Frame building beginner

[billyjones454]

Hi!

I'm interested in building a fame for my ebike build vs converting one. But I'm not sure where to start. I've watched several youtube videos, and plan to make a simple wood/metal jig. I plan on tig welding it, and want to use cromoly tubing. I'd like to make it similar to this style of construction (2 tubes flush with each other)


The parts I have already bought:
QS205 + kelly controller off of aliexpress. Balanced winding
20"x4" rims. they are just bike rims, I'm planning on upgrading to moped rims before too long. I have not purchased the tires yet.
24s lipo from HF (20,000 mah) with bluetooth smart BMS

My questions are:

1. What size tube should I use? What wall thickness?
2. Can I get away with a hole saw and harbor freight pipe notcher?
3. I would like to buy a head tube and BB. How do I know which ones to get? Are there common sizes?
4. How does the rear dropout attach to the bike frame? There must be some bushings or something.

I have spent literally years looking at posts, and planning my build, and finally pulled the trigger on some parts. These are the questions that I still have. Thank you to this awesome ebike community!

 

[Drunkskunk]

Looks like a fun project. I hope you'll post pics as you go

- 0.035" wall is likely overkill, but I went with 0.065" when I built mine, as it's still thin, but was easier for me to get a good weld.
- A hole saw, a vise, and a drill press are all you need. an actual pipe notcher is luxury. get one if you have the budget for it.
- Head tubes and BB are tricky. there are some common sizes, but it's a range of sizes, you need to know what fork you plan to fit, and what clearances you need at the pedals and BB. I made my head tube, as it's really just a piece of pipe without threading, but you may need a lathe to cut the inside to the right size.
- many Motorcycles use rubber bushings. Many high end bicycles use bearings. You could start a long thread by asking which is better, but likely the best is what every you are able to design and build yourself. I used a bushing on my last frame, but I've used bearings in other things

 

[Overclocker]

main frame and swingarm: 20.8mm OD, 1.8mm wall

saddle subframe: 20.8mm OD, 1.3mm wall

http://cq.cx/tubejoin.pl

i notch using sticker paper method

 

[CONSIDERABLE SHOUTING]

I'll be following this thread, because like you OP i'd like to learn how to make my own dumb crap . You're gonna need a torch OP.

I CAN say- from threads like this one on GRM, the concencus seems to be the "JD2 Model 3" is THE tubing bender to get from autocrossers and off-roaders for their roll cages. Probably overkill tho if all you're gonna do is bikes; this stuff really just needs basic geometry tools like a degree wheel, some wood and nails for the jigs, and math.

https://grassrootsmotorsports.com/forum/grm/learn-me-tubing-benders/131596/page1/

I can also say that rubber bushings are meant when you *need* a joint to flex and have some give; coming from an ex-boy racer who swapped in poly bushings once and wondered why his teeth were being rattled out. Of course, thats from the car world...

 

[serious_sam]

i notch using sticker paper method

Very neat job. A++.

 

[spinningmagnets]

There might be some useful ideas in here...

https://www.electricbike.com/adding-bafang-ultra-frame/

https://www.electricbike.com/nahbs-2014-pauls-custom-mid-drive/

https://www.electricbike.com/zlatkos-mental-manno/

https://www.electricbike.com/drunkskunk-fat-bike/

 

[billyjones454]

Thanks everyone for the great advice! I'll start a thread when I get going on the project.

I think I'm going to start with just regular cold rolled 3/4 or 1 inch .06 wall tubing and do some practice bends and welds. As far as strength goes, it's probably strong enough, right? I mean if chromoly is .035 and this is regular cold rolled but twice as thick? We'll see.

I'm definitely going to use the sticker paper and other resources you guys have linked. Thank you!!

 

[amberwolf]

I do recommend using thinner cromoly if you can manage it, vs thicker "regular" steel--it'll probably be stronger and will be lighter, but it will probably cost more and take more care in welding it up (or you could braze it).

The stuff I've built is often from regular junk steel, with some cromoly tubing from old bikes. They're rather extreme examples....

CrazyBike2 was mostly old bikes but all the heavy duty cargo rails and whatnot were heavy thick junk steel. Most of the failures I had with it were design flaws rather than materials, but some were problems with the steel itself.

SB Cruiser is almost all junk steel (mostly from old retail fixtures), with just the headtube and bit of downtube/toptube of an old bike frame, and the main keel is good heavy thick square tubing. The fork is old toptubes and downtubes from thinwall cromoly bikes, two layers one inside the other for stiffness. All of the problems so far have been from the junk steel materials, except for one main keel failure due to design flaw at an extreme stress concentration.


I'd love to rebuild SB Cruiser with all cromoly, but last I checked at AircraftSpruce, it'd cost over a couple thousand dollars just for the metal, not including shipping/etc. Maybe someday, if I win the lottery...but for now, whatever new one I'll build is gonna be the same mostly-junk-steel with some bike frame stuff in there. But if I could do it, it might take off half the weight of the frame itself--not really sure.



BTW, I'd never heard of the sticker paper method, but in googling it I found this tool that is probably very useful:

https://dogfeatherdesign.com/ttn_js/