Jazz, I bought my 1605 screws 2-3 years ago, don't think 1610 would've been available then, maybe, can't remember.

You are correct, I will be mainly cutting wood and MDF, next perspex, and dabble in ali. So I do hope my design will cope with the stress of cutting ali now and again.

Am I right in thinking for wood/MDF and plastic, 10mm screws are ideal as motors will be working in their ideal region giving 7mtrs/min cutting speeds, but 5mm geared up will just about work without getting to close to the motors critical speed and screws whip speed. The calculations suggest 1200mm 1605 screw will whip at around 1000 rpm. So even with gearing up, the motors can now spin at 500rpm, giving the screw 1000rpm which is still 5mtr/min. Will I be able to go up to 7mtr/min cutting or just for rapids.

Then for machining ali, 5mm pitch is best, but can we cut with 10mm screws, or do we have to gear down? What is the cutting speed for ali? I had a number of around 2-4mtr/min. When you mainly machine ali why are you using 1:2 on your 5mm pitch screws?

Adil