Getting started with Vacuum turning/chucking

Discussion in 'Tutorials and Tips' started by Jeff Jilg, May 20, 2005.

  1. Jeff Jilg

    Jeff Jilg

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    Why use a vacuum system
    In general, the primary use for vacuum chucking is to finish turn the bottom of an almost finished piece. The vacuum system is used to hold the piece firmly towards the headstock while you turn away the remnants of the foot.

    A vacuum system can also be used to turn platters top and bottom.

    Safety
    Turning is inherently a potentially dangerous activity. You should observe all the normal caution and procedures you normally use during turning. In addition, the piece you will be turning using the vacuum system is not fastened to the lathe. Ensure you are using sufficient vacuum. Additionally be aware that a power outage or an accidental flip of a switch can turn off your vacuum source - and the piece on your lathe will no longer be secured to the lathe.

    Getting started
    There are various commercial vacuum systems available. A simple suggestion is to browse the catalogs or websites from woodturning vendors. A cheap alternative is to build your own.

    Homebuilt system 1 - using a shopvac
    The following system was built by Al Hockenbery and it works. If your lathe has an outboard spindle and you have a shop vac, you can make an inexpensive vacuum system that works in a few minutes. Use a block of non-porous hardwood like maple and turn a fitting to connect your shop vac hose to the outboard spindle of the lathe.

    This fitting needs:
    1. a through hole about the same size as the hole in the spindle
    2. a hole the diameter and depth of the spindle on one end
    (this is a loose fit since the spindle threads must turn freely inside but not leak too much)
    3 the other end is turned to fit inside the shop vac hose with a slight taper.

    This adapter fitting should sit against the spindle nut and or the end of the spindle tightly enough when the vacuum is on so it won't leak too much so those surfaces have to be smoothly cut.

    To use this system secure the shop Vac hose to the adapter with duct tape. Slide the adapter over the out board spindle and hold it in place by either taping it to the head stock or clamping or taping the hose to something so that the fitting can't fall off.

    Put a drum chuck on the inboard side, center you work piece on the drum chuck and turn on the shop vac. Test to see if you can pull the work off. If there s a good fit to the drum chuck it should be quite a struggle to pull the work free and you may not be able to.

    This system is only as quiet as your shop vac and has no adjustment, but it works fine for bowls. It is an easy way to use vacuum with out much expense. Don't try this or any vacuum system on any thin walled pieces until you have some experience with vaccuum. It is very easy to crack pieces with walls less than 1/4 inch and certainly possible to crack much thicker ones.

    Homebuilt system 2 - using a vacuum pump
    Basically you can gather parts from various sources and build a vacuum system. The heart of the system is a vacuum pump. Then you need to connect various pieces listed in the Minimum Setup section below.

    Vacuum pump sources (for homebuilt system 2):
    The system described above uses a shop vac. Many turners prefer to use vacuum pumps. Vacuum pumps can sometimes be found at:
    Surplus Sales of Nebraska
    or
    American Science and Surplus
    Look for rotary vane types of vacuum pumps, which are the least expensive - you'll want to get a unit that pulls at least 20 inches of mercury (vacuum) and is rated for continuous operation. If the vendor doesn't specify any ratings, call them and ask! it is important that you get a pump with enough capacity. Alternatively you can look on eBay or other auction sites for vacuum pumps. Some folks use salvaged refrigerator compressors for vacuum sources for veneering, etc. but I think I'd avoid these for lathe work (I don't think they're "beefy" enough). There are also venturi-type vacuum sources which generate some decent vacuum (quite suitable for veneering) using air flow from a compressor, but I don't know if I'd advise you to use this for lathe work.

    Minimum Setup (for homebuilt system 2):
    You'll need to do some minor plumbing to setup the vacuum pump. Mark Mandell has a good picture of his setup in this posting

    At a minimum you should have some sort of in-line filter on the vacuum line before it enters the pump - you don't want to suck sawdust and other debris into your vacuum pump. I use sintered metal filters ahead of my pump, and actually filter the "release" air that I let in to the system when I'm "un-chucking" the bowl from the vacuum drum. This may be another example of over-engineering, but one that's designed to protect the pump.

    Second, you cannot run full vacuum on many pieces since it can potentially crack or break them. See "how much vacuum" below. So you need to put a valve of some type between the vacuum pump and the lathe. I used a hose bib....yes the same kind of hose bib that comes out of your outside wall for the water hose. It works sufficiently fine to introduce a leak in the vacuum system. Mark Mandell uses a 1/4" ball-type bleeder valve. Both of these valves can be obtained from your local hardware store.

    Third, a vacuum gauge will be needed to measure the vacuum between the vacuum pump and the lathe. Just get a cheap one. They can be found at auto supply stores, pool stores, or in surplus catalogs.

    Fourth, you need a way to attach the vacuum source to the lathe spindle - a vacuum fitting. There are commercial setups for this such as the "EZ Vacuum Unit" discussed in this thread. You can also make your own setup using a sealed bearing. Documenting that fully here would take up too much room.

    It can be challenging to determine how to hook everything together, and figure out which components are needed. Jeff Jilg used PVC fittings and a couple of brass fittings to cobble together his system. -e- used all metal fittings (more elegant). The list of fittings and multiple detailed pictures of -e-'s system is listed here. The pictures are nearly self explanatory. If you can use a wrench and have some plumber's tape you can probably hook up a similar system.

    How Much Vacuum
    Consider that 20" of Hg (mercury) roughly translates to 10 pounds of atmospheric pressure for every square inch on your drum chuck's area, and a 4" chuck has an area of about 12.56 square inches. If you only pull 20" of Hg using a 4" chuck at sea level you're putting more than 125 pounds of pressure on the bottom of your bowl. Go to a 6" chuck and you more than double that to a bit over 280 pounds; at 8" it's over 500 pounds. Mark Mandell has held 18"-20" platters with an 8" drum chuck at less that 10" of Hg. without a mishap.

    A note of caution on vacuum chucking is worth noting. Many don't understand or forget that with vacuum fixing, your piece is being held on the chuck by atmospheric pressure, which is ~15 lbs per square inch. When you hold the piece to the seal and start the pump, the amount of physical pressure PUSHING THE BOWL onto the chuck is determined by the surface area inside the seal's contact ring as a function of the amount of vacuum created. So, if you could pull 30" of vacuum and your seal covered 1 sq. in of area on the bowl, the workpiece would be held as if you placed a 15 lb weight on it. Now, say you make your chuck 6" in diameter and your seal is at the rim, that it all fits inside your bowl. You turn on your pump and pull 30" of vacuum (full vacuum) you can calculate the weight holding your bowl as 3.14 (Pi) x 9 (radius squared) x 15 (air pressure) and you'll find you have 424 pounds pushing on your wood. Best consider your bowl, how thin and strong it is and whether it can survive a 400lb weight pushing against it.

    Keep in mind that the example is for a "hard" vacuum at sea level. Any vacuum pump in a woodturner's price range will, at most, pull a bit over 28" and usually a bunch less than that due to imperfect seals in the system. The point, however, is with vacuum chucking you walk a line between not enough pressure to hold the bowl and so much that the piece implodes. Usually when you just finished sanding the bottom, you here a "pop", and discover that you have a new funnel or a design opportunity. Pick a chuck with an area under seal which will provide enough area to develop the weight needed to hold the piece. Also have a bleeder valve in your vac line within reach so that you can reduce the vacuum (and so the pressure holding the bowl on) if you start to hear your piece creaking and making sounds.

    Trying to get a good seal with the rim of a bowl is difficult, if not impossible. It's rare that a bowl runs so flat at the rim that it will make such a seal as is needed for vacuum holding. Many turners are using drum chucks in a variety of diameters (namely 4, 6, and 8" versions).

    You also need to consider wood shear strengths as listed in the US Forest Service Handbook in Chapter 4, available online at US Forest Service Handbook

    A more detailed article on how much vacuum to use is discussed in the attached paper by Bill Marx (permission to post given by his son Jim Marx). The article is downloadable from the AAW site here: Allowable vacuum for woodturning


    Attaching wood to the lathe
    Commercially available chucks can be reviewed on product vendors' websites and in catalogs. Many folks make their own faceplates or chucks using MDF and/or PVC tubes.

    Outline to build your own vacuum chuck:
    • I made my own vacuum chuck using a cheap 3" dedicated faceplate. If you try to setup a reusable faceplate it may be more trouble than it's worth.
    • To the faceplate attach some 3/4" MDF with screws
    • Turn a small groove in the MDF and glue a 6" PVC tube into the groove
    • Drill or turn a small hole in the middle of the MDF so air can get pulled out by the vacuum thru the headstock (or the base of your spindle depending on your setup).
    • When you test the system, you'll find leaks which can be plugged with glue or silicon sealer.
    Reference threads:
    The following AAW forum threads provide various bits of info about woodturning vacuum systems:

    How much vacuum is enough

    Calling all Vacuum chuckers

    Vacuum chuck for Jet 1642 lathe

    Venturi Vacuum Question

    Vacuum setup

    EZ Vacuum Unit Question

    Edited by Bill Boehme to fix broken links.
     
  2. Mark Ost

    Mark Ost

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    Making MDF vacuum drum chucks/getting started with Vacuum turning/chucking

    Jeff: Excellent summary of vacuum chucks and how to do it. Your articles are clear and concise. My appreciation also to Johnny Tolly for his ideas on MDF chucking. He was kind enough to expand my knowledge on vacuum chucking and MDF chucks (even made and sent me several). They work like a charm. Thanks to both of you for all of your excellent efforts.

    I also want to applaud your job as web master. You do an excellent job. I'm sure that it requires much effort. You should be proud of your accomplishments.

    Mark
     
  3. Jeff Jilg

    Jeff Jilg

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    Thank you Mark. The article took about 4 or 5 hours but it should benefit a lot of people. Thanks for the website kudos too. Overall this is a fun website to work on - a good cause.

    Also I agree that Johnny Tolly did a great job on his vacuum chuck article. I was pleasantly surprised since I asked him for a couple of paragraphs and instead he sent me a whole new article!!!
     
  4. Steve Worcester

    Steve Worcester Admin Emeritus

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    Well, as they come up, I fix the links between the old forum and the new forum. This was a great thread, so it is well deserved to get replied to and "bubble up" back to the surface.
     
  5. Turnedoutright

    Turnedoutright

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  6. captjim

    captjim

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    I have a Gast 1/4 HP pump on the way after being the high bidder on EBay.

    After reading all of the tips and advice on this thread, my brain is spinning.

    I think this is what I will need to complete my basic system.

    The E_Z vacuum adapter

    One of the Hold Fast chuck heads

    A seal making kit for my later use for shop produced chucks

    The vacuum guage kit (Packard Catalog) with the bleeder valve, guage and misc stuff.


    Would appreciate your imput and any comments/suggestions to my choices above.
     
  7. Steve Worcester

    Steve Worcester Admin Emeritus

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  8. Steve Worcester

    Steve Worcester Admin Emeritus

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    What lathe? You may be better off with a vacuum union like Oneway sells. If is capable of more CFMs that the threaded rod and won't clog like it can.
     
  9. captjim

    captjim

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    Jet 1642. No outboard threads.

     
  10. Steve Worcester

    Steve Worcester Admin Emeritus

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    The threaded rod may be the only answer unless some other 1642 user has a better way.

    Can you put a hand wheel on the outside? If so, you can make a vac adapter by drilling out a hole for a bearing and air adapter.
     
  11. Turnedoutright

    Turnedoutright

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    An easy to make vacumm adapter

    I routinely use a shop built vacuum adapter on my jet, stubby and jet pen lathe.

    This design seals against the hand wheel. I got it from the fall issue of Woodturing Design.

    Since that time I have modified it to handle a threaded shaft for my stubby but a through the head adapter is not necessary for the Jet.

    It is easy and inexpensive to make only the sealed bearing needs to be ordered, the rest is in HD.

    Link to the design with the threaded shaft: through the shaft adapter on my site
    Link to the one I made for my jet: Chucks, face plates etc on my site
     
  12. Jred

    Jred

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  13. captjim

    captjim

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  14. Jred

    Jred

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    I had nothing to do with the compilation. Carl is a very generous woodturner. He gives his time and knowledge without reservation. If you go to his site and look under Demo and classes there are some other neat things to see. He was recently published in American Woodturner with an article on custom centers for the oneway live center.
     
  15. captjim

    captjim

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    With a little investigation, I found what I needed for a very reasonable price and thought I would share.
    David Brown (cudavid@hotmail.com) of Rhode Island produces a setup for most lathes with outboard spindles and for a very slight fee, machined an adapter for my Jet.

    Attached is a photo of my setup. I created the manifold and added a bleed valve and used an old filter but the package from Dave included all the rest. For $60. plus shipping, Dave provides the rotary adapter, all of the brass fittings, a check valve, the oil filled vacuum gauge several disconnects and an ample length of nylon tubing. For an additional $35. he machined an adapter for my Jet hand wheel.

    Seems like a good deal to me.
     

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  16. KEW

    KEW

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    Accumulator to sustain vacuum

    I know just enough about this to be dangerous:eek:.

    One of the concerns about a vacuum chuck is that if you lost power, the vacuum would release the bowl (etc) before the lathe stopped.

    To buy a bit more reaction time, it seems like it would be easy enough to just put a tank like this along the vacuum line:
    http://www.tractorsupply.com/webapp...10551_10001_43981_-1______?rFlag=true&cFlag=1

    Would the tank crumple?
    25inHG is 12.3psi

    Thanks!
     
  17. Steve Worcester

    Steve Worcester Admin Emeritus

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    Nope, I use one similar on my vacuum form machine.
     
  18. Dave Peebles

    Dave Peebles

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    Hi Kurt,

    I have found on my system that it retains some vacuum for a couple of seconds after I shut down the pump.

    I first discovered this when I shut off the pump accidently instead of the lathe. :) I would not advise this method, but I did have a couple of seconds to get my wits about me. This was using a 5" vac chuck. I think anything smaller and it would have launched pretty quickly.

    Best wishes,
    Dave
     
  19. KEW

    KEW

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    Thanks Dave and Steve!
    It seems like a good option to me. I'm just surprised it isn't mentioned as an option in any of the DIY vacuum.
     
  20. Steve Worcester

    Steve Worcester Admin Emeritus

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    I think it would only work in the case of a sudden leak, it would allow vacuum reserve to draw on, but then again, after the recovery it will not get back to full draw as quickly because it has to evacuate the reserve also. I suppose if you routinely used about 10 in/mercury, vs 26 or so, then it would work. Pumps draw vacuum real well in the lower numbers and slower as you get up to it's full number.
    It wouldn't help in a leaky vessel either.
     

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