**5.1. Research of bearing nodes characteristics**

In some cases it is very difficult, or even impossible, to gain experimental results from actual machine tools. This led us to develop an experimental device for research into spindle bearing node arrangement characteristics. Our department has developed such a device that can measure:


The variation in the stiffness of the bearing arrangement B7216 is shown in Figure 22, [19]. We can use the experimental measuring head for measuring the deflection and temperature of a varying number of bearings and bearing nodes (from 2 to 5), their preload value, dimensions, and the contact angle of the bearings with different radial and axial forces used, [19], [20].

We use this device to measure the deformation characteristics of the bearing node with different combinations of bearing arrangement, pre-stressed values, contact angles, loads and revolution frequencies. We use this experimental measuring head for verifying the theoretical calculation and real performances of the bearing node (stiffness, precision running and temperature).

78 Performance Evaluation of Bearings

load parameter and durability

**5. Experimental research** 

modified according to the user's wishes.

resultant stiffness for the chosen spindle fit system

graphical illustration of the chosen design (Table 1.).

and calculations show good correlation, never exceeding 10 %.

**5.1. Research of bearing nodes characteristics** 

angles and bearing node revolving speed settings

4. dimension of cutting forces in bearing nodes

3. increases in the temperature in the bearing nodes at various settings

changes in revolving frequency,

Theoretical results and hypotheses must be verified by experimental tests.

The "Spindle Headstock" software application product is a basic programme which can be

The programme has been written in the source code programming language, T-PASCAL v.7, with special additional modules for graphics. A number of interactive modules prepare user-specified data for use in AutoCAD utilising the DXF format. The programme can be used on any IBM/PC compatible computer using a HERCULES, EGA or VGA graphics

The applied software technology has been used in the industry to improve the working accuracy of the machine tools made by TOS Trenčín-Slovakia, for SN and SPSI type lathes , (2), and to design the boring headstocks for the modular single-purpose machine tools made by TOS Kuřim-Czechoslovakia, (5) TOS Lipník, SKF, GMN and INA Skalica. The programme is very effective and reliable and comparison of the results between experiments

In some cases it is very difficult, or even impossible, to gain experimental results from actual machine tools. This led us to develop an experimental device for research into spindle bearing node arrangement characteristics. Our department has developed such a device that

1. changes in the bearing contact angle at its mounting point, changes in loading, and

2. deformation from axial and radial loading for various preload arrangements, contact

The variation in the stiffness of the bearing arrangement B7216 is shown in Figure 22, [19]. We can use the experimental measuring head for measuring the deflection and temperature of a varying number of bearings and bearing nodes (from 2 to 5), their preload value, dimensions, and the contact angle of the bearings with different radial and axial forces used,

axial unit stiffness

adapter.

can measure:

[19], [20].

**Figure 23.** Radial stiffness of the bearing arrangement B7216 AATB P4 O UL, a - experimental, b -

cut is limited by the point at which self-exciting vibration starts.

The disadvantages of the classical construction are as follows: problems with the gears at higher revolving frequencies,

In the new design of a headstock which connects to a CNC system, the maximum width of

From a constructional point of view, the headstock design can be classified as

The classical headstock is a mechanical unit, where a spindle is driven by a motor through a

actual cutting speeds are not continual because of the discontinuous nature of the

The "Duplo-headstock" has been designed in order to achieve technological parameters comparable to the performance of standard electro-spindles, but at a lower production costs and with higher controllability. This particular headstock is assembled from readily available elements (bearings, single drives,). The demands on the other peripheral devices

The "Duplo-headstock" can be described as a spindle with double supports, driven by two separate motors which can operate independently or together. Figure 24 - 28 show a

accurate theoretical c- simplified average

headstock with an integrated drive unit

gearbox without any control system.

large dimensions of complete units

**New design "Duplo–Headstock"** 

are reduced, as are the costs.

"Duplo–headstock" design [20].

**5.2. New design of headstock** 

follows:

classical headstock

gearboxes,

**Figure 22.** Different variants of the experimental measuring head

In Figure 23 we have compared the experimental stiffness measurement, with the accurate theoretical and simplified average calculated radial stiffness of the B7216 AATBP4OUL bearing arrangement. The stiffness variation was examined with a 25% contact angle with nominal value of bearing arrangements: z1, z2= 14, dw1, dw2 = 19,05 mm, α1, α2 = 12º, Fp =340 N.

When static, the experimental values of radial stiffness are higher than the theoretical values. The dependence of stiffness on loading exhibits a decreasing pattern. The decrease is nearly linear, until a certain critical force "Fkr" is reached, at which point the roller with the lightest load becomes unloaded. The deformation characteristic of the nodal point is influenced by the type of flange. The degree and gradation of the stiffness change under the given operational conditions depend on their construction.

In this field the results of the precise and the approximate mathematical model are practically the same. Consequently it follows that in a preliminary mounting design, a simplified mathematical model for calculating the stiffness of the nodal points can be used, as suggested in this article. The convergence of the measured and calculated values provides good evidence for a wider application of the programme in practice.

**Figure 23.** Radial stiffness of the bearing arrangement B7216 AATB P4 O UL, a - experimental, b accurate theoretical c- simplified average
