Re: Hello from Switzerland
I would keep all the ballscrew sizes the same and use 2005. Just a question on your sizes. You have listed the Y axis as being longer than the X axis. Most cnc machines have the x axis as the rail and the Y axis as the gantry. Are you making a machine that is wider than it is long or making the rail axis the Y axis?
Regards
Ian
Re: Hello from Switzerland
Quote:
Originally Posted by
Ians
If I could ask a burning question straight away, Maybe it sounds a bit big but I'd like to build it to the dimensions of Y=1500mm X=1000mm Z=350mm with Ball Screws and Linear bearings, Would 2005 C7 Ball Screws on all axis with (fixed support bearings on both ends) be a bit overkill or should I use a 2005 on the Y axis and 1605 on the others?
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...)
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.
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.
Re: Hello from Switzerland
Quote:
Originally Posted by
Web Goblin
Most cnc machines have the x axis as the rail and the Y axis as the gantry. Are you making a machine that is wider than it is long or making the rail axis the Y axis?
Thanks Ian, in fact no I was going by that German engineer in the link I gave, he describes the rail as the Y axis
Ian
Re: Hello from Switzerland
Quote:
Originally Posted by
Jonathan
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
Quote:
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
Quote:
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?
Re: Hello from Switzerland
Quote:
Originally Posted by
Ians
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.
Quote:
Originally Posted by
Ians
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.
Quote:
Originally Posted by
Ians
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...
Re: Hello from Switzerland
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
