First a few things need to be known about the bike you plan on using as far as the axle receptacles go:
1) What is the diameter of the axle that extends outboard of the bike frame? Some common sizes are:
5MM for many Quick Release Axles
5/16"
3/8"
14MM
2) Does your bike have a Quick Release axle in the rear? If so the axle receptacle needs to be relieved with a .750" wide minimum slot to allow it to fit both the offset to side and center pull designs.
3) Does your bike have a multi-speed gear tree on the rear wheel with associated derailer? If so that is the side you need to put the axle nut on and relieve the axle receptacle by making a flat to fit past the derailer. If the distance from the center of the axle to the closest edge of the derailer anchor / pivot is more than 5/8" then you only need to make a flat on the axle cap until you see the threads and then drill the hole for the axle in the center of the cap. If the clearance is 5/8" or less, you still need to make the flat until you see the threads (this gives you just 5/8" from center) and offset the axle hole either 1/16" or 1/8" closer to the flat to give you a little clearance fron the derailer anchor / pivot..
4) If you have a Three Speed English Racer hub, the easiest thing is to remove the shifter mechanism coming out of the center of the hub. These are not too common anymore and I couldn't find one to examine closely, but with a little ingenuity the axle extension / axle receptacle could be modified to leave the shifter installed.
This is a good time to clean up your axle receptacles. Use a solvent first like Alcohol, Mineral Spirits, Paint Thinner or?? to clean off dirt, grease and oil. Then second pass put under hot water faucet with a brush and dish washing detergent.
If you are using galvanized 1" pipe caps then cleaning is all that is necessary. If you are using Black pipe 1" caps (especially if you chose to machine smooth the exterior surfaces) then it is a good idea to paint them. Don't put very much paint on the internal threads though!
Later on in the build we will be putting Friction Tape onto these nipples and adhesion will be a lot better when they are clean.
Y11-09-13
** Note **
There's a new dimension for the flat on the starboard axle cap. Mill down until the threads just begin to show through (no longer 3/4" (.750")). This will yield ~ 5/8" (.625") from the center of the axle cap. If necessary the hole for the axle can be located 1/16" to 1/8" closer to the flat (instead of being located in the center of the axle cap) to allow more clearance for the derailer anchor / pivot. A self sticky tile can be used as a spacer to level things by adhering one or more layers to the starboard Bucket 2 x 6 between the 1 x 2 guides (or you can screw or glue in place a paint mixing stick). Alternative ideas to increase clearance is to remove material from the anchor / pivot if feasible, or file the frame to allow the axle to be moved further from the anchor / pivot (best do both sides of the frame to keep the wheel true to frame), or you could tap the starboard axle cap and eliminate the axle nut. This would allow more offset for a 1" pipe cap, or you could probably go down in size from a 1" pipe cap to a 3/4" pipe cap. If even more clearance is necessary, since there is no axle nut that needs accessing, the axle extender and axle cap could be machined further than just breaking through to the point you see the threads coming through. In this later scenario one would not be able to unscrew the axle extender, but could just unscrew the entire axle cap and axle extender (now an assembly) and reinstall the original axle nut.
