100 Tips and Techniques for Getting the Job Done Right by Tom Kendrick_6 doc

Mounting and Adjusting Milling Cutters Possibly the most crucial cutter body to correctly mount and adjust, for the individual cutting inserts, is that of a side-and-face cutter Fig.. In

storage magazine The latest tool presetting machines

equipped with a full suite of tool management features

and functions, can play a big role in improving shop:

productivity/component quality, tool life, inventory

control, whilst minimising down-time, reducing

com-ponent cycle times and part scrappage

Mounting and Adjusting Milling Cutters

Possibly the most crucial cutter body to correctly

mount and adjust, for the individual cutting inserts,

is that of a side-and-face cutter (Fig 138) The reason

why it is important to set the cutter assembly up

cor-rectly, is that invariably the width of the slot in the

ma-chined workpiece is identical to that of the respective

rotating face widths of the cutting edges Moreover,

whole cutter assembly must ‘run true’ as it rotates on its

arbor – with no discernible ‘wobble’ – as this effective

‘wobbling’ will influence the machined slot geometry

At its most extreme, some of these special-purpose

slotting cutters can be >2 tonnes in weight and larger

than 1.5 m in diameter, having segmented cartridges

that are precisely and accurately fitted onto the

periph-ery of the cutter body As a general ‘rule of thumb’ ,

most of these types of slotting cutters are used to

ma-chine component features to a depth of four times

their slot width0 If a deeper slot is required, then the

cutter has to be ‘optimised’ in some way Perhaps by

using a smaller width cutter than that required for the

component’s slot width and, if possible, cutting each

slot face separately and eventually taking it to the

de-sired width/depth – arbor interference permitting

Mounting cutting inserts in the case of the

stag-gered-toothed side-and-face cutter body shown in Fig

138, is relatively straight forward, due to the lateral

adjustment available by the splined cartridge seatings

Here, it is important to ensure that the insert seat is

thoroughly cleaned prior to commencing fitment

Moreover, ensuring that the contact against the

bot- ‘Arbor’ , is the workshop term used for the extension from the

machine tool’s spindle that the slotting-type cutter is located

and driven from It can be cantilevered – termed a

‘stub-ar-bor’ , or supported at its free-end, by an arbor-support –

nor-mally fitted with adjustable and suitable matched-bearing

di-ameters.

0 When full slotting, using a side-and-face milling cutter at 40%

of the maximum radial cutting depth, a typical feed per tooth

would be around 0.25 mm tooth–.

tom face of the seat occurs, prior to tightening the set screw – normally to a final torque value of 5 Nm (i.e illustrated in Fig 138b) Each set screw should be lu-bricated with the recommended lubricant before re-use In order to ensure that each cutting insert runs true, the slotting cutter, or face mill assembly, should

be correctly mounted – in the former case, onto the ar-bor, the latter into the correct spindle nose taper – be-ing held on a suitable presettbe-ing machine The whole assembly is then rotated to ensure that each cutting in-sert is both radially and axially positioned, thereby en-suring that no edges ‘stand-proud’ of each other and at the same time confirming that no discernible ‘wobble’

in the rotating assembly occurs (i.e see the deep-slot-ting cutter, held in a stub arbor with support, allowing the whole tooling assembly to be rotated and each cut-ting insert to be inspected/measured, in Fig 139) Although cutter keyways are not strictly-speaking a mounting problem, the subject does need to addressed,

as if the cutter’s diameter and its associated driving keys are not considered, this will limit the overall mill-ing performance of the cutter With most slottmill-ing, and side-and-face cutters fitted to arbors, they normally require a keyway/key for rotational driving purposes for the whole cutter assembly Usually cutters that

are <φ125 mm with insert sizes ranging between 6 to

8 mm, then one key will suffice, but cutters >φ140 mm with insert sizes of between 11 to 14 mm, they would frequently need two keyways

Cutter diameter and driving key limitations, are de-termined by the cutter’s bore and its connected key-way, together with the DOC being limited by several factors: the arbor OD, its mechanical strength, plus any deformation of the driving key(s) For vertical slotting applications, mounting the cutter on an large diameter arbor with the minimum of overhang is de-sirable If the feed per tooth can be reduced – assum-ing component cycle-times will allow – then this will reduce the tendency of key deformation during mill-ing Milling calculations and key strength, can be ob-tained from the following expressions and are valid for

new cutting inserts:

 Keyway positioning for two keys – is usually given by the

dis-tance between them as: 180° minus half the peripheral pitch

of adjacent cutting inserts – as shown in the diagrammatic sketch in Fig 138a.

Figure 138 The correct mounting

and setting of a cutting inserts in a staggered-toothed side-and-face cutter body [Courtesy of Sandvik Coromant]

Torque (T) = P [kW]/n [rpm] × 60,000/2π [Nm]

Shear [keyway] stress (τ) = F/area = F/A × E [N mm–]

NB As the cutting inserts wear, the above values will

increase by approximately 30%, therefore, it is usual

to add a ‘safety factor’ to the key(s) material shear strength, by multiplying this value by 1.5.

Figure 139 Cutting inserts for large diameter cutters require pre-setting to

mini-mise any run-out [Courtesy of Starrag Machine Tool Co and Sandvik Coromant]

If special-purpose applications are required, such as

when form milling the ubiquitous ‘Vee-and-Flat’

con-figuration for an conventional engine-/centre-lathe

bed, ‘gangs’ of: side-and-face, angled- and

helical-cut-ters are deployed to form and generate these slideways

Here, it is important to ensure that when presetting

the cutters on the tool presetter, that the whole

cut-ter assembly is held in the exact manner that they will

be utilised when ‘gang-milling’ This ‘gang-milling’

set-up, allows their dimensions and forms to be inspected/

measured, while slowly rotating the whole assembly If

two ‘helical cutters’  are utilised in a ‘gang-milling’

op-eration, then their helices should be of the same pitch,

but of different ‘hands’ (i.e left-ward and right-ward

respectively), as this arrangement will balance-out any

end-thrust due to opposite cutter helices

Setting up ‘Long-edge milling cutters’ – these are

sometimes termed ‘Porcupine cutters’ (i.e see Fig

124 – centre), which are normally required for the

heavier and longer cutting applications, is quite a

com-plex presetting process As the individual cutting

in-serts must be slowly rotated to ensure that axial and

ra-dial run-out values are kept to a minimum Otherwise

those inserts ‘standing-proud’ of the remainder will

suffer from greater wear rates, thereby prematurely

re-ducing the cutter’s effective life quite significantly while

milling an unwanted step into the machined sidewall

On standard face mills, ‘face run-out’ can be as high

as >50 µm, so when close tolerances and good milled

surface texture is mandatory, then extreme care must

 ‘Gang-milling’ , is a complex forming process utilising two,

or more milling cutters adjacent to one another So, a

side-and-face cutter, located directly together with a helical cutter,

represents a ‘gang’ in its simplest form This ‘gang’ of cutters, is

normally permanently mounted together for re-grinding and

tool presetting – this is assuming that the cutting edges are

not made-up from a series of strategically-positions indexable

inserts (see Fig 76)

NB ‘Straddle milling’ , should not be confused with

‘gang-milling’ , as here, it is normal to use two side-and-face cutters

with spacing collars between them – of a specific and known

dimensional size Therefore, the cutters ‘straddle’ the part –

hence its name – while they machine two faces at the required

distance apart in one pass along the workpiece

 ‘Helical cutters’ , are sometimes known as ‘Slab-mills’ ,

hav-ing either a left-, or right-hand helix, which ensures that the

length of cut and its shearing mechanism are reduced by a

‘quick-helix’ , which is necessary for the milling of more

duc-tile materials.

be taken when presetting such tooling assemblies In order to assist the presetting of such tooling on some face mills, ‘barrel screws’ allow fine adjustment to the cutting insert (Fig 140a) Such ‘barrel screw’ designs are quite simply-designed, but surprising effective in both adjusting and retaining the cutting inserts, the following remarks explain how they are designed and their method of operation ‘Barrel screws’ (Fig 140a), are hardened to resist deformation and have a black-oxide finish to minimise corrosion To prevent them from shifting during a face milling operation, a nylon pellet is embedded in the thread of the ‘barrel screw’ Right-hand cutting inserts use left-hand ‘barrel screws’ and vice versa, as this counter-acting rotation keeps the insert locked firmly in its pocket The mating surface

of a ‘barrel screw’ is reamed produce a minimum con-tact of 120° occurs, which ensures accuracy and preci-sion, while minimising wear The ‘barrel screw’ hole is off-set toward the reamed surface, to provide positive contact with the mating surface throughout the range

of adjustment of this screw It should be noted, that these ‘barrel screws’ cannot adjust the effective ‘gauge-length’ of the tooling, as the amount of adjustment is limited by the position of the cutting insert’s clamping screw

The face-milling cutting inserts shown in Fig 140a are tangentially-mounted, offering considerable sup-port and additional strength to the cutting edge When presetting the face mill’s cutting edges when the cut-ter body is equipped with ‘barrel screws’ , the following procedure should be adopted:

in-sert tight and simply turn the ‘barrel screw’ to move the insert to the desired setting

NB Adjustment to the cutting insert’s position,

should only be made in one direction only

cut-ting insert and ‘barrel screw’ , push the insert in-ward, then tighten the insert’s screw and adjust out again to the desired position

In Fig 140b, the simple ‘flow-chart’ highlights why it is important to keep any face milling cutter insert’s

run-out to a minimum If the run-run-out of both the minor and peripheral cutting edges is large, then this can

create several undesirable problems for the tooling as-sembly, including:

• Poor surface finish – if a cutting insert

‘stands-proud’ of the others in the face mill, then it will cut

Figure 140 Cutting inserts need to be precisely and accurately seated in their respective pockets of the cutter body, to eliminate

potential run-out

.

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,

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 effects creating the likelihood of

chipping here on the most exposed cutting inserts,

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

Mounting and Adjusting Single-Blade Reamers

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

 ‘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 conditions

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

 Taper reamers – typical machining details: Cutting speed 4 to

20 m min– (Stainless steel 2 to 6 m min– ), Feed 0.2 to 0.8 mm

rev–, Machining allowance 0.2 mm and up to 0.5 mm – for large taper reamers, plus Coolant soluble oil @ 10% dilution.

Figure 141 Presetting equipment and ‘guidelines’ for the setting of single-bladed reamers

.

treated with almost contempt, until they are required

for a repeat order, or utilised for a new machining

op-eration Here, when the tools are not in use, problems

arise because of the following:

either simply ‘floating around’ in an ‘ad hoc’

sys-tem, or are just sitting on top of each other –

dam-aging the precision-ground tooling surfaces – while

being kept in the open,

form of tool management, tools must be looked for

located, then assembled – under less than ‘ideal

con-ditions’ – so the minimum of tool control occurs,

• Lack of efficiency – as a result, more effort is

re-quired by personnel who must try to find tools,

changing front- and back-ends to suit the selected

machine tool for the production run causing

lead-times to lengthen

Considering that up to 10% of the machine tool cost

is tied-up in the purchase of tooling, then tools need

to be looked after with some degree of care and

atten-tion An area adjacent to the workshop, should be set

aside for the purposes of storing tools and associated

equipment in purpose-built tooling cabinets (Fig 142)

and form a basis for tool presetting activities There

are several advantages in utilising telescoping drawer

cabinets for tool storage (Fig 137a and b), these

in-clude:

drawer space to be completely efficiently filled-up

in the minimum of space,

tool damage, while keeping tools dust and

debris-free,

read-ily to hand – tooling drawers can be completely

open-up, so that the contents are both easy to see

and to arrange,

places – the drawers appropriately sectioned, to

to-tally enclose the tools and their component parts,

making it impossible for them to drop out and be

damaged,

sys-tem is achieved – within the tool store and

pre-setting facility Therefore, all of the tooling

com-ponents can be classified and categorised in the

respective drawers – with every tooling part clearly

seen

As a result of this efficient tooling component

lay-out and tool-kitting facility, consumable tools can be

‘tracked’ within the tool store, but when these consum-ables leave the store vicinity (Fig 142c), they are to all intents and purposes ‘scrapped’ as far as the tool stores

are concerned Returnable tools destined for eventual re-use can be ‘tracked’ around the machine shop by

a number of tool-identification means (i.e as seen in Figs 116 and 117 – using ‘tagged tools‘), or at the most basic of identification levels, by judicious labelling,

or bar-coding of tools, with feed-back of information

to the tool stores Often, for the most frequently used tools, they are assembled into a composite forms, then issued as ‘grouped-tools’ in the form of kits for a spe-cific job (i.e see Fig 142c)

Sometimes, tools are individually issued to ma-chine tool setters/operators and are not assembled into ‘kits’ , under such circumstances, the stores will keep a record to show: to whom they were issued, the machine tool on which they will be used, the num-ber and identification of these tools, together with the date of issue

A major benefit of creating an area set-aside close

to the machine tools for dedicated tool management,

is that tool kits can be made-up ahead of the time – this being dictated by master schedule, so that they are

ready just-in-time before any machining commences

A result of this timely tooling strategy, the lead times

are reduced, which is of prime importance to a com-pany in a competitive fast-developing market

Often, it is the case that all tooling is assembled in

the tool stores /preparation facility (Fig 142b) This advanced preparation means that metrology-based

 ‘Lead times’ , refer to the time taken before manufacture of

the part, or prior to a production run beginning These ‘times’ are dependent upon a range of interrelated factors, such as: component stock quantities and their availability, the machine

tools that are available, plus ‘line-balance’* factors, etc.

*‘Line of balance’ (LOB), refers to a technique which permits

the calculation of the quantities of the particular activities, or components which must have been completed by a particular intermediate date, in order that some final delivery schedule might be satisfied Therefore, in this instance, it can be con-sidered as a machine tool scheduling and a control technique

In most of the LOB activities undertaken concerning machine

tools, plant utilisation levels are paramount and if possible, a smooth and consistent LOB across all of the production ma-chines is desirable – for both high efficiency and consistent

work-throughput.

supplies such as ‘limit gauges’ , together with jigs and

fixtures , are also the responsibility of the tool stores

personnel, being despatched with the tool kits for a

particular production run When this is the case,

to-tal packages are issued, containing: cutting-tool and

work-holding kits, plus the limit gauges necessary for

metrological checking/inspection A tool store and

prepartion facility with responsibility for all of these

tooling-related aspects, becomes a ‘focal point’ for

the machine shop for all matters relating to tooling,

whether they are for breaking-down of previously used

kits, calibration of gauges, or even purchase

require-ments for the latest tool available Specialist personnel

in the tool stores/preparation facility, have

consider-able responsibility in servicing tooling for the overall

manufacturing resources on these machine tools and

as a result, will have amassed a large

working-know-ledge of the production tooling requirements, so their

opinions should be sought prior to any purchasing

de-cisions on new tooling

6.5.6 Computerised-Tool

Management – a Practical Case

for ‘Stand-alone’ Machine Tools

If one considers the tooling requirement for a

stand-alone machining centre, then today the market

de- ‘Limit gauges’ , are based upon the stated International

Stan-dards agreed for ‘Limits and Fits’ for component

toleranc-ing The use of limit gauges, is a form of ‘attribute sampling’*

where no attempt is made to determine the size of the

work-piece toleranced feature, but they are simply utilised to

estab-lish whether the component’s critical dimension is within the

specified limits of size, or not In practice, a component that has

hole that has simply been drilled and reamed, might require a

double-ended plug gauge, with one ‘Go’ end of the plug gauge

being of full form and checking the maximum material

con-dition and as many dimensions as possible, with the ‘Not go’

end checking the minimum material condition and only one

dimension – which as its name implies, this latter end should

not go into the reamed hole This limit gauging technique

ful-fils ‘Taylor’s Theory of Gauging’

*‘Attribute sampling’ techniques, are a means of sampling

im-perfections that are not in the strictest sense, measurable

quan-tities For example, a mirror-surface that has been produced,

might be scratch-free, or may have other blemish marks, these

factors might be cause for its rejection Hence, ‘attribute

sam-pling’ can be considered as a two-way classification system for

either acceptance, or rejection of the workpiece

mands for its manufactured products has become much more diversified, with the number and multiplic-ity of tools required having also increased As has been shown previously in this chapter in the preparation for workpiece machining, confirmation that all the tool-ing – includtool-ing spares (i.e ‘Sister-tooltool-ing’ – see Foot-note 1 in this chapter), must be loaded into the tool magazine A computerised-tool management system (Fig 143a), eliminates the possibility of mistakenly se-lecting the wrong tool and exacerbating the situation

of placing it in the incorrect tooling pocket in the tool magazine With these ‘tagged tools’ (Fig 143d) having non-contacting read/write embedded microchips in say, the pull-stud region of the assembled tool – allow-ing coolant-through-spindle applications The follow-ing toolfollow-ing data can be automatically registered into the CNC memory (Fig 143b), such as tool: number and its ID number; name and the nominal diameter; length, plus its ‘working-diameter’; thrust and power coefficients; interference data, with ‘large diameter’ tool data – if required; life accumulated/actual usage time, wear and breakage flags

Many quite complex and sophisticated computer-ised-tool management systems exist, but essentially the practical system depicted in Fig 143, can be use-fully applied to a machining centre in an efficient pro-duction environment Here, the system comprises of three modules, these are:

of the tool management system, where the tooling data is both read/written at the machine magazine tool loading/unloading position (Fig 143c) The tool data is automatically registered in the CNC memory at the push of a button, with this tooling-related data being continuously updated – as ma-chining continues,

with the ‘tool module’ (above), then tool manage-ment is conducted on a much larger scale, allowing not only all of the previous tooling data to be moni-tored and controlled, but additional information on the: toolholder’s bill of materials, insert inventory, and its location, together with a graphic tooling display of its build-up and information regarding the correct procedure to ensure fast and error-free tool measurement on the presetting machine (Fig 143a),

• Tool transportation module – consists of a tool

transporter robot having high positional accuracy (i.e not shown), which automatically transports