Designing Vacuum Systems
for the Lathe
Presented by
Phil Brooks
January 8, 2013
Introduction
•Presentation was originally part of Leonard’s
•Need to do two things in designing a vacuum
system:
• Seal the vacuum
• Decouple the rotation
•Will discuss 3 different approaches & their
advantages and disadvantages
•Theory of designing vacuum systems & key
parameters effecting performance
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Bob Leonard’s Vacuum Chuck
Seals and decouples at
the inboard side on
the chuck using a
sealed bearing.
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Pros & Cons of Bob’s Chuck
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Pro Features
Con Features
 Relatively easy and
 Need scroll chuck to hold
inexpensive to build a
single chuck.
 Works great for a limited
range of bowl sizes.
vacuum chuck.
 Need a complete vacuum
chuck for each size and
shape.
 Making multiple vacuum
chucks for different sizes
and shapes can get
expensive.
My Vacuum System
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My Seal & Decoupler
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Pros and Cons of My System
Pro Features
Con Features
 Vacuum chucks are
 Decoupler is industrial
simpler, cheaper and attach
directly to the drive
spindle.
 Can have many sizes and
shapes
 Don’t need a scroll chuck.
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grade decoupler which is
expensive. ($70)
Alternate Vacuum System (Outboard End)
Seals and decouples at the outboard end using
closed cell foam and sealed bearing
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Pros and Cons of Alternate System
Pro Features
Con Features
 Vacuum chucks are
 May be harder to get a
simpler, cheaper and attach
directly to the drive
spindle.
 Can have many sizes and
shapes
 Don’t need a scroll chuck.
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good seal on small
outboard handle.
Vacuum Chucks for My System
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Tapping Wooden Threads (Drum)
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Treaded Base w/Spacer
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Base Front View
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Gluing The Drum Chuck Parts
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Vacuum Chuck w/Goblet Head
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Origin of Measuring Pressure
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Effects of Creating a Vacuum
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Vacuum Holding Forces
•Atmospheric Pressure (Sea Level) =
•29.92 in Hg, or 14.7 lbs./in2
•Good vacuum pump gives
≃ 20”Hg
•20” Hg produces the following forces in lbs.
Dia.
2”
3”
4”
5”
6”
7”
8”
Force
(Lbs.)
30.8
69.5
124
193
278
378
494
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Table For Other Vacuums Pressures
•Use the same table and divide your actual
vacuum pressure by 20.
• (20”Hg was used to create the table)
•Multiply this number by the force in the
table.
•Example: 15”Hg & 8” bowl:
•15/20 x 494 lbs. (from table) = 370.5 lbs.
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Universal Calculation of These Forces
•To calculate the lbs./in2 for vacuum (in of Hg):
• (in of Hg) ÷ 29.92 x 14.7 = .49(in of Hg)lbs./in2
•
To calculate the area of the bowl in in2 :
• Area = ∏ x dia.2 / 4
•Force = Area(∏ x dia.2 / 4) x Pressure (lbs./in2)
•To calculate the force for any vacuum and bowl
dia., substitute your pressure and bowl dia.
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General Information
•Flat-plate chucks should have taper of ½”/ft. on its face.
•Need minimum force of 50 lbs. to be safe.
•Use CA glue before and after tapping wooden hubs.
•Use bleeder value on fragile pieces to prevent crushing.
•Put tape on any small voids in piece you want to hold to
maintain vacuum.
•When building vacuum system. Check maximum vacuum
by taping off at compressor. Add 1 piece at a time and check
pressure for leaks after each piece is added.
•Don’t vacuum chuck freshly lacquered pieces or it can
effect the finish.
•It’s a great tool if used properly and with appropriate
safety considerations.
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