Getting a Grip Under Vacuum Todd M. Reith MET 123.
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Transcript of Getting a Grip Under Vacuum Todd M. Reith MET 123.
Getting a GripGetting a GripUnder VacuumUnder Vacuum
Todd M. ReithMET 123
Hold-down DilemmaHold-down Dilemma
Clamps
Vise
Magnetic Chuck
Bolt Directly to the Table
Use What is Around Us!Use What is Around Us!
At Sea Level
14.7 PSI
3” X 3” ~ 132 lbs
Denver, CO
12.23 PSI
3” X 3” ~ 110 lbs
14.7PSI
Vacuum AdvantagesVacuum Advantages
Clamping of Thin Parts
Parts that Deform under Clamping
Non-magnetic Parts
Reduce Setup and Clamping Time
Machine Contours without Interference
Hold-Down Odd-Shaped Parts
The Real DealThe Real Deal
Altitude(feet)
Barometer(in-Hg)
% of Change of BarometricPressure
Downward Pressure perSquare Inch
(psi)
Effective VacuumPump rated
25 in-Hg83.5% Efficient
(in-Hg)
Effective PSIPump rated
25 in-Hg83.5% Efficient
(psi)
0 29.92 0.00% 14.70 24.98 12.64
2000 27.82 -7.00% 13.70 23.23 11.44
4000 25.84 -13.00% 12.79 21.58 10.68
5000 24.90 -16.80% 12.23 20.79 10.21
10000 20.58 -31.20% 10.11 17.18 8.44
Local Barometric Pressure
Vacuum Pump Effectiveness
Surface Area of Part Under Vacuum
Forces Against the VacuumForces Against the Vacuum
Machining Forces
Rotational from Edge of Cutter
Lifting from Aggressive Depth or Rake
Vacuum Pump Power & Flow
Slow Recovery (Flow) CFM
Lack of Vacuum Draw (Power) in-Hg
Fixture Design
Vacuum Loss or Vacuum Restriction
Surface Finish Too Smooth, Twisting
Machining AdaptationsMachining Adaptations
Reduce Aggressive Depth of Cut
Use Ideal Rake for Material
Reduce Size of Cutter Diameter
Slow the Feed Rate
Use Down-Cut Geometry if Applicable
Choosing the Right PumpChoosing the Right Pump
Understand the Physical Properties of the Material you are Machining
Rotary Vane Pumps
<1 to 112 cfm, 20 to 29.5 in-HG
More Efficient and Quieter
Slow Recovery
Blower Pump
27 to 1350 cfm, 20 to 25 in-Hg
Loud and Inefficient
Fast Recovery
Vacuum SystemVacuum System
Rotary VaneVacuum Pump
Vacuum Tank
Flexible Hose withShut-off Valve and
Fixture Fittings
Vacuum PressureLimit Switch
Hi/Low
Vacuum PressureGauge in-Hg
In-LineParticulate Filter
Dedicated Vacuum FixturesDedicated Vacuum Fixtures
Single Purpose
High Initial Cost
Maximized Part Surface Area under Vacuum
Minimal Vacuum Loss
Machining Through Material or Through Pocketing
No Break-Out or Excessive Pre-Finish Prep Work
Dedicated FixturesDedicated Fixtures
© All-Star Adhesives © All-Star Adhesives
© Custom Luthier © Custom Luthier © Custom Luthier
Universal Vacuum FixtureUniversal Vacuum Fixture
Multi-Purpose
Low One-Time Cost
Flexible Grid System
Reduced Setup Time
Greater Loss of Vacuum
Less Surface Area
Universal FixturesUniversal Fixtures
© Horst Witte Gerätebau
© Horst Witte Gerätebau
© Horst Witte Gerätebau
© Horst Witte Gerätebau
© Vac-U-Lok
SummarySummary
Lower Stability Higher Stability
Universal Fixture Dedicated
Heavy Machining Aggressiveness Light
High Air Seal Loss Low
Low Pump Flow (cfm) High
Low Pump Power (in-Hg) High
Low Barometric Pressure High
Small Part Size (Surface Area) Large