Re: CYCOBILLY DELUXE - "Old School" packed sand pipe bending
I got nearly all my bending done today....will probably have to do one small bend in the middle tube I will add.
Before I was a shop teacher, I was a Coppersmith in the railway workshops for 12 years. A large part of our job was pipe bending, and I have bent everything from 1/16" copper tube up to 6" steel pipe using a variety of methods. I have a friend with a mandrel bender, but chose to use the packed sand method for this frame. Maybe I'm crazy :shock: , but I prefer to use hand tools and basic equipment when I build bikes, even though I have access to some high tech workshop toys.
I'll do a basic step by step on how I bent the tube. It's 31.9mm ERW tube with a 1.6mm wall thickness.
I like to use the sand you can buy for kid's sandpits because it's clean, has no other materials in it, and is very fine, so it packs really well. The only problem with it, is that it is usually wet, and it has to be dried out before you can use it. If wet sand is heated it will create steam, and if steam is created in a sealed vessel the pressure has to move somewhere......think pipe bomb :shock: , so if anyone decides to use this method, please
make sure your sand is dry.
I usually spread it out on a sheet of metal and leave in the sun for a few hours
Make a wooden plug and tap it in to seal off one end, or weld a blank onto the end of your tube
Fill the tube with sand. I usually make a funnel from a plastic water bottle
Tap the tube from bottom to top with a mallet to assist the sand to pack, refill and keep repeating until the level of sand does not drop. When the level will not drop, the sand is packed as tight as it can be. Flick a bit out of the end, so you have about 3" of empty tube, and jam a piece of rag into the tube with a screwdriver or something similar.
When bending with this method, a rule of thumb for the length of bend is approx 4 x tube diameter for a 90degree bend. Even though this bend is less than 90degrees, I still made the length of the bend 120mm (which is approx 4 x diameter). Clamp in a vise and support the other end, otherwise it will droop when it is heated. You will need a big tip for your oxy acetylene torch to heat successfully. I used a cutting torch for this bend, but a dedicated heating tip would have been better. When you have heated the tube to a nice even red, the entire length of the bend marks, it is time to start bending. It is much easier if two people are doing this job (one to heat and the other to bend), but I was working by myself today, which is why the pics are not so great, as I was holding the camera with one hand. I had bent a piece of 1/4" rod to my CAD image :lol: , and used it as a template.
There are plenty of variables when bending pipe or tube using this method, and I would suggest having a few practice goes first, and make sure you have a sacrificial piece to clamp in the vise. Also give yourself plenty to pull around when you bend......you can slide a cheater pipe over the end to give yourself more leverage as well.
Starting to lay out the frame to cut angles and mitres
Rough mock up......still using the already bent piece of gym equipment for the seat tube
. A couple of phone calls found me some 19mm, and I went and picked some up in my lunch break, and bent the rear stays after work. I forgot to take my camera, so no before, during and after pics. The powdercoater also phoned to tell me my rims were done 
