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