[peteeng]

Hi - It does not need grinding - milling is fine... the rail lands do need to be flat and parallel. Doing the surfaces by hand on both sides is unlikely to result in parallel surfaces... Craig Ozzies must make horrible sections, 1mm cup on a SHS is quite common. Mogi will need to hand pick his gantry section... Peter

The std allows for 0.8% concave or convex so for a 200mm SHS the max allowable is 1.6mm so beware! The straightness spec is 0.15% so over a 1500mm piece it could be 2.25mm bowed. Again beware!! but in general its much better than these... but don't rely on someone else to pick your piece! They will not care if its bruised, bent, twisted, fork lifted or hammered etc etc...

[joeavaerage]

Hi,
agreed milling would be fine, although as it turns out grinding is cheaper...it takes but a few minutes to set up a grinder and then turn it on and come back an hour
late and its done. It takes longer to set up a mill and run it either manually or CNC.

I just ran a straight edge over my 100 x 100 x 9 SHS, and on any side any dishing or cupping must be less than 0.005 inch, its less than visually detectable.
So it may be that you Ozzies are a bit slack when makes RHS....mind you with all the hot air you guys spout I doubt anything needs thermal stress relief off the mill!!

Craig

[peteeng]

Yeh I agree 6 of us can heat treat something over morning tea sometimes. Peter

[joeavaerage]

Hi,
I notice that the UN has issued a cease and desist order against both the Kiwi and Ozzie parliments on the basis of hot air they produce, the climate effect must be untold!

Craig