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Modular Fixturing System
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System Accuracy
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SYSTEM ACCURACY |
| Stevens
Modular Fixturing is built to the highest standards for
accuracy. SIP and DIXI jig-boring machines, operating in a
temperature controlled area, are used to produce exceedingly
accurate hole patterns. Frequent calibration of these machines
and other inspection equipment assures consistent
accuracy.
Prior to finish boring and final
inspection, modular components are placed in the environmentally
controlled area until they reach the ambient temperature of 72
Degrees F. This assures exact correspondence between measurement
standards and the finished product. |
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Q:
How accurate does modular tooling need to be?
A: Modular fixturing must allow for
interchangeable assembly of tooling components while eliminating
the need to indicate for alignment during setup. This requires
that tooling tolerances be 5-10 times better than allowable
workpiece locating tolerances.
Modular fixturing must have a
precisely controlled clearance between dowels and bushings. This
clearance must be large enough to accommodate bushing
concentricity and position tolerances as well as bushing/dowel
diameter tolerances. At the same time, the clearance must be
tight enough to properly align fixtures, angle plates, and other
components which are doweled in location.
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| ACCURACY
OF GRID |
Bushings
(All locating holes are bushed)
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Inside
Diameter +I- .000050” |
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Concentricity
.0001” TIR |
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| Dowel
Pin Diameter +/- .000050” |
| Span |
30” span |
45” span |
60” span |
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.00015 |
.00025 |
.00035 |
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Bushing
Concentricity (1/2 TIR) |
|
.00005 |
.00005 |
.00005 |
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| Bushed
Hole Centerline Accuracy = |
+I-.0002 |
+I-.0003 |
+1-
.0004 |
Clearance
Between Dowels and Bushings
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minimum
.0004” · maximum .0006” |
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Accommodates
span, concentricity, and diameter tolerances to assure
100% interchangeable
assembly. |
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| ACCURACY
OF SURFACES |
| Parallelism
of Qualified Surfaces (Subplates, Columns, etc.) |
.0005”/
40” |
| Perpendicularity
of Qualified Surfaces (Angle Plates, Columns, etc.) |
.0005”/
12” |
| Stevens
Modular Fixturing is carefully designed and manufactured so
users will achieve accurate position and alignment of fixtures
and workpieces. The confidence that components are located
accurately allows users to eliminate indicating or probing
routines when doing setups.
Before purchasing fixturing or making
fixturing in-house, the result of accumulated fixturing
tolerances on the performance of the fixturing should be
considered. A fixturing system which does not allow for
interchangeable assembly or which does not eliminate the need to
indicate or probe setups is unlikely to offer maximum
productivity. |
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COMPARISON OF
STEVENS MODULAR FIXTURING TOLERANCES VERSUS TYPICAL INDUSTRY
RANGE |
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Stevens
Modular Fixturing |
Typical
Industry Range
For Modular Fixturing
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| Eccentricity
of bushings used in Subplates, Fixturing Plates, and
accessories. |
.0001”
max (all locating holes bushed) |
.0003”
- .0004” (some accessories not bushed) |
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| Bored
hole location (+/- over 30” span in x and y relative to
a perfect grid). |
.00015” |
.0003”
- .001” |
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| Design
clearance between pins and locating holes/ bushings this
number must be twice the bored hole location accuracy plus the
bushing eccentricity to assure interchangeable assembly. |
.0004” |
.0007”
- .0012” |
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| ID
tolerance of bushings used in Subplates, Fixturing Plates, and
accessories. |
+/-
.000050” (all locating holes bushed) |
+/-
.0002” - .0005” (some accessories not bushed) |
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| Pin
diameter tolerance. |
+/-
.000050” |
+/-
.0001” (dowel pins)
+/- .0002” - .0003” T-Pins
&
precision shoulder screws |
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| For
more information on modular fixturing accuracy and its affect on
your machining operations, contact our Technical Assistance
Department. |
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Stevens Engineering, Inc., 3946 W. Clarendon Avenue, Phoenix, AZ 85019
1-(800)635-0657 or (602)272-6766 - FAX
(602)272-0717
info@stevenseng.com
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E-Mail Webmaster
©2005 Stevens Engineering, Inc. |
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