A Custom Bicycle Mod

by ClaudeA
(Tacoma, WA)

My TREK 800, Cro-Moly steel frame cargo bike mod calls for a good welder. But, retired, my left-over spending $$ would require saving for 6 months just to buy a good used Miller or Hobart TIG unit, and then I'd need a plasma cutter to cut the stainless parts!

If the Chinese 3-in-1 TIG, Plasma, and Sick welder does this project, I would be tempted to offer my services for other bike mods, and then I'd move up to the pricey welders.

I' looked at renting, but at half, up to even full price of a used unit, that makes no sense.

Amazon is a reliable retailer, and carries a good Chinese 3-in-one welder I've waited to purchase for two months.

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Jul 15, 2012
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My Mod Details -Cont'd NEW
by: ClaudeA


The 300 spaces and characters limit got me!:-))

To finish this mod, compression-less brake cable and custom brake levers are used. Another feature is using the Nuvinci N360 CVP Hub, and a dynamo front hub. Also, as I am more weight than bikes for shorter, smaller-framed persons are built to carry, the spokes, rims, and axles are spec'd for those used in downhill racing, and other extreme bicycle use. In fact, the failure of axles under the loads I carry, and my frame weight caused me to look for a solution.


The second mod is starting with a Yuba Mondo long-tail frame. It is a stiff, beefy frame, and has room for FAT tires, lots of cargo, and lends well to custom building. It also was better priced than similar long-tails, and is USA made.

That's the next planned project.

Jul 15, 2012
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My Bicycle Mod - some details for those who looked NEW
by: ClaudeA

I'm retired now, but, in my high school Vo-Ag Shop Class, I learned the rudiments of Oxy-acetylene welding, brazing, and heating. We learned buzz-box stick welding, too. In my employment in Navy Sea Bees, and subsequent civilian employment through the years, I put those skills to work on many maintenance jobs I encountered.

When I first was considering this mod, I was afraid of being unable to do much of the frame mod work without the expensive tools a manufacturer uses for welding, brazing, machining, and fitting tubes and pre-formed adapter pieces, such as drop outs.

Under melt-point local heat, metal forms sharp lines of brittle and soft borders, rendering those areas worthless for strength and stress use of the part. To either braze or weld the very thin cro-mol tubing of a bicycle requires annealing and blending the metal malleability out from the weld to regain the border-less strength characteristics of the tube. That process requires an oven to hold the entire frame. Way outside my modest project.

Now, my first bicycle to mod is a TREK 800, 1990s version, good, solid cro-moly. The mad is to adapt a disk brake mount to the front and rear forks, which will Not cause the tube each is mounted on to deform and collapse from the braking force. Disk brake mount tubes on recent bicycles are heavy enough to hold up under this vertical stress; the pre-disk tubes are not.

If I were to either braze OR weld the adapter to the 800 fork tubes, the local weld would need annealing to blend the tensile and malleability over a wider area, AND, the tube would require some form of reinforcing over much of its length to spread the braking stress. If I welded this reinforcement, it would add to the annealing process.

The compromise I decided on is to design a steel adapter plate, welded to a length-cut section of schedule 80 pipe, which has both ends secured to the fork by heavy-duty worm-drive pipe clamps. To assure the adapter does not creep with braking forces, the adapter is anchored to the fork at one point. Between it and the tube is a section of bicycle inner tube, to protect the tube paint and metal wear.

The disk brake caliper rests on two rod ends with eyes, that in turn are riding on steel rod, with clearance to move laterally, to center the caliper on the disk as brake force is applied. The key to this design is that the metals used, and the heat-less mounting to the frame tubes have properties that both hold up to the braking forces, and spread those forces evenly over frame tubing that retains all its factory characteristics of strength and finish.


Jul 15, 2012
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Good luck with the project. NEW
by: John at the Falls

Let us know how the project turns out.

You do need a lot of space for gas welding and brazing. Needs to be fireproof too.

TIG is very clean and much easier to control the fire hazards. All very important in small spaces.
Also much less intimidating to a landlord than MIG, Stick and gas.

Even MIG can be dirty and shoots sparks.

Keep your Plasma Air dry. I made an inline desiccant drier with 1 1/2 inch schedule 40 PVC. You will get better and more consistent cuts.

Jul 06, 2012
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Well, My Purpose Is Not What You Assume! NEW
by: ClaudeA

Perhaps a little carification is in order!:-))

My Trek 800 mod includes a disk brake. Rather than compromise tube strength, I'm creating a clamp-on assembly that uses 1/4" SS plate for backing, and schedule 80 SS pipe section for clamping the assembly to the rear fork members. To cut the curves out of the plate with a band saw is possible, but dangerous. The caliper is to mounted on rod ends, riding on round bar welded to the backing plate, allowing for free lateral float on the disk.

The front disk adapter is similar, just mounted different to the fork tube. I may buy a disk brake bossed fork, but I still want a floating caliper design.

I agree about the use of a band saw for tubing - it's far better than any plasma cutter for the accuracy and cutting ability. But, I'm not redoing the frame, so for my case, it is not applicable.

As for future frame mods, who knows . . .?

I have a Yuba Mondo long tail frame coming this month, and I will use the same floating caliper design for it, using the plasma cutter and TIG welder for that mod.

For other metal projects I have held on the back burner for years, lacking a welder and means to cut, this unit will open the door to finally doing them. I do not have a shop, nor the $$ to rent one. My apartment is tiny, and the owner allows use of the back yard. I fit my tools to the situation I live in.

BTW, thank you for your good response!

Jul 04, 2012
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Cutting Stainless Steel NEW
by: John at the Falls

Buy yourself a cheap combo horizontal and vertical bandsaw that pivots to cut stock and goes vertical with a table to cut small stuff by hand. My $350 band saw with removable table is more useful and precise than a plasma cutter especially for bicycle sized projects. Jody also posted a project on turning a Portaband into a small table type bandsaw. You have to match the blade to the material you are cutting but it seem that Starret Bi-metal 14 TPI variable pitch has cut everything I have ever asked of it. I also run at the lowest of 3 gears. Unless you are doing production, high speeds will kill your blades if not careful.

Watch your blade while cutting, if you are not making chips, then you are making friction which is going to kill your blade.

You can cut stainless steel using the proper jig saw blades and a quality jig saw with good low speed power. I use a Bosch variable speed Jig saw and the proper size Bosch brand jig saw blades.

YOU HAVE TO MATCH THE NUMBER OF TEETH TO THE THICKNESS OF THE MATERIAL. Then you have to keep everything rigid and press the saw into the material so the teeth are cutting and not just the points rubbing and creating friction which causes heat and burns the blade up.

I probably would have never bought my plasma cutter if I had known about this. .... Then there are cold cut saws.

I rarely use my plasma cutter anymore.

Jul 04, 2012
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Brazing Cro-molly NEW
by: John at the Falls

I think MIG and TIG are better suited for mass produced bicycles and necessary for aluminum and Titanium. But if you are working with steel and Cro-molly, Gas brazing is the way to go.

Bicycles can be brazed and a bead of brazing material built up around joint to distribute the load.

You can buy a small sized inexpensive gas welding set for around $100. Then another 6o to rent small gas bottles. The smaller torch size the better. I think I was using 000 or 00 tips.

I think it takes a lot of skill to get a safe and reliable MIG or TIG weld on thin wall tubing. I would go with brazing thin wall steel. Mostly you have less chance of burning through your tubing which is around .032 inch on good bicycles.

I consider bicycle welds to be life critical welds. Just remember, do you trust that top tube to headset weld going down that rocky hill. You will need lots of practice and testing your practice welds. There are lots of old bicycle frames in the trash to practice on but those frame are generally mild steel with wall thickness of .045 inch. Practice a lot, no matter which method you choose.

I will add this from the Polytechforum on brazing 4130;

But bike builders are pushing the envelope for thickness/diameter ratios. It may be that bikes (and similar structures) are the only case where braze welding (AKA fillet brazing) and fusion welding strengths are comparable. Airframes (and just about everything else) are made of smaller
diameter, thicker walled tubing than bicycles. While brass/bronze isn't as strong as steel, on a bicycle the cross section area of even a small fillet is many times the cross sectional area of the tube. A thicker, smaller tube of the same cross section wouldn't give you as much periphery for a fillet.

Jul 04, 2012
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What bicycle mod? NEW
by: Anonymous

I came looking about the mod. This is just about equipment costs. No mention whatsoever on what is planned for the bike.... The topic should be "High Equipment costs versus Chinese".

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