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Simple Centering Aid

Discussion in 'Tutorials and Tips' started by Dennis J Gooding, Aug 13, 2020.

  1. Dennis J Gooding

    Dennis J Gooding

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    This is so simple that I would expect everyone to know about it, but I keep running into turners struggling to center a work piece on the lathe. One common example is trying to optimize the orientation of a previously roughed-out bowl to allow a proper mounting tenon to be cut. Typically, the inside of the bowl would be pressed against a faceplate or a large chuck by a live center in the tailstock. Then the desired orientation would be obtained by tapping the bowl so that it slides on faceplate/chuck and adjusting the position of the live center as appropriate. The problem is that if you drive the center barb into the bottom of the bowl at wrong place, you can no longer slide the foot of the bowl to where it is needed. This raises two problems: First, if you loosen the live center to adjust its position, the bowl may slide on the faceplate/chuck. Second, once the barb has penetrated the work piece, it is almost impossible adjust its position by just a small amount.

    A simple solution to these problems is to put a small block of sacrificial wood between the live center and the turning and let the center spur penetrate one side of this block as shown in the figure. Now, the workpiece can be mounted as described above with just enough tailstock pressure to keep everything in place. This allows each end of the bowl to be adjusted independently to optimize the position of the bowl. When adjustment is complete, I usually run a bead of CA glue on two or more sides of the block to assure that it will not move. A final point: If you expect to need to remount using the live center again after the block has been removed, first drill a small hole through the block at the center point just deep enough into the workpiece to provide a guide for the barb.

    The bowl orientation application described above is only one of many applications of the technique.

    CenteringAid.jpg
     
  2. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Or, you just remove the center pin of the Oneway live center.
     
  3. hockenbery

    hockenbery AAW Advisor Staff Member

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    Had the same thought. But it is a technique for centers without removable pins or if you can’t leave any marks.

    My first step in turning NE bowls is to remove the center point.


    first step I do in remounting a dried warped bowl is to find the center of the tenon. Use this center for the bottom an then adjust the rim endgrain edges and side grain edges to center the rim.

    twice turned bowl centered on the grain I leave the center point in the tenon - it is still the center point in the oval dried tenon.

    If the dried bowl was turned off center from the grain I find the center point of the tenon with a ruler.
    Mid point between the endgrain edges and mid point between the side grain edges. That is the center to use for trueing the tenon.
     
    Bill Boehme likes this.
  4. GRJensen

    GRJensen

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    I use Dennis' technique a lot when I am turning the blanks I use for floating base segmented bowls.
     
  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    That's also what I do. The sharp edge of the cup holds better than a center pin with no tendency to drift back to a previous position.
     
  6. Dennis J Gooding

    Dennis J Gooding

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    Sure, that will work also, but I believe there are a few advantages of using the block. First, although I have not run the experiment, would expect that the centering process would go more smoothly using the flat block instead of the sharp edges of the live center. Second, the glued-on block automatically leaves a record of where center is on the piece after the tenon has been turned. Third, how many center pins have you lost in the shavings? ;)
     
  7. Randy Anderson

    Randy Anderson

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    My standard practice when I'm done with a rough turned traditional or a natural edge that's turned to final is to use my circle center jig and make a small center hole on the bottom with my steel scribe. I also leave the pencil lines that intersect across the bottom through the center. The tenon, foot and bowl will warp of course while it dries but the small hole and lines tells me where center was when it was turned. Of course if the initial mark from the live center is still there then great but it's rare that I end up not having to take down the tenon and chisel off the nib, sometimes a long nib, when I'm done. And of course, sometimes I forget, and then I do the tail stock live center dance to try and find the center so I'll keep this tip in mind.
     
  8. Roger Wiegand

    Roger Wiegand

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    I try awfully hard to remember to run the tailstock up to the blank and leave an impression when roughing and cutting the tenon in the first place. Makes re-centering it much easier. I'm up to remembering to do it perhaps 60% of the time ;-(
     
    Russ Braun likes this.
  9. Dave Landers

    Dave Landers

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    For those times when you forget, make yourself one of these: https://dlwoodturning.com/bowl-bottom-center-finder/
     
    Steve Nix likes this.
  10. Don Wattenhofer

    Don Wattenhofer

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    Then it would be even harder to reposition a small amount.
     
  11. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    You have it completely backward. It is impossible to reposition a small amount if you have the pin. The pin tends to go back into the same hole. @Bill Boehme
     
    hockenbery likes this.
  12. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Not true. The pin is notorious for creeping back to an existing dimple if moving only a tiny distance. Also, the pin tends to follow the grain when there isn't already an existing center dimple.
     
    hockenbery likes this.
  13. hockenbery

    hockenbery AAW Advisor Staff Member

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    See my first post above.
    Pin out for repositioning or the pin moves back into its hole.
    The center point is great for hitting a known center center mark - not useful for finding the center through trial and error when aligning grain or rims.
     
  14. Brian Deakin

    Brian Deakin

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    Another variation I have had success with is to use a tap washer which I place over the tip of the cone center The washer prevents the tip of the cone center from marking the wood and you can cut right up to the rim of the washer to leave just a small circular nub of wood to cut off
    The use of the rubber washer also allows you to more easily control the amount of pressure you apply to the bowl
    The image is of a UK tap washer 3/8 inch in diameter as an example other sizes are available
    The washer are made from a rubber which is of a firm construction

    [​IMG]
     
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  15. Timothy Allen

    Timothy Allen

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    Here in the US, these are more often called "faucet washers" and they come flat or cone-shaped (beveled) as well as in different sizes; should be able to find them at any decent hardware store.
     
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  16. Brian Deakin

    Brian Deakin

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    Thank you Timothy for your post I did make the effort of spelling the word center ...ter and not the correct way centre
    The United States and Great Britain are two countries separated by a common language.
     

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