Ballscrew Size and Pitch

[GTJim]

Thanks for the comments, I haven't really thought about the electronics but like the idea of the Leadshine AM882 drives but I'll wait until the machine is built or at least fully designed so I know what I'm trying to move around. The design keeps changing and developing but now that I've got the rails at least the size is fixed.
The rotating ballnut has intrested me but seems to add another layer of complexity that may not be needed if 10m/min is possible with BK blocks.

Jim

[Web Goblin]

Work out the rpm of the screw for your wanted travel speed and look at the info pdf for the BK15 bearing block to see if you are exceeding the max value. Why do you want to get travel speeds of 10m/min?

[GTJim]

I don't know if that speed will be needed but it was mentioned in a previous post and seemed like a good target.
What kind of rapids and acceleration are needed for wood and aluminium, and what do you all have and feel comfortable with?
Also it seems very difficult to get torque/performance profile curves for the various stepper motors so I'm not sure what RPM you can expect without losing torque.
Sorry if my terminology is wrong.
Jim

[JAZZCNC]

Jim for this size machine to cut the materials your after cutting then you really need 2010 screws but it's not so much for the speed and more for putting the usable Torque in the place where it's needed.? When cutting.!

With correct voltage and decent drives Expect around 900-1100rpm for nema 23 motor before torque starts dropping off fast. So like has been said with 10mm pitch then 10mtr/min rapids is no problem really but that's a minor plus. Whats really important is that the bulk of the motors torque will be around 4-600rpm and that's where you'll be when cutting woods,plastics etc.
Now for Aluminium then 10mm pitch is waste and you'd be better with 5mm pitch for the increase in resolution and torque. Again 5mm pitch will give 5mtr rapids but when cutting the motors will be working much lower up the torque curve giving best torque where it matters while cutting.

You workout what you'll be doing most off and then decide what's important to you.? Resolution or speed.?
All I say is 10mm pitch will Cut Aluminium just at lower resolution which unless doing fine detail engraving won't be a problem and if you do plan on doing fine engraving then you've built the wrong machine anyway.!!

Forget rotating ballnut Idea it's not needed for this length machine and makes things overly complicated and an expense that's not needed.
The BK15 blocks will easily handle any RPM a stepper can reach so don't worry your self with that.!. . . It's a NON issue.

[Shinobiwan]

Doesn't matter what rapids are since its irrelevant to cutting. On a larger machine such as yours its nice to have since it'll get from one side of the bed to the other quicker but other than that its not important.

As for cutting. Its dependant on material, machine rigidity, spindle power, end mill size, depth of cut etc. But very rough ballpark speeds for a typical DIY CNC cutting wood would be 3m-5m/min at 4-6mm DOC. Aluminium is often cut at 0.7-1m/min with 1-2mm DOC. No firm answer though so don't take that as gospel.

Acceleration is really about reducing cutting time with short moves such as 3D/2.5D. Higher it is, the quicker you accelerate after a direction change.

[GTJim]

Thanks Dean and hopefully I'll post a new thead in the build section but I have so many questions like us newbies.
I have sketches so hopefull I will get even more good advice.
Jim

[Wattstar]

I've got 1.5m long screws, one a 1610 and the other is using dual 2010. With the AM882 and 75v I have no probs with 10m/min and high acceleration 1m/sec^2. Before with the cheap chinese 70v's I was lucky to get even 4m! Rubbish.

How are the ballscrews holding up, I was told that if the acceleration is too high it can seize the ballscrew bearings, but you have them a lot faster