+- Woodnet Forums (https://www.forums.woodnet.net)
+-- Thread: Drilling hole slightly larger than 3/4 inch (/showthread.php?tid=7338820)
Drilling hole slightly larger than 3/4 inch - Engineer - 04-11-2018
I am trying to drill holes in 3/4 inch plywood that are slightly larger than 3/4 inch. I start with a 3/4 inch Forstner bit, but my holes need to be .78 inch in diameter. How can I do that?
RE: Drilling hole slightly larger than 3/4 inch - FS7 - 04-11-2018
You only need to remove 0.015 from the edge? I would simply use sandpaper. It's such a small amount of material.
RE: Drilling hole slightly larger than 3/4 inch - Bill Holt - 04-11-2018
A 20mm drill bit or hole saw will be close but oversized. Not sure how you get exactly .78". Out of curiosity, what is this for?
RE: Drilling hole slightly larger than 3/4 inch - joe1086 - 04-11-2018
A 25/32 drill bit gets you to .7813. A 20mm is slightly larger.
There are a few options on Amazon Prime.
RE: Drilling hole slightly larger than 3/4 inch - Splinter Puller - 04-11-2018
grind down a 1" spade bit to the exact size you need.
RE: Drilling hole slightly larger than 3/4 inch - CLETUS - 04-11-2018
(04-11-2018, 08:42 AM)Engineer Wrote: I am trying to drill holes in 3/4 inch plywood that are slightly larger than 3/4 inch. I start with a 3/4 inch Forstner bit, but my holes need to be .78 inch in diameter. How can I do that?
I'm not sure how accurate you need to be.... you could buy a 25/32" (.781) drill bit.
RE: Drilling hole slightly larger than 3/4 inch - Rob Young - 04-11-2018
(04-11-2018, 08:42 AM)Engineer Wrote: I am trying to drill holes in 3/4 inch plywood that are slightly larger than 3/4 inch. I start with a 3/4 inch Forstner bit, but my holes need to be .78 inch in diameter. How can I do that?
.78" is 19.812mm. Could you live with 20mm or 0.787"?
metric Forstner bits :
First place that comes up in search : http://www.rockler.com/individual-metric-forstner-bits-metric-forstner-bits-3-8-shank Around $12 plus shipping
19.8mm seems to be a "common" size in metal working drill bits but the prices at MSC are a bit high ($285) Probably with some decent googling, one could find something much cheaper.
RE: Drilling hole slightly larger than 3/4 inch - Alan S - 04-11-2018
(04-11-2018, 08:42 AM)Engineer Wrote: I am trying to drill holes in 3/4 inch plywood that are slightly larger than 3/4 inch. I start with a 3/4 inch Forstner bit, but my holes need to be .78 inch in diameter. How can I do that?
1. Get an adjustable auger bit, and plan on taking time to get it set precisely. 1. and 2. are not helpful if you've already drilled your 3/4" holes.
2. Grind down a spade bit. That's easiest but not likely to be very precise. Grinding a very small amount off a closely-sized forstner bit might be better.
3. Make a reamer from a slotted dowel with an inserted piece of steel, like the tapered reamers used by chairmakers. This should remain the proper size a bit longer than sandpaper on a dowel.
4. Make one precise hole as a template, and use it with a flush trim or pattern bit in a router to slightly enlarge a 3/4" hole.
5. Use a tapered reamer or chamfer bit to enlarge one face of the hole, and a flush trim bit riding on the taper at the correct spot to bring the rest of the hole to size.
This works well on small changes to large holes, such as 6" to 6 1/8" to fit DC duct.
RE: Drilling hole slightly larger than 3/4 inch - Cooler - 04-11-2018
I never tried it but perphaps wrapping the forstner bit with self-adhesive sand paper.
I doubt it will remain perfectly round however.
RE: Drilling hole slightly larger than 3/4 inch - KC - 04-11-2018
(04-11-2018, 12:09 PM)Cooler Wrote: I never tried it but perphaps wrapping the forstner bit with self-adhesive sand paper.
I doubt it will remain perfectly round however.
Wrap a 5/8 dowel twice with self adhesive paper or regular paper with spray adhesive. Just tight enough to go in and then rotate a few times. I did this with game board sections that rotate on a dowel.