Mechanical
Design Notes for Students
The design notes are intended to assist students in the
construction of their projects , they are not in any specific order .
Practical examples of how to apply the various design notes
can be found on this page and as worked examples on my
Amateur Radio Projects
Before commencing your drawing it is " Advisable
" that you set ALL of the drawing parameters in your chosen
CAD package ( for Quickcad &
Autosketch it's " Tools / Drawing
Options also do not forget to Set Paper size from the file menu ) , and having
set them DO NOT move your drawing around the page to center it
just so it look's neater because the drawing will invariably end up "
off grid " and you will waste considerable time dimensioning it &
moving it repeatedly. There is a simple guide to using Quickcad &
Autosketch software available
http://boeingconsult.com/tafe/dwg/Skf-Manual.pdf
it is free to download.
The commonest settings I've found for drawings are listed
below
Units "
mm "
Scale "1:1 "
Grid spacing
" 0.25 mm "
Major grid
" 4 "
Minor grid
" 2 "
Autosave
" 5 " mins
For clarity
on the drawing you may wish to use different colours for centre lines &
dimensions , my current preference is Red
for Centre lines & Blue for Dimensions
.
As mentioned in the
PCB Design Notes, use of the "
DXF " format for sending drawings to the mechanical workshop staff will
speed up the production of your hardware , because this is readily put into the
CAD / CAM package on the milling machines ( this is the industry
standard for exporting information between packages ) this does not however
replace the traditional paper sketch .
If your PCB requires mounting holes in it ( for fixing
screws ) then the area of the pad should be made large enough so that the screw
head does not foul any of the electronic components , typically for a metric
screw the pad diameter is twice the screw thread diameter ( eg for M2=4 mm ,
M2.5=5 mm & for the M3 screw allow 6mm dia ) this also covers the hexagonal
pillars often used .
If you are using screws to simply hold a PCB down to a
chassis or another PCB but NOT for earthing then the pads can be drilled away
provided they are less than the screws outside diameter , this is essential if
you are using non metallic screws to fix multiple boards together to produce an
Aerial .
This page last updated 15th Nov 2014