Welding Tips and Tricks

Posted: **Tue Dec 01, 2015 11:41 pm**

Hello, this is my first post. I am from Canada and I am doing a home project.
I want to build a "Folding" bicycle, its not really folding, but can be stored in a compact bag.
Basically I will cut the top bar, and down bar, 2 bars, to a desired length on both sides.
Then I want to put in a rod into the bicycle tubes, and have a pipe on the outside of the pipe to sandwich the bike tubes for strength. Another thing I thought of last night was to put a down bar on both sides, then I could bolt that down, but my idea of sliding pipe would need to be changed slightly. I will scrap the down bars for now.

OK For sliding bars, and pipes. I will copy and paste what I talked about in another forum, they did not help me.
I will just give you the link,
https://endless-sphere.com/forums/viewt ... 4#p1125450

Thats what I am doing, its a link to Endless Sphere forums, for electric bicycles and vehicles. Here is it copy and pasted.

re these tolerances BELOW, too tight?

Rods (Fit inside bicycle tubes, and slide)

Bicycle Tube is 31.5mm ID = 1.24015748031496"

1.250 ST 12L14 ROUND BAR

0.00984252" 0.25mm OVERLAP!
Will have to grind down the outter rod, or inner bicycle tube. Its easy to grind down the outter rod.
--------------------------------------------------------------------------
Bicycle Tube is 33.5mm ID = 1.31889763779528"

1.313 ST 12L14 ROUND BAR

0.0058976" 0.14979904mm GAP! Ifs its too small of a gap, can always grind down rod to make it slide easier.
--------------------------------------------------------------------------

Are these tolerances BELOW, too great for structural yet sliding action?

Pipes (Fit over bicycle tubes, and slide)

Bicycle tube is 33mm OD = 1.2992125984252"

1.375 X 0.065 ST CREW TUBE ROUND ID = 1.31"

0.075787" 1.9249898mm GAP!
0.065" is a very thin wall, 1.65mm thick wall, need to weld on lengthwise strips of metal to strengthen it.
Easy to shim with thin sheets of steel. They come in 24g, 22g, 20g, 18g, 16g 1.2908mm, 14g 1.6277mm, 12g 2.052mm, 10g 2.305mm.
--------------------------------------------------------------------------
Bicycle tube is 36mm OD = 1.41732283464567"

1.500 X 0.065 ST CREW TUBE ROUND ID = 1.435"

0.08267717" = 2.1mm GAP!
0.065" is a very thin wall, 1.65mm thick wall, need to weld on lengthwise strips of metal to strengthen it.
Easy to shim with thin sheets of steel. They come in 24g, 22g, 20g, 18g, 16g 1.2908mm, 14g 1.6277mm, 12g 2.052mm, 10g 2.305mm.

1.500x0.095 ST CREW TUBE ROUND ID = 1.405" (0.012322" 0.313mm difference) OVERLAP!
1.500 X 0.120 ST CREW TUBE ROUND ID = 1.38" (0.037322" difference.) OVERLAP!

Posted: **Wed Dec 02, 2015 5:26 pm**

I will clear a few things up, perhaps.

Rods fit inside bicycle tube.
Where you see "gap" and "overlap" that is what I calculated. From my calculations, there is a 0.25mm overlap (which means the round rod will not fit in the bikes tube) and a 0.15mm gap between the round rods that fit inside the bikes tubes. I am sure I can grind down 0.25mm worth of material, maybe more, same goes for the 0.15mm gap. Grinding down the solid round rod, and not any part of the bicycles tube.

The pipes that slide over the bikes tubes, both have gaps of 1.925mm and 1.417mm. With a 0.065 (1.65mm) wall thickness. Which is easily beefed up.

I really have no clue, or estimate as to how much space I need between both pieces (Rods and inside of bicycle tube. And the pipes and the outside of the bicycle tube) for a smooth, slide action, yet still have the structural strength.

You can view the concept of my idea here, this is where I got the idea, from. He only uses pipe that slide over the outside of the BMX bicycle tubes. I want more strength, so I choose to use rods for the inside of the bicycle tubes, and pipes for outside of bicycle tubes. These need to be able to slide, in order for the 2 sides to "disconnect" completely, and store compactly, in a bag for airplane travel, or Greyhound bus travel, or even the RV.

Theres a few images in this bicycle forum. Just scroll down abit.
http://www.bikeforums.net/folding-bikes ... r-diy.html

Thanks for any help or advice in advance, I really appreciate it.

Posted: **Wed Dec 02, 2015 5:55 pm**

I think the gap may be something you figure out through trial and error. To much play and it will loose strength not enough and if the frame flexes or twists then everything will bind up. For your test fits I would take a pin of desired length and diameter and weld a ring or washer on in the center so you can slide it in to both tubes using the washer as a spacer to keep the pin centered in the joint. Then if it's too tight you just slide the pin out and turn it down till you find the magic size.

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