What to use for rails/ways? pipe, mild, 304, box

[Apples]

What would be the best to use for a rail/way to run ABEC7 bearings on for a gantry? I went Metalcorp, this afternoon to look at different bits of steel to use as rails to run bearings on.

The choices that I had come up with were:

1. mild pipe 25mm up to 40mm diameter
2. mild flat 100mm x 8mm
3. mild bar 25mm x 25mm
4. stainless steel 304 grade pipe 25mm-40mm
5. brite (bright????) mild steel shafting 25mm

All of these types of steel are to have bearings running on them. I was going to use the 100x8 flat bolted to the side of my table, but I noticed how wobbly it was when I look along it, so I won,t be using that.

With the pipe steel, out of the mild or stainless which one would be the straightest and have the tighter tolarance?? Any ideas on what the tolorances exactaly are??

I was also told by someone that the brite mild steel shafting was pretty straight and that it might be better to use.

I am ready to spend money and move onto the x,y,z stage of my machine, can someone please help me out?

Cheers Peter

[andy_ck87028]

Hi Peter

I have just gone down that path and can provide my thinking. I am not an engineer and definitely a first timer. Thoughts are still very fresh in my mind.

I have used 32mm stainless pipe on the x axis. When the y gantry is assembled, I will see if the 32mm can support it and based on that ascertain whether I can go down to 25 mm for the y rails.

Cost for 32mm stainless was very similar to 40*40*4 mild steel square section but mild steel is a lot heavier and definitely rougher manufactured. Also, I believe that a tube is stronger than a square cross section.

I have used abec 7 and it slides bewwwwwtifully !! ... see attached

I opted away from mild steel and square section because I believe stainless has the better tolerance and lower weight. I could have used mild steel pipe on the x but then couldn't use it to benchmark y.

My rail assembly is straight forward .. see attached.

X axis potentially unsupported span is 1200 but I can add support as I require. Y axis span is around 1500 and I can engineer a supplementary support span using angle iron under the stainless tube if I require. I am trying to keep y axis weight down so would prefer not to have the additional support. I can further enhance that need for reducing y axis weight down by using aluminium for the z assembly.

The stainless will go in those shiny galv plates that I found in the local metal shop. I think they might be used for galv. fencing. I have drilled and tapped three holes in each of those galv plates for micro adjustment of the stainless. It will look a lot prettier when finished but will give you an idea. Don't get confused by the mild steel pipe in two of the pictures.... it was laying around and I hadn't bought the stainless at that point ... I have now as per the third picture.

Hope that helps

Andy