't crack as easily. Again, you have to build your corners carefully -- they'll be the meeting of 3 radiused edges.
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Old 02-17-2013, 06:45 AM   #227
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Originally Posted by Salsa View Post
Here is a tip on sheet metal welding to minimize distortion.

Cut the metal .090-.120 inch or so long on each weld edge and bend it "out" 45 degrees. When you mate them together you get 2 edges to weld together. You might need rod to start it, but after you get started, try to not add weld. Just burn it down to the corner you want. You don't get much heat into the sheet of metal.

An alternative method is to round the corner "inward" about 1/4 - 1/2 inch from the weld to make a stiffened edge.

Charley Curnutt of Curnutt shock fame broke his collar bone in about 1970 and built a bike while he was recovering. A few months later I broke mine so I had to built a bike too. I built a sheet metal framed bike with the "tank" surrounding the engine including under the engine. I built a leading link front end.

Don
Don,

I think I understand what you are talking about with bending the two pieces outwards and then burning the seam, makes sense. I'm making this tank from aluminum seems like that would put more heat in the metal due to the amps required to melt back the seam. Do you have any pics of what you are talking about because I'm a little fuzzy on it right now and I want to make sure we are talking the same thing.

Thanks
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Old 02-17-2013, 06:52 AM   #228
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Originally Posted by Roadracer_Al View Post
Agreed -- you ***really*** want to radius the edges, because the weld will crack if you just put a bead on a 90* corner.

You can easily whip up a set of T-Dollies for this job. They're designed so the stake rests on the cross-bar of your vise -- make sure that the stake is long enough so the round dolly part sticks up 3~4 inches above the vise jaws.



Use the T-Dolly to form the half-round-over on each side of the edge ( the intersection of 2 planes). Corners (intersection of 3 planes) are a bit tricky, but a little practice and you'll get the hang of it -- basically, leave the corners long, and file them back to about 45* after you've rounded the corner over.

I suggest that you fit everything first, just taping the pieces together so you can weld it all at once, preferably with back-gassing.

Also, I strongly suggest investing in some aluminum files - you'll never know how you got on without them if you do much aluminum fab. They cut fast and don't clog. You'll like'em, I promise.

Regarding your bends, make sure that you use a generous radius -- aluminum doesn't like to be bent sharp or crisp -- it will break along a sharp bend. The minimum recommneded radius depends on the thickness of the material, but a wider radius is always better b/c it won't crack as easily. Again, you have to build your corners carefully -- they'll be the meeting of 3 radiused edges.
Al,

I looked up T dollies and found a youtube video of some guy doing this. looks cool. What's the difference though when you join the parts together? It's still a butt joint or am I missing something? I can make one of those dollies easy enough and the actual forming doesn't look difficult at all.

My other issue is that I have designed this part to fit fairly snugly in the hole and the wildcard of making those radius corners as that I'd have to redesign it and not really know how the bends would turn out.

I've been bending 90 degree sharp corners on 5052 aluminum and it comes out great. I made my second set of panniers this way and the bends worked great no issues with doing it that way.

I have some aluminum files and they do make a big difference. Cut aggressively and leave a razor sharp edge.

I'm going to make up a prototype from aluminum today and see if I can get it to work. I'll offer it up for critique and you guys can mark it up and tell me where I should be radius-ing corners.
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Old 02-17-2013, 11:20 AM   #229
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Quote:
Originally Posted by sailah View Post
Don,

I think I understand what you are talking about with bending the two pieces outwards and then burning the seam, makes sense. I'm making this tank from aluminum seems like that would put more heat in the metal due to the amps required to melt back the seam. Do you have any pics of what you are talking about because I'm a little fuzzy on it right now and I want to make sure we are talking the same thing.

Thanks
In my case, the sheet metal frame was steel (bend out), and the gas tank (inward) was aluminum.
I think the frame was gas welded, and I know the gas tank was gas welded in about 1959, so I had not built my first TIG.

In both cases, the bend makes the metal stiff at the edge. That is what keeps the distortion small.

Sorry, no pictures.

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Old 02-17-2013, 02:51 PM   #230
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Originally Posted by sailah View Post
What's the difference though when you join the parts together? It's still a butt joint or am I missing something? I can make one of those dollies easy enough and the actual forming doesn't look difficult at all.
Basically, it's a question of managing where the material flexes -- if it's a square corner, and the flat sheet "drums" (i.e. vibrates up and down in the middle), the welded corners will be where it flexes. That's why square welded corners break.

If you put some shape into the corners, it flexes where it's tangent to the large, flat area, and leaves the weld alone.

It's also a good idea to bead roll some stiffening "X" shapes into the large flat areas to prevent them from drumming in the first place.
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Old 02-17-2013, 03:44 PM   #231
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Well I'm going to see how this goes for a prototype. I plan to do it again, just want to make sure my dimensions are right.

I made the main part from one piece and bent the two sides and the end. I did weld the bottom on but have not snapped a pic of it.





Al & Don, I did note your points and will work that in when I build the final version. The one I have pictured is simply for mockup. What you both said makes sense and I will attempt to try and work in those points when I build the final version. I did try the bending two "lips" and burning them together and it made for a really nice bead.
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Old 02-17-2013, 11:56 PM   #232
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Your welding is starting to get nice and neat.
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Old 02-18-2013, 07:15 AM   #233
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Your welding is starting to get nice and neat.
You haven't see the other side

Plumbing questions:

The main tank I am going to seal off and weld in a bung. I have purchased some -6AN fuel fittings from Summit along with hose ends and hose. My plan is to run a feeder line from the main tank to the subtank.



Now if I never hit the subtank on "reserve", it's fill as usual. But say I run the bike completely out of fuel and start to fill it through the tank filler on the main tank. Obviously the fuel is going to fill the main tank faster than the feeder line can fill the subtank so in order to press the tanks, I'll need to be patient at the pump.

My question is this. Say I run the feeder line as -6AN which seemed a reasonable size. The fuel draining into the subtank is going to displace the air in the tank and it needs somewhere to go. If I vent the subtank to ambient air, it's going to need to be higher than the top tank level.

If I vent it back to the main tank, I'm going to need to run an internal line inside the tank and up to it's highest point?

Below is a crude schematic but I think shows what I am trying to accomplish.



I could go bigger on the fuel line with the hope that the larger diameter will fill and vent effectively in the same line, but I suspect that it will get annoying and create a bottleneck which will dramatically slow down the filling process.

Thoughts?
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Old 02-18-2013, 09:15 AM   #234
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Somewhere I saw a setup something like this,the vent line of the main tank was turn used as a suction line to the aux tank
,the aux was vented .
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Old 02-18-2013, 11:03 AM   #235
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If I vent it back to the main tank, I'm going to need to run an internal line inside the tank and up to it's highest point?
The ninja has a built in fuel overflow from just under the cap to the bottom of the tank. I tihnk it gets sealed off when the cap is shut.
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Old 02-18-2013, 01:44 PM   #236
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Somewhere I saw a setup something like this,the vent line of the main tank was turn used as a suction line to the aux tank
,the aux was vented .
If I use the vent from the main tank, then it won't have a vent at all as it will be sealed. The aux tank is below the main tank so I think it would create more problems.

Quote:
Originally Posted by sanjoh View Post
The ninja has a built in fuel overflow from just under the cap to the bottom of the tank. I tihnk it gets sealed off when the cap is shut.
The main tank must have a vent though correct?


Finished the protoype. Holds about 1.25 gals I filled it with a 2 qt apple juice bottle and it took 2.5 bottles, so the CAD model was pretty accurate. I had one minor pinhole that I went back over with the welder but other than that it was watertight the first time. I'll need to test with gas because I've found gas will find holes water won't.



I had to preheat the flange with a torch to get it hot. Welded fine I have to admit I was a little nervous with such a difference in thickness but it welded great.







Pump installed. I need to make a guard for the chain. It has plenty of clearance, I'm thinking more about sticks and flinging crap and keeping it off the wiring etc.





Need to make some brackets to weld to the tank so I can bolt to the subframe. I think rubber mounted is the way to go so I'll work on that.
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Old 02-18-2013, 02:38 PM   #237
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Great work.

A build I'm doing at the moment has a rear subframe tank and I've been trying to think of how to fill it without having to put a big filler cap on it some where.
I was thinking that the only way it would not be a pain to fill would be to have 1.5 inch hose running from the front tank to the rear.
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Old 02-18-2013, 03:42 PM   #238
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Joe,

Thanks I'm pretty happy with how it turned out. Now just need to work on a mount setup. My buddy called me and explained how his works on his Husaberg.

It's just a simple vent that he tees into the regular vent coming off his gas cap.

I looked inside the Ninja tank and there is a metal straw than runs internally and exits the bottom of the tank as an overflow like Sanjoh said.

I can make up a barb setup and zip tie it to the straw in there.

I just bought a bunch of gasoline grade barbs and tubing from McMaster to add to the fancy ass AN racing stuff.
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Old 02-19-2013, 10:55 AM   #239
Roadracer_Al
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Sailah -- I've had bad experiences trying to just weld flanges onto flat sheet metal -- they usually tear out a chunk of the sidewall of the tank because you can't spread the load enough with just a tab.

The way I have had succes is to make a top-hat shaped pocket on the the lathe, and weld this into the tank. The pocket needs to be sized to have a snug fit for a well nut (the expanding rubber nuts that you sometimes see on windshields). This has the benefit of both getting a very long bead/large surface area for the mount, and provides rubber isolation at the same time, and major bonus, is mostly flush.

Here's a link to well nuts on McMaster:

http://www.mcmaster.com/#well-nuts/=ljrsh8

Another excellent mechanism is to put a tube all the way through the tank, and support the tank with a rubber-wrapped stud that's supported at both ends. If this doesn't make sense, I'll make a sketch and post it.
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Old 02-19-2013, 10:59 AM   #240
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Nice work!!

I find it easier to put 10 lbs of air in little tanks like that and dunk them in the bathtub...don't do that when the wife is home. Use a grease pencil to mark the leaks and weld them up quick like, much faster than liquid because the tank is nice and dry inside.
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