# What size drill bit gives "interference fit" for wood doweling?



## JimGnitecki (Dec 5, 2015)

I want to dowel hardwood parts together using 3/8" commercial dowel stock that you buy at places like Woodcraft.

I used a digital caliper to measure the diameter of the 3/8" doweling, and it appears to run about.375", although it drops below that frequently and goes above that less frequently.

I suspect there are multiple factors that "could" affect the actual size of drill bit I need;

- the actual (not "nominal") diameter of the bit (the 3/8" carbide Forstner bit I measured today had an actual diameter of .377")

- the combined runout of the drill spindle, drill chuck, and drill (which I don't know how to measure properly)

I tried a quick little experiment today:

- I used first a carbide Forstner 3/8" bit and then a 1/2" spade steel bit

- I drilled first a 3/8" hole and then a 1/2" hole into a block of 3/4 plywood. I had the plywood firmly clamped when drilling each of the holes

- I measured the diameter of each drilled hole in the plywood using a digital caliper, and found that the hole was, in each case somewhere in the .007" to .010" range larger than the corresponding bit

I have a 1-ton arbor press to seat the dowels with an interference fit.

So, if I want a good interference fit for that 3/8" doweling:

1.Does the drill runout affect what size of drill bit I should use, or does the bit hold its hole diameter once it starts into the wood?

2. what size of (carbide Forstner) bit should I use?

3. Do all 3/8" bits have the same actual (not nominal) diameter, or do they vary? 

Jim G


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## ryan50hrl (Jun 30, 2012)

Drill bit diameter should not change, however runout will effect the hole, as well as the style of bit. 

Dowels will also vary quite a bit, and if you intend to use glue or not will have an impact. I'd measure each dowel, and then measure each bit for the right answer.


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## Tree Hugger (Sep 1, 2011)

Sounds like you drill chuck jaws are worn out. Some chucks like Jacobs can be pressed apart for new jaws replaced ( I've done plenty).
Otherwise time for a new drill chuck ( get one that is rebuildable).
Glue should make the wood swell and in my experience they can be tough to seat (dowels) at times.
007-.010 oversize seems way to big.
You could get a twist drill in letter U (.368) in a jobber length and experiment with that but even a new twist drill with a factory grind can be off. 
You would need a dial indicator with a magnetic base to check runout.


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## JimGnitecki (Dec 5, 2015)

Tree Hugger said:


> Sounds like you drill chuck jaws are worn out. Some chucks like Jacobs can be pressed apart for new jaws replaced ( I've done plenty).
> Otherwise time for a new drill chuck ( get one that is rebuildable).
> Glue should make the wood swell and in my experience they can be tough to seat (dowels) at times.
> 007-.010 oversize seems way to big.
> ...


The drill press is a brand new Jet JWDP-12 (the model that just became available), so the chuck can't be worn out. But, I suppose it could be crappy . . .

So, I can get drill bits that are "unusual" in diameter (like that .368 you mentioned)? Where?

What kind of dial indicator should I try to get to take the runout measurement?

Jim G


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## Jammer (Jul 15, 2009)

"Interference fit"? Are you a machinist? 

The main problem with this scenario is that the dowel is not a stable shape. The dowel will change diameter literally overnight.


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## ryan50hrl (Jun 30, 2012)

Dial indicator...

https://www.amazon.com/dp/B0000DD0VA/ref=cm_sw_r_sms_api_O4rnxb8RZABBK


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## ryan50hrl (Jun 30, 2012)

Any fastenal store for drill bits.


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## TerryQ (Apr 8, 2014)

For accuracy and consistency you can make your own dowels using something like this http://www.leevalley.com/US/wood/page.aspx?p=70555&cat=1,42524


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## Tree Hugger (Sep 1, 2011)

If the runout is from the chuck and is .007-.01" as you believe, you could see it with the naked eye( watch the shank when it is running).
Try drilling in soft or hardwood and see if you get the same effect...
I dunno ....plywood maybe isn't the best medium to test hole size with....maybe ripping off minute chunks and making the drill wander.
Small diameter holes need extra diligence with chip evacuation as that can make the drill walk.
Drilling undersize shouldn't be the answer ...something's not right.


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## Steve Neul (Sep 2, 2011)

For a 3/8" factory dowel I prefer to use a 25/64" drill bit. Being 1/64" oversized will let the dowel fit snug enough not to have to drive the dowel in with a hammer but loose enough to allow for the glue thickness. For myself I made the tooling to make dowels on a shaper and make dowels 23/64" in diameter so a 3/8" bit will do the same thing. Using a doweling jig and factory dowels I was having to drill the holes 3/8" and then come back and re-drill them 25/64".


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## JimGnitecki (Dec 5, 2015)

I should mention: I don't want to use glue. i want it to be a pure interference fit, where the dowel get pushed in via the arbor press, and that's sufficient to keep it there. The idea is for the item to be 100% wood with no glue and no metal fasteners.

Jim G


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## Jammer (Jul 15, 2009)

Dowels swell with glue.

An interference fit made in winter will fall out in summer; in reverse it will split solid wood.


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## Steve Neul (Sep 2, 2011)

JimGnitecki said:


> I should mention: I don't want to use glue. i want it to be a pure interference fit, where the dowel get pushed in via the arbor press, and that's sufficient to keep it there. The idea is for the item to be 100% wood with no glue and no metal fasteners.
> 
> Jim G


That just won't work. You can drill 3/8" holes and use 3/8" dowels to where you have to force the joint together but it won't stay together or even make a joint. I've seen cabinets made to where dowels were used for alignment but had screws or some other fastener to hold the joint together but it has to have something.


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## Jig_saw (May 17, 2015)

I think I have a unique method (?) for making dowels. I make my own dowels with long pieces of thin scrap wood and an axe. There is a natural taper to the dowels I make, which helps in getting a tighter fir that what is possible with standard dowel of uniform thickness.


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## Tree Hugger (Sep 1, 2011)

JimGnitecki said:


> I should mention: I don't want to use glue. i want it to be a pure interference fit, where the dowel get pushed in via the arbor press, and that's sufficient to keep it there. The idea is for the item to be 100% wood with no glue and no metal fasteners.
> 
> Jim G


Even in metal working where steel dowel pins may be used there is still fasteners .
I did a lot of that back in the day using manual machines , trying to hold +/- .0005 on dowel pin locations.
Centerdrill,drill, reaming end mill ( a few thou less than finish size to bore the hole) then oversize or undersize reamer.
Worked for a Automation machine builder, some projects as big as a house , then disassembled and shipped to different parts of the world.
Yeah wood is not stable enough for this idea.


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## Jammer (Jul 15, 2009)

I don't know if it would work in machine work, I went the other direction. My background is all wood, when I recently started fiddling with baby steps working in metal, the most difficult concept to work around for me is that the two materials are very different.

Things, methods and solutions that work in wood simply will not work in metal.


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## BWSmith (Aug 24, 2010)

Sounds like you need to make your own"dowels"Don't make them round,look at jigsaws' post above.The edges of the dowel bite into the wood.

It can be done,just ain't gonna happen with round pegs.


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## JimGnitecki (Dec 5, 2015)

Two things:

1. I don't know where the "metal" discussion comes from. I have never worked with metal and never mentioned it! 

2. I know I DID do this doweling thing successfully about 3 decades ago, but have forgotten how I did it! I used normal commercially available dowel stock then, and no glue. It worked. But I can't remember what I did differently. 

I think I may have softened the edges of the ends of the dowels, which suggests that i might have drilled the holes slughtly undersize compared to the diameter of the dowels. Would wooden dowels forced into a slightly undersize hole by a 1-ton arbor press "compress" enough to slide in, or would the dowel splinter instead?

Jim G


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## shoot summ (Feb 21, 2014)

JimGnitecki said:


> Two things:
> 
> 1. I don't know where the "metal" discussion comes from. I have never worked with metal and never mentioned it!


Precision sized, round holes are machined in metal, when it comes to precision, which is what you seem to be after, metal working is the standard. 

Traditional twist drills don't make a round hole, and they don't hold the precision you are talking about. In metal working a hole is drilled under sized, then reamers are used to bring it to the correct size, and make it perfectly round. 

Not sure what your project is that is driving this particular discussion, I never use dowel stock for doweling, I always buy the pre-made dowel pins, and I always use glue.


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## JimGnitecki (Dec 5, 2015)

shoot summ said:


> . . .
> 
> Not sure what your project is that is driving this particular discussion, I never use dowel stock for doweling, I always buy the pre-made dowel pins, and I always use glue.


The driver is the desire to make assemblies that contain ONLY wood. I know it sounds "unnecessary" since glue is such a good solution, but it is a challenge I want to undertake. I did it before, 3 decades ago, just cannot remember what I did differently then.

Jim G


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## JimGnitecki (Dec 5, 2015)

It might be possible I bought and used dowel pins like these from Home DEpot:

http://www.homedepot.com/p/General-Tools-1-13-in-x-1-4-in-Fluted-Dowel-Pins-840014/202252099

The flutes, although INTENDED to accommodate glue, would enable the dowel to "compress" a bit for a tight friction fit, wouldn't they?

Jim G


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## FrankC (Aug 24, 2012)

Good luck in reinventing the wheel, there is a reason why wood parts are glued together, if this is a commercial product you intend to produce hope you have a good refund policy for your customers sake.


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## bzguy (Jul 11, 2011)

I think I know what you're shooting at.
A project that can be assembled and stays that way without using glue or fasteners.
Gravity is usually your friend, for instance dowels that are vertical can be used to lock pieces together.
Other joints, like dovetails, blind dovetails and sliding dovetails can be used to "lock" pieces in place.
They are held there by the next piece of the puzzle.
I've seen some very intricate pieces made this way, unfortunately no pictures.
I did find this one link to simpler projects with no fasteners or glue.....http://www.instructables.com/id/Woodworking-Making-wood-projects-without-using-na/


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## JimGnitecki (Dec 5, 2015)

Ok, turns out that Lowes also handles fluted dowels, but a different brand, with different cost perm piece and different lengths. But, here's the product description from the "Madison" brand handled by Lowes:

Poplar Dowel Pin (Actual: 0.375-in)

USA manufactured from kiln dried Poplar
Machined to close tolerance
Environmentally friendly -annual growth exceeds harvest
Multi groove - chamfered on each end
22 pieces per package
Easily joins two pieces of wood together without nails or screws
3/8-in x 2-in

Note:

- The dowel diameter for the 3/8 size is exactly 3/8" (.375")

- The wood used is Poplar, which is both low density and soft, and therefore compressible more easily

- Chamfered at each end for easier start into an interference fit hole

- Note the statement "Easily joins two pieces of wood together without nails or screws"

There is hope . . .

Jim G


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## JimGnitecki (Dec 5, 2015)

bzguy said:


> I think I know what you're shooting at.
> A project that can be assembled and stays that way without using glue or fasteners.
> . . .
> 
> I did find this one link to simpler projects with no fasteners or glue.....http://www.instructables.com/id/Woodworking-Making-wood-projects-without-using-na/


Yes!! That is the target.

Jim G


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## Jammer (Jul 15, 2009)

The tolerances you work to depend on what you're trying to achieve, and what you're working with. There's no sense in cutting something to a thousandth of an inch if the material is going to grow fifteen or twenty thousandths in that dimension over night, but if you're working the other direction in the grain, or you've seasoned the wood to the cut, it can make perfect sense.

I usually start with rough cut wood, dry it out to around 12%, plane one side flat on the jointer, square one edge on the jointer, mill parallel in the face, rip parallel on the table saw and cut square ends. I do all that a quarter to a half inch over size, then I either leave it alone for a week or put it in the kiln if I'm in a hurry. (And willing to risk losing the piece.)

As the fresh cuts (and the new surfaces) dry, the board changes shape. Maybe it bows, maybe it cups, maybe it warps. Maybe it grows, maybe it shrinks. You don't want any of that to happen after you've cut fine dovetails. 

After a week, ten days, or two or three days in the kiln, I go back to the wood (usually all the wood for a small project) and speak harshly to it, demanding to know if it's finished screwing around. Sometimes it gets uppity, and has twisted too much to use, or shows signs that it's not done moving. For that very reason, in my old age, I've taken to rough cutting extra pieces, particularly with Home Depot pine, "white wood" or other known ne'er-do-wells. I've cut "hem-fir" (no such tree in nature) that sprayed water in my face at the table saw.

If it's down below 10% (I used to try for 8%, but I ruined a lot of wood trying to get there) and isn't moving, I go back to the jointer and start again, taking it right down to finish size. Plane, parallel, parallel, rip, crosscut, right at finish dimension. If it's at 8 or 9%, it's probably okay to go ahead and cut joinery without further ado.

If you buy pretty dry wood in the first place (close to 10%) it usually only takes four or five days air drying between rough cuts and finish cuts.

I've never tried to interference fit a dowel, because the grain in the dowel will run end-to-end, because a dowel that swells slightly is usually a good thing.

This book changed the way I look at wood: https://www.amazon.com/Understandin...&btkr=1&redirect=true&ref_=dp-kindle-redirect


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## JimGnitecki (Dec 5, 2015)

Jammersix said:


> . . .
> 
> This book changed the way I look at wood: https://www.amazon.com/Understandin...&btkr=1&redirect=true&ref_=dp-kindle-redirect


Yes, I have that book. 

Today, in between work tasks, I am researching dowels - wood species available, types (plain, fluted, spiral), etc.

The fluted type is apparently the "best" for situaitons where you want an interference fit, as the flutes compress while the dowel is being pushed into the hole, creating a tight bond.

I plan to use well seasoned hardwoods, and to finish the completed subassemblies and assemblies with a generous coating of pharmaceutical mineral oil, so post-construction wood movement will at least be minimized.

What I want is dowel & hole size combination that results in a reliable interference fit that won't become loose enough over time and conditions to "come apart".

Jim G


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## TomCT2 (May 16, 2014)

...Yes!! That is the target.

lemme' just say this about my 40+ years of doing things with dowels....

not a single commercial source I've ever encountered has a reliable tolerance for the actual diameter of their product.

which kinda' sorta' really smacks the issue of "how big the hole" in the face.

last week: local sources having nothing but $0.0002 bamboo (? - dunno. gets wet, bends in half...) dowels, ordered a 3/8 dowel - ash - for a project. because dowels don't do things right....I purchased a cheapo drill index at Harbor Freight - all letters, all numbers, up to 1/2 inch by 64ths. how can you miss, right?

it's easy. drilled some scrap (hard maple) for test fit.... been here before, know better....
3/8 was too big. 3/8 dowel fell into the hole. 23/64th - too small. go figger. I could have beveled an end and pounded it in, but the hole is less than 1/2 inch from the end grain edge. pounding invites splitting - not suitable for this project... wound up cutting off a chunk of dowel and spinning it down via 240 grit sand paper to fit the 23/64th hole.

somebody pointed out the DIY Lee Valley dowel making kit. I need to look into that. wouldn't it be nice to have a dowel of a size it said it is . . . .


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## Brian(J) (Feb 22, 2016)

Hi, have you considered running a saw halfway down the dowel lengthwise, then tapping a tapered shim into it? I used to do that all the time when I was still using dowels, whenever I felt like the dowel was a little loose. Makes a huge difference, plus looks interesting.

Runout in drilling, once spent too much time delving into this. The runnout in a drill bit not under load is very different than a drill bit drilling a hole. In metal and hard wood there is very little runnout as the drill press and chuck don't have the rigidity to hold the bit off center, the bit tends to center up. Anyway, if you want to determine the end result you really want to measure the resulting hole, perhaps with a pin gauge. To the best of my ability to measure, a 1/2" diameter hole in Ipe drilled with a Norseman bit results in a hole that is exactly .500". For whatever reason the hole is almost .002 out of round (larger) over 1/4 of it's arc, acording to a Blake CO-AX.


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## JimGnitecki (Dec 5, 2015)

TomCT2 said:


> . . . drilled some scrap (hard maple) for test fit.... been here before, know better....
> 3/8 was too big. 3/8 dowel fell into the hole. 23/64th - too small. go figger. I could have beveled an end and pounded it in, but the hole is less than 1/2 inch from the end grain edge. pounding invites splitting - not suitable for this project... wound up cutting off a chunk of dowel and spinning it down via 240 grit sand paper to fit the 23/64th hole.
> 
> somebody pointed out the DIY Lee Valley dowel making kit. I need to look into that. wouldn't it be nice to have a dowel of a size it said it is . . . .


I almost always will be able to keep the dowel joint far from any edge, which prompts this question which I hope someone can answer:

If you make the hole size smaller than the dowel diameter, and use a chamfered dowel (plain or fluted), how MUCH smaller can you make it and still be able to press fit the dowel in there using an arbor press, without splitting the dowel?

The very small parts being joined are typically thin enough that dowel penetration of 1/2" to 5/8" into each piece is all I need or want (i.e. total dowel length is 2 x 1/2" = 1" or 2 x 5/8" = 1.25". So, the force required from the arbor press should not be anywhere near large enough to split the dowel, if the degree of interference is sensible.

Jim G


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## Brian(J) (Feb 22, 2016)

I think most of us would just give it a try a few different ways. There are so many variations in each of the parameters I'm not sure any information you get is going to be accurate in you situation.


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## TomCT2 (May 16, 2014)

the right size will depend on the wood species.

and I'm not all too sure it's the dowel that will fail first. you should be pressing it in with full surface contact - it's more likely the base piece will split first. then again, I have never worked with multi-ton arbor presses in wood.

drilling a pilot hole for (any size screw...) varies quite wildly between something soft (eg poplar) and something really hard (eg hard maple)

this I learned after shearing off way too many brass screws going into maple. . . .
did you know, a #10 brass wood screw will twist in half just as easy as a #6?

I keep a list of hole sizes per screw size and per wood specie.....

one ignores the wood specie at one's risk. I have twisted off 5/16 inch lag bolts going into maple thinking "it'll fit"


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## epicfail48 (Mar 27, 2014)

JimGnitecki said:


> le
> 
> - Note the statement "Easily joins two pieces of wood together without nails or screws"
> 
> ...


Note the fact that nowhere in that statement does it also say "without glue". Wood is a very much dynamic material, even if you did find the right sized drill and managed to use an arbor press to force the dowels in place without cracking your workpiece, once the relative humidity changes, the wood will either shrink and fall out of those holes, or expand and destroy itself. 

Long story short, even if you nailed a perfect interference fit it won't stay that way for long. Use glue, or bolts if you want to disassemble it


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## bzguy (Jul 11, 2011)

Wooden things that stay together with no glue.......http://www.designboom.com/design/praktrik-burr-puzzle-furniture/

Many pictures of wooden things that stay together no glue..........................https://www.google.com.bz/search?q=...N2x2djMAhWEKh4KHaPjAHQQ7AkITg&dpr=1.2#imgrc=_

A picture of a "Friction-fit"? dowel-like joint......


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## JimGnitecki (Dec 5, 2015)

bzguy said:


> Wooden things that stay together with no glue.......http://www.designboom.com/design/praktrik-burr-puzzle-furniture/
> 
> Many pictures of wooden things that stay together no glue..........................https://www.google.com.bz/search?q=...N2x2djMAhWEKh4KHaPjAHQQ7AkITg&dpr=1.2#imgrc=_
> 
> A picture of a "Friction-fit"? dowel-like joint......


Inspirational! Thank-you!

Jim G


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## ducbsa (Jul 6, 2014)

Brad point bits come in more sizes than Forstner bits, so one of them might be an option.


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## JimGnitecki (Dec 5, 2015)

ducbsa said:


> Brad point bits come in more sizes than Forstner bits, so one of them might be an option.


Yes, you are right. I like the flat bottomed hole that the Forstner makes, as it allows me to drill a deeper hole in relatively small pieces of wood, but the quality of friction fit is clearly more important here, so yes, a brad point drill size that is closer to ideal than the "nearest" Forstner bit size would be better.

Jim G


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## JimGnitecki (Dec 5, 2015)

*Did some measuring and testing*

I did some measuring and testing.

First, I checked the "runout' on my new Jet JWDP-12 benchtop drill press. This is the brand new model,pn 716000,not the earlier 12" model.

My technique is open to challenge, as I have no idea how to do this "right", but here's what I did: 

- I don't have any "drill rod", but I do have a costly 11/32" carbide tipped drill bit (cost $24), which appears to be high quality.

- I mounted it in the chuck, being careful to center it within the 3 chuck prongs while I slowly hand tightened the chuck. 

- Then, I tightened the 3 jaws individually, progressively, with the chuck key. 

- Then, I set up my digital dial indicator which claims accuracy within .0005" on a magnetic base and arms setup, so that it could indicate the runout of the drill bit shaft. Because once the bit is in the chuck only the top 1" of the exposed bit is "non-twist", I took the measurement about 3/4" below the chuck, so I was well away from the twisted section, on the absolutely round section of the drill shaft. Then I turned the chuck through a complete revolution, multiple times.The maximum runout indicated by the indicator was .00030, which is less than the claimed accuracy, so I think I can conclude the runout is well under a thousandth, which seems astonishingly good for a relatively inexpensive ($375 new) benchtop drill press.

Next, I drilled a few 11/32" holes with this bit. 11/32" of course is .03115" less than 3/8". I drilled these holes into 3 separate pieces of scrap planed 2 x 6 pine.

Then I used the arbor press to pressfit 2 standard 3/8" commercial dowels (manufacturer = Excel) into the largest of the pieces of pine. These dowels are grooved along their full length, to provide for escape of air and excess glue. I did not use any glue. The dowels required a decent pull on the arbor press handle, but not extreme.

Then, I used the arbor press to individually fasten the 2 smaller pieces of pine to the larger piece.

The net result was a strong fit that did not allow rotation of the doweled pieces.

I left the large piece with the 2 smaller peices doweld to it on my porch, where it will undergo some impressive temperature and humidty changes within just a very few days, as our Spring temperatures here in Austin are varying from about 60 degrees to 85 degrees each day, and the humidity is swigning between 20% and 100% multiple times per week. I want to see what effect these temperature and humidity swings have on the tightness of the doweled joints.

I'll report back on the results.

IF the joints do not loosen up with time spent in these varying conditions, I will next try an exotic hardwood - i have some 1 x 6 unplaned Zebrawood in the house that I can cut some sample from after I cut and plane about an 18" piece.

IF the joints do loosen up, I will next repeat the experiment but this time i will coat the component parts with mineral oil (NOT the dowel or dowel holes  ), to see if the mineral oil finish makes enough of a difference in protecting the wood from temperature and humidity changes.

I really would like to be able to say "nothing but wood with mineral oil finish" in the items I want to make. 

Jim G


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## Shop_Rat (Dec 22, 2015)

If you're getting somewhat the force you want to drive your dowels now, it may be that you only end up tweaking your bit size. I think you said you used an 11/32 bit, which is .3438 (omitting whatever spindle runout you may have). Maybe an R (.3390) or Q (.3320) or an in between metric 8.5mm (.3346) would give you an even tighter resistance fit. Drill bits are cheap and easy to get, even the "exotic" sizes. 

I think your project is probably going to be worthy of the effort. Almost anyone can build with fasteners and chemicals, but not just anyone has the patience or skill to craft with just, well... wood.

Cheers


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## JimGnitecki (Dec 5, 2015)

Shop_Rat said:


> If you're getting somewhat the force you want to drive your dowels now, it may be that you only end up tweaking your bit size. I think you said you used an 11/32 bit, which is .3438 (omitting whatever spindle runout you may have). Maybe an R (.3390) or Q (.3320) or an in between metric 8.5mm (.3346) would give you an even tighter resistance fit. Drill bits are cheap and easy to get, even the "exotic" sizes.
> 
> I think your project is probably going to be worthy of the effort. Almost anyone can build with fasteners and chemicals, but not just anyone has the patience or skill to craft with just, well... wood.
> 
> Cheers


Yes, I plan to fine tune the drill bit size as needed. I just needed to do some initial testing of basic feasibility as a starting point!

Jim G


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## woodnthings (Jan 24, 2009)

*I think the dowels will vary ...*

I would not "tune" the drill bit as you will chase your taill all over the place. It's the dowels that will have the most variation. If you want accurate dowels, make a steel dowel plate with the drill you intend to use and drive them through the plate to make them uniform:


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## Leo G (Oct 16, 2006)

A "V" gauge drill bit is .377" That should give you the interference fit you want 

https://en.wikipedia.org/wiki/Drill_bit_sizes


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## Jammer (Jul 15, 2009)

One problem you will face is that drill bits don't drill straight holes; they drill spirals. In machine work, they are then reamed straight.

There's really no parallel in woodwork, because the dowel changes size overnight.


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## Steve Neul (Sep 2, 2011)

If one is going to skip the glue this kind of dowel better be used.


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## JimGnitecki (Dec 5, 2015)

Steve Neul said:


> If one is going to skip the glue this kind of dowel better be used.


Steve, I need dowels that grip BOTH pieces of wood. The top one in your photo goes THROUGH one piece of wood and only grips the other piece.On the second dowel only half of it is grooved, while the other half of the dowel is smooth.

Jim G


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## JimGnitecki (Dec 5, 2015)

woodnthings said:


> I would not "tune" the drill bit as you will chase your taill all over the place. It's the dowels that will have the most variation. If you want accurate dowels, make a steel dowel plate with the drill you intend to use and drive them through the plate to make them uniform:
> 
> Making a Dowel maker,the easy way - YouTube


The idea behind using the GROOVED dowels is that the ridges on the dowel compress and crush as the dowel is being press fitted. This gives the dowel a "variable diameter" that adjusts the degree of compression - a dowel that starts at the upper end of the dowel diameter tolerance compresses more than a dowel that starts at the lower end of the diameter tolerance, so that both extremes can "compress enough to fit into" the drilled holes and hold sufficiently.

The commercial dowels only vary by about .010". The 11/32" drill bit is .03125" smaller than .375" (the nominal target diameter of the dowels). This means the degree of interference between the dowel and the hole is 3 times the variation in the dowel diameter, so the dowel diameter variance becomes relatively unimportant. The reason the "oversize" dowel fits into the 'undersize" hole is that the ridge height on the grooves CAN be compressed sufficiently to fit.

So, the key question again comes down to this: As temperature and humidity change, does the compressed dowel continue to hold sufficiently? We'll see.

Jim G


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## JimGnitecki (Dec 5, 2015)

Leo G said:


> A "V" gauge drill bit is .377" That should give you the interference fit you want
> 
> https://en.wikipedia.org/wiki/Drill_bit_sizes


The 11/32" bit , which has a .34375" diameter, is fine, as it makes a hole size that does allow the dowel to still fit once the ridges on the grooves have been compressed. Since I am not having any trouble getting the dowels seated via the arbor press, i don't see a need to "loosen" the fit by going larger on the drill size.

Jim G


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## JimGnitecki (Dec 5, 2015)

Well it's been 6 days since I assembled those "test" dowel joints using interference "frictional press fit" only (no glue). 

During that 6 days, the joints have been stored outdoors within a screened-only porch, while the weather during that time period has varied from 20% humidity to 100% humidity, temperatures from 65 degrees to 90 degrees, and multiple cycle of pouring rain through bright sunshine.

So far, the dowel joints show no loss of resistance to being pried apart. Looking good . . .

Jim G


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## TimPa (Jan 27, 2010)

- I was told that if you drill a slightly smaller hole before your finished size, there is less tear-out and a more accurate sized hole (never personally tried this)


- early craftsmen used to build farm implements by inserting a (very) dried pin into a green or less dried board. the outer green board dries and the over dried pin swells making a tighter joint.


- it is small, but you may consider inserting a hidden wedge.


- install the grain of the dowel perpendicular to the boards they are going into.


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