AtomicZombie Tutorial - Diamond Frame Chopping

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Diamond Frame Chopping - Page 2 of 21

Even if you are planning to build your own frame completely from scratch, you will still need to salvage the head tube and bottom bracket from a steel tube bicycle frame. Some of our plans such as the Warrior Racing Trike use only square tubing and require a pair of head tubes along with a bottom bracket. For this reason, even a bent up or damaged steel bicycle frame can be a good source of reusable tubing and components, so never pass up a free or good deal on an old bicycle. Also, aluminum frames are not used in any of our plans, so ensure that you are acquiring a steel tube bicycle frame when looking for salvageable parts.

The head tube is another round steel tube that will have an outer diameter somewhere between 1.25 inches and 1.5 inches. The head tube carries a set of press fit bearing cups, which in turn carry the fork bearings and supporting bearing hardware. Since there are varying diameters of head tubes, you should keep the bearing cups and head tube together as a set to ensure that you have a matched set.

The bottom bracket is a threaded round steel tube that must carry the crankset, as well as the weight of the rider. The bottom bracket also forms a junction for many frame tubes, so it is by far the thickest wall tubing on a bicycle frame. There are two common types of steel frame bottom brackets: a threaded type for a 3 piece crankset and a non-threaded type for a single piece crankset. The threaded bottom bracket is by far the more useful of the two, as there will be a large assortment of quality 3 piece cranksets available. Single piece cranksets are normally found on very inexpensive bicycles and kids bikes. If you have a choice, always choose a frame with a threaded bottom bracket.

The threaded bottom bracket has a set of threaded bearing cups that carry the crank axle bearings and supporting crank hardware. The bearing cup on the left side of the frame is the easiest to remove. It has standard threads, so removal is done by turning the cup in the counterclockwise rotation. The cup in the right side of the bike is much more difficult to remove as it has only a small flat ridge to grip and is a reversed thread. It is usually best to just leave the right side bearing cup installed on the frame as this will help protect the shape of the bottom bracket when the extreme stresses of welding heat are applied. If for some reason you do want to remove the right side cup, turn it out in the clockwise rotation using a large crescent wrench to grip the flat ridges.