recently in another thread, a subscriber showed some interest in building a manual pipe rotator for welding... This type of rotator is one that works horizontally, rather than a turntable style rotator.
Id like to offer my experiences and ask others to share theirs....
Ive used a few types of rotators, from small simple manual up to medium-largish automatic rotators used for welding 45 tonne water ballast rollers.
The manual types also have some variation in size and type, but they share some common elements. All the ones i have used had two sets of two wheels... sometimes each set of two wheels were on their own individual mounts so they can be spaced apart as fas as necessary, and sometimes mounted on a common frame. The common frame type seems a bit more stable, but the individual frames are more adaptable to different lengths of pipe.
In terms of wheels, there seem two styles; those that use the wheels as an earth, and those that dont. The ones that use the wheels as the earth obviously have steel wheels, and they vary from the simple being just a wheel oxy cut out of some steel and suspended on a bit of rod. the rod quite often drops into a slot, or several slots, allowing the wheels to be easily replaced, or the spacing between the wheels changed for larger diameters of pipework. the more complex types have a threaded adjuster to space the wheels apart and use something similar to a bearing as the wheel. I find that the type which uses the wheel as the earth suffers from arcing out sometimes, so when using them i still try to clamp the earth lead to the pipe. there is a technique to this.
The ones that dont use the wheel as the earth can use any type of wheel... plastic, rubber, etc etc... you could use old skateboard wheels, or wheels off anything. these wheels do roll very nicely and smoothly compared to steel wheels, but have the downside of melting very easily... you have to be careful.
To attach the earth clamp in a usable manner, i usually attach the earth lead to the inside of the end im not welding, then wind the lead a couple of times around the pipe *opposite to the direction i will be rolling*. This means that as i roll, the lead will be unwinding off the pipe.
rather than trying to rotate smoothly and keep the gun still with a manual roller, i start at about 11:00, weld over through 12, 1, 2 and as i get to about 3:00, i rotate the pipe with my free hand fairly sharply, then continue in this way. I usually only need to do 3 or sometimes 4 rotations to fully weld pipe.
This tenchnique is really not so useful on small diameter pipes, for anything under about 3" in diameter, i just do two runs, starting at 12:00 and running straight around to 6:00, then a second run the same on the other side. keeping the gun/electrode parallel to the face of the pipe is my strategy for getting a consistent and neet weld. most people who have trouble doing positional welding also have trouble controlling their gun angle.
I find the rotator most useful for doing flange work on large pipe; read 12" plus. Most drawings call for this pipework to be welded in a single run, and even if you rotate slowly, you can do a really neat job if it. the inside of the flange also usually needs to be welded to the pipe, creating a double seal, but i usually get an apprentice to do the rotating while i weld the face. for the inside, i start at about 3:00 (or 9:00 is welding left to right) and head for 6. as i get there, i ask the apprentice to rotate... its not hard to keep the gun/electrode on target if he rotates slowly. the final result is a very consistent bead, and you'd have to be *really* looking closely to find the point i rotated at.
Shaun