Newbie- Gas Pipe vs. Drill Rod?

[Stuey]

Hi!

Quick question - are there any advantages to using gas pipe vs. solid drill rod? I see a lot of designs utilizing gas pipe for the X and Y axes, while drill rod is used in the Z axis or elsewhere on the machine.

Is cost the only reason pipe is used instead of say, 3/4" OD solid drill rod?

[fatal-exception]

Why drill rod at all? Seems to be an excessive waste of material.

There's lots of choices for round bar. How about 1040 Cold rolled? It's strait, smooth, and relatively cheap. What about 1045 turned ground and polished? Probably cheaper than drill rod and ground to a tight diametral tolerance. Call up you local steel supplier and chat with them a bit. They will point you in the right direction.

Drill rod is tool steel that is mostly used to make parts that need to be hardened. I doubt anyone would be hardening any length of drill rod longer than a foot or two, and expect it to stay strait. Even case hardening would be iffy.

Black pipe would be the cheapest, with the loosest tolerance for straitness and diameter.

Paul

[Stuey]

Ah, got it. Thanks!

I assumed that drill rod could be used without additional hardening. I'll take a look into the other options you mentioned as well.

[rlwoodjr]

A solid rod is not much stiffer than a hollow tube of the same size and the tube would be a lot lighter.

Soft steel has the same modulus so harden steel does not make it significantly stiffer. Harness is typically used for wear resistance.

Of course if you are supporting the rod or tube stiffness is gained by the support.

[Stuey]

Originally Posted by rlwoodjr A solid rod is not much stiffer than a hollow tube of the same size and the tube would be a lot lighter. Soft steel has the same modulus so harden steel does not make it significantly stiffer. Harness is typically used for wear resistance. Of course if you are supporting the rod or tube stiffness is gained by the support.

So basically there's no advantage towards using solid rod over steel tubing aside from slightly better dimensional tolerances?

[rlwoodjr]

Originally Posted by Stuey So basically there's no advantage towards using solid rod over steel tubing aside from slightly better dimensional tolerances?

.

That is correct. The tolerances that are held on the ground and polished rods are for the linear bearings. the straightness of the length of the tube varys depending on where you buy it.

I have used the ground and polished because I use the Thompson bearings. If I were making my own linear slides out of the skate bearings I would use the pipe or tall plate.

[revwarguy]

The tolerances that are held on the ground and polished rods are for the linear bearings. the straightness of the length of the tube varys depending on where you buy it.

Funny you mentioned that. I used gas pipe on mine, and went to 6 different suppliers in my area, including Home Depot, Lowes, a local hardware store, Ace Hardware, and 2 plumbing suppliers. Believe it or not, Ace Hardware had the best pipe by far - I judged this based on straightness (put a store straight edge along it and looked for light gaps) and secondarily on the condition/surface of the pipe. There was a wide variation between stores.

However, this was true for my area last spring - the point here is not to automatically go to Ace Hardware, but to go to several places and see what they have!

More about how it worked out at my build site at www.liming.org/cnc