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Old 03-02-13, 05:23 PM   #1
MrkiMedo
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tube through tube joint type

As a part of learning process, I am thinking about brazing a frame for bicycle trailer, with standard cheap steel non bicycle tubes. I was wondering how difficult is to make a joint type where one tube goes completely through hole in bigger one, like for instance in this stem (although theirs is not brazed, but I think I saw such brazed joints elsewhere)

- What is a strength of such joint?

- Are there some restriction in dimensions, like min ratio of tube diameters, or tube wall thickess? I was thinking of 0.5 to 1.0 mm thick tubes where smaller one (which goes through hole) would be 12mm in diameter and bigger one 24mm

- What should be the dimension of the drill in the bigger one, exactly the diameter of smaller one?

- Brass or silver?

Many thanks!
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Old 03-02-13, 08:10 PM   #2
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You mean 1 tube pierces the other? Ca 90 , Burly Tandems uset a long top tube peirced by both ,
a slip fit, then they were tig welded together.

as the VO stem is likely made in Asia, they have a capacity to make a tube stepped down so top for bolt
head is potentially part of the quill .


Strength ? one way to find out. Do a destructive test, measuring force applied just at failure point


seems other than collecting data, there is limits to talking about relative strength,
on tifosi forum.

Last edited by fietsbob; 03-04-13 at 11:49 AM.
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Old 03-03-13, 03:43 PM   #3
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You mean 1 tube pierces the other? Ca 90 , Burly Tandems uset a long top tube peirced by both ,
a slip fit, then they were tig welded together.
yes, I did not know how it is called, thank you!
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Old 03-03-13, 04:11 PM   #4
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If you Tig with plain steel filler wire, you can overlay that with Brass and get the smooth look
typically stainless steel filler is used. brass bonding to stainless ... a maybe..
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Old 03-03-13, 04:35 PM   #5
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If you Tig with plain steel filler wire, you can overlay that with Brass and get the smooth look
typically stainless steel filler is used. brass bonding to stainless ... a maybe..
Well, I am planing to make a trailer frame with ordinary steel tubes, something like:

+--+-----------+--+
|....|................|....|
|....|................|....|
|....|................|....|
|....|................|....|
|....|................|....|
+--+-----------+--+

And I thought that pierced joints could be used on places where + are. I do not have welding equipment, and also one of the goals would be to get some practice in brazing. So aesthetics is also not primary concern at this time, but getting everything decently aligned, and not falling apart on first bump on the road.

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Old 03-03-13, 09:53 PM   #6
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There are a lot of methods to clamp tubes to hold their relationships before tacking with a spot of brass. Doing single or pairs of joints might be easier then the whole framework. I have used hose clamps to act as a ledge as well as to clamp a temp cross brace as an example. The biggest reason to use a through hole is cosmetic. If the tube specs and joining process (miter and weld/braze) is properly chosen then the second joint (the 'through" one) only adds complexity and weight. Andy.
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Old 03-03-13, 10:53 PM   #7
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Destructive testing in cool, but often the case is way more extreme than what the object is intended to carry. Destructive testing properly done will show whether your welds are full strength but failure modes for structures are a lot more subtle than that.
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Old 03-04-13, 07:05 AM   #8
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I don't have experience making such joints, but I think they might be overly complicated. You need to pierce the mating tube at two spots and then cap the protruding end. For a stem (or tandem) it makes sense because you need the bolt (or seatpost) throught and the second tube has a larger diameter. In your case a simple mitred joint, with brass, would be as strong.

Your tube dimensions look okay, but stay with a 1 mm wall (you probably won't find a 0.5 mm walled tube anyway). For the pierced mitre the tube needs to slip in without resistance but without gaps. The size of of the drilling cutter will depend on the rigidity of your setup. With a hand drill, it would be next to impossible to keep the two holes of each mitre centred on the tube, not to mention keeping the series of holes in phase on the larger tube.

Last edited by tuz; 03-04-13 at 07:08 AM.
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Old 03-04-13, 10:01 AM   #9
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Originally Posted by MrkiMedo View Post
As a part of learning process, I am thinking about brazing a frame for bicycle trailer, with standard cheap steel non bicycle tubes. I was wondering how difficult is to make a joint type where one tube goes completely through hole in bigger one, like for instance in this stem (although theirs is not brazed, but I think I saw such brazed joints elsewhere)

- What is a strength of such joint?

- Are there some restriction in dimensions, like min ratio of tube diameters, or tube wall thickess? I was thinking of 0.5 to 1.0 mm thick tubes where smaller one (which goes through hole) would be 12mm in diameter and bigger one 24mm

- What should be the dimension of the drill in the bigger one, exactly the diameter of smaller one?

- Brass or silver?

Many thanks!
Not sure specifically what you are referring to a "cheap steel non bicycle tubes" especially if you want to use thin wall. If I source a tube from say "Aircraft Spruce" I consider it a bike tube even if it is marketed for aircraft construction. AFAIAC, a bike tube is any tube used to make a bike, give or take a bit of common sense.

As to strength of a pieced tube design...although I have seen advertising from major brand builders to the contrary, I am not really seeing a driven difference specifically due to that point. Many other aspects of the design and execution will likely have as much or more effect on the strength of the joint.

I was once handed an 8 foot long stick of oval chromoly tubing about 1.0mm wall and 1.7"x1.25" in dimension with a request "can you make me a tandem using this as a continuous top tube?" Sure 'nuff, easily done. Of course if one wanted the look and didn't have the long tube to use, it is simple to achieve the same look with two pipes meeting at the center of the seat tube...any builder could do it and most would if asked.

/K
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Old 03-05-13, 01:55 AM   #10
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I don't have experience making such joints, but I think they might be overly complicated. You need to pierce the mating tube at two spots and then cap the protruding end. For a stem (or tandem) it makes sense because you need the bolt (or seatpost) throught and the second tube has a larger diameter. In your case a simple mitred joint, with brass, would be as strong.

Your tube dimensions look okay, but stay with a 1 mm wall (you probably won't find a 0.5 mm walled tube anyway). For the pierced mitre the tube needs to slip in without resistance but without gaps. The size of of the drilling cutter will depend on the rigidity of your setup. With a hand drill, it would be next to impossible to keep the two holes of each mitre centred on the tube, not to mention keeping the series of holes in phase on the larger tube.
Here are the reasons why I am thinking about using this kind of joint:
- could not find such lugs
- with classic mitered joints I would need to miter 4 tubes on both sides to exactly matching length.
- I am not sure if it is con or pro, but in difference to the bicycle, on this trailer forces would be acting in different direction regarding a joint i.e rotating

For the holes drilling, I have hand drill with stand to mount it in, and I was thinking of creating some fixture to hold the tubes in right position while drilling. But maybe I could also give tube to some machinist for dirlling.

As for dimensions you were right, ones that are thick 0.5 are only in catalog, but not in the stock where I am buying.

Someone else asked what do I mean by non bicycle tubes, I was referring to steel tubes bought at common local hardware store. How are they called in english I am not sure, here they are referred to as precise thin walled non welded steel tubes (in my rough translation).

Thanks to all for suggestions.
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Old 03-05-13, 05:29 AM   #11
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the issue with doing this is that it's going to be hard to clean the inside of the tubes. If you don't get them clean, it will not be a very strong joint. You would get very good at mitering fairly quickly.

You can try it and tell us how it works. Looks like it has its own issues. Drilling a series of holes accurately is not particularly easy
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Old 03-05-13, 08:06 AM   #12
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With the right tube brush you can get the inside pretty clean. Besides, the outside fillet should give the joint most of it's strength.

It's true that a standard mitre will have its own challenges (keeping the two ends in phase, and all the tubes at the same length). You can creep your way into equal lengths, checking every second file stroke or so... You can always keep the shortest and adjust the others. It's possible you'll have to bin some tubes, but that might also happen while attempting to drill the through holes.
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Old 03-05-13, 08:25 AM   #13
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I don't think a brush will get rid of the cruft inside a tube. Sure, it will get rid of most of the dirt. The outside fillet isn't particularly strong either, it's the filler between the miter and the tube that gives most of the strength. It's just that it's hard to get good penetration without having the inside of the tube really clean. I think the OP is underestimating how hard it will be to get good holes in tubes, it's really the same problem as mitering.
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Old 03-05-13, 08:58 AM   #14
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I use steel tube brushes with an OD bigger than the tube ID. Spun by a drill they leave the inside surface clean and shiny (and hot!). That is for drawn cromo whose surface finish is already pretty nice.
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Old 03-05-13, 09:10 AM   #15
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Having learned to braze copper I can tell ya cleaning the inside is important and that a wire brush in a drill the appropriate size will certainly do the job well enough provided it's cleanish steel you're working with.

Through-holes look cool I guess but it's not going to be anything but a headache to fab. If you haven't done much fab work before I'd suggest using angle to build your trailer so you can get a better handle on making square cuts and making good 90° cuts and joints first, they are much easier than cutting mitres. Look at existing trailers and other things made out of tubular steel (tables, chairs, etc.) to see how they are braced and joined.

If you're gonna braze this just use brass, there's no need to waste money on silver. Personally I use nickel where most people use silver but I'm cheap like that. If you're looking for an excuse to work with tubing specifically just get some 1" and 1.125" cr-mo and make a pile of small pseudo-frames.
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Old 03-05-13, 09:26 AM   #16
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what kind of brush do you use? I see McMaster Carr has a wide selection of brushes
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Old 03-05-13, 09:50 AM   #17
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I've used the Spyrakleen brushes from KBC, 1" and 1.25" dia.
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Old 03-05-13, 12:16 PM   #18
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[OP Partial Qote; Someone else asked what do I mean by non bicycle tubes, I was referring to steel tubes bought at common local hardware store. How are they called in english I am not sure, here they are referred to as precise thin walled non welded steel tubes (in my rough translation). Thanks to all for suggestions. Unquote]

Interesting. Personally, I have never been to a local hardware store which stocked or even could order seamless thin wall steel tubing. If is either welded up water or gas pipe or it is something on the rack with the angle iron stuff. If you take a piece of that tubing and hold it up to the light you will guaranteed see the seem running down the inside. Thee real problem with that tubing is that it is of rather soft steel (easily bent by hand), that it is fairly expensive per foot for what it gives you, the selection is usually limited to a couple of diameters and lengths, and the volume in stock is undependable (often only 1 or two sticks per size). Apologies if you live near the worlds best hardware store with a better situation. Wish I did. I have to push my local ones to just keep the metric bolts in stock...

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Old 03-05-13, 01:24 PM   #19
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Interesting. Personally, I have never been to a local hardware store which stocked or even could order seamless thin wall steel tubing. If is either welded up water or gas pipe or it is something on the rack with the angle iron stuff. If you take a piece of that tubing and hold it up to the light you will guaranteed see the seem running down the inside. Thee real problem with that tubing is that it is of rather soft steel (easily bent by hand), that it is fairly expensive per foot for what it gives you, the selection is usually limited to a couple of diameters and lengths, and the volume in stock is undependable (often only 1 or two sticks per size). Apologies if you live near the worlds best hardware store with a better situation. Wish I did. I have to push my local ones to just keep the metric bolts in stock...
Thank you for the advice, I will inspect them as you suggested.

But please keep in mind that my command of English is rather poor so that might be the cause of some misunderstanding as well. I am looking at their catalog, and they do have separate section of catalog and product numbers for seamless precise pipes, and separate section of catalog for welded pipes so I guess they do stock different ones. For the material, they quote number St44.2 (S265TR2).

I would need to buy them in chunks of 6 meters.
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Old 03-05-13, 04:48 PM   #20
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When i was starting out learning to build the guy who taught me was into making transportation things like trailers. For the light duty ones he used closet clothes hanging rods as the tubing (take care of any plating, it can be unhealthy when heated up). The heavy duty trailers used steel channel or angle and had more truss work. Ply wood was used for the floors or sides as needed. One thing he found out early was that his designs needed tweaking after initial attempts were ridden. Weight balance, tongue placement and weight, ground clearance, frame stiffness under loads all were subject to a learning curve. He cut off bits and redesigned changes a number of times before he begun to have an understanding to what did and didn't work. The other thing he found out was that it's easy to overload a bike's braking capicity... Andy.
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Old 03-05-13, 05:58 PM   #21
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In Metal Arts Studio at Uni, I used the idea of a Klein bottle [the 3D version of a Mobius strip]
and made a trumpet into a conundrum,.. [where does the air go in?]
http://en.wikipedia.org/wiki/Klein_bottle..

Its the piercing of the bell/cone with a tube, formed of an inner bell/cone that does It.
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Old 03-06-13, 04:55 AM   #22
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"A mathematician named Klein.
Thought the Möbius band was divine.
Said he: "If you glue
The edges of two,
You'll get a weird bottle like mine"

*swiped from the internet
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