Kamis, 16 September 2010

Sketsa Gambar Teknik


 Gambar skesta merupakan gambar ide awal untuk mengekspresikan gagasan tertentu ke dalam gambar disain.  Merangkum aspek-aspek disain gambar awal yang memerlukan olahan lebih lanjut.
Gambar sketsa merupakan sarana komunikasi awal untuk perancang (yang menggambar) maupun orang lain.
Menggambar sketsa pada dasarnya adalah menarik garis dengan tangan bebas, tanpa dibantu mistar atau penggaris. Dengan demikian kualitas garis harus diperhatikan sesuai dengan karakter dan jenis gambar yang akan disajikan. Kualitas garis yang dibuat oleh pinsil akan ditentukan oleh tingkat kehitaman (ketebalan) garis dan lebar garis.
Pada gambar sketsa, semua garis harus dimulai dan diakhiri dengan tegas dan harus mempunyai kaitan yang logis dengan garis lainnya dari awal sampai akhir. Bila dua garis membentuk sudut atau perpotongan, kedua ujungnya harus bertemu, tidak boleh kurang atau lebih.
Langkah-langkah untuk membuat garis lurus vertical maupun horizontal dalam gambar sketsa, sebagai berikut.
Tandai  titik awal dan titik akhir.
 Buat beberapa gerakan percobaan antara kedua titik tersebut untuk menyesuaikan mata dan tangan dengan garis yang akan dibuat.
 Buat sketsa garis yang sangat tipis. Mulai dari titik awal sampai titik akhir. Tujukan mata ke titik akhir.
 Buat  garis sketsa jadi dengan menghitamkan garis percobaan yang tipis tadi. Pada saat ini mata ditujukan pada ujung pensil digaris percobaan.
 Apabila ingin membuat garis lengkung yang bertemu dengan garis lurus, mulai dari ujung garis lengkung tadi, untuk menghindari titik pertemuan yang tidak tepat.

Dalam membuat gambar sketsa kamu perlu mengikuti urutan-urutan berikut ini.
 Membuat kerangka gambar yang terdiri dari garis-garis vertical, horizontal maupun lengkung secara tipis-tipis.
 Menggambar garis sekundernya, misalnya melukis kerangka kotak/kubus dalam keadaan tipis.
 Menebalkan garis-garis sketsa yang sudah benar. Ketebalan sesuai dengan karakter jenis garis yang diinginkan.
 Dalam menggambar sketsa teknik kamu akan belajar menggambar dengan arah pandang isometris. Biasanya gambar dengan pandangan secara isometris dilihat pada posisi miring sehingga arah pandangan yang kelihatan bisa terlihat dari beberapa bidang yaitu bidang atas, bidang depan, dan bidang samping atau biasa disebut pandangan depan, pandangan atas, dan pandangan samping.

Prinsip dasar menggambar sketsa proyeksi isometris (proyeksi miring) adalah sebagai berikut.
 Semua garis vertikal tetap kelihatan vertikal.
 Semua garis horizontal tetap kelihatan horizontal.
 Semua garis yang sejajar sumbu X, Y, Z dapat digambarkan berdasarkan skala atau proporsi tertentu.
 Dalam proyeksi isometric ketiga permukaan yang tampak mendapat perhatian yang sama.
 Pada proyeksi miring tampak sebuah bidang vertikal tetap sejajar dengan permukaan bidang gambar dan terlihat seperti keadaan sebenarnya.

Di bawah ini contoh arah pandangan isometris (proyeksi miring) yang terlihat beberapa sudut pandangannya.
Untuk dapat menggambar sebuah benda dengan proyeksi miring (isometris) ada beberapa ketentuan.
 Sebuah garis vertikal akan tetap vertikal.
 Semua garis yang miring ke bawah membentuk sudut 30 derajat terhadap horizontal atau cakrawala.
 Semua garis digambar sesuai dengan ukuran sebenarnya atau pada skala yang sama.
 Sisi yang tidak tampak digambar dengan garis putus-putus, sedangkan sisi yang nampak digambar dengan garis yang utuh.
 Ketebalan garis utuh digambar dua kali ketebalan garis putus-putus.

Sisi yang  tidak  tampak      dapat juga    digambar    dengan    garis tipis dengan  ketebalan  kira-kira seperempat garis.   

Dalam mempelajari materi pengetahuan dasar teknologi banyak menggunakan alat gambar untuk membuat suatu benda. Dengan gambar biasanya akan semakin mudah dijelaskan dan dimengerti   daripada hanya kata-kata, sehingga keberhasilan pembuatan benda kerja lebih baik.  Dalam teknik, gambar yang digunakan untuk membuat suatu benda disebut gambar teknik atau gambar kerja. Pada gambar tersebut diperlihatkan ukuran sebagai petunjuk besaran dari benda yang akan dibuat.
Gambar Teknik secara harfiah berasal dari kata :
GAMBAR – Suatu alat “ komunikasi visuil “
TEKNIK – METODE : Cara kerja bersistim, atau cara sistimatis dalam mengerjakan sesuatu

GAMBAR TEKNIK Adalah metode komunikasi secara visual dalam menyampaikan informasi hasil rancangan suatu produk secara :

 KOMUNIKATIF ( mudah dimengerti )
 NORMATIF ( sesuai aturan )
 AKURAT ( presisi-tepat teknisnya)
 TERUKUR ( memiliki skala )
 EFEKTIF ( tepat guna )


PERALATAN GAMBAR
Walaupun keterampilan tangan dan kemampuan sendiri yang akan menentukan hasil gambarnya, tetapi kualitas peralatan dan bahan-bahan yang digunakan ikut membantu proses penggambaran.  Dengan demikian  dapat menjadikan pengalaman yang menyenangkan bagi kamu dan akhirnya kamu akan lebih mudah untuk mencapai hasil gambar yang berkualitas.

Kualitas gambar yang disajikan tergantung pada beberapa hal di bawah ini.
 Media Gambar : kertas gambar macamnya (kertas HVS, kertas manila, kertas padalarang, kertas roti, kertas kalkir)
 Alat gambar manual : pensil, rapido
 Alat gambar digital : computer dengan program Computer Aided design (CAD)
 Alat bantu gambar : meja gambar, mesin gambar, mistar gambar segita, jangka, busur derajat, mal, sablon, dan  penghapus.
Untuk menggambar teknik diperlukan berbagai macam peralatan seperti di bawah ini.

KERTAS GAMBAR
Ketas gambar yang digunakan untuk penyajian gambar teknik telah mempunyai ukuran yang sudah distandarkan. Ukuran yang banyak di gunakan adalah seri A. Ukuran ini mempunyai standar yang dinyatakan dengan angka nol di belakang huruf A (A0).
Ukuran standar kertas gambar
No
Seri
Ukuran
1
A0
841 mm  x   1189 mm
2
A1
594 mm  x    841 mm
3
A2
420 mm  x    594 mm
4
A3
297 mm  x    420 mm
5
A4
210 mm  x    297 mm


Semua ukuran kertas sudah proporsional sehingga memudahkan pengerjaan pengecilan dan pembesaran gambar. Lembar tersebut akan dengan mudah dilipat guna penyusunan dokumen dan pencariannya kembali. Ukuran yang lebih kecil relatif lebih mudah dilipat dan disimpan baik di kantor maupun di lapangan. Usahakan untuk melipat lembar kertas sekecil mungkin sehingga memudahkan penyusunan dan pencariannya (pemeriksaannya).
Untuk mendapatkan ukuran kertas yang lebih kecil dapat dilakukan dengan membagi luas seri A0, menjadi ukuran seri A  yang  lebih kecil.


PENSIL GAMBAR
Ketika kamu menggambar tidak boleh sembarangan dalam menggunakan pensil. Apabila pensil yang digunakan terlalu lunak akan menghasilkan garis tebal dan terlalu hitam sehingga tidak baik untuk menggambar. Sangat dianjurkan pensil yang kamu pakai tidak terlalu lunak, tidak cepat putus, dan dapat menghasilkan garis tipis. Ujung pensil harus tajam sehingga disarankan menggunakan pensil H,  HB atau 2B.

PENGHAPUS PENSIL
Penghapus yang kamu gunakan untuk menggambar harus lunak dan bersih.

MISTAR UKUR
Cara pemakaian mistar ukur agar mendapatkan hasil pengukuran atau penggarisan yang tepat adalah posisi strip-strip ukuran pada

MEJA GAMBAR
Kertas gambar dijepit di atas papan gambar dengan jepit yang tersedia pada papan tersebut. Pada bagian samping kiri dan bawah papan tersedia hantaran yang dapat digunakan untuk menggerakan dan memindahkan penggaris tanpa mistar harus rapat dengan kertas gambar harus mengubah posisi kertas.

MISTAR SEGITIGA
Mistar segi tiga digunakan untuk menggambar garis-garis vertikal, garis-garis dengan sudut 30, 45 dan 60 derajat, dan untuk menggambar arsiran.

GARIS
Simbol dasar dari semua gambar adalah garis. Garis menentukan batas-batas ruang, membentuk isi,menghasilkan susunan dan  menghubungkan bentuk abjad dan angka. Garis kerja dalam gambar rencana dan potongan harus tajam dan padat, dengan lebar yang sama dan nilai yang tetap. Ada lima jenis garis dasar : titik-titik, garis pendek, garis panjang, garis ekstra panjang dan garis menerus. Macam-macam garis adalah sebagai berikut.

Garis Tebal  
Garis tebal disebut   juga  garis gambar. Kegunaannya, mengambar apa yang terlihat, dan apa yang  tampak. Garis tepi atau garis batas suatu gambar.

Garis Tipis
(1/4 tebal dari garis gambar)
Kegunaannya, sebagai penolong atau garis untuk ukuran.

Garis Putus-putus Singkat
Kegunaannya adalah untuk menggambarkan bagian yang akan dibuang, dibongkar, atau menggambarkan bagian yang akan diperluas.

Garis Putus-titik/Sumbu
(1/3 tebal dari garis gambar)
Kegunaannya sebagai garis sumbu, penunjuk tempat penampang, batas lukisan bila sebagian benda yang dilukis dihilangkan.

Garis Titik-titik/Putus-putus
Kegunaannya adalah untuk menggambarkan bagian yang tidak dapat dilihat, karena letaknya dibelakang pandangan/tampak.


PROYEKSI SIKU-SIKU
  1. Dalam proyeksi siku-siku akan dijelaskan arah pandang terhadap benda.
  2. Umumnya gambar proyeksi siku-siku dilihat dari enam arah pandang yaitu :
  3. Pandangan Atas (PA) adalah tampak benda bila dilihat dari atas
  4. Pandangan Bawah (PB) adalah bila tampak benda dilihat dari bawah
  5. Pandangan Samping Kanan (PSKA) adalah tampak benda bila dilihat dari sisi kanan
  6. Pandangan  Samping Kiri (PSKI) adalah tampak benda bila dilihat dari sisi kiri
  7. Pandangan Belakang (PB) bila tampak benda dilihat dari belakang
  8. Pandangan Depan (PD) adalah tampak benda bila dilihat dari depan
  9. Agar suatu benda  terlihat jelas, dapat dilihat dari 3 sudut pandang yaitu dari arah depan, atas dan samping kanan

Senin, 06 September 2010

Time to say goodbye. -- Con te partirò


Sarah:

Quando sono sola

sogno all'orizzonte

e mancan le parole,

si lo so che non c'è luce

in una stanza quando manca il sole,

se non ci sei tu con me, con me.

Su le finestre

mostra a tutti il mio cuore

che hai accesso,

chiudi dentro me

la luce che

hai incontrato per strada.



Time to say goodbye. -- Con te partirò.

Paesi che non ho mai

veduto e vissuto con te,

adesso sì li vivrò.

Con te partirò

su navi per mari

che, io lo so,

no, no, non esistono più,

it's time to say goodbye. -- con te io li vivrò.



Andrea:

Quando sei lontana

sogno all'orizzonte

e mancan le parole,

e io si lo so

che sei con me, con me,

tu mia luna tu sei qui con me,

mio sole tu sei qui con me,

con me, con me, con me.



Time to say goodbye. -- Con te partirò.

Paesi che non ho mai

veduto e vissuto con te,

adesso sì li vivrò.

Con te partirò

su navi per mari

che, io lo so,

no, no, non esistono più,



Both:

con te io li rivivrò.

Con te partirò

su navi per mari

che, io lo so,

no, no, non esistono più,

con te io li rivivrò.

Con te partirò



Io con te.

Jumat, 03 September 2010

Engineering Drawing and Sketching

Introduction

One of the best ways to communicate one's ideas is through some form of picture or drawing. This is especially true for the engineer. The purpose of this guide is to give you the basics of engineering sketching and drawing.
We will treat "sketching" and "drawing" as one. "Sketching" generally means freehand drawing. "Drawing" usually means using drawing instruments, from compasses to computers to bring precision to the drawings.
This is just an introduction. Don't worry about understanding every detail right now - just get a general feel for the language of graphics.
We hope you like the object in Figure 1, because you'll be seeing a lot of it. Before we get started on any technical drawings, let's get a good look at this strange block from several angles.
Figure 1 - A Machined Block

Isometric Drawing

The representation of the object in figure 2 is called an isometric drawing. This is one of a family of three-dimensional views called pictorial drawings. In an isometric drawing, the object's vertical lines are drawn vertically, and the horizontal lines in the width and depth planes are shown at 30 degrees to the horizontal. When drawn under these guidelines, the lines parallel to these three axes are at their true (scale) lengths. Lines that are not parallel to these axes will not be of their true length.
Figure 2 - An Isometric Drawing

Any engineering drawing should show everything: a complete understanding of the object should be possible from the drawing. If the isometric drawing can show all details and all dimensions on one drawing, it is ideal. One can pack a great deal of information into an isometric drawing. However, if the object in figure 2 had a hole on the back side, it would not be visible using a single isometric drawing. In order to get a more complete view of the object, an orthographic projection may be used.

Orthographic or Multiview Drawing

Imagine that you have an object suspended by transparent threads inside a glass box, as in figure 3.
Figure 3 - The block suspended in a glass box

Then draw the object on each of three faces as seen from that direction. Unfold the box (figure 4) and you have the three views. We call this an "orthographic" or "multiview" drawing.
Figure 4 - The creation of an orthographic multiview drawing

Figure 5 shows how the three views appear on a piece of paper after unfolding the box.
Figure 5 - A multiview drawing and its explanation

Which views should one choose for a multiview drawing? The views that reveal every detail about the object. Three views are not always necessary; we need only as many views as are required to describe the object fully. For example, some objects need only two views, while others need four. The circular object in figure 6 requires only two views.
Figure 6 - An object needing only two orthogonal views

Dimensioning

Figure 7 - An isometric view with dimensions

We have "dimensioned" the object in the isometric drawing in figure 7. As a general guideline to dimensioning, try to think that you would make an object and dimension it in the most useful way. Put in exactly as many dimensions as are necessary for the craftsperson to make it -no more, no less. Do not put in redundant dimensions. Not only will these clutter the drawing, but if "tolerances" or accuracy levels have been included, the redundant dimensions often lead to conflicts when the tolerance allowances can be added in different ways.
Repeatedly measuring from one point to another will lead to inaccuracies. It is often better to measure from one end to various points. This gives the dimensions a reference standard. It is helpful to choose the placement of the dimension in the order in which a machinist would create the part. This convention may take some experience.

Sectioning

There are many times when the interior details of an object cannot be seen from the outside (figure 8).
Figure 8 - An isometric drawing that does not show all details

We can get around this by pretending to cut the object on a plane and showing the "sectional view". The sectional view is applicable to objects like engine blocks, where the interior details are intricate and would be very difficult to understand through the use of "hidden" lines (hidden lines are, by convention, dotted) on an orthographic or isometric drawing.
Imagine slicing the object in the middle (figure 9):
Figure 9 - "Sectioning" an object

Figure 10 - Sectioning the object in figure 8

Take away the front half (figure 10) and what you have is a full section view (figure 11).
Figure 11 - Sectioned isometric and orthogonal views

The cross-section looks like figure 11 when it is viewed from straight ahead.

Drawing Tools

To prepare a drawing, one can use manual drafting instruments (figure 12) or computer-aided drafting or design, or CAD. The basic drawing standards and conventions are the same regardless of what design tool you use to make the drawings. In learning drafting, we will approach it from the perspective of manual drafting. If the drawing is made without either instruments or CAD, it is called a freehand sketch.
Figure 12 - Drawing Tools

"Assembly" Drawings

An isometric view of an "assembled" pillow-block bearing system is shown in figure 13. It corresponds closely to what you actually see when viewing the object from a particular angle. We cannot tell what the inside of the part looks like from this view.
We can also show isometric views of the pillow-block being taken apart or "disassembled" (figure 14). This allows you to see the inner components of the bearing system. Isometric drawings can show overall arrangement clearly, but not the details and the dimensions.
Figure 13 - Pillow-block (Freehand sketch)

Figure 14 - Disassembled Pillow-block

Cross-Sectional Views

A cross-sectional view portrays a cut-away portion of the object and is another way to show hidden components in a device.
Imagine a plane that cuts vertically through the center of the pillow block as shown in figure 15. Then imagine removing the material from the front of this plane, as shown in figure 16.
Figure 15 - Pillow BlockFigure 16 - Pillow Block

This is how the remaining rear section would look. Diagonal lines (cross-hatches) show regions where materials have been cut by the cutting plane.
Figure 17 - Section "A-A"

This cross-sectional view (section A-A, figure 17), one that is orthogonal to the viewing direction, shows the relationships of lengths and diameters better. These drawings are easier to make than isometric drawings. Seasoned engineers can interpret orthogonal drawings without needing an isometric drawing, but this takes a bit of practice.
The top "outside" view of the bearing is shown in figure 18. It is an orthogonal (perpendicular) projection. Notice the direction of the arrows for the "A-A" cutting plane.
Figure 18 - The top "outside" view of the bearing

Half-Sections

A half-section is a view of an object showing one-half of the view in section, as in figure 19 and 20.
Figure 19 - Full and sectioned isometric views

Figure 20 - Front view and half section

The diagonal lines on the section drawing are used to indicate the area that has been theoretically cut. These lines are called section lining or cross-hatching. The lines are thin and are usually drawn at a 45-degree angle to the major outline of the object. The spacing between lines should be uniform.
A second, rarer, use of cross-hatching is to indicate the material of the object. One form of cross-hatching may be used for cast iron, another for bronze, and so forth. More usually, the type of material is indicated elsewhere on the drawing, making the use of different types of cross-hatching unnecessary.
Figure 21 - Half section without hidden lines

Usually hidden (dotted) lines are not used on the cross-section unless they are needed for dimensioning purposes. Also, some hidden lines on the non-sectioned part of the drawings are not needed (figure 12) since they become redundant information and may clutter the drawing.

Sectioning Objects with Holes, Ribs, Etc.

The cross-section on the right of figure 22 is technically correct. However, the convention in a drawing is to show the view on the left as the preferred method for sectioning this type of object.
Figure 22 - Cross section

Dimensioning

The purpose of dimensioning is to provide a clear and complete description of an object. A complete set of dimensions will permit only one interpretation needed to construct the part. Dimensioning should follow these guidelines.
  1. Accuracy: correct values must be given.
  2. Clearness: dimensions must be placed in appropriate positions.
  3. Completeness: nothing must be left out, and nothing duplicated.
  4. Readability: the appropriate line quality must be used for legibility.

The Basics: Definitions and Dimensions

The dimension line is a thin line, broken in the middle to allow the placement of the dimension value, with arrowheads at each end (figure 23).
Figure 23 - Dimensioned Drawing

An arrowhead is approximately 3 mm long and 1 mm wide. That is, the length is roughly three times the width. An extension line extends a line on the object to the dimension line. The first dimension line should be approximately 12 mm (0.6 in) from the object. Extension lines begin 1.5 mm from the object and extend 3 mm from the last dimension line.
A leader is a thin line used to connect a dimension with a particular area (figure 24).
Figure 24 - Example drawing with a leader

A leader may also be used to indicate a note or comment about a specific area. When there is limited space, a heavy black dot may be substituted for the arrows, as in figure 23. Also in this drawing, two holes are identical, allowing the "2x" notation to be used and the dimension to point to only one of the circles.

Where To Put Dimensions

The dimensions should be placed on the face that describes the feature most clearly. Examples of appropriate and inappropriate placing of dimensions are shown in figure 25.
Figure 25 - Example of appropriate and inappropriate dimensioning

In order to get the feel of what dimensioning is all about, we can start with a simple rectangular block. With this simple object, only three dimensions are needed to describe it completely (figure 26). There is little choice on where to put its dimensions.
Figure 26 - Simple Object

We have to make some choices when we dimension a block with a notch or cutout (figure 27). It is usually best to dimension from a common line or surface. This can be called the datum line of surface. This eliminates the addition of measurement or machining inaccuracies that would come from "chain" or "series" dimensioning. Notice how the dimensions originate on the datum surfaces. We chose one datum surface in figure 27, and another in figure 28. As long as we are consistent, it makes no difference. (We are just showing the top view).
Figure 27 - Surface datum example

Figure 28 - Surface datum example

In figure 29 we have shown a hole that we have chosen to dimension on the left side of the object. The Ø stands for "diameter".
Figure 29 - Exampled of a dimensioned hole

When the left side of the block is "radiuses" as in figure 30, we break our rule that we should not duplicate dimensions. The total length is known because the radius of the curve on the left side is given. Then, for clarity, we add the overall length of 60 and we note that it is a reference (REF) dimension. This means that it is not really required.
Figure 30 - Example of a directly dimensioned hole

Somewhere on the paper, usually the bottom, there should be placed information on what measuring system is being used (e.g. inches and millimeters) and also the scale of the drawing.
Figure 31 - Example of a directly dimensioned hole

This drawing is symmetric about the horizontal centerline. Centerlines (chain-dotted) are used for symmetric objects, and also for the center of circles and holes. We can dimension directly to the centerline, as in figure 31. In some cases this method can be clearer than just dimensioning between surfaces.

These drawing notes were developed by E. Blanco in the mechanical engineering department at MIT, and subseqently modified by other MIT faculty and students. Original link is http://pergatory.mit.edu/2.007/Resources/index.html