The center of a Bell

Discussion in 'Castings, finishing/ repair/ and patina's' started by HT1, Jun 21, 2018.

  1. HT1

    HT1 Silver Banner Member

    OK I just cannot think of a good way to find the center of a bell for drilling the hole without chucking it up in a lathe... and no the very top is not a perfect circle so the center attachment for a combination square wont work... the rotory table on my drill press is not dead center of the chuck... Chinese $hit!!!

    Thanks in advance

    V/r HT1
     
  2. Jason

    Jason Silver Banner Member

    I'm sick of stuff like this too. We sold our souls to the devil for cheap disposable tools. Remember in the mid 1980's the cheap crap came from Poland? After that, the US experienced a rise in Taiwanese goods, today it's the chinese. I'd go back to polish stuff in a heart beat. Today I get excited if I see Taiwan and not china.
     
  3. Kurtis Kiesel

    Kurtis Kiesel Copper

    Are you trying to balance the center? If it is not too large try to balance it on a bouncy ball upside-down and once you find the balance market the spot the ball is at.
     
  4. Jason

    Jason Silver Banner Member

    How about floating it upside down in water with a marble in the bottom? There's your center.
     
  5. HT1

    HT1 Silver Banner Member

    really? I'm looking for a +/-.oo4 location... how would I mark the location that either one of your ideas would locate with any sort of accuracy closer then eyeballing it ???

    V/r HT1
     
  6. Jason

    Jason Silver Banner Member

    lol.. maybe the top should have been cast in a perfect circle? :p
     
  7. HT1

    HT1 Silver Banner Member

    I did not make the pattern
     
  8. oldironfarmer

    oldironfarmer Silver Banner Member

    I'm assuming you want to center it so hanging it from the hole will result in the lower rim being level. So it doesn't matter whether the top is round or centered. If the bell varies in thickness up a little from the rim that will make more difference than the top. If it is out of balance can you dress the inside to remove material on the heavy side?

    To use your rotary table, use a marking pen fixed from the post and draw a circle as you turn the table. That can give you a circle a little larger than the bell rim which you can then center and clamp down. Then do the same thing to the top of the bell to draw a small circle which will be centered on the rim.

    If the table has too much slop I would set the bell on a level surface and use a pair of small squares to mark equal distances from the rim. You clamp the squares together to make a Zee shape so one tongue hangs over the middle of the bell with 1/16" or so clearance. Then touch the rim of the bell with the bottom of the square and mark something you know is short of the center while holding the squares plumb. Do that six times around the rim and you have a rough circle centered on the rim.

    But those methods only center you on the rim, but at the top.

    To do better I would epoxy a disc of plastic with three holes around the rim to the top being careful to get it parallel with the bottom rim (not critical but good practice). Then lift it with three strings from an eye a couple of feet above and adjust the strings to get the bottom to hang level. Then use a plumb bob from the eye to locate the center. Drill through the plastic and bell before removing the plastic. The only inaccuracy is the weight of the plastic being offcenter.
     
  9. Petee716

    Petee716 Silver Banner Member

    You could use one of the above methods (pretty damned neat) or eyeball it and use eccentric hardware.

    Pete
     
  10. HT1

    HT1 Silver Banner Member


    That is alot of great information, But it does not answer the question "a good way to find the center of a bell for drilling the hole " perhaps I was unclear Navy Bells have a hole through the center that mounts the bell if it is not in center with the rim, if you rotate the on the mount it is obviously wonky... I dont like that


    [​IMG]
     
  11. oldironfarmer

    oldironfarmer Silver Banner Member

    So you don't care whether it's balanced. That make life easy. You only need to center it perpendicularly to the rim. If your table is square to the spindle on your drill press you just need to center it on the center of rotation of the table as I described, then find the center of the top the same way and drill it. Key, and the biggest variable, is making sure the table is square to the spindle.
     
  12. HT1

    HT1 Silver Banner Member

    the rotory table on my drill press is not dead center of the chuck... Chinese $hit!!!
     
  13. oldironfarmer

    oldironfarmer Silver Banner Member

    I know you said the table is not centered. Center it on the rotary table by drawing a line while spinning the table, then center the bell and draw a line on the top while spinning the table and you have the center located on top of the bell. Up to this point it does not matter if the table is warped or not perpendicular to the spindle. Then move the bell and drill into the center. This is when the table must be square to the spindle. If the table is not square put a piece of plywood on the table and trommel it in by shimming it. Do this by bending a 1/4" rod into a Zee shape so you can chuck up the rod and have it offset at least the radius of the bell. Lower it close to the plywood and turn it by hand and shim unto it drags equally all the way around. Trommeling it also makes sure the table is square to the spindle, not the drill press support tube. The support tube and spindle may not be parallel.

    Tell me when to quit.:rolleyes:
     
  14. Melterskelter

    Melterskelter Silver Banner Member

    Perhaps another method to chose from:

    You could cut a dead center in it by chucking a cutter in the drill press. The cutter would be a piece of hard steel/HSS roughly ground so it would cut like a lathe tool and at a roughly 60 deg angle.

    Center the bell on your rotab and secure it to the rotab and center the rotab as best you can under the chuck. Now rotate the bell and press the cutter down into the stub on the bell. It will make a true (as true as the bell is centered on the table depression in the stub. Use that as a location and starting point to drill the stub. The cutter might leave a little nub in the center of the hole. That can be picked out prior to drilling.

    Also make sure the stub is faced off dead square. Any untrueness will cause bad wonkiness---probably more annoying to your eye than being slightly off center. It sounds like you do not have access to a mill. If you use a file carefully and use the rotation of the rotab and a pin in the chuck of the press you can mark high spots and true up the stub pretty well. Hollowing the stub out a bit will make truing for squareness much easier. In other words, if the stub is 3/4 diameter, drill it on center (more or less) with a 1/2" dill for a depth of say 1/8" That leaves you with an 1/8" rim of material rather than a solid bar of material to square up. Much much easier to true that rim with a file than a solid bar which tends to stay high in the center as you attempt to file it flat.

    That is one nice bell you showed in a prior thread.

    PS I see oldironfarmer posted another good idea while I was keyboarding. Tramming the table may indeed improve the squareness of the drilled hole. I wish I had mentioned that.
     
  15. Jason

    Jason Silver Banner Member

    Be on the lookout for new stuff from this guy. His channel is actually pretty cool.
     
  16. HT1

    HT1 Silver Banner Member

    I can see that working, Not insanely accurate, but probably better then my best Eyeball method.
    My table is a tilt table and is at a perfect right angle to the drill... super important when doing pattern work or pattern parts wont line up


    V/r HT1
     
  17. Zapins

    Zapins Silver

    Your bell's outer surface is perfectly round because it was made with rotation. Use the outer edge as a guide to find the center. Put the bell on a flat surface (mouth down). Make a cardboard cutout of the outer edge of the bell. Attach a marker to the top of the cutout. Now rotate the cutout along the edge and the marker should spiral around the top in a circle. Readjust the marker until you find the center point.

    Just like this video but instead of using a metal pole through the center put the marker there and it will pinpoint the center even if the top is lumpy.

    It took me 30 mins to find this video because I couldn't remember what it was titled hope it helps:
     
  18. Jason

    Jason Silver Banner Member

    I'm not sure what that thing in the mud is, but it just hit me. I'd stick that bell on a pottery wheel and center it with some clay. Then just use a sharpy to find the center on top.
    DUH... And my folks probably dumped 10grand on ceramics classes in college. Don't tell them. DOH!

    This video SUCKS, but watch the last 30 seconds to see how to center on the wheel. Once it's centered, we would put blobs of clay around it to keep it from moving while we carved the foot of the pot... or ashtray. I made lots of those.
     

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