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Thread: How much vacuum do I need

  1. #1

    How much vacuum do I need

    I just picked up a Sargent Welch vacuum pump model 8805 at an auction. For $10 I did not think I could get hurt too bad. My question is how much vacuum do I need for a vacuum chuck. I plan on getting a gauge to check the unit out.

  2. #2
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    I generally don't pull more than 18 hg to 20 hg.
    Bernie W.

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  3. #3
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    I'll agree with Bernie. My pump will pull up to about 23 hg, but in use, the gauge is usually more down in the 16 - 20 hg range.
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  4. #4
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    If you are doing a 1 inch diameter bowl, I have never been able to get enough vacuum. Remember with a perfect vacuum inside, you only get about 15 psi force on the workpiece.

    On the other hand, I have successfully used a shop vac (rather than pulling out the vacuum pump stored elsewhere) for something like a plate, with a relatively large surface area and a light weight.
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

  5. #5
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    Charlie, did you mean one inch thick bowl? It must be hard to vacuum chuck a one inch diameter bowl.
    Chinese Proverb: Man who eats many prunes gets good run for the money.

  6. #6
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    I don't know what my shop vac would pull in a vacuum, but it will pull enough to hold a good sized bowl to the chuck... I don't have a dedicated vacuum pump and use my 6 gallon shop vac to create the vacuum... it works well.... I only use the vacuum chuck on bowls larger than I can handle in the cole jaws... which is about 8 inches...
    Chuck
    Tellico Plains, TN
    https://www.etsy.com/shop/TellicoTurnings
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  8. #8
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    Quote Originally Posted by Mohammad Madha View Post
    Charlie, did you mean one inch thick bowl? It must be hard to vacuum chuck a one inch diameter bowl.
    When I am goofing off, I sometimes make bowls only an inch or so in diameter - it is amazing how people love them for paper clips or pins.

    My vacuum chick consists of a 12 inch diameter piece of plywood attached to the faceplate of my lathe, with a closed cell rubber pad and a hole, about 1/4 inch diameter, through the center, through the headstock, through the vacuum adapter (which is just a sealed ball bearing that fits in the center of the lathe handle. Part of the "lathe vacuum adapter" was a small pipe that fits in the the center of that ball bearing. I have a piece I can clip my vacuum pump to (much like a tire air nozzle), but I also turned a block that functions as an adapter from my shop vac to that pipe.

    With a 1 inch diameter bowl you only have about .78 square inches for the air to push on (you are only interested in the force against the face plate, so it doesn't matter how tall the bowl is), or only about 10 pounds holding it to the face plate. Not very much when you push the side with a chisel.

    By the time you get to 2 inch diameter, you have about 3.141559 square inches, or are approaching 50 pounds against the faceplate... Not as much as the tailstock might push, but getting useful.

    With a 4 inch diameter bowl, you have 12.5 square inches, approaching 180 pounds against the headstock, and the vacuum chuck starts to be useful. Or maybe you can use less vacuum, such as a shop vac.

    But try turning a 1 or 1 1/2 inch bowl out of a scrap of 3/4 inch hardwood, and see how many friends you make!
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

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