6. Technological Processes for Manufacturing Feather Key Joints and Profile Shaft Joints

There are only slight differences between the sequences of operations for manufacturing the different kinds of feather key joints.

6.1. Fitting Key Joints

Preparation of the keyway

For the manufacture of feather key joints it is necessary that keyways are cut into the parts to be connected for receiving the keys. This premachining is done by milling, broaching or shaping.

Figure 17 Individual parts with premachined keyways

Do not scrape or file shaft keyways by hand - they will be inaccurate and the correct position of the fitting key will not be guaranteed.

Checking of the individual parts

The external condition and dimensional accuracy of the hub and the shaft must be checked. In doing, so find out if

- the shaft has a clean surface (no defects);

- the hub bore hole has no steps or marks;

- length, width, depth and alignment of shaft keyway and keyway in hub are true to size (according to working drawing by vernier caliper, depth gauge and others);

- the fit size of the shaft is exactly maintained (according to working drawing by external limit gauge);

- the fit size of the hub is exactly maintained (according to working drawing by plug limit gauge).

Figure 18 Checking of the individual parts

1 length of the keyway of the shaft, 2 depth of the keyway of the shaft, 3 fit size of the shaft, 4 alignment of shaft keyway, 5 width of the keyway of the shaft, 6 width of the keyway of the hub, 7 depth of the keyway of the hub, 8 fit size of the hub

Deburring of the individual parts

Fitting key and keyways in shaft and hub are to be checked for buns. If burrs are found, they are removed by file or triangular scraper.

Fitting in of the fitting key into the keyway of the hub

The hub is clamped in a vice between protective jaws.

The fitting key is shoved through the keyway of the hub by slight pressure of the hand. If the fitting key gets stuck, the lateral surfaces of the keyway of the hub are carefully refiled - pay attention that the surfaces are worked evenly in order to guarantee that the fitting key is situated right in the middle.

Figure 19 Fitting in of the key in the keyway of the hub

Fitting in of the fitting key in the keyway of the shaft

By a press or screwing device, the fitting key is forced into the keyway of the shaft evenly and without canting.

Figure 20 Fitting in of the key in the keyway of the shaft

Do not force in the fitting key by a hammer - it will be canted and damaged at the top and side surfaces.

The key must perfectly fit to the internal side surfaces of the keyway of the shaft, otherwise it may be torn out of the keyway when the rotary power is applied.

If absolute accuracy is required, the fitting key must be fitted in by scraping: By this technique, the side surfaces of the fitting key are worked in such a way that it is placed in the keyway in a slight press fit

Checking of the fit of the fitting key

The fit of the fitting key has to be checked. In doing so, make sure that

- the fitting key is parallel to the axis of the shaft;
- the height of the fitting key is invariable over the total length.

For testing this, profile gauges, go gauges or dial gauges can be used.

When a dial gauge is used, the shaft must be placed safely on Vee supports. For the dial gauge, a stand that can be locked in position is required.

Figure 21 Checking of the fit of the fitting key for central and parallel position

1 profile gauge ring, 2 dial gauge

If the fitting key does not fit properly, find out if there had already been shortcomings with the machining of the keyway. In this case, the shaft has to be replaced or the fitting key has to be reworked till the correct fit is achieved.

Assembly of the individual parts

The shaft journal with the key and the hub bore hole are slightly greased. With clearance fit between shaft and hub, the hub is put on the shaft straight and shoved over the fitting key by hand power.

With press fit (interference fit) between shaft and hub, the hub must be forced over the shaft in hot condition and with the help of a press.

The shaft may be previously cooled, if possible.

When heated, the hub expands slightly thus causing a widening of the bore hole, too. When cooled, the shaft shrinks slightly and thus the diameter of the shaft becomes smaller.

When putting the parts together, make sure that the hub is not applied in a canted way and that the keyway of the shaft and the keyway of the hub are aligned.

Figure 22 Assembly of the individual parts

Checking of the joint

After assembly, make sure that

- between the back of the fitting key and the keyway of the hub there is a clearance of approximately 0.2 mm;

- the fitting key does not clatter;

- the hub is seated in its correct place on the shaft;

- true-running of the hub on the shaft is ensured.

Figure 23 Checking of the joint

With clearance and transition fits between shaft and hub, the hub must be locked on the shaft to prevent an axial displacement of the hub.

For this purpose, shaft snap rings or retainer rings (circlips) are fixed on the right and left side of the hub. The therefore required radial grooves in the shaft must be free and placed exactly on the left of the hub.

Figure 24 Axial locking by shaft snap ring

1 hub, 2 shaft, 3 grooves for shaft snap rings, 4 shaft snap ring

What are the criteria for checking the individual parts, if a fitting key joint shall be made?
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How tight must be the fit of the fitting key in the keyway of the shaft?
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How can a hub be placed on the shaft, if there is press fit (interference fit) between the two parts?
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What are the criteria for checking after a fitting key joint has been made?
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How can the axial displacement of the hub on the shaft prevented?
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6.2. Sliding Key Joints

The sequence of operations is similar to that for manufacturing fitting key joints:

- Preparation of the keyway.
- Checking of the individual parts.
- Deburring of the individual parts.
- Fitting in the sliding key into the keyway of the hub.
- Fitting in of the sliding key in the keyway of the shaft.
- Checking of the fit of the sliding key.
- Assembly of the individual parts.
- Checking of the joints.

Differences in comparison with the fitting key joints are to be found with the fitting in of the key in the key-way of the shaft as well as with the assembly of the individual parts.

Fitting in of the sliding key in the keyway of the shaft

The sliding key is pressed into keyway of the shaft by hand - it must slip in easily. If this is not possible, the side surfaces of the key must be reworked.

According to the dimensions of the bore holes for the holding screws, the shaft is marked at the side. The sliding key is removed, so that the holes can be tapped for the holding screws.

Then, the sliding key is put into the cleaned keyway of the shaft and locked by matching holding screws.

Figure 25 Fitting in and securing of the sliding key

Assembly of the individual parts

Between shaft and hub there must be an easily adjustable clearance fit. Otherwise, the hub must be reamed by a spiral-fluted reamer.

After this has been checked, shaft and hub are sligthly greased and assembled by hand - large parts with the help of hoisting machines.

What enables the firm fit of the sliding key in the keyway of the shaft?
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What kind of fit is required between shaft and hub with a sliding key joint?
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6.3. Profile Shaft Joint

The following steps have to be completed:

- Preparation of the keyways.
- Checking of the individual parts
- Deburring of the individual parts.
- Assembly of the individual parts.
- Checking of the joint.

Corresponding to the characteristic design of the various profile shafts, the individual steps are carried out as described for the fitting key and sliding key joints. Special attention has to be paid that

- the external profile of the shaft and the internal profile of the hub match accurately;
- the parts have no scratches or other defects;
- any burrs are removed from the external edges;
- no chips or other contamination are to be found in the keyways;
- the machine parts are assembled carefully and without canting.