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Designing Vacuum Systems for the Lathe

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

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Designing Vacuum Systems for the Lathe

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  1. Designing Vacuum Systems for the Lathe Presented by Phil Brooks January 8, 2013

  2. 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

  3. Bob Leonard’s Vacuum Chuck Seals and decouples at the inboard side on the chuck using a sealed bearing.

  4. Pros & Cons of Bob’s Chuck Pro Features Con Features Relatively easy and inexpensive to build a single chuck. Works great for a limited range of bowl sizes. Need scroll chuck to hold vacuum chuck. Need a complete vacuum chuck for each size and shape. Making multiple vacuum chucks for different sizes and shapes can get expensive.

  5. My Vacuum System

  6. My Seal & Decoupler Seals at headstock end with O-ring Decouples at the outboard end with decoupler

  7. Pros and Cons of My System Pro Features Con Features Vacuum chucks are simpler, cheaper and attach directly to the drive spindle. Can have many sizes and shapes Don’t need a scroll chuck. Decoupler is industrial grade decoupler which is expensive. ($70)

  8. Alternate Vacuum System (Outboard End) Seals and decouples at the outboard end using closed cell foam and sealed bearing

  9. Pros and Cons of Alternate System Pro Features Con Features Vacuum chucks are simpler, cheaper and attach directly to the drive spindle. Can have many sizes and shapes Don’t need a scroll chuck. May be harder to get a good seal on small outboard handle.

  10. Vacuum Chucks for My System Faceplate Drum Flat Disc Wooden Hub Drum

  11. Tapping Wooden Threads (Drum)

  12. Treaded Base w/Spacer

  13. Base Front View

  14. Gluing The Drum Chuck Parts

  15. Vacuum Chuck w/Goblet Head

  16. Origin of Measuring Pressure

  17. Effects of Creating a Vacuum

  18. 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.

  19. 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.

  20. 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.

  21. 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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