B GIO DC V O TO I HC NNG NGHIP H NI GVC.Ths. HONG TH CHT V K THUT C KH H NI2008 Trng i hc Nng nghip H Ni Gio trnh V k thut c kh 1.M U V k thut l mn hc k thut c s c dy cc trng i hc k thut nhm cung cp cho sinh vin nhng kin thc c bn v cch c v lp bn v k thut. Nh nhng bn v ny m ngi cn b k thut ni r c thit k ca mnh v thc hin . Ngy nay khi m mc chuyn mn ho v hp tc ho trong hu ht cc lnh vc sn xut v i sng t ti mc cao, th bn v k thut tr thnh Ting ni ca k thut. Cc bn v k thut c xy dng bng cc phng php biu din khoa hc, chnh xc tun theo nhng quy tc thng nht c quy nh trong cc Tiu chun Nh nc. Nhim v ca mn V k thut l cung cp cho ngi hc nhng hiu bit c bn v v k thut c th c kh nng thnh lp v c bn v. Bn v phi c v chnh xc , sng sa ngi cd hiu v trnh nhm ln v th i hi phi v chnh xc, t m v cn nhiu thi gian khi v bngdng c cm tay. Cn khi vbng my tit kim c thi gian nh cc tin ch ca cc thao tc nhanh v chnh xc. Mn v k thut cn rn luyn cho sinh vin tc phong lm vic khoa hc, c thc t chc v k lut, tnh cn thn, kin nhn ca ngi lm cng tc khoa hc k thut. Vkthutlmnhckthutcsmangnhiutnhthchnh.Trongqutrnhhc tp,ngihccnphinmvngcckinthccbnnh:llunvccphpchiu,cc phng php biu din vt th, nm vng cc quy nh ca Tiu chun Nh nc v bn v, mt khcphi thng xuyn rn luyn cc k nng thc hnh. Nm 1963, U ban Khoa hc v K thut Nh nc nay l B Khoa hc & Cng ngh ban hnh cc tiu chun Vit Nam v Bn v c kh. cng l nhng Tiu chun Nh nc u tin ca Vit Nam. Nm 1964 cc Tiu chun v h thng qun l bn v c ban hnh.Cc Tiu chun trn bc u thng nht cc quy nh v bn v k thut nc ta. n nay cc Tiu chun ngy cng c sa i v hon thin cho ph hp vi s pht trin ca sn xut v stin b ca khoa hc, k thut. Hin nay cc Tiu chun v bn v k thut ni ring v cc Tiu chun v ti liu thit k ni chung c Nh nc ban hnh trong nhm cc tiu chun v H thng ti liu thit k. thngnhtTingnicakthuttrnphmvirnglnhn,tchcquctv tiuchunha(InternationalOrganiazationforStandardization)vitttlISOthnhlpt nm 1946 ban hnh cc Tiu chun quc t v bn v k thut.VicpdngnhngTiuchunQucgiavQuctcngnhccTiuchunngnh, Tiu chun x nghip vo thc tin sn xutc ngha rt ln i vi nn kinh t quc dn. N thcycctinbkthut,nngcaonngsutlaong,chtlngvhgithnhsn phm. Gp phn gio dc ngi lao ngv t tng, v l li lm vic trong nn sn xut ln . L nhng ngi lm cng tc khoa hc, k thut trong tng lai chng ta phi c thc trong vic tm hiu v chp hnh cc Tiu chun Quc gia v Quc t cng nh cc Tiu chun ngnh, Tiu chun x nghip trong qu trnh hc tp mn v k thut cng nh vic p vo cng vic thit k v ch o sn xut sau ny.Trng i hc Nng nghip H Ni Gio trnh V k thut c kh 2.CHNG I VT LIU V DNG C V lp cc bn v k thut cn phi c nhng vt liu v dng c v thch hp. La chn ng v s dng thnh tho cc dng c v l mt trong nhng iu kin m bo cht lng bn v v nng cao hiu sut cng tc. . Sau y l mt s vt liu v dng c thng dng trong v k thut. 1.1. VT LIU V 1.1.1. Giy v Thng c cc loi giy sau y: -Giyvtinh(giycrki),lloigiydy,hicngcmtmtnhnvmtmtrp. Khi v bng ch hay bng mc u v trn mt nhn. - Giy can dng sao chpbn v. - Giy v phc l loi giy thng, giy k li hoc giy k vung. 1.1.2. Bt v Ch dng bt ch en thc hin cc bn v k thut.Bt ch enc nhiu loi, bt loi cng k hiubng ch H(2H, 3H ...6H) v bt loi mm k hiu bng ch B (2B, 3B ... 6B). Ch s ng trc ch H hoc B cng ln th bt c cng hoc mm cng ln. Bt ch loi va c k hiu l HB. Trong v k thut, thng dng loi bt ch HB v m, v cc nt mnh v bt ch 2B t m cc nt v hoc vit ch. Bt ch thn g c vt nhn hay vt theo hnh li c (H. 1-1). Hnh 1-1 Ngy nay ngi ta thng dng cc loi bt ch bm (H. 1-2), rt thun tin khi s dng. Nn dng loi bt li ch c ng knh v cng ph hp.Trng i hc Nng nghip H Ni Gio trnh V k thut c kh 3. Hnh 1-2 1.1.3. Ty Chnndngloitymm,khicntyxoccntvbngmcen,cthdngli dao co hoc bt ph mc trng.Ngoi ra cn c mt s vt liu khc nh mc en, giy nhm ( mi u bt ch), inh m c nh giy v trn bn v ... 1.2. DNG C V V CCH S DNG 1.2.1. Bn v Mt bn v thng lm bng g mm, mt bn phi phng v nhn, hai bin tri v phi cabnvthngnpbnggcngmtbnkhngbvnh.Mtbintricabnvphi phng v nhn c th trt thc ch T mt cch d dng (H. 1-3).

Hnh 1-3 1.2.2. Thc ch T ThcchTlmbngghocbngchtdo,ngmcthnngangmngvuT. Mp trt ca u T vung gc vi mp trn ca thn ngang, u T cng c th quay c so vi thn ngang.

Hnh 1-4 Thc ch T dng vch cc ng thng nm ngang, khi vch, bt ch c vch theo mp trn ca thn ngang. cc ng v song song vi nhau, ta c th trt mp ca u thc T dc theo bin tri ca bn v (H. 1-4). Trng i hc Nng nghip H Ni Gio trnh V k thut c kh 4. 1.2.3. ke ke v k thut thng l mt b gm hai chic, mt chic c hnh tam gic vung cn v mt chic c hnh na tam gic u. ke thng lm bng g mng hoc cht do. CthdngkephihpvithcchThoc haikephihpvinhauvchcc ng thng ng, cc ng nghing song song v cc gc (H. 1-5).

Hnh 1-5 1.2.4. Thc cong Thc cong l thc dng v cc ng cong m khng v c bng com pa nh cc ngelp,parabon,hypebon...Thccongcnhiuloikhcnhauclmbngghoc cht do. Khiv,trchtcnxcnhcmtsimcangcong,saudngthc congniccimli,saochomtcungnocathccongiquatnhtbaimca ng cong ng cong c trn u (H. 1-6).

Hnh 1-6 1.2.5. Hp compa Hpcompavkthutthngdngcccdngcsau:compavngtrn,compa o, bt k mc Di y trnh by cch s dngmt s dng c . -Compa v ng trn Trng i hc Nng nghip H Ni Gio trnh V k thut c kh 5.Compa v ng trn dng v cc ng trn c ng knh ln hn 12mm. Nu v nhng ng trn c ng knh ln th chp thm cn ni (H. 1-7).Khi v cn ch my im sau y: - u kim v u ch (hay u mc) t vung gc vi mt bn v. -Khivnhiungtrnngtm,nndngkimcngnuhocdngcchnh tm kim khng b n su xung vn v lm cho l m to ra dn n nt v khng chnh xc. -Dngngntaytrvtaycicmunmcompa,quaymtcchunvlintc theo mt chiu nht nh. - Compa v ng trn b Compa v ng trn b dng v ng trn c ng knh di 12mm (H. 1-8).Cch s dng compa nh cc hnh di y:

Hnh 1-7 Hnh 1-8 - Compa o Compa o dng o di on thng t thc k li t ln bn v. Hai u kim ca compa t ng vo hai u mt ca on thng hoc hai vch trn thc k li, sau a ln bn v bng cch n nh hai u kim xung mt giy v. (Hnh 1-9).

Hnh 1-9 - Bt k mc Btkmclbtdngkmclngiycrki,giythnghoclngiycanbng mc en. Khi dng bt k mc cn ch my im sau y: - Khng trc tip nhng u bt vo bnh mc, m phi dng bt st hoc bt lng ly mc,tramcvokhegiahaimpcak,cngichocaocamcctrongbtkcao khong t 6 n 8 mm m bo cho nt v u. Trng i hc Nng nghip H Ni Gio trnh V k thut c kh 6.- Trc khi v, cn iu chnh c u bt nt v c b rng ph hp. - Khi v, gi cho hai mp ca u bt u tip xc vi mt giy nt v u n, cn bt hi nghing v hng di chuyn ca bt. (H.1-10). Ngy nay, thng dng bt mc kim c cc c nt khc nhau (H. 1-11).

Hnh 1-10 Hnh1-11 1.3. TRNH T HON THNH MT BN V hon thnh mt bnv bngch hay bng mc, cn phi tin hnh theo mt trnh t nht nh. Khi v cn chia thnh hai bc ln, bc v m v bc t m. Dng loi bt ch cng H, 2H v m, sau kim tra li bn v ri mi t m. Dng loi bt ch mm B hoc 2B t m cc nt c bn v bt ch c k hiu B hoc HB t cc nt t v vit ch. V cc ng trn nn chn ch mm hn chv ng thng. Cnmi u ch trn giy nhm cho nhn u . Khng nn t i t li tng on ca nt v. Ni chung, nn t cc nt kh v trc, cc nt d v sau, t cc nt m trc, cc nt mnh sau, k cc ng nt trc, ghi con s, ghi cc k hiu v vit ch sau.Trnh t t cc nt v nh sau: 1- Vch cc ng trc v ng tm bng nt chm gch mnh. 2- T m cc nt c bn theo th t: - ng cong ln n ng cong b. - ng bng t trn xung di. - ng thng t tri sang phi. - ng xin gc t trn xung di vt tri sang phi. 3- T cc nt t theo th t nh trn. 4- K cc ng ging, ng ghi kch thc, ng gch gch ca mt ct 5- V cc mi tn, ghi cc con s kch thc, vit cc k hiu v ghi ch bng ch. 6- T khung v v khung tn. 7- Cui cng kim tra bn v ln cui v sa cha. Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 7 CHNG II NHNG TIU CHUN V CCH TRNH BY BN V 2.1. TIU CHUN V BN V K THUT m bo cho bn v k thut lphng tin thng tin gia nhng ngi lm cng tc k thut, l ti liu k thut lin quan n sn phm v vy n phi c thc hin bng nhng phng php biu din khoa hc, chnh xc theo nhng quy tc c quy nh thng nht trong cc Tiu chun Nh nc Vit Nam v Tiu chun quc t v bn v k thut.Nhng Tiu chun Nh nc v bn v c ban hnh v thng qua vo nm 1963. n nm 1974 th cc tiu chun ny c sa i li v in thnh "H thng ti liu thit k". Di y l nhng Tiu chun v cch trnh by bn v. 2.2. KH GIY 2.2.1 Cc kh giy TCVN2-74 quynhkhgiycaccbnvvnhngtiliukthutkhccattc cc ngnh cng nghip v xy dng. Trong k hiu trn: TCVN:l ch vit tt ca "Tiu chun Vit Nam". 2: S hiu ca tiu chun ng k. 74:L hai ch s cui ch nm 1974 ban hnh hoc sa i tiu chun.Ring nhng tiu chun ban hnh sau nm 1991 c ghi y tt c cc ch s ch nm. Kh giy l kch thc ca t giy sau khi xn tnh theo n v o l mm. C hai loikhgiy chnh v cc kh ph.Kh giy chnh ln nht c din tch 1 m2, cc kh giy chnh tip theo c c bng cch chia i kh ln hn k vi n bng cch dc i theo ng song song vi cnh ngn (H. 2-1). a, Hnh 2-1 Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 8 Tt c cc kh giy chnh ng dng vi nhau (H. 2-2).

a, b, Hnh 2-2

K hiu v kch thc ca cc kh chnh theo bng 1-1 di y: Bng 1-1 K hiu kh giy4424221211 Kchthccccnhkh giy tnh bng mm 1189x841594x841594x420297x420297x210 Khiucatgiytng ng viTCVN 2-74 A0A1A2A3A4 Ngoi cc kh chnh ra, cho php s dng cc kh giy ph, kch thc cc cnh ca kh ph l bi s kch thc cc cnh ca kh 11. V d t kh giy 1.1 (297x 210) ta c th to ra kh ph 1.3 (297x631) hoc kh 3.2 (892x420). 2.2.2. ngha ca k hiu kh giy K hiu ca mi kh giy gm 2 ch s, ch s th nht l kch thc mt cnh ca kh giy chia cho 297, ch s th hai l kch thc cnh cn li ca kh giy chia cho 210. Tch ca hai ch s trong k hiu l s lng kh 11 cha trong kh giy , v d kh 24 gm c: 2 x 4 = 8 kh 11 2.3. KHUNG BN V V KHUNG TN Mibnvuphickhungbnvvkhungtnring.Nidungvkchthcca chngcquynhtrongTCVN3821-83.Sauygiithiucchvkhungbnvvkhung tn thng dng trong nh trng. Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 9 2.3.1. Khung bn v Khungbnvcvbngntlinm,kcchccmpcakhgiy5mm.Khicn ng thnh tp, cnh tri ca khung bn v c k cch mp tri ca kh giy mt khong bng 25 mm (H.2-3a). 2.3.2. Khung tnKhung tn c th t theo cnh di hay cnh ngn ca bn v v c t gc pha di, bn phi, cnh di ca khung tn xc nh hng ng bng ca bn v.Nhiu bn v c th c thc hin trn cng mt t giy, song mi bn v phi c khung bn v v khung tn ring. Khi khung tn ca mi bn v phi t sao cho cc ch v ch s ghi trong khung tn c u hng ln trn hoc hng sang tri i vi bn v (H. 2-2b).

a, b, Hnh 2-3Khung tn ca bn v dng trong nh trng c ni dung nh hnh 2-4 di y: Hnh 2-4 Trong : 1: Tn ca bi tp hoc tn gi ca chi tit. 6: Ngy v 2: Vt liu ch to chi tit. 7: Ch k ngi kim tra 3: T l ca bn v. 8: Ngy kim tra Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 10 4: K hiu ca bnv. 9: Tn lp, khoa, trng 5: H v tn ngi v. 2.4. T L-Tlcamthnhbiudinltsgiakchthcoctrnhnhbiudinv kch thc tng ng o c trn vt tht. - Tu theo ln v mc phc tp ca vt th c biu din m ngi ta chn t l nguyn hnh, t l phng to hoc thu nh. - Tr s kch thc ghi trn hnh biu din l kch thc thc, khng ph thuc vo t l ca hnh biu din . -TCVN3-74tngngviTiuchunQuctISO5455:1979quynhtlcacc hnh biu din trn cc bn v c kh phi c chn trong cc dy s sau: T l thu nh1:2 ; 1:2,5 ; (1:4) ; 1:5 ; 1:10 ; (1:15) ; 1:20 ; 1:25 ; (1:40) ; 1:50 ; (1:75) ; 1:100 ... T l nguyn hnh1:1 T l phng to2:1 ; 2,5:1 ; 4:1 ; 5:1 ; 10:1 ; 20:1 ; 40:1 ; 50:1 ; 100:1 Ch : - Nn hn ch dng cc t l ghi trong ngoc. -Constlcghitrongdnhringcakhungtntheokiu1:1;1:2;2:1...v khng cn ghi ch t l na.-Nu hnh biu din ca mt b phn hay mt chi tit no khc vi t l chung ca bn v th ghi theo kiu sau: 1 : 2 TLA ; 1 : 4 TLB;1 : 5 TLI 2.5. NG NT Trn cc bn v k thut, cc hnh biu dincavt th c v bng nhiu loi ng nt c hnh dng v kch thc khc nhau. TCVN 8-1993 quy nh cc loi ng nt v v ng dng ca chng trncc bn v nhm lm cho cc hnh biu din r rng , p mt v d c..2.5.1. Cc loi nt v Cc loi nt v trn bn v c kh c lit k trong bng 2-1 di y:Bng 2-1 TTDng nt vTn ging dng1A Nt lin mA1 - Cnh thy, ng bao thy Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 11 A2 - ng ren thy, nh rng thy 2BNt lin mnhB1 - Giao tuyn tng tng B2 - ng kch thc B3 - ng dn, ng ging kch thc B4 - Thn mi tn ch hng nhn B5 - ng gch gch mt ct B6 - ng bao mt ct chp B7 - ng tm ngn B8 - ng chn ren thy 3C D (1) Nt ln sng Nt dch dc (2) C1 - nggii hngia phn hnhct vi phn hnh chiu trong hnh ct kt hp C2 - ng ct la 4ENt t m (2) E1 - ng bao khut, cnh khut 5FNt t mnhF1 - ng bao khut, cnh khut (2) 6GNtgchchm mnh G1 - ng tm G2 - ng trc i xng G3 - Qu o G4 - Mt chia ca bnh rng 7H Nt ctH1 - Vt ca mt phng ct 8JNtgchchm m J1 - Ch dn cc nghoc mt ct cn x l ring 9KNtgchhai chmmnh K1 - ng bao ca chi tit ln cn K2-Ccvtru,cui,trunggiancachi tit di ng K3 - ng trng tm K4-ngbaocachitittrckhihnh thnh K5-Bphncachititphatrcmt phng ct Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 12 (1) Thch hp khi s dng my v. (2) Ch c s dng mt trong hai loi nt trn cng mt bn v. Hnh 2-5 minh ho mt s p dng i vi cc nt quy nh. Hnh 2-5 2.5.2. Nhm ng nt Nhm ng ntc phn theo b rng nt v. Trong mt bn v b rng ca cc nt mnh, m, rt m phi c chn trong cng mt nhm theo bng 2-2 di y: Bng 2-2

Nhm ng nt Nt mnh (mm) Nt m (mm) Nt rt m (mm) 10,180,350,7 20,250,51,0 30,350,71,4 40,51,02,0 50,71,42,0 Ch : - Nhm 2, 3 v 4 c u tin s dng. - Chn b rng ca nt v ph thuc vo kch thc v mc phc tp ca vt th cnbiu din. Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 13 - Nhm ng nt phi chn ging nhau trn tt c cc hnh biu din vi cng mt t l trn cng mtbn v. -Chiurngcacngmtntvtrncngmtbnvkhngcthayitrncc hnh biu din khc nhau. 2.5.3. Quy tc v cc loi ng nt - Nu trn hnh biu din c hai hay nhiu nt v khc loi trng nhau th v theo th t u tin sau: ng bao thy, ng bao khut, ng trc, ng tm v ng ging kch thc - i vi cc nt t, nt chm gch mnh v nt hai chm gch mnh cn v chiu di cc on gch v khong cch gia cc on gch trong cng mt bn vphi nh nhau.-Ccntchmgch,nthaichmgch,nttticcchbtu,chktthc,ch giao nhau, ch un ln u c v bng cc nt gch. Ring nt t ti ch tip gip vi nt linm th ch tip gip cn v h (H.2-6a) - Cho php vng tm ca hnh trn, van ,. . . bng nt lin mnh thay cho nt chm gach mnh khi kch thc ca cc phn t nh hn 12 mm trn bn v (H. 2-6b). Trong mi trng hp, tm ca ng trn c xc nh bng giao ca hai nt gch. Ti ch bt u v kt thc nt chm gch phi vt qu ng bao khong 2 n 5mm (H 2-6).

a, b, Hnh 2-6 2.6 CH V S Trnbnvkthutngoicchnhvracncccconskchthc,nhngkhiu bng ch, nhng ghi ch bng li khc ... tt c chng phi c theo cc quy nh thng nht d c, p mt v trnh nhm ln. TCVN 6-85 ph hp vi tiu chun Quc t ISO 3098-2:2000 quy nh ch vit gm ch, ch s v cc du dng trn cc bn v v ti liu k thut. 2.6.1. Kh ch Khch(khiulh)lgitrcxcnhbngchiucaocachhoatnhbng milimt, c cc kh ch sau y: 2,5 ; 3,5 ; 5 ; 7 ; 10 ; 14 ; 20 ; 28 ; 40. Chiu rng ca nt ch (k hiu l d) ph thuc vo kiu ch v chiu cao ca ch. Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 14 2.6.2. Kiu ch Kiu ch k thut: c hai kiu ch c dng trong k thut . Kiu A khng nghing (ng) v kiu A nghing 750 vi d =1/14h Kiu B khng nghing (ng) v kiu B nghing 750 vi d = 1/10h Cc thng s ca ch c quy nh trong bng 2-3 v hnh 2-7 di y. Bng 2-3 Kch thc tng iThng s ca chK hiu Kiu AKiu B Chiu cao ch hoah14/14h10/10h Chiu cao ch thngc10/14h7/10h Khong cch gia cc cha2/14h2/10h Bc nh nht ca cc dngb22/14h17/10h Khong cch gia cc te6/14h6/10h Chiu rng nt chd1/14h1/10h Chiu rng ca chg6/10h6/10h : Hnh 2-7 Kiuchxydng:ngoikiuchkthuttrncdngchoccngnhkthut. Trong bn v xy dngcn cho php c dng hai kiu ch khc theo TCVN 2233-77, l kiu ch gy nt m v kiu ch m thut. Hai kiu ch ny ch yu dng ghi tn cc bn v v cc mc ln, y khng trnh by.

Hnh 2-8, hnh 2-9 l mt s th d v cch vit ch, s v ch s La M. Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 15 Hnh 2-8 2.7. GHI KCH THC Trn bn vkch thc th hin ln ca vt th c biu din. Vic ghi kch thcphi c theo cc quy nh thng nht ca TCVN 5705-1993, tiu chun ny ph hp vi Tiu chun Quc t ISO 129:1985. 2.7.1. Quy nh chung - C s xc nh ln v v tr tng i gia cc phn t c biu din l cc con s kch thc, chng khng ph thuc vo t l ca bn v. - Mi kch thc ch c ghi mt ln trn bn v. Kch thc c ghi trn hnh chiu th hin r rng v c trng nht v cu to ca phn t c ghi. S lng kch thc ghi trn bn v phi ch to v kim tra chi tit - Kch thc di trn bn vdngn vo l mm, nn khng cnghi n v o sau con s kch thc. Nu dng n v khc nh centimet, mt th n v o c ghi ngay sau con s kch thc. - Kch thc gc ghi trn bn v dngn v o l , pht, giy. 2.7.2. Cc thnh phn ca kch thc Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 16 Hnh 2-9 Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 17 a, b, Hnh 2-10 - ng kch thc dng biu th phn t c ghi kch thc, n c v bng nt lin mnh (H. 2-10). -ngkchthccaonthngcksongsongvionthngvcchon thngmtont5n7mm(H.2-10).ngkchthccadidycunglng thng song song vi dy cung (H.2-11a). ng kch thc ca gc l mt cung trn c tm nh gc (H 2-11b). ng kch thc ca di cung trn l mt cung trn ng tm (H 2-11c) - Khng c dng ng trc, ng tm, ng bao lm ng kch thc a, b, c, Hnh 2-11 -Nuhnhvlhnhixngmkhngvy,hochnhvlnahnhchiuv na hnh ct kt hp th cho php khng v y ng kch thc (H. 2-12). Hnh 2-12 2.7.2.2. ng ging kch thc - ng ging kch thc dng gii hn phn c ghi kch thc, c v bng nt lin mnh v thng k vt qu ng kch thc mt khong t 2 - 5 mm. -nggingcakchthcdickvunggcvingkchthc(H.2-10). Trng hp c bit cho php k ng ging xin gc khi trng vi ng bao (H. 2-13). Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 18 - Nhng ch c cung ln, ng ging c k t giao im ca hai ng bao ni tip vi cung ln (H. 2-14).

Hnh 2-13 Hnh 2-14 -Chophpdngccngtrc,ngtm,ngbao,ngkchthclmng ging kch thc (H. 2-15). 2.7.2.3.Mi tn hai umt ca ng kch thc c v mi tn, ln ca mi tn t l thun vi chiu rng nt v ca bn v (H. 2-16). Hnh 2-15 Hnh 2-16 - Trong trng hp ng kch thc ngn qukhng ch v mi tn th mi tn c v pha bn ngoi hai ng ging (H. 2-17). - Trng hp c nhiu kch thc ni tip nhau m khng ch v mi tn th dng du chm m hoc gch xin thay chomi tn (H. 2-18). Hnh 2-17Hnh 2-18 2.7.2.4. Con s kch thc -Conskchthcphivitchnhxc,rrngphatrnvvokhonggiaca ng kch thc. Chiu cao ca con s kch thc thng khng b hn 3,5mm. - Chiu ca con s kch thc di ph thuc vo nghing ca ng kch thc so vi ng bng ca bn v (H. 2- 19). Nu ng kch thc c nghing qu ln th con s kch thc c ghi trn gi ngang (H. 2-20). Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 19 Hnh 2-19 Hnh 2-20 - Chiu con s kch thc gc ph thuc vo nghing ca ng thng vung gc vi ng phn gic ca gc (H. 2-21). Hnh 2-21 Hnh 2-22 - Khng cho php bt c ng nt no ca bn v chia hay ct con s kch thc, trong trng hp cn thit th phi vit con s kch thc lch hoc v ngt on cc ng (H. 2-22). - i vi nhng kch thc qu b, khng ch ghi kch thc th con s c vit trn ng ko di ca ng kch thc hoc trn gi ngang (H. 2-23). - Khi c nhiu ng kch thc song song nhau hay ng tm th kch thc nh t trong, kch thc ln t ngoi. Cc ng kch thc phi cch nhau 7 n 10 mm v con s ca cc kch thc t so le nhau (H.2-24). Hnh 2-23 Hnh 2-24 - i vi cc phn t ging nhau, phn b c quy lut th c th ghi kch thc ca chng nh (H. 2-25).Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 20 Hnh 2-25 2.7.2.4.Cc ch v k hiu-ngknh:Trongmitrnghp,trcconskchthccangknhphighi km k hiu c kh bng kh ca con s kch thc, ng kch thc ca ng knh c k qua tm ng trn (H. 2-26). Hnh 2-26 - Bn knh: Trong mi trng hp, i vi cc cung trn c gc tm nh hn 1800 th ghi kch bn knh. Trc con s kch thc ca bn knh c km theo ch R bng kh ca con s kch thc (H.2 - 27). i vi cc cung trnc bn knh qu b, khng ch ghi kch thc v v mi tn th cho php ghi nh (H. 2-27b,c). ivicungtrncbnknhquln,tmcacungbnngoigiihncnv,cho php ng kch thc v gy khc v khng cn xc nh tm (H. 2- 28).

a b c Hnh 2-27 Hnh 2-28 - Hnh cu: Pha trc con s kch thc ng knh hay bn knh ca hnh cu phi ghi ch cu hoc du kmdu hay ch R (H 2-29).- Hnh vung: phn bit phn mt phng vi mt cong dng nt lin mnh gch cho phn mt phng. Pha trc con s kch thc cnh ca hnh vung ghi du(H.2-30). Trng i hc Nng nghip H Ni Gio trnh V k thut c kh ........................................... 21

a) b) Hnh 2-29 - di cung trn Pha trn con s di cung trn ghi du , ng kch thc l mt cung trn ng tm, ng ging k song song vi ng phn gic ca gc chn cung (H.2-31).

Hnh 2-30Hnh 2-31 Trng i hc Nng nghip H Ni Gio trnh V k thut c kh .................................................22 CHNG III V HNH HC Trong qu trnh thc hin mt bn v ta thng phi thc hin mt s vn v dng hnh phng nh: chia u mt on thng, chia u mt ng trn, v cc cung ni tip, v cc ng cong hnh hc . Trong chng ny chng ta ln lt nghin cu ccvn . 3.1 CHIA U MT ON THNG V MT NG TRN 3.1.1. Chia u mt on thngChia on thng AB ra n phn bng nhau. - Qua imA k ng thng Ax bt k (nn k sao cho gc BAx l mt gc nhn). - K t im A, t lin tip ln Ax, n on thng bng nhau bng cc im chia 1, 2, 2',... n. - Ni n vi B v qua cc im 1, 2', 3, ... k cc ng thng song song vi nB. Giao imcaccngthngviABchotaccimchiatngng1,2,3,lcc im cn tm (H. 3-1). Hnh 3-1 3.1.2. Chia u mt ng trn Cch chia ng trn ra 2, 3, 4, 6, 8phn u nhau ta u bit. Di y lcch chiang trnra 5, 7, 9, 10, 11, 13,... phn u nhau. 3.1.2.1Chia ng trn ra 5 v 10 phn u nhau Chia ng trn ra 5 phn u nhaubng cc dng di cnh ca hnh 5 cnh u ni tip trong ng trn theo cng thc : a5 = R/25 2 10 (trong R l bnknh ng trn). Cch v nh sau: - Qua tm O k hai ng knh AB v CD vung gc vi nhau. - Xc nh trung im M ca bn knh OA. - V cung trn tm M, bn knh MC, cung trn ny ct OB ti im N, CN l di cnh hnh nm cnh u v ON l di hnh 10 cnh u ni tip ng trn (H. 3-2).3.1.2.2.Chia ng trn ra 7, 9, 11,13...) phn u nhau Trng i hc Nng nghip H Ni Gio trnh V k thut c kh .................................................23 Phngphpgnng(H.3-3)diythngdngchiangtrnra7,9, 11,13 phn u nhau. V d chia dng trn ra 7 phn u nhau: - K hai ng knh vung gc AB v CD. - V cung trn tm D, bn knh CD, cung ny ct A ko di ti E v F. - Chia ng knh CD ra 7 phn bng nhau bng cc im chia 1, 2', 3 -NiEvFviccimchiachn2,4,6(hocccimchial1,3',5...),cc ng ny ct ng trn ti cc im 1, 2, ... 7 chnh l cc nh ca hnh 7 cnh u ni tip ng trn phi v. Cch chia ng trn ra 9, 11, 13,... lm tng t khi ta chia CD ra 9, 11, 13,... phn u nhau. Ta c th v mt hnh c n cnh ni tip mt ng trn cho trc bng cch tnh di an ca mt cnh. Khi di an c tnh bng cng thc sau:an = 2rsin n0180

Hnh 3-2 Hnh 3-3 3.2. V DC V CN 3.2.1. V dc dcgia ng thngAB v ng thngAC chnh l tang cagc to thnh gia hai ng thng (H. 3-4).S = ACBC = tg dc c trng cho nghing gia ng thng ny so vi ng thng kia, c tnh theo phn trm hoc t l. V dc l v gc theo tang ca gc. Hnh 3-4 Trng i hc Nng nghip H Ni Gio trnh V k thut c kh .................................................24 Cch v dc ca mt ct thp hnh theo kch thc cho, c dc 1:10 (H.3 - 5). v dc 1:10, ta v tam gic vung c mt cnh gc vung (cnh ng) l 10, cnh gc vung kia (nm ngang) l 100. Hnh 3-5 3.2.2. V cn cn l t sgia hiu s hai ng knh ca hai mt ct vung gc ca hnh cn trn xoay v khong cch gia hai mt ct (H. 3-6).K = hd D = 2 tg V mt hnh cn c cn K l v hai cnh bn ca mt hnh thang cn c hai y l D v d m cc cnh bn u c dc bng K/2 so vi ng cao ca hnh thang (H 3-6a). V d: v mt hnh cn c cn 1:5, nh l A, trc l AB. -QuahaiimAvBxcnhvhaingthngcdcvitrcABbngS = K/2 = 1: 10.

Hnh 3-6 Trong ngnh ch to my, cn dng cho cc loi mi ghp hnh cn c quy nh trong TCVN 135-63, theo cn K c cc gi tr: 1:200 ; 1:100 ; 1:50 ; 1:30 ; 1:20 ; 1:15 ; 1:12 ; 1:10 ; 1:8 ; 1:7 ; 1:5 ; 1:3 ; hoc tnh theo gc 2 ta c: 300 ; 450 ; 600 ; 750 ; 900 ; 1200.3.2.3. Cch ghi kch thc dc v cn TCVN 5705-1993 quy nh v ghi kch thc cho dc v cn nh sau: a) b) Trng i hc Nng nghip H Ni Gio trnh V k thut c kh .................................................25 - Pha trc con s kch thc ch dc hay cn phi ghi du dc hay du cn