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 |