Prelude

 

The SAAZOR Premium hobs are very resistant. Your maintenance is very simple after a brief instruction, which you can read in our following text. This will show you the power and accuracy of these tools. The achievable quality of the teeth to be milled and the achievable gear performance are very much dependent on how the tools have been treated during their use.

For the expert on the hobbing machine who deals directly with our SAAZOR hobs, we have put together some brief notes on the most important uses and handling below. We would like to give you a little help to achieve optimum quality and performance with our tools.

 

Unpacking and storage

 

Depending on the customer's wishes, type or size, the SAAZOR Premium hobs are shipped in cardboard boxes, wooden boxes or STS boxes. The tools are greased against rust and wrapped with shock and impact with oil paper.

During storage, after the incoming inspection, the tools should be greased. When storing, using and transporting within the customer's premises, care must be taken that the hobs are not damaged by impact or shock.

 

Clamping the hobs

 

The SAAZOR Premium hobs can withstand the highest loads due to their durable construction. An important prerequisite for their high load capacity, however, is their correct and stable clamping in the hobbing machine.

In order to ensure perfect working, the SAAZOR Premium hob must be clamped at the ends, as far as possible to the surfaces ground precisely parallel to the plane, if possible up to the largest clamping diameter. Clamping without intermediate rings is recommended where high requirements in terms of performance and accuracy are required.

Short, as far as possible not stepped on abutment and exactly round hob teeth spines are to be used. The hob should be allowed to sit while sucking on the hob cutter sucking. It is to be applied against the longitudinal wedge so that the cutting pressure can no longer cause a twist.

Since the cutting forces are already absorbed by frictional engagement on the clamping surfaces even with good clamping of the hob, the longitudinal wedge only serves as an additional safeguard. A hob tooth or tooth gap adjustment on the center of the workpiece is usually not necessary. For workpieces with smaller numbers of teeth, as well as for splined hobs this is useful, otherwise unbalanced profiles are generated.

The hob is swiveled in the milling head of the machine in the case of straight-toothed workpieces by the size of the hob cut-off angle. For helical workpieces, the helix angle of the workpiece must be taken into account when setting. For the same direction of rotation, adjustment angle minus, for non-identical direction of rotation adjustment angle plus. Figures 2 to 9 show the setting angles for the different options In DC and reverse hobbing (? = Pitch angle of the hob, ß = helix angle of the helical gear).

Of course, only flawless, concentric and correctly clamped hobs guarantee the flawless operation and perfect working of the hobs. The inner cone in the milling spindle bearing is to be cleaned as well as the cone on the hob cutter before inserting the mandrel. The hob cutter concentricity error should not exceed 0.002 to 0.004 mm both near the milling spindle bearing and near the counter bearing. Figures 10 to 12 show mis-mounted spur gear hobs and the resulting profile distortions on the workpiece teeth.

Module range	Concentricity clamping accuracy grade	Planarity clamping accuracy grade
AA	A	AA	A
more than 0,5 to 1	5	10	3	5
more than 1 to 1,6	5	10	3	5
more than 1,6 to 2,5	5	10	3	5
more than 2,5 to 4	5	10	3	5
more than 4 to 6,3	5	10	3	5
more than 6,3 to 10	7	15	4	7
more than 10 to 16	10	20	5	10

Table 1: Tolerances in 1/1000 mm

For the hob, a clamping accuracy as shown in Table 1 is recommended. The concentricity accuracy should be measured after each clamping on both concentricity test coils provided for this purpose. It must be ensured that the indicated concentricity errors do not occur offset by 180 °, otherwise the hob will wobble unacceptably despite good concentricity on the test coils. The highest accuracy of the hob is ineffective, unless the necessary care is applied during clamping.

 

Clamping the workpieces

 

Also, the correct clamping of the workpieces is of great importance. For larger cutting pressures often the workpiece abutment tip is no longer sufficient as a support, so that it is more expedient to provide on the workpiece mandrel abutment guide pin, ähnlcih as at the abutment of the hob cutter. The abutment tip is otherwise given too large surface pressures and grinds out. She does not wear anymore. As a result, the workpiece mandrel will oscillate and vibrate, causing workpiece inaccuracies and tool life losses. A good clamping of the workpiece thus also helps to increase the accuracy and extend the service life of the hob.

The quality of a gearing is the result of an error overlay, which usually has an equal share in the case of the corresponding milling cutter accuracy, machine errors, hob milling errors and clamping errors. For example, hobs of the same accuracy can produce different results when used on the same machine and with equally good clamping, and that is because once the errors between the hob and machine and clamping can add up and subtract another time.

 

Tooth data

 

The applicable cutting speeds and feeds can not be specified without precise knowledge of the working conditions and the accuracy requirements. They are mainly based on the machinability of the material, the stability and the working range of the machine, the rigid clamping of the workpiece as well as the cutting oil or the cutting oil quantity.

Finally, the module size has an influence on the spline data, because the specific cutting force per millimeter of cutting edge increases with larger hobs. The specified feed rates apply in the tooth direction. In the case of multi-speed hobs, the feed rate must be multiplied by the number of turns, which then gives an approximate value that can serve as a comparison to the feed of a single-start hob.

The radial feed rates should not exceed 0.7 mm / WU, because the gear teeth of the hob teeth are extremely heavily loaded, especially during thawing.

Usually the radial feeds should be 1/3 or 1/4 of the axial feed. For the hob cutter life, pure axial hobbing is more advantageous, and one should compare the length of the gate path with the length of the dip path. The time for the passage of the two lengths at the respective feed sizes is then contrasted.

In many cases it will then be recognized that the most economical hobbing process does not always have to be the radial-axial process. It is expedient not to use the radial-axial method for medium and larger axial feeds.

For finish milling, smaller feeds and higher cutting speeds should be used; when pre-milling larger feeds and slightly lower cutting threads. Optimum conditions prevail when roughing in the same direction and finishing in the opposite direction.

 

Lifetime

 

When using a tool, the operating situation may require that the tool be turned off during a certain time, e.g. during a shift in which machine must remain. In this case, cutting speeds and feed are to be selected so that the wear mark width remains within economic limits for the required service life. For operations where the cutting speed and feed are fixed or determined, an economic wear mark width determines the service life.

In order to avoid loss of tool value, the hob should show uniform wear on all teeth before sharpening.

By systematically moving the hobs in the direction of their longitudinal axis, it is achieved that the position of the tool changes to the workpiece and that again and again unused or little used cutting edges reach the larger load range. The service life of the hobs is increased. The displacement size and sequence depends in part on the axial pitch of the hob to the other according to the number of teeth of the workpiece, the length of the teeth to be milled and the machinability of the workpiece material.

Figure 18 shows the wear characteristics of a hob. The length of the cutting hob teeth area depends on the number of workpiece teeth, the workpiece skew angle, and the feed size.

If possible, set the hobs in such a way that the teeth on the outlet side advance by moving them towards the inlet side; This will always get unused hob teeth in the engagement section.

For shifting in step sizes, in some cases it is expedient, in order that the envelope position remains unchanged, to shift at intervals corresponding to the hob-axial slope: number of flutes or an integer multiple of this size. The axial pitch is written down on our SAAZOR Premium hobs.

 

Sharpening

 

The most economical consumption of the hobs is achieved if they are reground early. Larger wear widths than 0.5mm should be avoided if possible. It is most appropriate to regrind at wear widths of 0.2 to 0.3 mm.

Re-sharpening is the most important maintenance process. The most accurate and best hob can become unusable due to careless or incorrect regrinding treatment. He can lose in two ways: cutting ability and accuracy.

By locally excessive heating of the cutting edges, a decrease in the surface hardness and the occurrence of grinding cracks is to be feared. The delivery of the grinding wheel must not be too large. It should also be ensured that the grinding wheel used is suitable for machining the respective high-speed steel, i. The disc must be properly selected in terms of bond, hardness and grain size. However, the best advice is to be provided by your grinding wheel suppliers, who know our tools.

A non-sharp grinding wheel produces high sanding pressure, equivalent to heat and thus defined sanding cracks. A sufficiently often deducted grinding wheel is always the guarantee for correct rake surface training.

When finish grinding, make sure that the disc grinds out properly. During grinding, it should grip evenly over the chip surface to be ground with the least sparking.

 

Errors while sharpening

 

The SAAZOR hobs are manufactured with a radial flute position (see Fig. 20). This position must be maintained when sharpening. Should a desired change be desired here, this consideration must be found in the profile design.

Figures 21, 22 and 23 show the errors in the hob milling reference profile and workpiece profile caused by the incorrect flute position.

The flute division can be a further source of error if the sharpening is carried out improperly. Soannuten-Teilungsfehler cause inaccuracies in Hüllschnittbildung and larger errors even uneven wear and thus shorter life.

Figure 24 shows the faulty flute pitch of a helical gear hob and the effects on the workpiece profile. Compliance with the axis parallelism of the flutes is a prerequisite for maintaining the profile accuracy. Figure 25 shows an example of how the reference profile of a cylindrical bevel hob and thus the workpiece profile can be distorted with not axially parallel flutes.

Table 1 lists the deviations that can be tolerated when sharpening the hobs without causing delicate inaccuracies on the workpiece. The effort that is spent on maintaining the hobs is worthwhile if you want to work fast and accurately. Our SAAZOR Premium hobs have the prerequisites for the highest performance to produce the best workpiece quality. Please note, however, that these precision tools are used correctly and properly maintained.

 

measures

 

Did you give us all the necessary information for your desired offer?

 

In addition to the transmission of workpiece drawings, we also ask for the following information for all hobs: Milling cutter dimensions, the bore diameter, the number of gears, the gear direction, as well as for:

 

We thank you for all the information provided by the fast and conscientiously prepared offers and deliveries of SAAZOR Premium hobs.