Question for frame builder/metal workers - Mountain Buzz
 



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Old 03-27-2016   #1
 
Missoula, Montana
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Question for frame builder/metal workers

What is the process of thinning a pipe so that it fits inside another pipe (swaged joint)? How does a metal worker make that style of breakdown frame?

I have an NRS style frame with breakdown side rails which are just an aluminum plug connecting the two pipes. Would this be significantly stronger than a swaged joint?

I like the clean look and lower weight of swaged joints but can't help but think it might sacrifice strength. Also I couldn't go boating today and am bored...

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Old 03-27-2016   #2
 
Great Falls, Montana
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In the ammo world we call it "necking down". I've had a local fabricator "neck down" the ends of pipe for a project I'm working on. I'm not sure what you mean by "plug connection". can you show us some pics?
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Old 03-27-2016   #3
 
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Originally Posted by ob1coby View Post
I'm not sure what you mean by "plug connection". can you show us some pics?
I believe he is referring to the NRS Breakdown Side Rails use a solid piece of aluminum in a slip joint (see pic), versus doing a swaged joint to achieve a breakdown side rail.

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Old 03-27-2016   #4
 
Carbondale, Colorado
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I wont pretend to have all 5the answers here but I do have a little input. Swage joints as you describe can be made by expanding one end of a tube into a lathe and using a special tool inserted into the pipe to exert enough pressure to expand the hole. We do this in the motorcycle frame construction (steel) - it is a good strong joint. I don't know about aluminum but am sceptical since it is a very "sticky" metal. It would be hard to machine in this way and I thing the joints would be hard to get apart unless they were really sloppy. I have the NRS joint pictured above on my cat frame and it is cheap simple and works fine. 20 years and no problem. My $.02 is its the way to go
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Old 03-27-2016   #5
 
Missoula, Montana
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Yes that is the type of "plug" that I am using for my side rails. I run a four bay frame with the front bay removable via this system. It makes for a very strong "trailer bay" that can be added or removed quickly.

My goal is to reduce weight and lo pros where possible and I am curious about using these "necked" or "swaged joints" to connect my cross bars to my side rails.

Having little to no aluminum welding skills I'm just curious about the difficulty of such a project for someone.
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Old 03-27-2016   #6
 
Great Falls, Montana
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Quote:
Originally Posted by riverdoghenry View Post
I believe he is referring to the NRS Breakdown Side Rails use a solid piece of aluminum in a slip joint (see pic), versus doing a swaged joint to achieve a breakdown side rail.

I thought that was what he was talking about. IMO this is a stronger Joint. AL doesn't like to bend. Necking or swaging I think will be weaker but I would be interested in knowing for sure.
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Old 03-27-2016   #7
 
Meridian, Idaho
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The weight could be reduced by using tube or pipe in place of the plug. Wouldnt weigh much more than the expanded or necked down joint. Its rafting, since when do we worry about ounces anyway.
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Old 03-27-2016   #8
 
Missoula, Montana
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Originally Posted by Mopdog View Post
Its rafting, since when do we worry about ounces anyway.
Ha, very true but every bit helps when trying to launch or takeout in areas that I can't use a trailer!

I did consider using smaller diameter pipe instead of the aluminum plug but wondered about strength issues. Anybody see an issue with that?
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Old 03-27-2016   #9
 
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The problem with reducing or expanding to create a swedge is that the aluminum will have to be annealed to soften it before these operations are performed.
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Old 03-27-2016   #10
 
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Whether the metal can take it or not depends on what grade it is really. Annealing isn't hard to do with aluminum anyways, just get a blow torch. If you are really slick you can even harden it again afterwards.

You can go either way...neck it down or expand it out. They do the expansion method at automotive exhaust places so you could try that...

Like this


You can buy a tool that will do it as well, and appears to just need a decent sized wrench to do it (though it would probably be easier with an impact driver)...



Again, it depends on the grade of the Aluminum, but I would be willing to bet that normal 6061 grade would expand a bit just fine without cracking cold. I've read up to 10% diameter expansion without annealing. It certainly would be easier with it annealed though. I'd have to do some more reading to tell how big a hit you are taking on stiffness after annealing it, but with it being two layers thick through that section it might not be bad. I guess there is a possibility of it being softer beyond the expansion area though.

Like people have said though, the sleeve style will definitely be stronger and if you can tubing sizes that have a slip fit automatically then its probably easier too. Just cut 4-6" sections of the smaller tube, fit it in, drill holes and put bolts through to hold it all together.
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