Modular Tooling and Tool Management Part 6 pps

in a similar fashion to that of a fly-cutter, creating a

periodically scored surface – after each cutter revo￾lution – degenerating the milled surface texture,

• Chipping due to vibration – as all of the inserts are

not set the same, then the most prominent one will

take the largest cuts on both the minor and periph￾eral cutting edges, causing shock loading as the cut

is engaged, thereby increasing cutter vibration and

potential thermal effects44 creating the likelihood of

chipping here on the most exposed cutting inserts,

• Rapid growth of wear – because of a prominently

set and poorly positioned cutting insert in relation

to the others in the cutter body, it will absorb the

greatest cutting loads, which will lead to shortened

tool life, this being exacerbated by pronounced vi￾brational tendencies, resulting from unbalanced

cutting forces and torque.

NB All of these factors will contribute to a short￾ened cutter life.

Conversely, if the face milling cutter’s insert run-out is

small, then a good surface finish and stable and predict￾able tool life will result.

M o u n t i n g a n d Ad j u s t i n g S i n g l e - B l a d e Re a m e r s

The cutting head of a single-blade reamer was previ￾ously illustrated in Fig. 74a. The replaceable blade

is positioned longitudinally by a blade end stop and

44 ‘Thermal fatigue’, can be present when cutting is interrupted

– as is the case for milling with a prominently exposed ce￾mented carbide cutting insert. Numerous cracks are often ob￾served at 90° to the cutting edge and are often termed: ‘Comb￾cracks’ – due to their visual appearance to that of a typical

hair-comb. These cracks, are the result of alternating expan￾sion and contraction of the surface layers as the cutting edge

is heated during cutting, then cooled by conduction into its

body during intervals between cuts. This very fast alternating

heating and cooling cycle, develops the cracks normally from

the hottest region of the rake face – this being some distance

from the cutting edge, which tends to spread across this edge

and down the insert’s flank face. Once these cracks become

quite numerous, they can join up and promote partial tool

edging to break away – creating cutting edge chipping.

NB Today, many cemented carbide tooling manufacturers

use structures and compositions that are less sensitive to ther￾mal fatigue, moreover, coatings also play a significant role in

reducing thermal fatigue effects, when milling.

diametrically adjusted using the front and rear adjust￾ing screws. The blade is micro-adjustable over a lim￾ited range of radial movement and can be preset in

a special-purpose setting fixture (Fig. 141a and c), to

ream the desired diameter that the tool can then con￾sistently produce. This reaming blade normally has a

back taper of: between 0.01 to 0.02 mm over a linear

distance of between 10 to 25 mm, respectively – when

positioned in the pre-setting fixture (Fig. 141b shows a

three-guide pad designed single-blade reamer). A fea￾ture of the blade’s adjustment, is that it can be reset to

compensate for any subsequent blade wear. A clamp,

plus two clamping screws securely holds the blade in

place, with the wedge-type clamp providing support

along the entire blade length (Fig 74a). In the case

of the single-bladed reamer design illustrated in Fig.

74a, the blade is located and positioned in the ream￾ing head at an 12° positive rake angle. For this type of

reamer design, additional standard blades can be fit￾ted, offering both 6° and 0° rake angles.

Taper reaming setting can be achieved by mounting

the taper reamer (i.e a taper reamer is shown ream￾ing a component feature in Fig 73b), into the spe￾cial-purpose setting fixture (Fig. 141c). At least two

dial-, or electronic-indicators are positioned along the

blade’s length, then adjusted so that a very light pres￾sure is applied to the cutting edge of the blade – to

prevent it from inadvertently chipping. With the

blade ‘semi-clamped’, adjustment is made so that its

is parallel along its length – relative to the tapered

guide pads. Once the blade has been ‘fully clamped’,

adjustment occurs to position it higher than its guide

pads’ diameter, by between 10 to 20 µm – all along the

blade’s length, which achieves an accurate setting, but

this setting will depend on both the workpiece mate￾rial and the prevailing machining conditions45.

6.5.5 Tool Store and its Presetting

Facility – a Typical System

In the worst case scenario, for many of the ‘old-style’

traditional workshops, the tools are as often as not

45 Taper reamers – typical machining details: Cutting speed 4 to

20 m min–1

(Stainless steel 2 to 6 m min–1

), Feed 0.2 to 0.8 mm

rev–1

, Machining allowance 0.2 mm and up to 0.5 mm – for

large taper reamers, plus Coolant soluble oil @ 10% dilution.

Modular Tooling and Tool Management 261