Drilling hole slightly larger than 3/4 inch
#11
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?
Engineer
Reply
#12
You only need to remove 0.015 from the edge? I would simply use sandpaper. It's such a small amount of material.
Reply
#13
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?
"I tried being reasonable..........I didn't like it." Clint Eastwood
Reply
#14
A 25/32 drill bit gets you to .7813. A 20mm is slightly larger.

There are a few options on Amazon Prime.
Reply
#15
grind down a 1" spade bit to the exact size you need.
WoodNET... the new safespace
Reply
#16
(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.
Mark

I'm no expert, unlike everybody else here - Busdrver


Nah...I like you, young feller...You remind me of my son... Timberwolf 03/27/12

Here's a fact: Benghazi is a Pub Legend... CharlieD 04/19/15

Reply
#17
(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...-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.
Don't sweat the petty things and don't pet the sweaty things. -- G. Carlin
Reply
#18
(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.
Reply
#19
I never tried it but perphaps wrapping the forstner bit with self-adhesive sand paper.

I doubt it will remain perfectly round however.
No animals were injured or killed in the production of this post.
Reply
#20
(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.
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)

Product Recommendations

Here are some supplies and tools we find essential in our everyday work around the shop. We may receive a commission from sales referred by our links; however, we have carefully selected these products for their usefulness and quality.