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Thread: Bowl wall thickness calipers

  1. #1
    Join Date
    May 2009
    Lafayette, Indiana

    Bowl wall thickness calipers

    I don't have a way to measure the wall thickness of a hollow form. I've seen the metal calipers that look like a figure 8. I assume that is about the best way to do it. Does anyone make their own calipers or just purchase the metal ones?
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  2. #2
    Join Date
    Jul 2011
    The Gorge Area, Oregon
    For small stuff I just use a regular 8" caliper from as a go/no go guage.

    For bigger stuff I got one of these (the 10" which is rather larger than I'd have imagined - like really big much bigger than 2" more than the 8" big horn kind of comic book big really - unless you have a large lathe the 7" ones are probably big enough) : - its actually not all that accurate (maybe a bit better than 1/8" or so if you use it carefully) but gets you pretty close. I don't think either of them would fit inside a hollow form unless the mouth is pretty good sized.. did I mention these are large?

    This fellow made some: - I'm 99% sure that that's based on a commercial design but can't recall what it is (or if its even made anymore). I believe that that measurement would be more accurate with these than with the double sided ones. You could also adjust the jaw shape as desired more.

    If I was doing actual hollow forms with narrow mouths something more like: would be attractive - that looks fairly easy to replicate in the home shop.

    After a bit of practice (and depending on how much turning I've done lately) I can get pretty close with just my fingers and I find that invaluable anyway as they can feel small variations that the calipers can "float" over (especially dips). Obviously that wouldn't work as well inside anything with a narrow mouthed piece..

  3. #3
    Join Date
    Dec 2006
    Yorktown, Virginia
    I just make them out of 10 gauge fence wire. Bend a circle or oblong shape of the heavy wire until the ends touch, then spread them apart a measurable amount (say 1" or 1 1/2"). Insert into the form with the inside tip of the wire touching the inside wall and then measure the distance between the outside wire tip and the outside of the HF wall. Subtract that from the distance you spread the wire apart and you have the current wall thickness. They were popularized by David Ellsworth and get the job done for me.
    See page 9:

  4. #4
    Join Date
    Feb 2008
    Roanoke, Illinois
    Here is one I made from 1/8 Baltic birch. It has about a 8 inch reach.
    Attached Thumbnails Attached Thumbnails 14093159162951.jpg  
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  5. #5
    Join Date
    Oct 2009
    Harrisburg, NC
    If I made them they would be like Terry shows.
    I tried the figure 8 type but it was very hard for me to see the variations with the tips hanging out in the air (Even with my bifocals)
    I use this type and just watch the outside wing move to or from the side. I can see the gap just fine.
    A 8" is fine for any bowl 16" or probably more given you can't gauge the foot.

    Not suggesting this set, just this type. The friction keeps the wings in place.
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  6. #6
    Join Date
    Jul 2011
    The Gorge Area, Oregon
    Quote Originally Posted by Ted Calver View Post
    I just make them out of 10 gauge fence wire.
    Niiiice! I like those.

  7. #7
    Join Date
    Feb 2012
    St. Catharines, Ontario, Canada
    I have a pair of thickness calipers, the ones that the arms are semi-circular. I wasn't sure what to do with them, but the method explained by Ted is easy and sensible. Is this the normal way of using these calipers? The inside calipers can obviously be opened until they touch both sides, then squeezed together, taken out, released and the distance between the arms measured, but there doesn't seem to be an analogous way of using the thickness calipers.

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