[stj5566]

Hi

I am new and I am trying to build my first CNC router. I am trying to develop a detailed plan of a CNC router that could cut wood as well as soft metal. My question concerns the mounting of guide rail on a pair of Y axis beam.
Please see the attached image. I plan on using a 1.5" x 1.5" steel square pipe (1/4" thickness)for the beams. I am using steel pipe because I can get it for free.

When mounting the guide rail (15mm width), I will use M4 bolts of length 2". My question is, Is it necessary to thread the bolt holes on the pipe? I am a beginner and I don't have much experience with hand tapping and I want to avoid threading if possible. Or should at least one side of the pipe contain threading?

I am hopping a tight nut at the end will be robust enough but if I have to thread, then I guess I will do it.

Thank you
Steve.