# Drill hole size



## klr650 (Apr 4, 2010)

Simple as it may sound, when drilling out a hole, is the bit size the hole size? Yeah I'm guessing you might be scratching your head wondering what's wrong with me, but I need to pin a mortise and my brain started running with this thought.

3/8" hole, should be a tight but usable fit for a 3/8" dowel - right????:bangin:

Really where I'm going with this is, if I use a 3/8" dowel to pin a joint, should I go one size up when drilling the hole or will the exact size bit be the best? I'm working with a joint that has a depth of 7/8", so I don't have a lot of wiggle room if I get it wrong and oversize the hole.


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## JMC'sLT30 (Oct 26, 2010)

If it is a store bought dowel made for that purpose it should be exact for the said drill size. If it is linear dowell stock I would be more cautious.


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## H. A. S. (Sep 23, 2010)

A good quality bit will make a 3/8 hole, as long as you feed it right, don't cram it in there.


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## H. A. S. (Sep 23, 2010)

If you're drilling a super tight fit, try the fit out on a scrap piece first.


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## GeorgeC (Jul 30, 2008)

JMC'sLT30 said:


> If it is a store bought dowel made for that purpose it should be exact for the said drill size. If it is linear dowell stock I would be more cautious.


What is "linear dowell stock?"

G


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## GeorgeC (Jul 30, 2008)

Going up one size depends upon what sizes of drills you have.

If going up one size means using a bit 1/64" larger than that may be good. If it means using a bit 1/16" larger that would not be good.

If the dowel is exactly the size of the hole you will have a problem getting any glue remaining in the hole when the dowel is forces in. That is why you see commercial dowels made for this purpose fluted.

George


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## jack warner (Oct 15, 2010)

GeorgeC said:


> Going up one size depends upon what sizes of drills you have.
> 
> If going up one size means using a bit 1/64" larger than that may be good. If it means using a bit 1/16" larger that would not be good.
> 
> ...


i take the dowel a score it along its length. that way when its forced in, it takes glue with it. you can flute your own with a sander. fluteing is only good if one side is is showing. i also like to round over the edge that goes in first, makes an easier start.


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## klr650 (Apr 4, 2010)

H. A. S. said:


> If you're drilling a super tight fit, try the fit out on a scrap piece first.


I'm definitely doing that - in fact, probably in about 5 minutes.


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## klr650 (Apr 4, 2010)

GeorgeC said:


> Going up one size depends upon what sizes of drills you have.
> 
> If going up one size means using a bit 1/64" larger than that may be good. If it means using a bit 1/16" larger that would not be good.
> 
> ...


I never knew that. I always assumed the fluting was for the purpose of fitting when the dimensions aren't perfect or consistent.

I'll definitely have to keep this in my back pocket for later, although in my case I'm using a tension pin to secure the tenon, and a dowel to cover the hole.


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## sawdustfactory (Jan 30, 2011)

Hole should be size of drill bit. Make sure dowel is actually diameter it is supposed to be.


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## klr650 (Apr 4, 2010)

*Update - with pics*

Well, that was a simple enough task - just had to test fit first.









Starting hole








Arm/branch partially fitted to the hole








Whoops - now I know not to align the grain of the fixture in that direction








Tension peg installed, dowel covering hole

Yeah yeah I know it's rough, but this is essentially still work in progress. Now I have to wait about 24 hours before I can fit the shelf to the arm/branch and load it.


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## JMC'sLT30 (Oct 26, 2010)

GeorgeC said:


> What is "linear dowell stock?"
> 
> G


 Linear dowell stock would be what you find in a rack at your local hardware store 3-4 foot lengths. They are almost never precise.


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## cabinetman (Jul 5, 2007)

JMC'sLT30 said:


> Linear dowell stock would be what you find in a rack at your local hardware store 3-4 foot lengths. They are almost never precise.


I've used those and they aren't that bad. I flute the dowell with the teeth of a large adjustable pliers. I cut the dowel long, and place one end in the jaws of the pliers, and then go to my machinists vise and hammer the dowel down through the teeth. Takes a bit of rotation to get around the side, but do it one more time.

Then cut the dowel to length on both ends and chamfer the lead edge.










 







.


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## thegrgyle (Jan 11, 2011)

*I realize this maybe a little too late.....*

I own an indexed drill bit set for this exact reason. An indexed set has all the fractional bits, plus bits that are lettered and numbered. These lettered and numbered bits have dimensions that are different from your everyday fractional bits, and might be the right bit to use for those slightly undersized lineal dowels.

Another reason that those indexed bits are lettered and numbered is because if you have to tap(thread) a hole in steel, the Tap requires a very specific diameter, so as not to damage the tap.

FYI......


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## jack warner (Oct 15, 2010)

i use these, they work well. face it the choices of dowels out there are very limited

http://www.traditionalwoodworker.co...in-Wooden-Box/productinfo/614-4848/:thumbsup:


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## woodnthings (Jan 24, 2009)

*Drill sizes vs dowel sizes*

Twist drills are manufactured to much closer tolerances than dowels. So you can determine a match several ways.
Drill the "correct size" hole in a scrap and fit the dowel to see if it's snug or loose as a test. You will get a feel for the fit over time. If the dowel is to be glued, flute or groove the dowel to allow for the glue to squeeze out so the hydraulic pressure will be relieved at the bottom of the hole. 
The second way is to use a drill size gauge like this for drills under 1/2":










Fit the dowel in the hole that is appropriate, then select the drill size for that hole. A complete fractional twist drill set will have 1/64th sizes. There will be one that is a best fit. 
For sizes greater than 1/2", Forstner or spade bit can be used. For a specific hole/dowel a spade bit can be edge ground for an exact fit. :thumbsup: bill


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## klr650 (Apr 4, 2010)

You never realize how complicated this stuff is until you have to do it yourself and it really matters.

To whit the entire experiment was bust, but I learned something new so I consider it a success anyway. Back to your original comment about this - way back in a thread I posted about the strength of wood. Indeed the mortise and tenon approach is simply to unstable for the load I'm placing on it. I've gone back and re-engineered a more elegant solution (or so I think) using steel rod painted to look like a tree sucker. While it's still a bit "bouncy", I have no doubt it will hold. Now I just have to figure out how to cover the retaining nuts to make it look like a growth collar.


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