Steel Framed Router

[Jonathan]

The extra beef of thicker screws takes up the slack of DIY building no matter what the calculations say should happen.!!!

Perhaps, but you can't deny the simple calculations I did in the previous post demonstrate a significant torque disadvantage from using a bigger screw with lower pitch.

My setup being a prime example that your figures dont work in the DIY world, . . . It happly spins 20mm screws at twice the critical speed you quote.!! . . Those figure say it shouldn't . . . but it does and has done for the last few years without any problems.!

I know, my RM1610 ballscrew happily exceeds the critical speed by quite a lot. The thing is the critical speed formula doesn't take into account the position of the ballnut, which acts as another support hence leading to the calculation being an underestimate in a lot of cases. This is partly the reason I concluded that 16mm screws are optimal - from a torque point of view they are far superior to the others and in reality it seems the critical speed is higher than what I worked out, so ultimately you'll end up much better off than with the other options.

The calculations of critical speed may not mean as much as they imply, but I feel they mean more than nothing and give a good basis.