Enlarging a hole and keeping it centered - Router Forums
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post #1 of 12 (permalink) Old 01-11-2019, 01:42 PM Thread Starter
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Default Enlarging a hole and keeping it centered

I've been making some lazy susan shelves for my corner cupboards. I have a pilot hole in them from machining them round to start with but I needed to enlarge the hole to 1" for the pipe column that the shelves are supported by. The pilot is only 3/16". I also need to keep the hole centered so that they turn true inside the cabinet. My original plan was to take them to the drill press and chuck a 3/16" bit in the DP and then with the bit in the pilot hole I would clamp the shelf to the DP table and tehn replace the 3/16" drill with a 1" Forstner. Except when I got to the DP I found out that the throat depth on it wasn't wide enough. So I had to come up with a way to do it by hand. It me a few minutes to devise a plan and around 45 minutes to carry it out but it worked well and some may find it useful.

The plan became drilling 2 guide blocks on the DP with one matching the 3/16" pilot hole and the next matching the 1" hole I needed for the pipe column. By clamping a fence and stop on the DP's table I could insure that I was drilling centered at the same spot on both blocks. I marked both blocks so that I could be sure that I kept the same orientation from one block to the other. I never bothered measuring where on the block I drilled. I only needed to make sure that I could keep both the same.

From there I laid a backing panel on one of the lazy susan shelves and clamped it.Then I put a 3/16" drill bit in the pilot guide block and into the pilot hole in the shelf. With that block in place I hot-glued two stops to the backing panel so that I had something to register the guide blocks against. Then it was just a matter of replacing the pilot block with the 1" block. The last picture shows the shelf with the pipe in it. I did need to smooth the hole a bit with an abrasive sleeve on a drill to get the pipe to slide though easily plus give me enough clearance in the hole to make sure the pipe could sit vertical. I'm guessing that even with that step at the end that I'm no more than 1/32 off dead center, 1/16th at the worst and that is plenty good enough for this application.
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Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #2 of 12 (permalink) Old 01-11-2019, 03:41 PM
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post #3 of 12 (permalink) Old 01-11-2019, 04:02 PM Thread Starter
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I bought one of those for my son for Christmas. I suppose another method would be drilling out the pilot hole to match the bit on the hole saw (I think they are either 1/4" or 5/16" in that size cutter) and then using it. The Forstner I used did a really smooth job of it. A little better than a hole saw would have done but that isn't a big deal in this situation. I posted this as much for the concept of how to locate the 2 holes in the same place as much as the job itself.
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post #4 of 12 (permalink) Old 01-11-2019, 04:32 PM
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just offered a plan '' B''...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #5 of 12 (permalink) Old 01-11-2019, 06:03 PM
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Would plan C be a combination of a rabbeting bit and a flush trim bit. Rabbeting bit to enlarge the hole halfway and then the flush trim bit to enlarge the other half to the same size as the first half?
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post #6 of 12 (permalink) Old 01-11-2019, 07:33 PM
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Quote:
Originally Posted by Cherryville Chuck View Post
I bought one of those for my son for Christmas. I suppose another method would be drilling out the pilot hole to match the bit on the hole saw (I think they are either 1/4" or 5/16" in that size cutter) and then using it. The Forstner I used did a really smooth job of it. A little better than a hole saw would have done but that isn't a big deal in this situation. I posted this as much for the concept of how to locate the 2 holes in the same place as much as the job itself.
Good thing you didn't have to go for a Woodpeckers jig...

Nice approach...will keep this in mind for "bigger than throat" projects...thanks
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post #7 of 12 (permalink) Old 01-12-2019, 12:33 AM
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Guess this is Plan "B"

https://www.amazon.com/wolfcraft-452.../dp/B000JCIMEA

- Chuck a bit the same diameter as the original pilot hole in the drill, set the guide on the part and start the bit in the pilot hole.

- Screw the base of the guide to the part (assuming that you have the underside up).

- Remove the pilot drill, chuck up the larger bit and drill the required hole.

Guess this assumes that you have one of the guides.
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post #8 of 12 (permalink) Old 01-12-2019, 03:46 AM Thread Starter
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The hole saw works as long as the pilot hole used to cut the shelf rounds isn't already larger than the bit on the hole saw. The Milescraft tool could work if it was already larger as would my method. The Milescraft jig was suggested once as a way to drill dog holes in a bench or holes in a sheet of ply where you still need vertical accuracy and if you have a job for one and buy it then you've pretty much paid for it on the first use. I look at a lot of tool purchases that way.

As usual plans B and C prove that there is almost always several ways to do a job. In the end it usually boils down to the tools you have to work with, your experience and knowledge, and often how much money and time it will cost.
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post #9 of 12 (permalink) Old 01-12-2019, 04:07 AM
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the smaller holesaw is the pilot/guide for the larger holesaw...



Plan ''D''...
register a drill guide...
clamp in/to what needs to be drilled...
switch registering bit/pin to desired size of fostner...
bore away...

.
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This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #10 of 12 (permalink) Old 01-12-2019, 12:08 PM
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I can see where Stick's method of using two hole saws with the smaller one being a guide for the larger one will work well for some situations. For small holes that need to be opened up and kept on the same center, I use a step drill bit to open the surface to the the size needed and then use a straight drill bit of that size to clean out the smaller diameter steps, if the piece being drilled is too thick for one step of the bit to cut completely through.

For drilling larger holes I have Forstner bits in 1/8" steps from 1/4" up to 3 1/2". By using a scrap piece already drilled to the diameter needed and clamped in place to use as a guide for the desired size Forstner bit, I can drill out a hole to the new diameter, up to 3 1/2". Beyond that I resort to a router, 1/4" bit, and usually my CRB7 jig. I can go to over 4' diameter using that.

Many ways to get this done.

Charley

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