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Thread: Help finding my center

  1. #1
    Join Date
    Feb 2007
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    Idaho Falls, Idaho
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    1,356

    Help finding my center

    I have a beautiful burl cap whose maximum dimension is exactly the maximum diameter my lathe can handle. In fact I may have to grease one of the tips to get it to side across the ways. I don't want to cut anything off the edge, because I will lose the natural edge in that spot, and I want it continuous around the entire edge. How do I measure an odd shaped blank, and find the exact center? I can get close by measuring multiple spans, and dividing by 2, but because of the tight tolerances, I need to be more exact. Surely somebody has figured out a way to find the exact center. I'll try and get a pic uploaded as soon as possible. TIA for your help.
    Brian

    Sawdust Formation Engineer
    in charge of Blade Dulling

  2. #2
    Join Date
    Nov 2004
    Location
    Belden, Mississippi
    Posts
    2,742
    I would use a compass.
    Bill
    On the other hand, I still have five fingers.

  3. #3
    Join Date
    Feb 2007
    Location
    Inver Grove Heights, MN
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    798
    I use a series of disks that I made to mark circles on blanks prior to cutting with chain saw or band saw. Just lay the disk on the wood and move around until it looks like all edges are covered, then push a nail or pencil through the hole in the disk center. If it is hard to see because of the irregular shape of the burl, you might try setting the burl in a bucket or other container that is just a bit larger than the burl. Arrange it so the sides of the burl are equal distance from the edge of the bucket and use the lid or a plywood disk with a center hole to mark the center of the burl.

  4. #4
    Join Date
    Jul 2015
    Location
    Central IL
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    257
    I would a stand 2 pieces of straight boards on opposite sides at widest width with another across the top and use a plumb bob at the exact middle

  5. #5
    Join Date
    Sep 2008
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    Gassaway, WV
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    1,221
    What Paul said.
    Fred

  6. #6
    Join Date
    Mar 2011
    Location
    Pendleton, KY
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    803
    Brian, I am experiencing the same dilemma with some burls I'm turning. Using the above mentioned methods will get you close. Here is what has worked for me: I start with estimating the center, place the piece between centers and then adjust the piece while it is on the lathe. This allows me to find the precise angle that avoids hitting the ways while aligning the natural edge to get it where I want. This may require relocating the headstock or tailstock end, or both. Of course, this is all done while moving the piece around by hand until I get the right alignment. I will occasionally adjust it further after I have turned away some wood. I start virtually everything this way. Start between centers, adjust if needed, turn a tenon and mount in the chuck.

  7. #7
    Brian...if you have a set of calipers large enough to go around the edge you wish to keep (or you can tack two strips of wood together and trim one set of ends off to ensure equal length), have someone hold the calipers over the widest portion of the edge you wish to keep and then hang a weighted line over the 'X' made where the calipers pieces are joined. This poor man's plumb bob has worked for me in the past to find the true center of the best side I want to maintain. Good luck...John

    Quote Originally Posted by Brian Brown View Post
    I have a beautiful burl cap whose maximum dimension is exactly the maximum diameter my lathe can handle. In fact I may have to grease one of the tips to get it to side across the ways. I don't want to cut anything off the edge, because I will lose the natural edge in that spot, and I want it continuous around the entire edge. How do I measure an odd shaped blank, and find the exact center? I can get close by measuring multiple spans, and dividing by 2, but because of the tight tolerances, I need to be more exact. Surely somebody has figured out a way to find the exact center. I'll try and get a pic uploaded as soon as possible. TIA for your help.

  8. #8
    Well, I have found this to be very handy on more than one situation. You can always improvise...

    https://www.woodturnerscatalog.com/p...le%20templates

    robo hippy

  9. #9
    Join Date
    Mar 2003
    Location
    Redding, CA (That's in superior Calif.)
    Posts
    832
    Quote Originally Posted by Reed Gray View Post
    Well, I have found this to be very handy on more than one situation. You can always improvise...

    https://www.woodturnerscatalog.com/p...le%20templates

    robo hippy
    Robo is right. I only got one of these recently. Before, I used the circles of plywood. I still use them but not as often.
    Project Salvager

    The key to the gateway of wisdom is to know that you don't know.______Stan Smith

  10. #10
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    12,298
    I like to use circles made from plexiglass. That lets me slide the circle around and watch the figure and avoid any defects. A big circle with a bunch of smaller diameters inscribed is also useful - drill a small hole in the center and at least one pencil hole on each radius. Hold a nail or awl in the center and rotate to draw a circle where needed.

    For a 16" lathe a 16" circle is nice. Note, if you don't usually turn outboard that might be an option to get it round to fit over the ways.

    Oops, I just noticed the link in the quote above is to a commercial version of what I was describing. Cheap to make if you have a piece of plastic handy.

    JKJ

  11. #11
    Join Date
    Sep 2015
    Location
    San Diego, Ca
    Posts
    1,647
    Brian, you have received a lot of good advice.

    Another way to skin the cat is to put the burl between two centers and adjust the two center positions until you can spin the burl. Yes, there are two center positions. Even if you find the center position on each end, it doesn't guarantee that something is not sticking out somewhere in between. If you can't find that sweet spot, it means that the thing is too big in one or more ways.

    BTW, I would like to bring up the issue of safety. If you are going to the max limit of your lathe, you'll end up needing to position the banjo to one side of the burl. That means that for part of the turning, you may be working to the limit of your tool rest. If you get too close to the end you could have some excitement - - especially if you have one or more fingers tight against the tool rest at the time that you get a catch. In my own case, the tip of my left index finger was on the flat part of a comfort rest. When I got a catch at the end of the tool rest, it propelled the gouge downward and into the middle of my index finger. So, each end of my finger was supported in some way and the middle go hit by the gouge. The middle bone (the distal) suddenly changed from being one bone into being composed of seven pieces. It was a painful and expensive lesson. So my advice would be to keep away working to the end of the tool rest. If you must, consider drilling a hole in the rest and inserting a pin so that you can't over-run the rest.

  12. #12
    Join Date
    Feb 2007
    Location
    Idaho Falls, Idaho
    Posts
    1,356
    Thanks for the suggestions everyone. I used a couple of the methods above, and was able to find the exact center. Unfortunately, no mater how accurate I was, it was still too big for my lathe. I was going to call a friend to see if I could use his larger lathe, then it dawned on me that because of the rim style I am using, I was going to lose some diameter anyway, So with my perfect center marked, I loaded it on my circle cutting jig, and cut it on the band saw. It is amazing how little I needed to remove. Now it is mounted on my lathe ready to turn. Sorry I didn't post the picture I took, My internet service can't stay operational long enough to get a pic out. What a pain. I'll try to post the final turning after I get it done. Thanks again.
    Brian

    Sawdust Formation Engineer
    in charge of Blade Dulling

  13. #13
    Quote Originally Posted by Brian Brown View Post
    I have a beautiful burl cap whose maximum dimension is exactly the maximum diameter my lathe can handle. In fact I may have to grease one of the tips to get it to side across the ways. I don't want to cut anything off the edge, because I will lose the natural edge in that spot, and I want it continuous around the entire edge. How do I measure an odd shaped blank, and find the exact center? I can get close by measuring multiple spans, and dividing by 2, but because of the tight tolerances, I need to be more exact. Surely somebody has figured out a way to find the exact center. I'll try and get a pic uploaded as soon as possible. TIA for your help.
    There are all sorts of centers like center of mass, geometric center, and "what looks good" center. I would go with the last one and I like the clear plastic tool that Reed suggested. Whatever you choose, nothing is perfect and in all likelihood you probably won't be able to make something that encompasses the full size of the burl cap. My suggestion is to make the best looking piece that you can and get past the feeling of needing to make something that utilizes the most wood. When maximizing wood usage is your primary concern, you generally wind up compromising the artistic aspect.
    Bill

  14. #14
    Join Date
    Nov 2007
    Location
    Fort Pierce, Florida
    Posts
    3,498
    Quote Originally Posted by Bill Boehme View Post
    When maximizing wood usage is your primary concern, you generally wind up compromising the artistic aspect.
    Exactly! Lyle Jameison has a saying that we all have a gene that makes us want the BIGGEST piece we can turn when we need to overcome this and make the BEST piece we can. That and starting between centers to find the best orientation and then mounting with a face plate were my best take-aways from his demos.
    Retired - when every day is Saturday (unless it's Sunday).

  15. #15
    Put the burl on your potters wheel... Use wedges between the burl and wheel head to level as you want it. Move it around on the wheel head until it is centered. Mark the center... Mark the plane to trim a place for the faceplate or chuck.

    we all have a potters wheel don't we... It is just a vertical wood lathe for clay...

    or turn your car or truck on its side and use one of the wheels for a potters wheel.

    There are other ways I'm sure.

    c

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