4. Setting-up and operation of horizontal or vertical milling machines

Setting-up of milling machines means the preparation of the milling machines for milling. The selection of the clamping tools for the cutters, of the clamping tools for the workpieces and setting of the cutting values, speed rate, feed rate and depth of cut, are necessary prior to milling.

Proper setting-up and operation of the milling machine are prerequisites for carrying out the milling operation successfully. Errors, such as the selection of an unfavourable way of clamping or sequence of the individual steps, will result in defects in quality of the workpieces machines. The amount of work will be considerably increased.

Setting-up and operation of horizontal or vertical milling machines involves the following steps:

1. Planning the work cycle.

2. Making available the cutting tools, measuring and testing tools as well as clamping tools.

3. Checking the cutting tools, measuring and testing tools and clamping tools for serviceability.

4. Checking the milling machine for proper working order:

- existence and state of controls (switches, push-buttons, crank handles),
- oil level (bubble glasses and sight glasses) as well as identified lubrication points,
- existence of safety facilities on the milling machine (covers, hoods, cutter guards).

5. Making available sufficient and adequate coolant.

6. Checking for existence and serviceability of end stops on the milling table, knee and saddle.

Any defects found with the milling machine are to be reported immediately to the serviceman in charge to arrange for immediate repair.

If any additional or special attachments are to be used, such as vertical milling heads, universal milling heads, slotting attachments or power driven rotary indexing tables, they are also to be checked for serviceability and safety in operation prior to putting them into operation.

Defective additional attachments are to be replaced. The defective attachment is to be reported for repair.

- The cutting values (cutter speed and feed rates, number of cuts and the relevant depth of cut) are either to be read from the attached documents or to be calculated. They can also be read from the nomogram of the milling machine.

Nomogram

Example

The necessary rotational speed is to be determined for a cutter of 100 mm diameter (d) at 30 m/min cutting speed.

v = 30 m/min (value from table of cutting speeds for milling)

d = 100 mm

Reading for rotational speed (n) = 90 r.p.m.

The rotational speed read from the nomogram is to be set at the milling machine (see Fig. 8 in section 2, 19 - speed selector lever).

· The values determined are to be set by means of the relevant control elements of the milling machine (speed selection lever, feed selection lever and hand adjustment by means of the crank handle).

· For setting the machine table with the clamped workpiece into working position at the cutter, coarse adjustment of the knee, saddle and machine table is made by rapid traverse and fine adjustment by hand.

· The coolant unit is to be positioned and set so that the coolant jet is directed directly on the cutting area. The coolant return line to the coolant tank in the base of the machine must be free from impurities.

- Functions of the coolant:

· Reducing the heat generated by friction between the cutter and workpiece (cooling and lubricating effect), and flushing away the chips from the immediate cutting area.

If necessary, a splash guard and chip guard are to be fitted.

- The cutting value (depth of cut) is set after the “first scratch”. When the cutter is running, the milling table is moved by hand adjustment (crank handle) into the position where the cutting edges of the cutter take the first cut (first scratch).

- After the first milling pass (first cut) it is necessary to check the size and surface finish achieved (comparison with the data on the working drawing).

- After further setting of the depth of cut (until the final size is reached) and finish-milling and subsequent checking of

· the specified dimensions (tolerances),
· the accuracy of shape and position (flatness, parallelism, squareness)
· surface finish (roughness),

machining of the first workpiece is completed.

- For workpiece change (unclamping and clamping) the cutter must be stopped to prevent accidents (hand injuries).

- Metal chips must not be removed by fingers or cleaning rags (danger of injury by sharp-edged or pointed chips). A chip brush or hand broom is to be used.

Note

When chips are removed by means of compressed air, safety goggles are to be used to avoid injuries to the eyes.

For proper fulfillment of the work order it is necessary to observe and follow the specified steps (technological sequence) for setting-up and operating horizontal or vertical milling machines, including maintenance and servicing.

How are the cutting values for milling be determined?
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What steps are required in setting-up and operating a milling machine?

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What are the functions of the coolant in milling?
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