7 Attachment(s)
Ball Screw Non Drive End Floating Bearing Design Variants and Help
I have a work station setup for a tribute to university lab.
The previous ball screw was 40 mm diameter and 2078 mm travel with 5 mm pitch.for a vertical application.
For the motor drive end, there is standard FK30 fixed bearing. (with angular contact bearing pairs 16x30x62 mm and lock nuts and spacer collars)
For the loose end there is FF30 floating bearing arrangement. (with one piece of deep groove ball bearing and a snap ring 16x30x62 mm)
Due to excess vibration and resonance at ball screw I plan to shorten the ball screw from 2078 down to 1552 mm to increase tolerance to the critical speed. I also changed the frame design for motor drive end to shorten screw.
In addition I want to modify the floating end bearing arrangement by increasing the supported journal length with 1 additional bearing set and increasing the misalignment tolerance to the floating end.
Because even if I reduce the length by 50 cm the screw is still very long and I am sure there will be misalignments.
Using deep groov ball bearings misalignment tolerance is low, for the double row deep groob ball bearing it is not permitted.
For the FF30 bearing the exising deep groobe ball bearing grade is P5.
I want to replace it wilth a self aligning ball bearing and/or spherical roller bearing with a P5 grade tolerance.
The width of the FF30 bearing housing is 27 mm while the deep groove ball bearing has 16 mm width.
For the same inner/outer diameter equivalent self aligning and spherical roller bearing the width is 20 mm. Therefore 7 mm distance will be left instead of 11 mm for the floating of the shaft.
For the loose end there are only radial loads to be carried. I wonder what is your gentlemen idea about using 2 bearing sets. or only 1 bearing set?
I dont know if there is any shielded and sealed spherical roller bearings off the shelf but I am sure self alignng ball bearings with seals and shields are easy to procure.
Revised drawings
Attachment 26081
Attachment 26080
Attachment 26083
Previous Drawings
Attachment 26082
Attachment 26085
Attachment 26086
I will upload videos showing the resonance of the ball screw.
According to the calculations for a fixed - free bearing arrangement the critical speed for a 40x2078 mm ball screw with a 37 mm root diameter : 1036 rpm.
For the same bearing arrangement the with a shortened screw 40x1552 mm critical speed : 1857 rpm
Link for the ball screw critical speed calculation sheet according to end fixity :
http://www.nookindustries.com/Engine...cCriticalSpeed
7 Attachment(s)
Re: Ball Screw Non Drive End Floating Bearing Design Variants and Help
Re: Ball Screw Non Drive End Floating Bearing Design Variants and Help
On the video it looks like the ballscrew is not straight, rather than whipping. If this is the case then no amount of end support change will help this.
Do you have the means to check if it is straight by setting it on some V blocks and rotating it by hand and measuring with a DTI ?
Most ballscrews I have bought are bent and need straightening. You can do it yourself with a hydraulic press but best to send them away to a specialist.
3 Attachment(s)
Re: Ball Screw Non Drive End Floating Bearing Design Variants and Help
Quote:
Originally Posted by
routercnc
On the video it looks like the ballscrew is not straight, rather than whipping. If this is the case then no amount of end support change will help this.
Do you have the means to check if it is straight by setting it on some V blocks and rotating it by hand and measuring with a DTI ?
Most ballscrews I have bought are bent and need straightening. You can do it yourself with a hydraulic press but best to send them away to a specialist.
It was th first thing came to my minnd when i saw it from the video. Actually I am out of city and did not check it on V blocks. But I will. It is a rolled ball screw so it will be hard to check the straighntess
on the ball screw grooves with a standard dial gage contact point (ball point). I need a flat point which will float on the rolled screw pitch grooves rather than entering inside.
Something like this.
Attachment 26094
Attachment 26095
Attachment 26096
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Re: Ball Screw Non Drive End Floating Bearing Design Variants and Help
I saw a design for angular contact bearings with a back to back arrangement for a floating bearing arrangement.
So I placed my FK30 fixed bearing to bottom without lock nut and spacer collars.
Do you think,it is possible the shaft can have a relative movement with the bearing inner ring like that ? normally floating space is given to the bearing outer ring, and it can slide inside the housing.
https://www.myodesie.com/index.php/w...ading/Bearings
Attachment 26097
Attachment 26098
Re: Ball Screw Non Drive End Floating Bearing Design Variants and Help
Not tried it but should be OK
