HollowForm inside???

Discussion in 'Newbie' started by Regis Galbach, Aug 26, 2017.

  1. Regis Galbach

    Regis Galbach

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    I've never done a "real" hollowform until today (still working on it). I made an articulating arm this week and put a camera on it with a 19" tv monitor. Technically, it works but, I question how smooth I should expect to get it. Should I be able to get it as smooth as the outside and require little sanding? Or because that arm sticks out 8" or so from the rest is it inherently going to be rough and need very course sanding?

    Thanks
    Regis

    [​IMG]
     
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  2. Mark Wollschlager

    Mark Wollschlager

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    Depending on practice and skill level you might be able to achieve a fairly even surface on the inside from the tool.
    If you are using a 3/16" cutter it is going to be rough ( until you get lots of practice ), a round carbide ( like a Hunter tool ) can leave a very nice surface, other scrapers will usually fall somewhere in between.
    As far as what to do next,there are a couple of schools of thought.
    One is to sand the inside reachable areas and perhaps the bottom. Places where an average person would see through the opening or feel.
    Another is to make a collar of some nice wood that has a small opening that a finger would not fit through and leave the inside rough.
    Still another would be to apply black gesso on the inside to make it 'dark and mysterious' and leave it mostly rough.
    And finally try your best to sand the interior after carefully using a larger scraper to even the high spots out.
    A few folks advocate putting some rough gravel or other sharp edged material on the inside, sealing the hole and letting the lathe turn at low speed for a while to "sand" the inside. Not sure how that works out.
    Just my $.02.
     
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  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I think that woodturners are the only people who worry very much about the inside smoothness. As Mark indicated, the smoothness is more a function of your skill level than your tools. It's really personal choice on how far you want to go on the interior finishing. I made a sanding-ball-on-a-stick using an old repurposed broom handle, rubber tape wrapped around one end to make a ball, Velcro on top of that and finally strips of Abralon to do the sanding.. I use this on really deep hollowforms and have a smaller version for hollowforms less than a foot deep. I've done the small hole and black gesso tricks. On one piece I used carvers rasps to intentionally make the interior much rougher and then used terra cotta colored paint.
     
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  4. john lucas

    john lucas

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    Regis and I talked on the phone today. My first suggestion was to take very light cuts to sort of skim the top off of any undulations caused by the first hollowing. John Jordan taught me to take 2 or 3 cuts from the middle toward the outside and then pull the cutter toward you smoothing up those areas and trying to blend this into a previous cut. If you constantly make cuts from middle to left you often get a series of undulation kind of like waves in the wall thickness. By pulling the cutter gently trying not to push toward the wall you can take off the top of these "waves" and hopefully get the wall smoother. Then its just a matter of taking very light cuts to clean it up. It's still a scrape so it's never going to be really clean without sanding. I also recommended changed to something like a teardrop shaped cutter so you have a longer cutting edge to help smooth out the waves. On a vessel the shape he has you can clean up the bottom for a few inches with a hunter #4 or #5 by rubbing the bevel. You can clean up under the lip with one of his back cutting tools. The outer edges of both the top, bottom and side would require a different tool entirely. All of the ones I have that would reach this area are scrapers only.
     
  5. Regis Galbach

    Regis Galbach

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    I appreciate all the helpful tips. And, it's always a treat to talk with John.
    Thanks,
    Regis
     
  6. Mark Wollschlager

    Mark Wollschlager

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    Getting a tool on the inside of the flat top part for cleanup is tough, especially towards the outside and inside just past the opening.
    It is very easy to suddenly make the opening bigger. DAMHIKT.
     
  7. hockenbery

    hockenbery AAW Advisor Staff Member

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    I clean the surface inside with a tear drop scraper.
    This smooths the surface for appearance leveling any ridges left bu the small cutters

    The inside is nowhere near the smoothness of the outside.
    I don't sand the inside of HFs.
     
    Last edited: Aug 26, 2017
  8. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Resist the temptation to stick your fingers inside a small opening to sand where a tool can't reach with the piece spinning on the lathe. You don't want to find out first hand how much it hurts when the lathe twists your hand around a couple turns.
     
  9. Regis Galbach

    Regis Galbach

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    Well, to wrap this up with my 1st ever hollow form.
    [​IMG]
    Thanks for the tips and help.
    Regis
     
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  10. john lucas

    john lucas

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    Looking pretty good. That's a hard shape for your first one. The captured bar systems sure do help. I remember trying one of these by hand many many years ago. It ended up in the trash after I blew it up, like I did several before I finally got the hang of hand hollowing. Once I went to a capture bar system I never looked back.
     
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