I know this is beating a dead horse... But still interesting
"Are there any strength difference between the pipe I can get from the hardware store compared to DOM steel tubing? I'm not sure if I could use the pipe in place of DOM and still retain the strength?
There is a difference in strength between ordinary pipe and DOM tube; for the same OD and wall thickness DOM will be considerably stronger but if you are planning on using the material for the tracks on a router or something like that this is completely unimportant.
The important property for a router application is stiffness not strength and there is a very important distinction between these two properties of material. Strength is a measure of how much force needs to be applied to something before plastic deformation occurs; i.e. it is permanently bent and does not return to the original condition. Stiffness is how much elastic deformation occurs under a given load and when the deformation is elastic the material or structure returns exactly back to the original condition when the load is removed.
With any material under load elastic deformation occurs first followed by plastic deformation when what is called the yield strength is reached. With DOM tube a great deal more load can be applied and a great deal more elastic deformation will occur before the yield strength is reached than with pipe.
Ok I got a question, What is the material difference between black pipe and DOM,I know black pipe has a lacquered finish to minimize rusting, pipe is measured ID, DOM is measured OD, DOM wall thickness is .120 where as pipe is .113, ( BTW I am talking 1" DOM or 3/4 black pipe) whats the metalurgical difference. I want to use black pipe to build a motor cycle frame. I talked to a pro TIG welder and he mentioned that pipe does not weld as good as DOM? Any input.
Black pipe is not suitable for this application; I could say definitely, absolutely not suitable. Black pipe is very low carbon steel with a low yield strength and a low ultimate strength. DOM can be obtained in low and medium carbon steel and in some alloy steels. It has a much higher yield strength and ultimate strength.
Making a motor cycle frame is something that you need to get experienced advice on. Having a weld break or having the frame crumple while you are riding could make life interesting for a short while."