Is black iron pipe really smooth enough?

[BubbaKahuna]

Hi all - another noob here. Forgive me if this is in the wrong place, I think this belongs here. If not, just let me know where it needs to be. I've tried searching for the answer to this myself both on & off the board but black pipe or iron pipe returns about 1000000 results so here I am.

Is black iron gas pipe I see used in some CNC routers really smooth enough to use for linear rails? The stuff I see installed in my home is very bumpy and rough on the outside. I'd think steel bearings running across it would be about as smooth as running them on a concrete sidewalk. Fine for sidewalks, lousy for CNC tolerances.

Are those using black pipe on their machines having them turned down on a lathe or something? Are they really 'close enough' as-is?

Cheers.

[ger21]

Or something. Look through the Joes 2006 threads and you'll see how guys have used a drill to make a "lathe" to sand them smooth.

[augustus c]

I had the same concern when I was looking for pipe to start my machine, what I was finding was very rough, depends on where it is manufactured, I found what I needed at home depot, it's sold for use as gas pipe, and it's as smooth as glass.

[Micro_CNC]

I am using some slightly smaller diameter steel pipe (5/8") on my router and i just pointed a laser pointer down the outside being held by a "helping hand" for soldering and scuffed down the high point with sandpaper until i had a uniform line on the tube i progressed from 100 grit, which in retrospect was too coarse, to 220, to 440 and finally 600. i did this twice on each pipe 90 degrees apart so there's two smooth lines about 1/4" wide. The table rides silky smooth.

Also, I have found that in actual use the bearings on the pipe will naturally form a smooth, flat groove on the pipe but only after a few months of operation. I changed out the pipes to 5/8" from 1/2" and the old 1/2" rails looked like they were polished where the bearings had been running.