Ballscrew Size and Pitch

[Jonathan]

Although I have not checked myself, it is apparent that Chai on eBay now sells RM2010 ballscrews, so for the X and Y axes they are probably the cheapest option that will perform well. RM1610 may be acceptable for the Y axis - it depends on how fast you really need the machine to go. If you can find 1616 cheaply then that will actually allow higher feedrates than 2010, since the feedrate you get close to the critical speed is greater and the inertia is much lower. I've posted the calculations for this many times before, so you should be able to find them.

It does depend on what you're cutting to an extent. If you're cutting at low feedrates (e.g. aluminium, engraving) then clearly optimising for high speed with high lead screws (=low resolution) is not sensible. However, the length of the Z-axis you have chosen implies you will be cutting large pieces of wood or foam, in which case you do want high feedrates and resolution isn't such a big concern.

Putting angular contact bearings at both ends will increase the critical speed of the ballscrews, enabling a higher feedrate but only if the motors you select are capable.

1605 is a good choice for the Z-axis. 620mm is a rather large Z-axis which means it will be hard to make a strong machine.

[GTJim]

Thanks for the reply. The z is rather long but as im having an adjustsble bed I'm hoping to make it as versatile as possible.
I have the the profiled rails and they dictate the size of the machine but I wanted a cutting area of 4×4.
I have looked into the critical speeds and the lengths seem just beyond 1610.