Precision boring


Here is a simple problem that I would like an answer to.
I have drilled a 3/8" hole exactly where I want it only it should have been 1/2". How do I overbore it to 1/2" without changing its exact position. Needless to say it cannot be done on a drillpress and the material is wood......
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One possibility: Mark the center of a 3/8" dowel, insert dowel into existing hole, drill new hole. A forstner bit might work best, depending on the original material.
Another possibility: Make a drill guide jig on a drill press with a through hole 3/8" dia. and a concentric 1/2" dia. hole drilled halfway through (like a deep counterbore) a scrap piece of wood. Use the small hole and bit to locate the jig, then clamp it to your workpiece. Then use the large hole to guide the 1/2" bit.
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I'd glue the dowel into the hole, let it dry, and then bore it out. Good idea to mark th center first.
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First: install a 3/8 drill in the drillpress. Do not start the motor....... Second: lower the drill into the existing hole and carefully clamp the wood to the drill base. You now have the exact center of the existing hole. Third: replace the 3/8 bit with the 1/2" bit.
John
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cannot use the drill press only indirectly.
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You could also buy a stepped drill bit. Insert it up to the 3/8" portion to line it up, then drill out to the 1/2" diameter.
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Regular twist bits are self centering. Experiment with using a regular 1/2" bit and see if the results are acceptable.
Or use the method for drilling larger holes for door lock and handle sets. Drill a hole with a 1/2" forstner bit through a 1x4 then center and clamp the 1x4 over the 3/8" hole. Then use the clamped 1x4 and its hold to guide the 1/2" bit.
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Define precision? 1/32", .001", etc...
Someone else said to use a step drill - if you have one and depth doesn't matter or it is a through hole, that might be the best answer. Insert the 3/8" portion and then turn the power on and drill out the 1/2" diameter...
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Joe Agro, Jr.
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Take a 3/8 dowel and mark the exact center. If you don't feel you can do this accuratly enough, turn one on a lathe and the center will already be there for you. Cut to length, glue in hole, drill out with 1/2 inch when dry.
Frank
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Percision boring?
I had a 12th grade Physics instructor that could probably help you out. :)
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Locutus wrote:

For some reason, I can still crack up my wife when I show here a "boring machine" in a catalog, and talk about more exciting things to buy.
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Make a hardwood boring jig with a 1/2" plug bored to 3/8. Stick a dowel in the hole and align the jig over the hole and clamp it in place. Pull out the plug and drill with the jig as a guide. This type of jig is easily made from shop scrap and should hang on the wall until the next time you need it. Years from now when you have passed on, people will look and wonder what all those odd looking 'tools' are for. <G> Bugs
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