Thx Gary for the chat. I now know where to start.

SPEED!

I have had a look around and here are some of my thoughts and assumptions:

It seems for a 20/5 (1500mm) screw you should stay under 800rpm to avoid whipping so it would go max 4000mm/min. Yet a lot of projects/threads claim 6000mm/min and above with 5mm pitch which makes me think that it is project/screw dependant and some people just get more because they are pusing it a bit. Oh and 800rpm is the "industry very safe limit".
I am sure there is a calculator somewhere which will tell me i am completely wrong about all this...:confused:

So I think realisticly, and this is my 2 hour research conclusion, is that you can probably do 5000mm/min without any issues and you can double that if you move to a 10mm pitch.

I think i'd like to stick to the 5mm pitch.

This is a symilar sized project which is where i got some ideas from.
[ame="http://www.cnczone.com/forums/showthread.php?t=30751"][/ame]
And here is a video of it in action
[nomedia="http://www.youtube.com/watch?v=ecWNTGk8AP4"]YouTube- DIY CNC Rapid demo[/nomedia]

Quote:
"The motors I am using are 1.8 deg 640oz in, these are running at 60v 5.5A which
is pretty close to their limit. This is deliberate so I can get better acceleration. At 13.5m/min the stepper
would be going 1350rpm, any faster and i'm sure the torque will drop off very quickly. "

So i have this figure of 4000-5000mm/min in my head and i hope it is not unrealistic.

Saying that i'd also like to mention that i intend to use a DeWalt 2kw for a spindle and the gantry will be from extruded aluminium and profile rails. I dont know how that affects the speed, but i am sure a heavy gantry/Z has all sorts of influences.

Thanks