ballscrew bearing support setup?

[dougie329]

Would the use of a double row angular contact bearing suffice at the fixed motor end of a ballscrew on a medium cnc router? Ballscew dia is 16mm. The 1st mockup shows the bearing in red, locknut and cover flange to hold it in place. Second diagram which isnt mine shows 2 bearings, I am just wondering which route to go and why?

[paul3112]

There is a lot of info here https://tech.thk.com/en/products/thk...ain.php?id=357

[Clementvs]

Hello dougie329.
Double row bearings will help to support the axial-radial effort of drilling. I saw bearings with a inductive encoder, may be this can help : http://www.allytech.eu/index_fichiers/Guidance.htm
good luck

[dougie329]

convention is pointing to the twin back to back bearing route but they are so expensive and for 4 motors aswell = 8 bearings! Perhaps I will test with 1 double row bearing 1st and see if it will suffice for this application. It has to be better than a direct coupling from motor straight to ballscrew.

[GMitchell]

Hi, I recently built my own CNC, and used double row AC bearings for ballscrew support.

It is important to use these at the driven end, and then a standard radial bearing at the free end. I can recommend the NSK brand "5200ZZ" series of bearings, I have managed to get backlash down to 0.01mm in my system, and that is just from the ballnut, I can't measure the bearing's play because it is smaller than my dial gauge's resolution!

Have a look at my website http://www.graetech.com/index_files/Page2371.htm where I have published some of my research and learning over the past couple of years, it's easier to direct you there than re type everything.

GOOD LUCK, and I hope you enjoy the journey of learing and discovery.

Graeme.

[dougie329]

thanks guys, really helpful info. Graeme, is the purpose of the spacer just so that it grips the inner race? im assuming I can make the spacer much shorter and use a nyloc type nut to lock it all in place.

[GMitchell]

The whole idea of the system is to keep all of the 'rotating' parts very solidly connected together, and Keep all of the 'stationary' parts also very solidly connected together.
The bearing is the only mechanical link between the two.

So- how do you hold a bearing onto the shaft... use a nut (yes nyloc nuts are great, but use a fine pitch thread for higher compressive force compared to a coarse pitch nyloc nut.) to squeeze the AC bearing up against the shoulder of the ballscrew shaft. Then the bearing is fixed to the shaft, and they can be considered as one part.

Ok, so the bearing is now firmly attached to the ballscrew shaft, make a block to hold the outer race of the AC bearing, and make it fit over the outside of what you have just made. You could have the nut hard up against the bearing's inner race, but the collar is used so that the nut is accessible outside of your bearing block, or so you can't get to it to tighten / adjust it once the bearing block is around the bearing, it also makes sure that the pressure is only applied to the inner race, and not to the dust shields.

Do you get it (I hope I am explaining it clearly)

Graeme.

[Mr.Chips]

Originally Posted by GMitchell Hi, I recently built my own CNC, and used double row AC bearings for ballscrew support. It is important to use these at the driven end, and then a standard radial bearing at the free end. I can recommend the NSK brand "5200ZZ" series of bearings, I have managed to get backlash down to 0.01mm in my system, and that is just from the ballnut, I can't measure the bearing's play because it is smaller than my dial gauge's resolution! Have a look at my website http://www.graetech.com/index_files/Page2371.htm where I have published some of my research and learning over the past couple of years, it's easier to direct you there than re type everything. GOOD LUCK, and I hope you enjoy the journey of learing and discovery. Graeme.

gramene

i am using a ball screw also. And face the same issues. AC bearings is that air conditioning brgs? i am not home now bit i think my dia is 12 mm. Where did you get your brgs?

Thanks
Hager

[dougie329]

yes thanks for the help, it is very clear what I need to do. Your website was most helpful. I have purchased some 12 x 32 x 15.9mm double row angular contact bearings and will see how I get on with them.


Hager the AC stands for angular contact bearings.

[tumutbound]

Originally Posted by Mr.Chips i am using a ball screw also. And face the same issues. AC bearings is that air conditioning brgs? i am not home now bit i think my dia is 12 mm. Where did you get your brgs?

I got my Angular Contact bearings from VXB. I haven't used them as yet but the plan is to CNC my X2 mini mill.

[Cruiser]

Why AC bearings? While it is true that AC are an extremely fine bearing, it is also true that a simple cup & cone roller or ball bearing would be just as fine on a ball screw! I used AC on my spindle, for the higher speeds involved, but I could have stayed with the roller. Cup and cone rollers with a tapered roller, would have a much higher load carrying capability than you need and be equally strong in both radial and thrust loading. It would be more forgiving in pre-loading and last forever with just a dab of grease as long as it is kept clean. The biggest advantage is that they are far less expensive and easily obtained nearly anywhere. Once installed, you would find that they will not wiggle and are much less likely to skate. Do not underestimate the cup & cone bearings, I designed a belt tensioner for my machine and the expensive bearings on the first two renditions failed quickly, then I put a much simpler unit together using some cheap cup & cone bearings with both axial & radial load capability as a temporary unit just to get the machine going. That ended up being just the ticket and has been happy doing its job for nearly two yrs. The belt runs @ close to 110,000" min. at full speed which is the norm. Again, don't underestimate the capabilities of the old cup and cone bearings !