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Discussion Starter · #1 ·
46works out of Japan just put up a new video on his latest project... he's a fantastic craftsman and quite the accomplished racer there, so noobs take note of what he does here:

 

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I think I would have sleeved it and used tubing the same OD of the frame, but that’s just me.
 
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Discussion Starter · #3 ·
I'm surprised he didn't sleeve it either as he's done so on other portions of the bike... so I suppose its an area where the added strength of a sleeve isn't necessary?
 

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I’m sure the added strength wouldn’t be needed, but aesthetically, it would be cleaner without the change in tube size. But either way the bike will be better than anything I will ever cobble together..,.
 

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Discussion Starter · #5 ·
You should see the episode where he machines a hub out of a solid block of aluminum.

I love the editing of his videos. Its all about showing the most important bits... and there's no talking, only the occasional subtitle
 
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That sort of joint, if properly welded, is perfectly adequate without a sleeve. The purpose of a sleeve is to move any bending stress away from the weld and into the tubes, but at the end of the sleeve there's a huge increase in stress if it's a straight cut. A seat hoop carries little to no stress despite what we all read online. It does add to frame stiffness between the shocks if that's the only cross tube behind the main cradle.

So add a cross tube to take the stress and leave the hoop as a way to tidy things up and attach a seat. If the join between two frame tubes was in a high stress area, then for sure step the joint or add a slug with tapered ends to spread the load. I thought I was the only one bending stock thickwall frame tubes that way.

On TZ frames, the rear loop was welded on top of the frame rails.
 

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That sort of joint, if properly welded, is perfectly adequate without a sleeve. The purpose of a sleeve is to move any bending stress away from the weld and into the tubes, but at the end of the sleeve there's a huge increase in stress if it's a straight cut. A seat hoop carries little to no stress despite what we all read online. It does add to frame stiffness between the shocks if that's the only cross tube behind the main cradle.

So add a cross tube to take the stress and leave the hoop as a way to tidy things up and attach a seat. If the join between two frame tubes was in a high stress area, then for sure step the joint or add a slug with tapered ends to spread the load. I thought I was the only one bending stock thickwall frame tubes that way.

On TZ frames, the rear loop was welded on top of the frame rails.
The purpose of a sleeve really depends on what you are using it for, doesn't it?

In this case, I would use the sleeve for alignment of the same sized tubing. And also to give me a buffer against burn through... which he wouldn't need.

I agree you wouldn't need them for strength. Which got me thinking, what percentage of body weight is actually on the seat of a bike with clip ons and rear sets?
 

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And of that weight, how much of it is exerted behind the seat and under the hump? I'd speculate that it's less than the weight of the tube. The rationale is that if there's no other significant structure between the shock top mounts, then the subframe, such as it is, will tend to flex. In reality, most people are cutting off the ends of two straight, or almost straight tubes.

But the point I think that people here try to make is that newbies need to understand what they are cutting off that the potential impact of the changes they make. And that is totally valid. That video was interesting tough and the fabricator clearly is thinking things through one step at a time to avoid future problems.
 

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i was watching in horror as he cut into a lemans frame, then realised it's a 4 or 5 and changed my horror to hack away my man.

not sure if i'm sold on his shortening the steering head tube. not sure what that little sheet metal bracket and extra inch or so of stem length really do, but it's not like it's that high anyway. maybe not what he wanted.
 

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