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Discussion Starter · #1 ·
i've come upon a few threads where the builder is making their subframe using a lot of butt joints.
What is the consensus? Avoid using them (bend the tube), use them with an interior plug or plate the outside, or are they ok?

example


all i can picture is shit shearing off, then balls to the rear wheel.
 

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sickboy
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3,544 Posts
IMO, any time you butt joint two pieces of tubing it should get slugged. No exceptions.
Exactly, any butt joint in line like that should get a slug in it and ideally a slug long enough to allow for a rosette weld (when you drill a hole in each side of the tube and weld the hole to the slug). IF a slug is not an option a cross bar at the joint could be used too. I.e. a bar stretching from the butt joint on one side to the identical but joint on the other side.
 
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Theres the reason for all the rules & regs most of us in europe have to put up with :mad:

An end to end butt joint has no place on a frame in my view its just lazy & could be unsafe, after all how long does it take to cut a piece of tube for a slug & drill a couple of holes to puddle weld it in place ?

A far better option would have been to cut it further back & slug on a new piece thats bent to shape but of course that would have involved spending a few quid :mad::mad:
 

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sickboy
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3,544 Posts
The correct way to do a butt joint... Drill rosette holes in tube, insert slug inside tube leaving gap roughly as wide as the tubing is thick. Align tube then weld up holes first then weld up the joint.

edit... better pic...

 

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King Ding-A-Ling
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806 Posts
Holy shit...people REALLY weld butt-joints together like that?! Obviously, someone doesn't like their dangle-down bits too much...sheesh.
 

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That pic just looks like a bad idea why wouldn't you just angle the tube right off the mount or bend the tube? I hope that's not someone on this site and we are letting him go through with it.
 

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sickboy
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3,544 Posts
Why is it a butt joint requires a slug or other re-enforcement, when a T joint with a similar amount of weld in the same tube is hunky dory?
Depends on the situation, if the T joint hits from the bottom and there is only down forces on it then theres no where near the stress on it and you can get away with just leaving it most the time. If the T joint has any lateral stress on it then you have to use a gusset on it, in most situations guys will gusset them anyway though (look at the pic I posted of the cafe hoop, the bar coming up hits in a T and it is then gusseted).
There is just no way to use a slug obviously so you gusset instead. Situations like people who build their own frames and dont gusset the backbone or legs off of the neck is just as unsafe as using a butt joint really.
 

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King Ding-A-Ling
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806 Posts
That pic just looks like a bad idea why wouldn't you just angle the tube right off the mount or bend the tube? I hope that's not someone on this site and we are letting him go through with it.


It actually IS a member of CF...Reed, a Noobie. He says in his build thread located here>>>> http://customfighters.com/forums/showthread.php?t=74010 <<<< that he just tacked it there, and is going to get a professional to weld it later on...lets hope he does!
 

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l&#592;&#647;u&#477;&#623;&#7433;&#633;&#477;dx&#4
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Depends on the situation, if the T joint hits from the bottom and there is only down forces on it then theres no where near the stress on it and you can get away with just leaving it most the time. If the T joint has any lateral stress on it then you have to use a gusset on it, in most situations guys will gusset them anyway though (look at the pic I posted of the cafe hoop, the bar coming up hits in a T and it is then gusseted).
There is just no way to use a slug obviously so you gusset instead. Situations like people who build their own frames and dont gusset the backbone or legs off of the neck is just as unsafe as using a butt joint really.
So a butt joint that is only under compression (as in a short column), tension (as in a cable shackle), or rotation (as in a drive shaft) would also be OK? But I guess such pure forces are rare in motorcycle fab, where you deal with a lot of flex and shear...
 

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sickboy
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So a butt joint that is only under compression (as in a short column), tension (as in a cable shackle), or rotation (as in a drive shaft) would also be OK? But I guess such pure forces are rare in motorcycle fab, where you deal with a lot of flex and shear...
I would never say its "ok" because I always slug every butt welded tube but itd be a lot safer than on a subframe that takes your weight and has the flex force as you said.
 

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Ive always wondered this cause If i wanted to do slugs itd prolly be costlier than id want, is there any disadvantage over a sleeve/plate welded over the joint?
Ive seen the diamond shaped plate bracing as well over tube. is there any difference in strength betweent that and a sleeve with the ID of OD of the tube with the joint?
 

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Oiler Boilereerer...er(s)
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All tubing butt joints should be slugged. If your gunna cut corners, at least sleeved with another smaller tube.

It needs some kinda sheer strength, especially with thin tubing, it's not like it's 1/4" wall where you can get a heluva bead in there.
 
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I always slug butt joints if i really HAVE to use them i always try to slug at a point where another tube is coming in to meet the butt at an angle as well even if it means cutting a tube further back than i really wanted to acheive this

slugs are usually a piece of tube of the same wall thickness as the original that fits tightly into the original & extends 3" either side on the butt, anything less is not good practice in my book , where a 3" either side of the joint slug is not possible due to bends etc & another tube is not being welded in to support the joint i simply find another way or brace as required with plates

For structural butt joints i usually angle the joint as well to allow more weld area, although the joint shown on the frame loop above is absolutly fine & ive done it that way hundreds of times i would have angled the joint out of habit :D
 
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