Dowel Jig Question

[Cary Falk]

If you're interested in a reasonably priced one for your project Rockler sells one for $15 (on sale today for $10). It uses the same face reference style as the Dowelmax and Jessem, but only has dual dowel guides. For the price it's worth trying it out.

http://www.rockler.com/product.cfm?p...9&site=ROCKLER

I have one and hate it. I now have the Jessem

[Martin Jodoin]

This leads to the conclusion that the greater the effective gluing surface, the stronger the joint. And as shown earlier, most dowel joints do not have as much effective glue surface as a M&T joint. [When a dowel is put into the end of a piece of wood, all of the area is effective gluing surface so this statement applies to dowels that go into the 'side" of another piece of wood, where half of the dowel is facing end grain. So if you wanted to attach two pieces of wood end-to-end, dowels may make the stronger joint.]Mike

Mike, i am not a pro dowels, i still believe a tight M&T joint is stronger. I did some M&T by hand, and some of them were not so nice. I don't have a mortising machine. I am sure you agree that it's easier, for a beginner like me at least, to drill couples holes with a dowel jig (they will be perfect every time) than to cut a tight M&T by hand. I still don't understand the logic about the gluing surface. To me a dowel is just a rounded mini tenon, and a tenon is like a big square dowel, the surface should make a difference, not the shape. If you take a 1/2 inch dowel and sand it down square to 3/8, does it still applies ? I don't understand why we are losing half of the effective gluing surface with a dowel but it does not apply with a tenon. Any picture maybe ?

I totally agree with you btw that more gluing surface = stronger joint.

Cheers

[Mike Henderson]

Mike, i am not a pro dowels, i still believe a tight M&T joint is stronger. I did some M&T by hand, and some of them were not so nice. I don't have a mortising machine. I am sure you agree that it's easier, for a beginner like me at least, to drill couples holes with a dowel jig (they will be perfect every time) than to cut a tight M&T by hand. I still don't understand the logic about the gluing surface. To me a dowel is just a rounded mini tenon, and a tenon is like a big square dowel, the surface should make a difference, not the shape. If you take a 1/2 inch dowel and sand it down square to 3/8, does it still applies ? I don't understand why we are losing half of the effective gluing surface with a dowel but it does not apply with a tenon. Any picture maybe ?

I totally agree with you btw that more gluing surface = stronger joint.

Cheers

Martin - read post number 21 in the thread at this link (click on the word "link"). Hopefully, that will make it clearer. The assumption in that post is that the dowel is going into the "side" of a piece of wood. If the dowel is going into the end of a piece of wood, the dowel is all long grain-to-long grain. On a chair, the dowels that go into the chair rail are going into the end of the wood, but the dowels that go into the chair back are going into the side of the wood so half of the surface area is long grain to end grain.

Mike

[Larry Rasmussen]

I also like the Rockler guide Harvey recommends above, it seems to match your intended use and the sale price is frosting. I did have a Dowel Max that I sold a couple years ago, I found it time consuming to align it precisely. Anyway enjoy the project. Larry R, Seattle.

[Brian Brightwell]

I have the Jessem and agree with you Bill. Actually, I bought it on your recommendation.

[Terry Therneau]

I have the Dowel Max and agree that it is a great jig. It's not as clear that I would buy it again given the price. I makes perfect edge glue ups easy, and I reach for it for that chore. I've not been as happy with carcass joinery. For longer dowels the angle has not always been perfect --- perhaps it's just me and I'm pushing at an angle with the drill, but it's not perfectly parallel to the face of the board.
I just built a slot mortiser and am now doing my first project with it. Happy so far; if that's still true at the end I'll write up a description.

Terry T.

[Phil Thien]

[And, come on now, Phil. You're going to justify dowel joints by claiming that M&T joints are not well made and therefore are not as strong as dowel joints???? Using that logic you can justify anything. The only fair test of joinery is to compare two well made joints. And certainly factory made joints, whether M&T or dowels, are going to be well made and well fitted since they're made by machine to very close tolerances. And in those joints we see many more real life failures in the dowel joints than in M&T joints. And it's easy to see why - because dowels do not have as much long grain-to-long grain gluing surface area as M&T joints.]

Interesting. Question:

Is it your feeling that because dowel joints are inadequate where chairs are concerned, that they should be avoided for non-chair projects?

[Mike Henderson]

Interesting. Question:

Is it your feeling that because dowel joints are inadequate where chairs are concerned, that they should be avoided for non-chair projects?

No, in less stressful joints dowels may provide very adequate strength. Note that my contention has always been that dowel joints are inferior to other types of joinery, not that dowel joints should never be used. We probably do a number of things in woodworking that are not always the "best" but allow us to build something quicker, or with what we have on hand, or for any number of other reasons. If dowels are used with an understanding of their limitations they may provide very adequate service.

But given that, I must admit that I avoid dowels because of their limitations. I do not have to build things fast, nor do I have to sell what I make so I lean towards what I feel is the best way of doing joinery.

Mike

[Phil Thien]

...Note that my contention has always been that dowel joints are inferior to other types of joinery, not that dowel joints should never be used. If dowels are used with an understanding of their limitations they may provide very adequate service.

Have you seen any of the articles that compare joint strength? My recollection was that dowels compared very favorably to M&T. Do you think the articles are inaccurate, or feel (as some others do) that over time the seasonal movement of wood components compress the dowels to out of round, which compromises joint strength over time?

Terry T. hit on an excellent point I've experienced myself. And that is, even with the best of jigs, the hole is sometimes not perfectly perpendicular to the surface of the wood. This results in a dowel that is slightly angled. In the worst-case scenario, you get two pieces you're trying to join, with holes angled such that the components torque when you try to assemble them.

The solution is to typically use shorter dowels.

I do on occasion remind myself that projects only need to be strong enough for their intended purpose. An end table need not support a strip-dancer unless I'm expecting strip dancers anytime soon.

[Bill Huber]

Terry T. hit on an excellent point I've experienced myself. And that is, even with the best of jigs, the hole is sometimes not perfectly perpendicular to the surface of the wood. This results in a dowel that is slightly angled. In the worst-case scenario, you get two pieces you're trying to join, with holes angled such that the components torque when you try to assemble them.

I had that problem a little with the angle when I had the DowelMax, it would happen when the nuts would get a little loose on the back side. With the Jessem I have never had it, I think it is the way the reference plate is made. The Jessem is much larger then the DowelMax and it bolted on in a more solid way. I use a lot of 2" dowels with panels and they are flat when assembled.

[Steve Wurster]

I do on occasion remind myself that projects only need to be strong enough for their intended purpose. An end table need not support a strip-dancer unless I'm expecting strip dancers anytime soon.

Well, that's certainly not happening in my house any time soon, unfortunately. I don't think SWMBO would appreciate it.

On a more relevant note, I just built two side tables for my mother and used M&T construction. I'm not an M&T expert so I had the typical fit problems. I used a router to make the mortises so there was also the rounded ends to deal with (on 32 mortises since each table has a shelf!). About halfway through I wondered why I didn't use my Jessem jig since these are only small side tables and won't be subjected to any kind of beating. They're going to sit on both sides of the couch in the basement and just hold drinks and such; dowels would have been sufficient. I really gotta remember that for next time!

[Mike Henderson]

Have you seen any of the articles that compare joint strength? My recollection was that dowels compared very favorably to M&T. Do you think the articles are inaccurate, or feel (as some others do) that over time the seasonal movement of wood components compress the dowels to out of round, which compromises joint strength over time?

All of the joinery tests I can recall had results that were in this order of joint strength (for these four options):

1. Standard mortise and tenon
2. Loose tenon
3. Dowels
4. Biscuits

And, of course, we have the observations of those who repair furniture. While not scientific, the anecdotal evidence points to much greater incidence of failure in doweled joints than in standard M&T.

Finally, there is good reason to believe that the amount of effective glue surface in a joint affects the strength of the joint and standard M&T joints have more effective glue surface than dowel joints.

Mike

[Brian Brightwell]

I saw a test where a bridle joint was actually stronger then a mortise and tendon. Not to many people use a bridle joint.

[mreza Salav]

All of the joinery tests I can recall had results that were in this order of joint strength (for these four options):

1. Standard mortise and tenon
2. Loose tenon
3. Dowels
4. Biscuits

And, of course, we have the observations of those who repair furniture. While not scientific, the anecdotal evidence points to much greater incidence of failure in doweled joints than in standard M&T.

Finally, there is good reason to believe that the amount of effective glue surface in a joint affects the strength of the joint and standard M&T joints have more effective glue surface than dowel joints.

Mike

I will try to address some of your points as I think they are not quite correct:

- First as I said before I agree M&T is the strongest of the joints *BUT*:
the difference is not substantial w.r.t. dowels. All tests results I have seen rank it only 10-20% higher than dowels. Now keep in mind that
using dowels is a lot easier than traditional M&T so for vast majority of joints one can forgive that extra 10-20% extra strength.

- You keep saying that alignment of dowels in a row is difficult. I understand your concern but it's not that difficult at all. I have built car-cases (cabinets) with dowels and not a single miss-alignment.

- And you say:

"Finally, there is good reason to believe that the amount of effective glue surface in a joint affects the strength of the joint and standard M&T joints have more effective glue surface than dowel joints.

That is not always true again. For example compare the following two:

- two rows of 6 dowels of 3/8", with 3/8" space in between each
- A tenon of size 4.125" wide * 1.125" thick

Note that both give you similar width & thickness. Assuming both are 1" deep, tell me which one has more glue surface area?

[Mike Henderson]

- And you say:

"Finally, there is good reason to believe that the amount of effective glue surface in a joint affects the strength of the joint and standard M&T joints have more effective glue surface than dowel joints.

That is not always true again. For example compare the following two:

- two rows of 6 dowels of 3/8", with 3/8" space in between each
- A tenon of size 4.125" wide * 1.125" thick

Note that both give you similar width & thickness. Assuming both are 1" deep, tell me which one has more glue surface area?

It's always possible to come up with a configuration that gives dowels an advantage. For example, suppose you compared three rows of dowels to a mortise and single tenon. The dowels would have greater effective gluing surface.

But I can make a double mortise and tenon, just as you can put two rows of dowels in. If I do that, the M&T has approximately twice the effective gluing surface as the dowels.

Let's look at the mathematics. The surface area of a cylinder (excluding the ends) is 2*pi*r*h, where:

r = radius, which is 3/16" (.1875") in this example.
h = the amount it protrudes into the wood, which is 1" in this example

The area of the dowels will be approximately 14 sq inches, but only half of this is facing long grain, so the effective gluing surface is approximately 7 sq inches.

Six 3/8" dowels with 3/8" between them is 4.125" so one face of a tenon is 4.125 sq inches. Since there are four faces on a double tenon, the total effective gluing surface is approximately 16.5 sq inches.

So the double tenon has approximately twice the effective glue surface of the dowels (actually, a bit more than twice).

Mike