As you can see from this guys videos if you have enough money you can collect an insane amount of machine tools. But for a low budget and low production shop there is no reason not to keep it simple. And for a single bike you must build with as few tools as possible. I used hand files to get the tubes close enough for welding and brazing. That is why I advocate using a rear end built with rectangular tubes and flat bar. The only way to compete with a factory in China is to make something unique and so heavy duty that it will last several lifetimes. And educate people about capitalism.
Most people are so weak from driving cars most of their lives that they can't even think about hauling more than 40lbs with a bicycle. Yet I haul 80lbs at least once a week.
I am a third degree backyard engineer so don't ask foolish questions about "how do I know if these bikes are strong enough".
For a long nose bike I recommend no more than 2.3" trail, with a steer angle less than 60 degrees. But for a short bike more than 70 degrees with 1.3" to 1.7" trail is best.
If you’re working with a BMX fork you have to make compromises.
A steer angle 68 degrees with a 1.5" rake is 2.4" trail. But a steer angle of 70.2 degrees will do a trail of 2", so 69.7 degrees will do a 2.1" trail, close enough. It would work better with more rake. Like maybe 2".
The reason these long bikes are so popular is that trailers can yank your bike around when full of heavy cargo.
How to motorize a heavy bike:
The distance between the axle and the derailleur hanger is 28 to 30mm
Forget about adding a disc brake to an old BMX fork
The only way is to use post mounts, and even then it is very difficult.
Tools to think about, but Not all these tools are needed:
Head tubes, steer tubes and a disc brake tab jig .
Construction of Utility bike (the prototype)
Some bikes will need new Heavy Duty drop outs (these also need a derailleur hanger) with disc tabs built in on the rear. Disc brakes will allow you to use a smaller rear wheel for an effectively lower gear.
a protractor square is essential for determining the head tube angle
|This is a frame alignment gauge|
fork alignment tools