ball screw check list-2

KWI Bangalore SUB ASSEMBLY CHECKS (Annexure to WI-QA/R/448/PC-3)

WORK INSTRUCTIONS/WORKMONSHIP STANDARDS

Machine No: Machine Name: Assembly Group: Ball Screw Feed Drive

PREPARATORY WORK FOR BALL SCREW NUT HOUSING

1.1 Measure the center heights of both bearing housing.

1.2 Check the difference in heights of bearing housing seating area on slide base from LM Guides seating area.

1.3 Grind the spacer of bearing housing bottom spacer so that center heights of both bearing housing remains same when mounted on slide base.

1.4 Transfer the ball screw nut fixing holes on to nut housing.Note: Ensure that nut housing lubrication hole should match with lubrication hole in the ball screw nut.

PREPARATORY WORK FOR BEARING HOUSING

2.1 Grind and lap inner and outer spacers to have the same thickness and parallelism within 2 microns. Note inner spacer should be either equal to or less by 5-10 microns than outer spacer but should not be greater.

2.2 Transfer end cover fixing holes to bearing housings, drill and tap.

2.3 Fix the inner cover in the bearing housing which is away from the motor.

2.4 Measure depth of housing from front face to end cap face. Measure thickness of bearings and spacers and accordingly remove fitting allowance from the outer end cover so that it would just butt against bearing.

2.5 Calculate thickness of spacer, which is fixed either below the nut housing or below bearing housing as per design, as follows, and grind it to final size.X = Height of the guideway top from bearing housing resting surface.Y = Height from the guideway top to nut housing seating area.Z = X-Y, distance between bearing housing and nut housing seating areas.P = Bearing housing center height.Q = Nut housing center height.Spacer thickness = [Z- (P-Q)]

Checked By Name & Supplier

Date of 16



Machine No: Machine Name: Assembly Group: Ball Screw Feed Drive2.5a

2.5b

ALTERNATIVELY to confirm that above calculations are OK w.r.t. nut housing spacer thickness,

1 Mount the slide and ball screw assembly without nut housing spacer.2 Move slide and nut housing to one extreme end of ball screw.3 Measure gap between slide bottom and nut housing top with slip gauges.4 Compare with the thickness of the spacer and proceed with earlier method.


Date of 16




DIMENSIONAL / GEOMETRICAL ACCURACIES:

Sl. No.

Description of characteristics Theoretical Actual

3.1

Thickness variation of spacers (inner and outer)

<0.005

3.2

Pre loading of bearings (Bearing housing depth) – [bearings + Spacers + End cap]

0.030 to

0.040


Date of 16




3.3a

3.3b

Parallelism of ball screw w.r.t locating guide way in horizontal and vertical planes.

H= 0.02/FLV= 0.02/FL

H= 0.02/FLV= 0.02/FL

Procedure to check ParallelityFor Vertical plane:

1. Bring the slide to middle of ballscrew length.2. Place the dial stand with dial on slide and track the high point on

ballscrew. Make it to zero.3. Repeat the same procedure at the other end of ballscrew.4. Difference in both readings should be less than 20 microns.

For Horizontal plane:1. Bring the slide to middle of Guide way length.2. Make use of L Block with dial on the Guide way and track high

point on Ballscrew. Make it to zero.3. Without disturbing the setup take L Block to far end and note

down the reading.4. Difference in both should not exceed 20 microns.

Machine No:


Date of 16



Machine Name: Assembly Group: Ball Screw Feed Drive

3.4

Run out of ballscrew on motor side.

0.03

3.5

Axial play of ballscrew.

0.005

Procedure for checking the Axial Play:1. On the ballscrew shaft tap with the help of a mallet.2. Fix the dial gauge on the same end and tap the other end.3. The deflection in dial gauge shows the axial play in the

ballscrew.

Machine No:


Date of 16




3.6

Radial play of ballscrew.

0.01

Procedure for checking Radial Play:1. Tap one end of Ballscrew with the help of a mallet on the

circumference (top of the ballscrew).2. Fix a dial gauge on a point where it was tapped.3. With the help of wooden bar lift the ballscrew by lever action as

shown in the figure.4. Note down the deflection in dial gauge, which gives the radial

play on the Ballscrew.

3.7

Torque for ballscrew bearingsProcedure for applying torque:

1. Hold the end of Ballscrew shaft by the help of spanner and constraint the rotary motion.

2. With the aid of a torque wrench on the lock nut turn clockwise for the given value.

Machine No:


Date of 16




FUNCTIONAL ACCURACIES:

Sl. No.

Description of characteristics Theoretical Actual

3.8 Torque required for rotating ballscrew with slide

3.9 Torque required to move the slide with all elements mounted.

3.10 Overall stroke between dead stops

Machine No:


Date of 16



Machine Name: Assembly Group: Ball Screw Feed Drive Assembly

ASSEMBLY PROCEDURE

CASE 1: FIXED / FIXED BEARING ARRANGEMENT:

4.1 Apply light coat of grease on the bearing seating areas of ballscrew and bearing housing.

4.2 Insert spacer onto ballscrew such that it butts against ballscrew shoulder.

4.3 Fix Inner end cover to bearing housing.

Machine No:


Date of 16



Machine Name: Assembly Group: Ball Screw Feed Drive Assembly

4.4 Insert bearings with spacers into bearing housing by tapping outer races. Insert the bearing in “O” or “X” or tandem arrangements as per drawing.

TYPES OF BEARING ARRANGEMENT

4.4a Back-to-back mounting

4.4b Face-to-face mounting

4.4c Tandem mounting

In feed drive assemblies major load acting on ball screw is axial load. From our application point of view either face-to-face (X arrangement) or back-to-back (O arrangement) can be used but we always use back-to-back arrangement due to:

A. It offers more resistance to tilting than face-to-face.

We commonly use 3 types of ball screw supporting bearing arrangements:4.4.1 FIXED TO FIXED TYPE

Used mainly when precision positioning is required.

Machine No: Machine Name:


Date of 16



Assembly Group: Ball Screw Feed Drive Assembly

4.4.2 FIXED TO SIMPLY SUPPORTED

When rigidity of ball screw is sufficient enough so that other side support is not that much critical.

4.4.3 FIXED TO FREE It is used in short length of the ball screw where rigidity of the ball screw required is high.

4.5 Insert the housing along with the bearings onto ballscrew shaft and again tap the inner races on the bearing with steel bush until they butt against the spacer on ballscrew.

4.6 Insert spacer and fix front-end cap to the bearing housing.Machine No: Machine Name: Assembly Group: Ball Screw Feed Drive AssemblyChecked By Name & Supplier

Date of 16



4.7 Lightly tighten ring nut to eliminate gaps between bearings.

CASE 2: FIXED / SIMPLY SUPPORTED BEARING ARRANGEMENT:

4.8 Insert spacer so that it butts against ballscrew shoulder. Insert bearing housing onto ballscrew.

Machine No: Machine Name: Assembly Group: Ball Screw Feed Drive Assembly


Date of 16



4.9 Tightly tap deep groove ball bearing with steel bush till it butts against spacer on ballscrew.

4.10 Fit circlip to hold the bearing in place on ballscrew. Fitting allowance on the spacer to be removed to assemble circlip without plug.

4.11 Tap the bearing housing back onto the bearing and ensure that it does not butt against bearing and has a clearance of 2-3 mm between its shoulder and bearing.



Date of 16



4.12 Fit end cap to prevent dust entry onto the bearing housing. For bearing housing mounted towards the motor (common for case 1 and 2).

4.13 Insert spacer such that it butts against ballscrew shoulder.

4.14 Fix rear end cap to bearing housing.



Date of 16



4.15 Insert bearings and spacers into bearing housing by tapping outer races in “O” arrangement.

4.16 Insert the entire assembly on ballscrew shaft until inner bearing butts against spacer.



Date of 16



4.17 Insert spacer and end cap which will just butt against outer races since fitting

allowance has been removed.

4.18 Lightly tighten ring nut to eliminate gap between bearings.


ASSEMBLY PROCEDURE FOR BALL SCREW FIXING ON SLIDE


Date of 16



1. Mount the entire assembly on slide base and lightly tighten bearing housing fixing screw.

2. Align ballscrew w.r.t locating guideway in both horizontal and vertical planes.

3. Alignment value should be between 10 and 30 microns horizontally depending on ballscrew length. Since bearing housing seating pads are of same height and since the spacers below nut housing/bearing housing has been accurately calculated vertical alignment will be less than 30 microns w.r.t locating guideway.

4. Fully tighten bearing housing fixing screws.

5. Transfer fixing holes from slide top to nut housing keeping the slide and nut housing in appropriate position on the slide.

6. Tighten nut housing fixing screws.

7. Check ballscrew alignment w.r.t locating guideway once again moving the slide along its entire stroke length.

8. Dowel the Bearing housing and nut housing.

9. Repeat 7


Date of 16

ball screw check list-2

Documents