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E ec o high‑speed s eel
sc ew d ill geome y on cu ing
pe o mance when machining
aus eni ic s ainless s eel
Jose Sedlak
1, Jan Zouha
1*, S epan Kolomy
1, Ma in Slany
1 & Emil Necesanek
2
D illing in o he solid ma e ial is one o he basic echnological ope a ions, which c ea es a cylind ical
hole in an app op ia e ime wi h equi ed quali y. D illing ope a ion demands a a ou able emo al
o chips om he cu ing a ea because a c ea ion o an undesi able shape o chips can impa a
lowe quali y o he d illed hole co esponding wi h he gene a ion o excess hea due o he in ense
con ac o he chip wi h d ill. The solu ion o a p ope machining is a sui able modi ica ion o he d ill
geome y i.e., poin and clea ance angles as p esen ed in cu en s udy. The es ed d ills a e made
o M35 high‑speed s eel cha ac e ized by a e y hin co e a he poin o he d ill. An in e es ing
ea u e o he d ills is he use o cu ing speed highe han 30 m min−1, wi h he eed o 0.2 mm pe
e olu ion. The su ace oughness (Ra and Rz lowe han 1 µm and 6 µm espec i ely), cylind ici y
(0.045 mm), oundness (0.025 mm), pe pendicula i y o he hole axis (0.025 mm), diame e s and
posi ion o he indi idual holes we e achie ed o a d ill wi h poin angle 138.32°and clea ance angle
6.92 espec i ely. The inc ease o he d ill poin angle by 6° esul ed in he dec ease in he eed o ce o
mo e han 150 N. In addi ion, an inc ease o he clea ance angle by 1° esul ed wi h a dec ease in he
eed o ce o 70 N. The esul s o he expe imen showed ha wi h he co ec geome y o he ool
he e ec i e machining wi hou using in e nal cooling can be ealised.
S ainless s eels a e used in a wide ange o indus ies due o hei excep ional p ope ies in he ield o esis ance
o he ex e nal en i onmen and ele a ed empe a u e. This s eel can be used as su gical ins umen s in medi-
cine, componen s o he exhaus sys em o ca s o la ge ese oi s and pipelines in he pe ochemical indus y.
When d illing s ainless s eel, se e al limi a ions can ac on he ool. These limi a ions include low he mal
conduc i i y, high duc ili y, suscep ibili y o s ain ha dening and high ab asi eness o he machined ma e ial.
Dolinšek1 examined s ain ha dening du ing d illing o aus eni ic s ainless s eel. Wi h he help o he cu b eake ,
i was ound ha he highes in ensi y o de o ma ion ha dening occu ed in he icini y o he axis o he d ill
close o he poin o he c oss cu ing edge. The esul o s ain ha dening was ha he mic oha dness o he
ma e ial inc eased om 300 o 600HV 50. Aus eni ic s ainless s eel is cha ac e ized by up o ou imes lowe
he mal conduc i i y compa ed o low-ca bon s eel, which causes an in ense inc ease in empe a u e a he edge
o he cu ing ool2. The highes hea occu s on he pe iphe y o he ool in he a ea o he ou e poin due o he
inc easing cu ing speed ou wa ds o he d ill pe ime e 3. Acco ding o he simula ion based on he expe imen
in he s udy3 pe o med on AISI 1045 ca bon s eel, almos 50% o he gene a ed hea ans e ed in o he ool.
The in ensi y o hea gene a ion can be educed by dec easing he a ea o he ine icien ly machining co e o he
d ill, as in he case o he CZ005 ool om his s udy, o by using he app op ia e clea ance angle o he d ill4.
E ec i e cooling o he ool edge is ano he op ion o elimina ing he gene a ed hea . In he s udy4, he e ec o
in e nal cooling wi h he p essu e o 80ba owa ds o he cu ing edge was analysed expe imen ally and h ough
he simula ion. I was ound ha , despi e he high speed o liquid supply h ough he cooling channels, ine icien
cooling o he ool edge occu ed due o an undesi able luid u bulence and ic ion on he d ill. Acco ding o he
esul s o a s udy5 conduc ed on aus eni ic s ainless s eel, an inc ease in he alue o he poin angle in he ange
o 82°–118° led o he inc ease in he empe a u e a he cu ing edge. Unde ce ain condi ions, he e may be a
educ ion in cu ing o ces due o he so-called so ening e ec 6 leading o an imp o emen o su ace oughness.
The e ec o he cu ing speed on he oughness o he machined su ace depends on he empe a u e a which
i occu s o p e en he o ma ion o g ow h in he gi en ma e ial, he alues o he cu ing speed used and he
OPEN
1Facul y o Mechanical Enginee ing, B no Uni e si y o Technology, B no, Czech Republic. 2NÁSTROJE CZ, s. .o.,
Kyjo , Czech Republic. *email: zouha @ me. u b .cz
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machined ma e ial. In he s udy7, he lowe su ace oughness o aus eni ic s ainless s eel (abou 20–50%) was
obse ed when he cu ing speed inc eased om 18 o 30m min−1. On he con a y, in he s udy8 when d illing
low-alloy s eel, he e was an inc ease in oughness mo e han 50% when he cu ing speed inc eased om 32 o
51m min−1. The so ening e ec ea u ed a majo impac in he expe imen used by Huang e al.9. They analysed
he in luence o indi idual pa ame e s on he magni ude o he eed o ce when d illing hin pla es made o
composi e ma e ial ein o ced wi h silicon ca bides. Inc easing he cu ing speed om 50m min−1 o he double
alue ea u ed a di e en e ec on he amoun o eed o ce a di e en s ages o d illing. Be o e en ance o he
en i e ool ip, he e was a sligh inc ease in eed o ce due o he inc ease o cu ing speed. In case o d illing
wo kpiece wi h a hickness highe han 1mm, when he cu ing speed inc eased, he empe a u e inc eased and,
bu due o he so ening e ec , he eed o ce dec eased by mo e han 15%.
The di icul condi ions o d illing aus eni ic s ainless s eel desc ibed in he p e ious pa ag aph equi e he
co ec selec ion o indi idual geome ic pa ame e s o he ool, o he wise he apid wea is obse ed. The ool
wea is accompanied wi h he lowe quali y o he hole co esponding wi h he inc ease o he empe a u e and
he high oughness o he ma e ial. F om he complex geome y o he helical d ill, he in luence o he poin
angle on he cu ing p ocess is mos o en discussed in he s udies. The i s pa ame e analysed is he eed o ce.
The dependence o he size o he poin angle on he eed o ce a ies in each s udy. I was ound ha when he
poin angle inc eased, he eed o ce sligh ly dec eased10,11. The same end was obse ed in he cu en s udy.
On he o he hand, he inc ease o he eed o ce when he poin angle inc eased was p esen ed by he o he
esea che s6,12,13. When he poin angle inc eased om 82° o 118° in he s udy5 and 110° o 118° in14 he in ense
de o ma ion o he ma e ial a he poin o he c oss edge caused he highe empe a u e. Ka pa 6 pe o med a
de elopmen o he special d ills wi h a double edge aimed o machining composi e ma e ials. The d ills ea u ed
he diame e o 6.4mm, while he leng h o each d ill a ied as well as he leng h o he cu ing edge, which
enabled o change he dependence o he eed o ce on ime. The d ill wi h a lowe poin angle exhibi ed lowe
eed o ce compa ed o he d ill wi h he highe poin angle. They ound ou ha he bes esul s we e achie ed
when he d ill had he longes cu ing edge wi h a poin angle o 120°6. The lowe eed o ce can dec ease he
delamina ion o he composi e laye s, o he o ma ion o bu s when d illing duc ile me al ma e ials. Mu ad
e al.15 p esen ed he pape e alua ing an e ec o poin angle when d illing o he i anium Ti6Al4V alloy. Due
o he empe a u e inc ease in he hole su ace, he hole ea u ed he ha dening laye . The highe poin angle
caused an inc ease in he hickness o he ha dened laye o he hole om 0.05 o 0.1mm. The inc ease in laye
hickness was also obse ed when ool wea inc eased.
When machining ough s ainless s eel, long helical chips, which causes ab asi e e ec in he d ill g oo e
and in he d illed hole a e o med. Due o he ic ion be ween he chip and he ool, an excess hea is gene -
a ed, and he su ace o he d illed hole may be damaged3. A he same ime, he long chip can block he access
o he cu ing luid in o he cu ing a ea4. When he con en ional d illing o ough ma e ials, i is no possible
o p e en he o ma ion o long chips. The solu ion can be ul asonic d illing echnology, whe e ib a ions a
he equency o ul asound a e in oduced in o he classic d illing p ocess. Zhu e al.16 ocused on d illing he
0.5mm diame e holes in nickel supe alloy wi h he ul asound echnology. The ib a ion added o he d illing
p ocess b oke he chip in o small pieces and he high-densi y ene gy inpu dis up s he ma e ial unde he ool
edge esul ing in lowe eed o ce.
The in luence o he poin angle se ing on he achie ed su ace oughness o he d illed hole a ies in indi-
idual s udies. In he case o he s udies8,11, hey obse ed an inc ease in su ace oughness when he alue o he
poin angle inc eased, bu con a y in s udies10,15 he au ho s p esen ed a dec ease in su ace oughness when he
poin angle inc eased. In he s udy16, au ho s ound ha he su ace oughness dec eased abou 20–30% when
implemen ing ul asonic d illing echnology.
Accu a e d illing o he ool is a p e equisi e o p oduce a high-quali y hole, when d illing o -axis, he diam-
e e o he en ance pa o he hole inc eases and he geome ic ole ances o he hole de e io a e. The ma e ial
wi h lowe ha dness de e io a es he s abiliza ion o he d ill in he d illed hole. Üllen e al.17 examined an e ec o
ma e ial s uc u e on he quali y o d illed holes when d illing low-alloy ch omium-molybdenum s eel subjec ed
o di e en hea ea men s. The moni o ed hole quali y pa ame e s we e ci cula i y, cylind icali y, de ia ion o
he diame e om he nominal alue and oughness o he machined su ace. I was ound ha he quali y o
d illed holes depends on he ha dness o he ma e ial. When he ha dness o he d illed ma e ial inc eased om
34 o 67 HRC (by applied hea ea men ), he e was an imp o emen o each indi idual pa ame e in he ange
30–50%, bu con e sely, when he ha dness o he ma e ial dec eased om 34 o 24 HRC (by applied annealing),
he dec ease in hole quali y o mo e han 15% was de ec ed17. Imp o ing he abili y o d ill in o so ma e ial can
be achie ed by implemen ing ul asonic d illing echnology. In he expe imen (ca ied ou by16) he e was he
dec ease in he de ia ion om he nominal diame e om 25 o 5µm and he conici y o he hole mo e han 30%.
The main aim o his pape is o s udy an e ec o he di e en d ill geome y (especially he poin and clea -
ance angle) on he quali y o d illed holes. The quali y o d illed holes was assessed by he su ace oughness,
cylind ici y, oundness, pe pendicula i y o he hole axis, he diame e s and posi ion o he indi idual holes and
hei mu ual compa ison. The cu ing o ces we e measu ed du ing he d illing ope a ion o e i y he e ec
o di e en d ill geome y. The in luence o he es ed ma e ial su ace ha dness was e alua ed. The no el y o
p esen wo k is a special design o es ed d ills, which ea u e a hin co e co esponding wi h he possibili y o
se he highe cu ing speed wi h espec o he inal hole quali y. The hin co e u ilises o p oduce a deepe heli-
cal g oo e, which p o ides he be e access o he g inding wheel enabling highe p oduc i i y o HSS d ills.
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Expe imen al se up and ma e ial
Expe imen al ma e ial. The ma e ial o d illing was he AISI 304 aus eni ic s ainless s eel. The ma e ial
was in he o m o olled pla es wi h dimensions o 206 × 120 × 20mm, which we e used o he expe imen . The
d illing ope a ions we e ca ied ou in o he solid ma e ial (wi hou he cen e ing o he hole). The mic oha d-
ness was measu ed on bo h si es o he es ed ma e ial, which ea u ed he signi ican di e ence on he bo om
and op si e. The mic oha dness ( he cou se o he mic oha dness ac oss he ma e ial) was obse ed on he
c oss-sec ion o he ma e ial, in which he mic oha dness exhibi ed he ange 200–400 HV 0.1 (Fig.1).
In o de o cla i y he cause o he change in ha dness, he s uc u e obse a ion was ca ied ou . The posi-
ion o indi idual mic oha dness measu emen s and mic os uc u e we e ealised on he c oss-sec ion o he
ma e ial ma ked in Fig.2a–d.
On he i s side o he pla e, he mic os uc u e consis s o aus eni e (Fig.2a), bu owa ds o he second side
o he pla e he needles o ma ensi e appea ed in he s uc u e (Fig.2b,c). The ma ensi ic s uc u e was ound
on he edge o he semi- inished p oduc in he place whe e he mic oha dness eached 400 HV 0.1 (Fig.2d).
The o ma ion o a ma ensi ic s uc u e in he semi- inished aus eni ic s eel was appa en ly caused by une en
s ain ha dening du ing shee olling. The side wi h he highe mic oha dness exhibi ed a highe deg ee o shee
olling de o ma ion. The simila e ec o he o ma ion o he ma ensi ic s uc u e connec ed wi h he inc ease
in he mic oha dness caused by s ain ha dening du ing olling echnology was also obse ed in he s udy18.
D illing ools. Fo he expe imen , 8 d ills (model CZ005) manu ac u ed by he company NÁSTROJE CZ,
s. .o. we e used. The d ills we e made o M35 high-speed s eel wi h di e en poin angle and clea ance angle on
he main cu ing edge (Fig.3). These angles we e used o e i y he in luence o he d ill geome y du ing he
d illing p ocess.
The poin angle o indi idual d ills was in ange 135°–145° and he clea ance angle was in ange 7° o 15° (see
Table1). The ange o a clea ance angle was selec ed as a minimum and maximum alue (and alues wi hin he
ange), which can be g inded wi h he g inding wheel and he poin angle was chosen as he simila angle used
o sin e ed ca bide d ill p oduc ion Each d ill (A–G) was p oduced wice due o e i ica ion o hei epea abili y.
The geome y o he d ill was based on he CZ005 model se ies o d ills designed o machining s ainless
s eel. The speci ica ions o he d ills used in he expe imen (see Table2) we e he same o all he es ed samples.
The geome y o indi idual d ills was measu ed on a HELICHECK PLUS op ical measu ing machine om
he company Wal e . The geome y o he CZ005 d ill is pa icula ly cha ac e ized by a e y hin co e, whe e he
diame e o he co e is 0.07–0.08 × D. Due o he hin co e, i is possible o p oduce a deepe helical g oo e in he
Figu e1. Ma e ial mic oha dness dis ibu ion on he c oss-sec ion o he d illed ma e ial.
Figu e2. Mic os uc u e o aus eni ic s ainless s eel in indi idual sec ions o he c oss-sec ion.
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d ill. The deepe g oo e he mo e posi i e geome y can be g inded (see Fig.4). The dependence o clea ance
angle on he dep h o he g oo e is gi en by he g inding p ocess. The deepe g oo e he bigge space o he
g inding wheel enabling be e g inding p ocess o he cu ing edge19.
The posi i e clea ance angle along he en i e leng h o he edge plays a signi ican ole in case o he machining
aus eni ic s ainless s eel. A posi i e clea ance angle o he main cu ing edge educes he none ec ual zone wi hin
he a ea in he icini y o he d ill axis. Wi h his geome y i is possible o each he educ ion o he cu ing
o ces, de o ma ion ha dening and hea gene a ion wi hin he a ea o he d ill ip. These aspec s a e conside ed
o cause a poo machinabili y o aus eni ic s ainless s eel20. The educ ion o he co e c oss-sec ion a he poin
o he d ill causes a signi ican educ ion eed o ce21.
The clea ance o he d ill CZ005 is c ea ed by h ee indi idual ace s depic ed in Fig.4, while he ace along
he main edge ea u es he o iginal shape. The second edge exhibi s he ace wi h i s wid h co esponding wi h
he d ill co e diame e . The ace is dec easing owa ds o he ou e pe ime e o he d ill o cause he lowe ic-
ion be ween he clea ance and he bo om o he d illing hole19.
The shape o he main edge is c ea ed om he 2/3 by he con ex cu e, which is ollowed wi h he la a ea
o he main edge co esponding o he es o 1/3 o he main edge19.
Figu e3. D ill geome y used in he expe imen wi h he clea ance angle α and poin angle ω.
Table 1. The alues o he poin angle and he clea ance angle o he indi idual compa ed d ills.
A B C D E F G
Poin angle ω (°) 135.68 135.62 138.32 138.35 141.61 142.14 145.03
Clea ance angle α (°) 8.09 7.20 6.92 7.07 7.76 8.37 14.65
Table 2. Speci ica ions o expe imen ally used d ills.
D ill diame e 13mm Helix angle 29.40 ± 0.40°
O e all d ill leng h 151mm Clea ance angle in he axis o he d ill 1.70 ± 0.80°
Flu e leng h 101mm D ill co e hickness 1.00 ± 0.10mm
Figu e4. De ail geome y o used d ill CZ005.
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Expe imen al and measu emen design. Tes ing o he indi idual lis ed d ills was ca ied ou on he
mul i unc ional e ical machining cen e TAJMAC ZPS MCV 1210 (BUT, Czech Republic, B no). To al o 14
holes (see Fig.5) we e d illed wi h each o he men ioned ools as pa o he expe imen . The numbe o 14 holes
was se o e alua e he geome ical ole ances and ind ou how hey change du ing he d illing ( om he 1s o
14 h hole). The d ill was no wo n a e he 14 h hole, bu he es was ended ( he necessa y da a o e alua ion
o he p ope ool geome y we e ob ained).
The d illed holes we e analysed conside ing he ollowing ac o s:
• cu ing o ces (1s and 14 h hole),
• oughness (1s and 14 h hole),
• geome ic ole ances—ci cula i y, cylind icali y, and pe pendicula i y o he axis o he hole o he su ace
o he pla e (1, 2, 5, 6, 9, 10, 12, 13 and 14 hole),—diame e (1, 2, 5, 6, 9, 10, 12, 13 and 14 holes),
• pi ch (x1, x2, x3, x4, x5).
Cu ing o ces measu emen . A KISTLER 9272 dynamome e (Feed o ce in ange − 5 o 5kN < 0.02, o que in
ange − 200 o 200 < 0.2Nm) wi h accesso ies was used o he pu pose o he expe imen o measu e he cu ing
o ces. The dynamome e was clamped o he wo k able o he machining cen e using T-slo sc ews, a ice was
a ached o he dynamome e o clamping he d illed pla e. Cu ing o ces we e measu ed only when d illing
in o he side co esponding wi h he highe obse ed mic oha dness (400HV). The cu ing o ces we e a ec ed
only by he change in he geome y o he d ill, he o he pa ame e s o he p ocess we e cons an du ing he
expe imen .
Su ace oughness measu emen . The su ace oughness o he holes was measu ed using a Taylo Hobson
Talysu CLI 1000 oughness de ice. Acco ding o he ČSN EN ISO 4288 s anda d, he indica i e alue o he
RSm pa ame e was i s measu ed and he co esponding basic and e alua ed leng h was chosen based on he
measu ed alues. A e le elling he su ace o a ho izon al posi ion, he p o ile o he en i e leng h o he hole
was measu ed. To ob ain he oughness p o ile, i was necessa y o pe o m h esholding, emo e he shape o
he measu ed p o ile using a 5 h-o de polynomial, and il e he measu ed da a using a Gaussian il e . The
e alua ed leng hs we e ex ac ed om he ob ained oughness p o ile (see Fig.6), and he equi ed oughness
pa ame e s Ra and Rz we e subsequen ly measu ed.
Geome ic ole ances measu emen . Measu emen s o geome ic ole ances i.e., hole diame e s and pi ches
we e pe o med on he Lei z Re e ence Xi coo dina e measu ing de ice. The ci cula i y, he pe pendicula i y
o he hole axis o he su ace and he spacing o he holes we e measu ed in wo places along he leng h o he
hole in places 3mm om bo h sides o he ma e ial (see Fig.7). Roundness was e alua ed based on he cen e o
he leas squa es acco ding o he ČSN ISO 4291 s anda d. The spacing o he pai o holes is conside ed as he
spacing o a pai o ci cles a he same heigh le el c ea ed du ing he oundness e alua ion. The ole ance ield
o he hole pe pendicula i y is conside ed as he cylinde in which he axis o he cylinde o he app oxima ed
hole alls.
Figu e5. Scheme o he expe imen ally d illed holes on he d illed pla e.
Figu e6. Me hodology used o he measu ing o he su ace oughness o d illed holes.

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The e alua ion o he cylind ici y and diame e o he d illed holes ook place in h ee places along he leng h
o he holes (3mm om he op o he hole, he middle heigh and 3mm om he bo om o he hole, he scheme
is depic ed in Fig.7). The cylind ici y o he holes was de e mined based on he c ea ion o he so-called w ap-
ping cylind ical su aces c ea ed by ex ac ing he ci cula i y p o ile acco ding o he ČSN ISO 12180-2 s anda d.
The diame e o he holes is conside ed as he diame e o a ci cle app oxima ed by he me hod o leas squa es.
De e mining he accu acy o he posi ion and dimension o he holes. The posi ion o he holes was assessed
based on he measu emen o he de ia ion o he pai o holes om he nominal alue o he spacing. In he case
o he dimension, he pa ame e was he de ia ion om he nominal alue o he diame e .
Cu ing condi ions. The cu ing condi ions we e se o he indica ed alues and emained cons an
h oughou he expe imen i.e., cu ing speed c = 32m min−1 (co esponding e olu ions n = 784 min−1) and
eed pe o a ion = 0.2mm (co esponding eed a e = 157mm min−1). Quake Cool 7350BFF cu ing luid
wi h a concen a ion o 5% ( ecommended by he p oduce o he d ills) was used du ing d illing.
Resul s and discussion
The ollowing chap e p esen s he ob ained esul s based on obse ing he in luence o he poin angle and he
clea ance angle on he quali y o he d illed holes. Using he simula ion in he Heli onic ool s udio p og am, he
e ec o bo h men ioned angles on he size o he angle o he c oss edge o he d ill was de e mined (see Fig.8).
Feed o ce and o que e alua ion. The eed o ce and o que we e measu ed o indi idual d ills used in
he expe imen . The Figs.9 and 10 a e depic ed o he d illing o 1s hole (new ool). The boxplo cha was used
o isualize he da a, due o he possibili y o display he agg ega ed s a is ical da a. Indi idual blocks ep esen
50% o he da a se , alling be ween he 1s and 3 d qua iles. The lines leading om he blocks show he dis ibu-
ion o he es o he alues o he se , he ou lie s a e exp essed by sepa a e poin s. The s aigh line inside he
block ep esen s he median o he se and he black block he mean alue o he da a se . The a e age alue o
he eed o ce when d illing wi h indi idual d ills was in he anged 2481–2929 N (see Fig.9).
Based on he acqui ed da a, i can be s a ed ha poin and clea ance angles in luenced he applied eed o ce
(compa e d ill A and d ill G, whe e he maximum di e ence 420 N was obse ed). When he clea ance angle
inc eased by less han 1° in d ills A and B, he eed o ce dec eased mo e han 70 N. The example o he in luence
Figu e7. Me hodology used o he measu ing o he ole ances o he geome y o d illed holes.
Figu e8. Dependence o he angle size o he c oss blade on he se ing he alue o he poin angle and he
clea ance angle o he d ill CZ005.
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o he size o he poin angle can be obse ed in d ills A and E, whe e he poin angle inc eased by 6°, he eed
o ce dec eased mo e han 150N (see Fig.9). An inc ease o he clea ance angle ( om 8.37° co ela es wi h d ill
F o 14.65°co esponds wi h d ill G) caused a dec ease (270 N, calcula ed om a e age alues) o he eed o ce,
which can be impa ed by he c ea ion o a sha pe cu ing edge esul ing in lowe esis ance agains pene a ion
in o he wo kpiece ma e ial. The o que was less a ec ed by he change o angles compa ed o he eed o ce.
The o que alue a ied be ween 10.5 and 11.1Nm, depending on he selec ed alue o he clea ance angle and
poin angle (see Fig.10). The highes o que alue was measu ed in case o d ill G, which is cha ac e ized by he
highes alue o bo h angles (poin and clea ance angle).
Hole su ace oughness. The su ace oughness o he d illed holes was e alua ed based on he pa ame e s
Ra and Rz, he measu emen was ca ied ou acco ding o he me hodology desc ibed in chap e 2.3.1. Using
he lowe alues o bo h obse ed angles esul ed in su ace oughness lowe han 1µm conside ing h ee com-
pa ed d ills i.e., A, B and C. The dependence o su ace oughness on he poin and clea ance angle is depic ed in
Fig.11a. D ill F exhibi ed he highes de ia ion ( ep esen ed by he ed line depic ed in each d ill) in ega ds o
oughness Ra, bu con a y he lowes de ia ion ea u ed d ill B wi h he lowes poin angle (132.62°). Figu e11b
shows oughness o he 1s and he 14 h hole eached o each d ill.
The obse ed dependence o su ace oughness on he poin and clea ance angles, showed he same end in
case o Rz pa ame e , he e o e he display o he measu ed alues o Rz was no pe o med. The su ace ough-
ness pa ame e Rz was e alua ed in he ange 5.7–11.7µm. The in luence o he angles on he su ace oughness
is based on he p emise o main ain a smoo h machining p ocess wi hou in oducing addi ional ib a ions
and une en o ce s ess. The d ill geome y wi h he lowe clea ance angle shows he sha pe cu ing wedge
and makes i easie o he ool o cu in o he wo kpiece ma e ial. Choosing a lowe poin angle in luences he
abili y o s abilize he d ill in he hole due o mo e a ou able o ce ac ion. When bo h angles desc ibed abo e
a e changed, he eme ging phenomena in e ac wi h each o he . In he case o choosing a lowe alue o he
angle o he poin and he clea ance angle (in case o A and B d ills, see Fig.11), he d ill is su icien ly s able
when cu ing in o he ma e ial. In he case o he highe alue o he poin and clea ance angle he cu ing edge
epea edly cu s in o he wo kpiece ma e ial and hen cause undesi able ib a ions. The desc ibed e ec esul ed
in highe su ace oughness no iceable in case o d ills E, F and G.
Geome ic ole ances o holes. The geome ic shape was assessed using he measu ed geome ic ole -
ances o he holes—ci cula i y (see Fig.12), cylind ici y (see Fig.13) and pe pendicula i y o he hole axis o he
su ace (see Fig.14). The lowes alues o geome ic ole ances we e measu ed in case o he d ill C, bu con a y
he highes alues o geome ic ole ances we e ound in case o uns able d ill G.
Figu e9. The in luence o he d ill bi geome y on he magni ude o he applied eed o ce.
Figu e10. The in luence o he d ill geome y on he applied o que magni ude.
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The measu ed alues o he geome ical ole ance (calcula ed as an a e age alue om holes desc ibed in
“Expe imen al and measu emen design” sec ion) o oundness anged om 0.025 (d ill C) o 0.045mm (d ill
G). Changing he angle o he poin and he clea ance angle on he main edge o d ills A o F ea u ed no e ec
on he oundness o he measu ed holes. A signi ican e ec o inc easing he clea ance angle was ound in case
o d ill G (Fig.12). D ill A exhibi ed he highes de ia ion conside ing a hole ci cula i y, bu con a y he lowes
de ia ion ea u ed d ill C wi h he lowes clea ance angle (6.92°).
The cylind ici y o he analysed holes (calcula ed as an a e age alue om holes desc ibed in “Expe imen al
and measu emen design” sec ion) was measu ed in a ange o alues om 0.045 (d ill C) o mo e han 0.095mm
Figu e11. (a) The dependence o he de ia ion alue om he nominal alue o he poin angle and he
clea ance angle o he d ill on he achie ed su ace oughness and (b) oughness o he 1s and he 14 h hole
eached o each d ill.
Figu e12. The dependence o he de ia ion alue om he nominal alue o he ci cula i y alue o he d illed
holes on he choice o poin angle and clea ance angle.
Figu e13. The dependence o he de ia ion alue om he nominal alue o he poin angle and he clea ance
angle o he d ill on he size o he d illed hole cylind ici y.
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(d ill G). Highe cylind ici y alues we e eached when using d ills wi h poin angle alues o 138°–142° and
clea ance angle alues om 7° o 8° (Fig.13). D ill B exhibi ed he highes de ia ion conside ing a hole cylind ic-
i y, bu con a y he lowes de ia ion showed d ill E (poin angle 141.61 and clea ance angle 7.76° espec i ely).
The measu ed alues o he pe pendicula i y (calcula ed as an a e age alue om holes desc ibed in “Expe i-
men al and measu emen design” sec ion) o he hole axis o he su ace anged om 0.025 (d ill C) o 0.06mm
(d ill G). The bes alues we e ob ained using a poin angle in he ange o 138°–140° (Fig.14). D ill E ea u ed
he highes de ia ion conside ing a hole pe pendicula i y (opposi e o hole cylind ici y), bu con a y he lowes
de ia ion ea u ed d ill C as in case o hole cylind ici y.
D ill G achie ed signi ican ly wo se hole quali y esul s in e ms o su ace oughness and geome ic ole -
ances compa ed o d ill D wi h a e y simila geome y. The cause o he desc ibed anomaly is appa en ly a
de ec in he d ill caused du ing i s p oduc ion i.e., ele a ion o he blade, when he ou e ips o he d ill ha e
a di e en heigh . This de ec causes a di e en engagemen o he wo edges o he ool, esul ing in he ib a-
ions and egula misalignmen o he d ill bi du ing d illing. The achie ed alues o geome ic ole ances a e
mainly in luenced by he abili y o accu a ely d ill in o he ma e ial and he subsequen s abili y o he cu ing
p ocess du ing d illing. Imp ope en e ing o he d ill in o he ma e ial can impa he axis o he hole o de ia e
and in oduce ib a ions.
Posi ion and size o holes. The alues o he de ia ion om he nominal alue o he hole pi ch we e o
indi idual holes om 0.06mm (in case o d ill C) o 0.1 o d ill E (see Fig.15). The bes alues we e achie ed
wi h d ills C and G. In he case o hole machined by d ill C, his alue was assumed as he high-quali y d illed
holes. The alue o he d ill G hole is no conside ed due o he e y poo quali y o he hole in e ms o assessed
pa ame e s. The s anda d de ia ion o he se o measu ed da a o pi ch de ia ions om he nominal alue is
only 0.01mm, his ac con i ms he s abili y o he d ill du ing d illing in o he ma e ial. D ill B ea u ed he
highes de ia ion conside ing a hole space de ia ion, bu he lowes de ia ion alue was eached by d ill C.
In e ms o he accu acy o he dimension o he d illed holes, he bes esul s we e ound o d ills C and
D, wi h a poin angle o 138° and he clea ance angle o 7° (see Fig.16). The de ia ion alues o he measu ed
da a om he nominal alue o he diame e a e 0.03mm and 0.036mm espec i ely o he men ioned d ills,
Figu e14. The dependence o he de ia ion alue om he nominal alue o he chosen geome y o he
compa ed angles on he achie ed pe pendicula i y o he axis o he hole o he su ace o he d illed pla e.
Figu e15. The dependence o he de ia ion alue om he nominal alue o he d illed holes spacing on he
choice o he poin angle and he clea ance angle on he d ill.