A condensed Product Design Handbook.........................
or splash page.......................
Electro-Mechanical Design Guidelines
- Black Box (Electronic Enclosure)
- ATR box
sizes. Length, width, height, volume, weight, and center line
mounting dimensions of standard Airbourne Electronics Enclosures. These
dimensions are in accordance with ARINC 404A
(Aeronautical Radio Inc., bought out by Collins Aerospace.) air transport equipment
cases and racking. For more information plus a little history,
check out www.vita.com.
You can also
find valuable information in the Cots Journal (here is a nice 2003 article). You might also want to check out
one of the leading suppliers of ATR boxes.
- Enclosure Venting, formula for the
- Power Supply Sizing. Most Power Supplies can be
packaged easily in a volume based on 3 to 5 watts per cubic inch.
- Weight Estimating. A good rule
of thumb for estimating the weight of
a module or enclosure assembly is to multiply the volume by 1/2 the
density of aluminum
(.05); although, a density of .03 can be achieved for aerospace
- Cable Assembly Design
should be started early in the design phase.
- Here are some basic specifications to help you
through the process. You may find copies of these by going to assist quick search or everyspec.com.
- MIL-W-5088 (s/s by SAE AS50881) wiring, Aerospace Vehicle
- MIL-STD-454 (s/s by MIL-HDBK-454) Standard General Requirements For
- ASME Y14.24 Types and Applications of Engineering
- ANSI Y14.15 Electrical and Electronics Diagrams
- ANSI Y14.15A Interconnection Diagrams
- IEEE-STD-315 (ANSI Y32.2) Graphic Symbols for
Electrical and Electronics Diagrams (Including Reference Designation
[click for commonly used industry standard reference designations] If link is broken, click one of these, pcblibraries.com or mentor.com
- ASME Y14.44-2008, IEEE-STD-200 (ANSI Y32.16) Standard Reference Designations for
Electrical and Electronics Parts and Equipment.
- MIL-STD-12 (s/s by ASME Y14.38) Abreviations for Use on Drawings, and in
Specifications, Standards and Technical Documents
- Castings. The
Aluminum Association is a good place to start; however, don't overlook the big boys, such as Dow and Dupont
when looking for design specifics on plastic hinges. etc.
(weights and Measures).
- Galvanic Corrosion. Electrical
current flows from + to -; therefore, no serious corrosion will result
if fasteners are selected from alloys in the same group as parts to be
fastened, or below. Coupling metals widely separated on the chart is
most likely to cause corrosion. Avoid combinations where the area of
the less noble material is relatively small. The current density is
greater when it flows from the small area to the large; hence, your
fastener should be lower in the galvanic series than the rest of the
assembly. Reference MIL-HDBK-454, guideline 16.
- Galvanic chart as depicted in MIL-STD-889B, Dissimilar Metals.
A newer chart is located in NOTICE 3.
You can also check out Table VI of MIL-F-14072Finishes for ground
based electronic equipment.
- Galvanic chart
as seen in the Assembly Engineering Master Catalog.
- Metalmart, International Inc. another pretty good
- Engineers Edge an excellent website
with a pretty good definition of galvanic corrosion.
- Corrosion Doctors
has a nice galvanic chart and much more.
- Conduit trade sizes are listed here with useful
information on bend radii and knock out sizes for thin wall (EMT) and thick
- Lumber Sizes, You might want to check
it seems they've gotten smaller since I created this list over 20 years ago.
Table of dressed lumber sizes.
|2 x 4
||1 5/8 x 3 5/8
||2 x 10
||1 5/8 x 9 1/2
|2 x 6
||1 5/8 x 5 1/2
||2 x 12
||1 5/8 x 11 1/2
|2 x 8
||1 5/8 x 7 1/2
- Metric Dimensioning:
- NMI 80201A Use of the Metric
System of Measurement in Nasa Programs.
- ASTM E380-91A Standard Practice for Use of the International
System of Units (SI).
- ANSI B4.2-1978 Preferred Metric Limits and Sizes.
- ANSI B4.3-1978 General Tolerances for Metric Dimensioned
- Estimating. Hours
required to make a drawing. These numbers where used back when work was
done on the drawing board. It still doesn't appear to be to far off, for
ANSI standard drawings.
Drawing sizes are multiples of
8-1/2 by 11 excluding F size. For example a B size is 11 by 17, and a C
size is 17 by 22, etc.
along with ASME Y14.100M, establishes the essential requirements and
reference documents applicable for the preparation and revision of
engineering drawings and associated list.
Drawing scales are specified in the form of a common fraction. (The
ratio of the size of the object as drawn to it's full size).
DOD-STD-100C documented this best. An excerpt from that
standard is listed below.
DOD-STD-100C standard scales.
||8/1, 4/1, 2/1
||1/2, 1/4, 1/8, 1/10, 1/20, 1/30, 1/40,
1/50, 1/60, 1/100
- Engineering Drawing Manual.
A Manual of
Engineering Drawing for Students and Draftsmen by Thomas E. French, M.E.,
- Complex shapes.
This is particularly useful when creating sheet metal parts, Mulit Layer Insulation (MLI), Printed Cable Assemblies, etc.
- Engineering Drawing Standards Manual.
This is Nasa's
1994 manual. I did not think I would stumble across this one.
- Military Part Numbers and the appropriate dash numbers for ordering
cres hardware in sizes #0 to 1/2 up to 3 inches long. Screws and bolts
are in Table 1, washers and nuts in Table 2.
- Screw Sizes.
Screw diameters advance .013 starting with#0(.060)upto1/4.Example:#1=(.060+.013=
- Screw Lengths (Inch). Lengths
of pnh screws typically increase by standard increments: (.062) for
.125 to .625 long, (.125) for .625 to 1.500, and (.250) for 1.500 to
3.000. Keep in mind each size has length limitations: (.086)#2=1.000
max, (.112)#4=1.500 max, (.138)#6=2.000 max, (.164)#8 through
(.375)3/8=3.000 max. Reference MS51957, Screw, Machine, Pan Head,
Cross-Recessed, Corrosion-Resistant Steel, UNC-2A. One exception
to the rule would be AN3, where screw lengths can be furnished in 1/32
increments, starting at 1/2 inch.
Reference AN3, Bolt - Machine, Aircraft (S/S By NASM3THRU20)
NOTE: You can purchase non-
standard lengths of screws and bolts by constructing your part number
using the appropriate length code of the style of screw you want (For
example a NAS1351N06H32 would yield a 2 inch long screw,
not available, according to the specification). Work with the supplier
to determine availability.
- Thread Binding External UNJ thds
iaw MIL-S-8879 are not compatible with standard UNF, UNC, and
UNEF nuts or tapped holes. Reference MIL-STD-454, guideline 12,
par. 4.1.1.b and MIL-STD-1515, requirement 119, par. f.
- Threaded Inserts. Keenserts, T-serts, Helical inserts (helicoils) and
Rivet nuts (Rivnuts) are covered here with sizes ranging from no. 1 (.073) to
1 1/2 diameter.
- TorqueRequirements. Screws sizes No. 0 to 3/8 are covered.
- Rivet upset
Here you will find upset head dimensions for rivets ranging in size
1/16 to 3/8 in diameter. The edge distance to the sheet or joint should
be less than two times the rivet diameter in sheet stock and three
times the rivet diameter in non-ferrous materials. Generally, rivet
spacing is called
out on all drawings in accordance with stress requirements. Reference
MIL-STD-403B, Preparation for and installation of rivets and
, Rocket and Missile Structure.
- Holes: Drill point angle.
the hole sizes listed here are created
with a single tool, machining both holes at the same time, reducing the
overall cost of the part. If your parts are toleranced such that
non-standard counterbore sizes are required, the cost of the part goes up.
Three basic styles are listed (Standard, 1/64 oversize, and 1/32 oversize)
with the recommended screw size (No. 4 through 1/2).
hole sizes for 100 degree rivets
(MS20426) used in painted and unpainted surfaces, as well as standard
machine screw countersinks for 82 and 100 degree head styles.
- Drill Sizes and tables listed
here are excerpts from the
Machinery's Handbook. A chart containing smaller
PCB drill sizes can be found at the Drill Technology website.
- Drill Drift
Twist drills tend to drift, when the depth exceeds five times the
should allow for this drift with true position tolerancing or a
notation which specifies the
maximum allowable drift.
Twist drills have a tendency to cut oversize. This variation in
size should be considered when determining minimum and maximum values
of tapdrill sizes.
- Hole sizes
recommended for standard screws
(using the coordinate dimensioning method), ranging from No. 2 to 1/2.
- Feature Size. Limits of size based on Air
Force-Aeronautical Design Standard AND10387, Drill Sizes and Drilled
Location Tolerance. Formula for calculating hole size relative to
- Impedance hole sizes, for maintaining a specific
impendance around a pin using an air or teflon dielectric as the
- Dowels and
dowel pinning practices. This will give you some insight into pin
clearances. Press fit, slip fit (normal and gear box pinning) and tight
fit, are covered. Diameters range from 1/16 to 1/2.
For a detailed description of classes of fits and aditional tables
Machinery's Handbook and Prefered Limits and Fits for
Cylinderical Parts, ASME B4.1.
- Pin Depth. Pins shall be pressed into the
tight hole to a minimum depth of 1-1/2 times the nominal pin diameter, and
a maximum of 1/2 the pin length.
- Pin Styles.
- When pressed into a blind hole, pins 3/16
diameter and larger may have a 1/16 flat on one side.
- A standard slip fit in one hole and a slot in
the other will prevent having to ream at assembly.
- A diamond shaped pin used
together with a round pin will
permit a larger locational tolerance than two round pins.
Standard reamers come in either fractional
, numbered, or metric drill sizes.
If neccessary the pin or hole can be sized at assembly, providing a fit
of .0002 to .0008 clearance.
- End Mill Depth. All end mills will deflect during the machining
operation. This table will guide you in
determining mazimum milling depths. If a greater depth is required
consult your local Machine
- Knurling Data. Standard
diametral knurling tools are designed to be used on common fractional
material sizes. Decide what diametral pitch you prefer and whether you
want ornamental or press fit knurling.
Additional information can also be found in the Machinery's Handbook
ASME B94.6, Knurling.
- Design Considerations.
- When knurling to a shoulder, provide an
undercut as in threaded parts.
- A chamfer at the end of the knurled section
allows for a lead in for press fits and improves the appearance of
- The tolerance on the length of the knurl should
be as large as function and appearance will permit.
- Diagonal and raised diamond knurling do not
have a tolerance on the angle of the knurl; therefore, it should be
specified as reference only.
- Pressing knurled metal parts into plastic materials
should be verfied by testing, since both the type of plastic and the
size of the cross section are of considerable importance.
- Knurling Tool Sizes. American
Standard ASA B5.30 covers knurling tools with standardized
and tolerances. Using the following table takes advantage of the most
economical knurling practices.
- Ornamental Knurling.
There are three types of knurling;
diamond, diagonal, and straight. A diametral pitch of 96 with a 30
degree helix angle should be considered standard for raised diamond or
Diagonal knurling shall be specified as either right or left hand.
Tolerances should not be
applied to outside of raised knurls. Click here for sample drawing callouts.
- Press Fit Knurling. Since
tolerances must be tightly controlled it is recommended that the after
knurling dimensions be selected from the tool
sizes section, the tolerances selected from these tables and the drawings be dimensioned
as shown here.
- Marking, Identification.
- Font Sizes (Point System).
When type is used as a method of printing characters or numerals, the
height is designated by a dimension equal to 1/72 of an inch, called a
- Printed Wiring Board
- Sheet Metal Forming
- Aluminum Alloy.
- Punch sizes This section
is a must for those designing sheet metal parts. Punch sizes for round,
rectangular, oval, hex, and square, are typically furnished in
fractional sizes. All others are considered to be special.
- Spinning. Acme Metal Spinning can spin diameters ranging from
.50 to 6 foot and a thickness up to .75, using materials such as aluminum,
mild steel, and stainless steel.
- Steel Alloy,
bend radii. An alloy with a carbon content of .10 or less may be bent over on itself.
- Wrench Sizes: Of course Snap-on Tools is always a good
resource. And don't forget about the closest equivalent to the old
TAD slider chart.
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Last updated on July 5, 2020