Custom frame.

Hello everyone!

Been on the hunt for a new frame for my 2WD 3K watt build. And came to the conclusion if I am going to spend $1k on a good mountain bike, why not just put that money into supplies to build one that I can customize to accommodate everything that will go on it. But I have lots of questions.

To start out, I am very comfortable with my brazing/welding skills. However my experience with brazing has been for tooling, and light sheet metal for aerospace applications. Can it gold up to the weight of a heavy e bike?

Are there sources where I could get rear suspension setup, basically the seat tube to drop out and bottom bracket. So I could just modify the front half.

Dont like the idea of cutting up other bikes and peacing together, would not be confident all materials would be the same.

Anyone have a recommendation for suppliers pf components?

Thanks

Brazing is brazing. Thicker material takes more heat, is all. You’ll be using brass or silicon bronze rod rather than silver alloy. If you can get your hands on a gas fluxer, it makes the process much cleaner and easier to see while you’re working.

If you’re brazing rather than welding, it doesn’t matter whether your steels are all the same. It rarely matters even if you are welding, as long as they are all weldable alloys.

Assuming rear suspension is something you must have, definitely start with a complete frame and cut off the part you don’t want. Try to find a chromoly steel frame, which will always be AISI 4130 alloy or the equivalent. If the frame is labeled “high tensile” or “hi-ten”, that usually means AISI 1020.

Aluminum frames are of no use to you, unless its’s just the swingarm, and the front triangle is steel. Aluminum must be heat treated after welding, and has greatly reduced strength if it’s not.

Nova Cycle, Paragon Machine Works, Solid Bikes, and Henry James all offer tubing and fittings for regular bike frames. Wicks Aircraft Supply and Aircraft Spruce sell seamless 4130 straight gauge tubing.

Cut up an existing bicycle to suit your needs, then braze, tig weld or tig braze.

I saw a mounting frame (they call it a cabinet) for Shimano E6000/8000 on frame building website, that sells tubes and such. I was looking to see if they would sell really long 27.2mm seat posts, but only the larger 30.8mm seat tubes.

Found it
https://www.bikefabsupply.com/electric-motor-mount

markz said:

I was looking to see if they would sell really long 27.2mm seat posts, but only the larger 30.8mm seat tubes.

Click to expand...

Those are for dropper posts, for those who must have something that reciprocates up their butts.

Love the name. "Planet Dad" makes me think of a B-52s song.

Balmorhea has it down pat- since you're a metal worker by trade you'd probably have the best experience building your own frame, assuming you're fine with making a jig to keep everything true. I wouldn't do what markz says, simply because the market is flooded with cheap Chinese bikes who's quality and strength can be laughable and it'll be easy to snag one by accident and learn the hard way.

You buy a quality bicycle, brand name like Trek, Giant, Kona, Specialized, Rocky Mountain and use the majority of it. I would prefer a full suspension bike, then you can build whatever custom rear triangle you wanted. I would look for a fs bike that has the rear suspension geometry the way I like it. For use ebikers, that want a triangle bag for battery placement a bike like the picture below. If you wanted more rigidity, then a DH frame would work, but you lose lots of triangle space. Once you start going completely custom, the costs start adding up. Rigging jig is crucial to keep everything straight, those arent cheap. Your time aint cheap. Welder, rod/wire, ppe, consumables, and frame parts. Frame parts would fit into what a conventional frame is, I doubt, for example, you could build an elongated cruiser from a frame parts store unless there is a specialized store in the UK or something with a 6' long tube then the shipping costs increase and so on and so forth.

Then who really knows if your googled frame geometry is stiff and correct. Then who really knows if your google suspension geometry and lengths and pivot points and forces and stress points are up to the task. Thats why go with a frame that the bicycle manufacturer probably spent a million bucks on refining the design of the frame over the decades. Then changing the rear suspension triangle gives you a whole new bag of worms for as mentioned.

If you can make a decent weld or even braze, Craigslist is your friend. Buy an ok fork and components and have fun switching stuff around. With a little imagination and a right angle grinder you'd be surprised what you can make.

If you were going with a traditional lugged style frame, then brazing makes sense. If you're going with something more modern, MIG or TIG makes far more sense. 4130 is easily welded.

You aren't going to find a "drop-in" suspension worth using. there are far too many variables in suspension design for that to ever work. However, You can build a single link suspension with minimal effort and no special parts. While a single link is inferior to a multi link when both have been designed for the bike, You can get a single link to be damn good with nothing more than a ruler, a scale, and a calculator. Getting a multi link to be better might take a team of engineers and a few million in research.