Hello from Switzerland

[Ians]

There's no point getting 20mm screws if you're not exceeding the critical speed of a 16mm screw - it will only serve to reduce your maximum feedrate and acceleration.

With angular contact bearings on one end and standard bearing on the other end with 16mm the critical speeds will be 7000mm/min and 3000mm/min. With 20mm 8500mm/min and 4000mm/min (approximately).

Remember that with 10mm pitch screws (RM1610 for instance) you will of course get twice the above feedrates. Since it's not that useful to have one axis (except Z) a lot faster than the others I think 10mm pitch, 16mm diameter on Y and 5mm pitch 16mm diameter on X would be a good setup (7000mm/min and 6000mm/min ... assuming your motors have enough torque etc...)

Hello Jonathan, I still have to learn about feedrates, I would be mainly working with wood and some aluminium, what would the advantage be of having 10mm pitch on the Y axis, I'd rather go for "resolution" than speed, I will be getting a System 4C with 3.1Nm motors setup from Roy at DIYCNC

It might be worth doing a rotating ballnut set-up like I did on my 1700mm (2092mm screw) X-axis on your longest axis. Depends how fast you want to go.

I definitley will be using rotating ballnuts on all axis with angular contact bearings on both ends, I've seen many on this forum recomend "Linear Motion Bearings" on eBay, I also thought I'd get a 2.2Kw Spindle from them

A 350mm Z-axis makes things tricky ... see my router (400mm Z)! You will want to either make it shorter or not have gantry sides.

Did you take a look at the P2 model from the link I gave, he uses 15mm thick AlMg4,5Mn Aluminium and the gantry sides are 440mm High!!
I'd like to have some height as I'm contemplating adding a 4th rotary table later, do you have a link to your router?

[Jonathan]

Hello Jonathan, I still have to learn about feedrates, I would be mainly working with wood and some aluminium, what would the advantage be of having 10mm pitch on the Y axis, I'd rather go for "resolution" than speed, I will be getting a System 4C with 3.1Nm motors setup from Roy at DIYCNC

If you would rather have resolution then the best option is to use the 10mm pitch screw and use pulleys with 2:1 ratio to got the resolution. That way the screw will not whip as the critical speed will limit the feedrate to twice what you would get with 5mm pitch. However with the stepper drivers you have chosen the motors will not run very fast as it is only a 30V driver, so it probably wont make a difference. If you got 75V drivers it definitely would.

I definitely will be using rotating ballnuts on all axis with angular contact bearings on both ends, I've seen many on this forum recomend "Linear Motion Bearings" on eBay, I also thought I'd get a 2.2Kw Spindle from them

I think you may have misunderstood me... this is what I was referring to:

http://www.mycncuk.com/forums/showth...t-design-ideas

Again not worth it unless you use a higher voltage stepper driver.

Did you take a look at the P2 model from the link I gave, he uses 15mm thick AlMg4,5Mn Aluminium and the gantry sides are 440mm High!!
I'd like to have some height as I'm contemplating adding a 4th rotary table later, do you have a link to your router?

I have ... it's still not very stable in my opinion. This is mine, skip to the end of the thread if you want to see what I mean by having no gantry sides as I started off not so good:

http://www.mycncuk.com/forums/showth...outer-building...

[Ians]

Thanks for your advice, yours looks quite a brute! If you say I'm only using 30V drivers and won't reach the 1605 critical speed, I think I'll use 1605 alround, I did misread about rotating ballnuts, I read ball screws, I'm not ready to go that far yet maybe another build, if you could read German and had the time, the engineer is very detailed in choice of components and build style, he even shows a thermal view of the critical points. As I said I'm mainly interested in wood and a little Aluminium, so I think this style will suit me. it still looks more stable than a router made out of wood.

Ian