I'm inthe process ofreplacing some of my doorknobs, and the new ones need a
bigger hole than the old ones. I know how to mount a doorknob when there is
*no* hole, but I'm wondering about the best way to enlarge an existing hole,
while keeping it on the same center point.... Any ideas? thanks
Got a router? Mount, say, a 3/8" cutter with a 1/4" shaft. Using the shaft as a bearing, cut around the hole about 3/4 of the way through. That has enlarged the diameter of the cut area by 1/4". If that's enough, mount a 1/4 inch cutter on a 1/4" shaft and use the shaft as a bearing to trim the uncut area flush. If it isn't enough, turn the door over and make another cut with the 3/8 cutter. Keep cutting, flipping, cutting until you have what you want.
The bit sizes above are just for example...the idea is to use a cutter bigger than the guide or shaft to cut rabbets ("shelves") on alternating sides until the diameter is correct, then trim flush. The smallest increment you can enlarge the hole diameter is 1/16" using a 5/16" cutter on a 1/4" shaft.
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Easy actually. First step is to at least partially plug the existing hole.
Just take a scrap of wood and snug it into the existing hole so it is flush
on the side to be drilled. Mark the center, then start with the hole saw.
Functionally, it only has to guide the center bit until the hole saw starts
to make its own path.
Use your hole saw to drill a hole of the right size in a piece of wood
a few inches larger than the hole, than clamp that piece of wood to
the door so the hole will guide the hole saw through the door.
Even simpler and often more applicable (you may not be able to cut a hole
a few inches larger than the existing hole, it may be tricky to clamp,
you may not have enough pilot length to compensate...):
Use the hole saw to drill a hole of exactly the same size as the existing
hole. Lay the door down on a flat surface (with some scrap behind the hole).
Drop the cutout "donut" into the door hole. Clamps not necessary.
Use the cutout (which is now flush with the door) to guide the proper size
If you're worried about it moving, glue the cutout to the scrap and then
[I think this tip was in last month's FWW.]
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
Yet another way is to use your hole saw to make a disk of wood the same
size as the existing hole. Then change over to the bigger hole saw. Put
the smaller disk you made on the pilot bit. It should fit into the
existing hole with a little slop and help guide the larger hole saw.
Once the cut is started, you can take the guide disk off.
Go to Lowes or Depot and buy a LOCK INSTALL KIT( tough plastic jig setup) for
like $11 - does 2 thicknesses of doors.
Nail to door edge with small nails and use drill to connect to the hole saws
provided for BOTH lock holes needed.
Use on your next job or sell.
Clamp a piece of 3/4" plywood to each side of the door. Drill thru with new
size hole saw with correct center as if there was no hole. Use the plywood
with the new hole as templates for the next door. Needs a bit of measurement
and setup but very low cost.
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