. .
  1. #1
    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

    Click image for larger version. 

Name:	Shortened screw-1550.jpg 
Views:	238 
Size:	74.2 KB 
ID:	26081

    Click image for larger version. 

Name:	Floating side- 2 bearings arrangement - SAB and SRB.jpg 
Views:	233 
Size:	94.9 KB 
ID:	26080

    Click image for larger version. 

Name:	Revised frame for top bearing.jpg 
Views:	213 
Size:	127.3 KB 
ID:	26083

    Previous Drawings

    Click image for larger version. 

Name:	Previous Design-2078.bmp 
Views:	231 
Size:	890.1 KB 
ID:	26082

    Click image for larger version. 

Name:	Previous floating end design-FF30.jpg 
Views:	218 
Size:	66.4 KB 
ID:	26085

    Click image for larger version. 

Name:	Previous motor end frame design-FK30.jpg 
Views:	227 
Size:	100.8 KB 
ID:	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
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Previous floating end bearing design-FF30.jpg 
Views:	188 
Size:	60.9 KB 
ID:	26084  
    Last edited by Halbmond; 28-07-2019 at 03:45 PM.

  2. #2





    Click image for larger version. 

Name:	IMG_5714.jpg 
Views:	209 
Size:	186.9 KB 
ID:	26087
    Click image for larger version. 

Name:	IMG_5708.jpg 
Views:	220 
Size:	225.1 KB 
ID:	26088
    Click image for larger version. 

Name:	IMG_5717.jpg 
Views:	215 
Size:	376.8 KB 
ID:	26089
    Click image for larger version. 

Name:	Previous Motor end.PNG 
Views:	206 
Size:	98.6 KB 
ID:	26090
    Click image for larger version. 

Name:	Previous floating end.PNG 
Views:	217 
Size:	132.1 KB 
ID:	26091Click image for larger version. 

Name:	motor end previous.jpg 
Views:	222 
Size:	224.4 KB 
ID:	26092
    Click image for larger version. 

Name:	floating end previous.jpg 
Views:	221 
Size:	175.6 KB 
ID:	26093

  3. #3
    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.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  4. #4
    Quote Originally Posted by routercnc View Post
    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.

    Click image for larger version. 

Name:	101188_360x.jpg 
Views:	212 
Size:	7.6 KB 
ID:	26094

    Click image for larger version. 

Name:	IMG_6875.PNG 
Views:	201 
Size:	14.4 KB 
ID:	26095

    Click image for larger version. 

Name:	Contact-Points.gif 
Views:	212 
Size:	317.8 KB 
ID:	26096

  5. #5
    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

    Click image for larger version. 

Name:	Back-to-Back Mounting-misalignment-floating.jpg 
Views:	226 
Size:	33.5 KB 
ID:	26097

    Click image for larger version. 

Name:	Top Fixed-bottom Modified Fixed to free.jpg 
Views:	218 
Size:	68.8 KB 
ID:	26098

  6. #6
    Not tried it but should be OK
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Design Study: Rail Inline With Ball Screw
    By Bravin Neff in forum Gantry/Router Machines & Building
    Replies: 27
    Last Post: 08-10-2018, 02:46 AM
  2. Replies: 4
    Last Post: 02-01-2015, 08:32 AM
  3. Simple Solution- Drive 1" Ball Screw Shaft with NEMA-23-Size Stepper Motor Shaft
    By LoveLearn in forum Gantry/Router Machines & Building
    Replies: 5
    Last Post: 08-02-2012, 01:52 AM
  4. Low cost 0 backlash transmission - Ball bearing + trapezoidal screw
    By LabSkis in forum Lead Screws, Nuts & Supports
    Replies: 14
    Last Post: 26-03-2011, 08:44 PM
  5. Twin ball screw drive on X - configuration question
    By HiltonSteve in forum Gantry/Router Machines & Building
    Replies: 13
    Last Post: 20-05-2009, 11:13 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •