4' x 4' x 8" Router Build

[Neale]

Interesting what you say about the R&P. My understanding of the ballscrew / R&P decision was that although ballscrews are more accurate & efficient anything over 1m should use R&P because the ballscrew whipping limits performance - is that correct? There doesn't seem to be much of a cost difference between the two?

This is where we get into real design decisions! I'm using 2005 ballscrews. There are a few online critical speed calculators available; the general consensus for 1750mm, fixed/floating bearing, screws is around 900-1000 rpm. That gives me 5000mm/min rapids, which is slower than ideal but which works for me using a hobby machine. In retrospect, I could have used 2010 and run faster. However, I am also using 2x3Nm motors to drive these. Pulley drive, but 1-1 gearing. This is because the motors are just about reaching their corner speed (where torque starts dropping rapidly) at about the "whip" speed of the ballscrews. I'm not entirely sure (because I haven't studied other people's designs) if the motors would handle the load of my heavy gantry using 2010 as there is also the acceleration/speed trade-off. I doa fair bit of small fiddly machining where acceleration is more important in overall cutting time than speed.

All I'm really saying is that you have to balance up all the conflicting requirements for an engineering compromise that is right for you and your intended use. My design/build might not be optimal, even for me, but at least it works! There are plenty of posts one this forum with other designs successfully using ballscrews of this kind of length and I would happily do the same again.