Transcript Slide 1

Fundamentals of mechanical
drawing and mechanical fabrication
ECE 156
Matthew Kay
Fundamentals of mechanical drawing
• Represent a 3d object in 2d.
• Show a scaled representation
of an object.
• Unambiguously capture all
geometric features of an object.
• Convey all required information
that will allow an object to be
produced from raw material.
Giant crossbow by
Leonardo da Vinci. His ideas
have survived 500 years
through his detailed sketches.
Representing 3d objects in 2d
Isometric projection: One view of an
object in which the three axes of space
(x,y,z) appear equally foreshortened.
Orthographic projection: Multiple views
of an object from points of view rotated
about the object's center through
increments of 90°. The views are
positioned relative to each other.
Orthographic projection can provide six planar
views of an object.
Show multiple views to convey every detail.
Center lines
are short+long
dashed
Hidden lines
are short dashed
Orthographic projection:
each view can be thought
of as projections of an
object onto the sides of a
glass box.
Top view
Front view
Side view
Orthographic projections
Isometric projections are useful for assembly drawings
Nice isometric sketches work well.
Assembly drawing
Isometric projection with dimensions.
Line types
A thick continuous line is used for
visible edges and outlines.
A thin line is used for hatching, leader lines, short
centre lines, dimensions and projections.
Dashed lines are used to show hidden edges and
important hidden detail, for example wall thickness
and holes.
Thin chain lines indicate center lines. Center lines
are used to identify the center of a circle, cylindrical
features, or a line of symmetry.
Center lines
Hidden lines
Section views reveal hidden details.
Section views are indicated by the direction of arrows.
Basics of dimensioning
-Always dimension from a common line or
surface (datum). This eliminates the addition
of measurement or machining inaccuracies
that would come from "chain" or "series"
dimensioning.
- Whenever possible dimension lines should
not touch or cross either edge lines or
extension lines.
- Locate as many dimensions as possible on
only one or two sides of an orthographic
view.
- Indicate on the drawing the unit of measure
(inches).
Anatomy of a dimension
An excellent tutorial by Richard Link at the US Naval Academy is
available from the Senior Design website. Take a look for
additional dimensioning tips as well as a checklist of
dimensioning Dos and Don’ts.
Suggested drafting or drawing software
•
•
•
•
•
•
•
AutoCAD
Pro/ENGINEER
Google SketchUp
TurboCAD
QCad
XFig
Typically NOT
• Microsoft Word
• Paint
• Photoshop
Dimension tolerances are important! Small or “tight” tolerances
are expensive. Overall tolerances should typically be specified.
One MIL is one thousandth of an inch.
1 MIL=1/1000 inch=0.001 inch=1x10-3 inch
1 MIL=0.0254mm=25.4 microns
Fundamentals of mechanical fabrication
•
•
•
•
•
•
•
•
•
Clamping (vice, C-clamps)
Cutting (hack saw, band saw, table saw)
Drilling (drill press, milling machine)
Grinding (grinding wheel)
Bending (press brakes)
Milling (milling machine)
Turning (lathe)
Punching (punch press)
Laser cutting (CNC laser cutter)
Hacksaw
Drill press
Vice
Band saw
Press brake
Lathe
Milling machine
Big tip: Keep your mechanical
design as simple as possible!
– Whenever possible use off-the-shelf components.
• Buy a box (“electronics enclosure”) instead of making
one.
• Erector set approach: bolt simple parts together to
create more complex structures.
– If you must have a part fabricated then keep the
design as simple as possible!
• Straight edges are much easier to cut than curved
edges.
• Few edges are better than many (rectangles instead
of pentagons).
• Round holes are easier to drill than square holes!!
KISS principle
Solid block with a
thru-hole
NO!
YES!
Erector-set approach
- Simple parts can be easily cut and drilled
from pre-formed raw material
-Drill and tap simple parts to join them
together with bolts and nuts.
- Complex structures can be fabricated
from simple components.
Excellent sources for off-the-shelf
components
• Home Depot
– Lowes, Ace Hardware, WalMart
•
•
•
•
•
•
McMaster-Carr
Grainger supply
Small-Parts
Cole-Parmer
DigiKey
Jameco Electronics
Mechanical Design
Critical steps before fabrication
1)
2)
3)
4)
5)
6)
7)
8)
Create a mental picture of the final product.
Determine overall dimensions. Sketch an isometric view.
List each part required (bolts, nuts, brackets, bearings, hinges, motors,
etc).
Determine which parts can be purchased off-the-shelf. (Hint: as many as
possible!) List them in a table that indicates the vendor, vendor part #,
description (size, thread type, etc), quantity needed, and price.
Create multi-view drawings for each part that must be cut, drilled, and/or
machined, or modified in any way.
Create assembly drawings that show how each part fits together to
produce the final product.
If a machinist is doing any of the fabrication then have your plans
reviewed by a knowledgeable engineer (Prof Kay).
Begin fabrication. If a machinist is doing the work for you then be
available to answer questions. Provide your contact information (cell
phone number) with your plans.
Create a mental picture of the final product.
Determine overall dimensions. Sketch an isometric view.
Use engineering paper.
Mechanical Drawing (1932) by Irene Rice Pereira
List each part required (bolts, nuts, brackets, bearings, hinges, motors, etc).
Determine which parts can be purchased off-the-shelf. (Hint: as many
as possible!) List them in a table that indicates the vendor,
vendor part #, description (size, thread type, etc), quantity
needed, and price.
Create multi-view drawings for
each part that must be
cut, drilled, and/or
machined, or modified in
any way.
HINT: Sketch the orthographic
views of each part on
paper before drawing
them with CAD software.
Create assembly drawings that show how each part fits together
to produce the final product.
Sometimes good sketches make fine
assembly drawings.
Another example of an assembly drawing
created by an ECE158 student (AutoCAD).
Illustration of the mechanomyogram sensor showing
the two accelerometers and lead wire innervations.
Mechanical Design
Critical steps before fabrication
1)
2)
3)
4)
5)
6)
7)
8)
Create a mental picture of the final product.
Determine overall dimensions. Sketch an isometric view.
List each part required (bolts, nuts, brackets, bearings, hinges, motors,
etc).
Determine which parts can be purchased off-the-shelf. (Hint: as many as
possible!) List them in a table that indicates the vendor, vendor part #,
description (size, thread type, etc), quantity needed, and price.
Create multi-view drawings for each part that must be cut, drilled, and/or
machined, or modified in any way.
Create assembly drawings that show how each part fits together to
produce the final product.
If a machinist is doing any of the fabrication then have your plans
reviewed by a knowledgeable engineer (Prof Kay).
Begin fabrication. If a machinist is doing the work for you then be
available to answer questions. Provide your contact information (cell
phone number) with your plans.
Machinists as skilled professionals
•
•
•
•
•
•
•
Will charge between $60 and $120 per hour.
May charge a minumum of one day’s work.
Must be able to understand your fabrication plan. If not then it costs money!
In the US machinists usually prefer English units (inches).
If you have a friend who is a machinist then ask them for advice to improve
your fabrication plan.
The machinists in the basement of Tompkins Hall are available for complex
fabrication procedures that you might not be able to accomplish yourself.
They are not ECE Senior Design instructors. Do not ask them to design your
project for you. They are professionals and their time is important.
If you would like the Tompkins Hall machinists to fabricate a necessary
component of your project then follow the machine shop procedures
available from the Senior Design Course website. When your fabrication plan
is complete it must be certified by Prof Kay. Once it is certified you may
submit your fabrication plan and drawings to the Tompkins Hall machinists.
Remember: Anyone should be able to build your
device using your fabrication plan …. even 500 years
in the future!
Questions?
Flying machine by Leonardo da Vinci.