Rotating Ballnut - design ideas

[Boyan Silyavski]

Can't I just get a larger ID bearing for near the machined on gears to compensate for this?

I could explain deeper why not, but isn't it easier to bore 4$ pulley than machine a complex part and buy twice as expensive bearing for which you will need bigger aluminum housing which is also more money?????


I would say generally No. The short answer is: do as i suggest, its best for many reasons or before jumping to buy bigger bearing, just sit down and make a detailed inertia calculation, what snappiness of the machine you need, what will be your maximum speeds and so on. And if that will change the motor you need to bigger!

Why? lets have as an example my machine 8x4 / in reality 1300x2600mm in metric/. If you invest in long ballscrews you generally make the machine right. Which means the gantry will be heavy around 180 to 300kg. If you gantry on that span is less than 160kg, then go with Rack and Pinion as that means your machine is not made to cut aluminum, so save yourself the trouble.


Generally if one is there already, one will use servo motors to move the gantry. But next is even more valid if steppers are used.To obtain the right speeds of the machine, the screw will be xx10 , best is the 2510. No need for bigger screw.

So most probably a gearing has to be used or bigger servo motor. Which means much more money if motor is not Chinese.

Also i have found that with normal servo motor the most desired ration is like on mine machine 20t:30t. fast enough and geared enough. It gives me a machine that has 307.2 pulse por mm ---- 1/307.2=0.003 mm resolution with maximum speed 20m/min . In reality that speed is 30-40 as my servos can spin to 6k rpm instead of the normal servos 3k rpm

Anyway, if you feel like, of course there are bigger bearings. But it seems easier for me to preload correctly 2x the same bearings than different sized ones.