Dowel Jig Question

[Art Mann]

Like you, I have repaired several chairs over the years that were doweled together. Perhaps you fix more of that kind of failure because there are so many more chairs built that way. All the failed dowel joints I have fixed were originally constructed using hide glue and undersized and short dowels. What do you think might have happened if those makers had used long large diameter dowels and epoxy or PVA for an adhesive? When I make new furniture, I don't have either of those problems. I just don't think your chair repair experience can be used to conclude that dowel joints are a substandard joinery technique. What do I know? I have only been using dowels to build furniture and cabinets for 40 years without any failures so far. Maybe all that stuff will fall apart tomorrow.

[Jim Dwight]

I've reviewed both the FWW and Wood joint strength tests and re-reviewed the Woodgears test this morning. I agree with Mike that the long grain area that is glued to both pieces is the best indicator of strength. I checked a few of the joints in either the FWW or Wood tests (can't remember which) and it explained their results well. The tests are somewhat flawed because they pretend to tell us which joints are best but the contact areas are quite different affecting the tests more than the joint construction. In one of the tests, they used a loose tenon about the same size as the traditional mortise and tenon. It failed at almost exactly the same force as the traditional. But the domino joint failed much earlier because it was much smaller.

Woodgears original result was about 25% less strength in a dowel joint as compared to a mortise and tenon. Then he got leaned on my Dowelmax and retested with a smaller tenon and got closer but the M&T was still stronger. I think 25% is about right. I think Mike is also right that in many cases this won't matter. But for chairs, I wouldn't use dowels. If nobody leans back, the dowel joints will probably work right. But in a light chair, with heavy people that do lean back, I want M&T. I have 4 chairs built this way as does my daughter and they've support 300 lb people with no issue. My son has four that are a little bigger cross section (due to the design he wanted) and they are working well too.

I wouldn't spend $300 on a dowel jig, I spent a little less on a Jet hollow chisel mortiser. With it and a shoulder plane + my table saw I can make M&T joints quickly enough. My lighter chairs actually have mortises made with a plunge router and jig. The routed mortises are nicer but Woodgears also tested M&T joint fit and found it didn't affect strength (within reason).

If you are going to get good at a few joints, M&T seems a better way to go to me than dowels. But if you want to go dowels, just be a little careful in the design. For drawers, I am setup to do machine dovetails because they are the best joint for that application. I doubt I will get good at every joint but I decided to get set up and reasonably proficient at the joints that I think are best.

[mreza Salav]

Every joint making tool has its own place and applications. I have both version of Jessem doweling jig, have had both versions of Domino, and a tilting head mortiser (sold that one actually). Most often I use Domino but there are situations (like a big entry door) where I'd use a true M/T. I also still use dowels as that gives me the most accurate joint of all IMO (for example, I had to join some walnut plywood in width to get a 80" wide section and dowels gave very flush surface that required no sanding of the seam). For my passage doors I used 1/2"x5" dowels (32 of them in a door) and I think they are as strong as any other joint.

[Mike Henderson]

Like you, I have repaired several chairs over the years that were doweled together. Perhaps you fix more of that kind of failure because there are so many more chairs built that way. All the failed dowel joints I have fixed were originally constructed using hide glue and undersized and short dowels. What do you think might have happened if those makers had used long large diameter dowels and epoxy or PVA for an adhesive? When I make new furniture, I don't have either of those problems. I just don't think your chair repair experience can be used to conclude that dowel joints are a substandard joinery technique. What do I know? I have only been using dowels to build furniture and cabinets for 40 years without any failures so far. Maybe all that stuff will fall apart tomorrow.

The failures I see are not glue failures - it's the wood that the dowel attaches to that fails. And most of the doweled chairs that I repaired were factory made and the dowels were fully inserted into the holes, and I have no reason to suspect the fit was not good when they were first made.

No matter how you slice it, if you do the math, you'll see that a tenon that fits into the same space as the dowels will have more long-grain-to-long-grain surface area and that's the best indicator of the strength of a stressed joint, such as you see on the back of a chair.

But this is easy for anyone to test for themselves - there are many, many commercially made chairs with two dowels in that joint. Offer to repair one of those chairs for a friend. Take the joint apart and look at the dowel that you pulled out of the hole that failed. It will have wood sticking to the dowel, and the hole will be larger than the dowel because of the wood pulled away from the back support. If you put another dowel of the same size in that hole, it will rattle around.

Make a mortise in that location and in the seat side rail and put in a loose tenon that is as wide as the outside spacing of the two dowels, and as deep as the dowels were. Glue with your choice of glue and return to your friend. I'll bet your friend never brings that chair back to you (but they will bring the rest of the set to you to repair ).

Incidentally, the Domino works great for these mortises. If you want a mortise wider than normal for the Domino, just move the tool over and plunge again. You can make your own loose tenons or glue two Dominos together to make a wider tenon.

Mike

[That particular joint on a chair is an excellent "real world" test of joinery in a long-term high stress environment.]

[Sean Tracey]

I guess the first question I have is will this be the only project you plan to use it on?
If so then just about any of the Dowel It type jigs will work just fine, now if you plan to use it for a lot of different projects then a better jig would be the best.

I have had the DowelMax and now have the Jessem, I like using dowels and for me the Jessem was much better and easier to work with. Both jigs work about the same way but the DowelMax requires shims were the Jessem does not when using different thickness of wood, which I really like.

Both jigs use a reference end and surface for placing the jig which is very accurate.

I will have to disagree with Mike on dowels, I think they are very good for all types of joinery and for panels when used with a good jig are great for alignment, spot on every time. Dowels are much faster then other methods and the strengths is just about as good, from the testing that I have seen.

Here is my write up on the Jessem. http://www.sawmillcreek.org/showthre...m+doweling+jig

I agree on the advantages of dowels. The Jessem Paralign and the Dowel Max make very good joints and are both able to be used in many different situations. My favorite jig is the Jessem Paralign, but I think they stopped making it. If I couldn't get a Jessem Paralign, I would probably opt for the Dowel Max.

[Jim Dwight]

Another simpler way to look at the strength question is to observe who tells you what. The ONLY people saying dowels are stronger are the companies who sell dowel jigs. The other tests say they are one of the stronger joints but not the strongest. In other words, a pretty good joint.

[Roger Marty]

I have this Woodcraft jig and I think it is great:

http://www.woodcraft.com/product/124...eling-jig.aspx

As far as doweling vs. M&T-- I love the ease and speed of dowel joints. I made 12 web stretcher frames using dowel joints since to me it seemed like the extra strength of M&T didn't matter (and they were then dadoed into a solid carcass). But for a post-and-panel dresser I'm starting, I'll go with M&T because those joints will bear the full weight of the drawers.

[Sean Tracey]

R. Bruce Hoadley (of the books "Understanding Wood" and "Identifying Wood") wrote an article in an early FWW magazine where he analyzed the failure of joints, such as the joints on the rear of chairs. His conclusion was that the failure was due to wood failure and not glue failure. That is, the wood separated at the joint - there was a thin layer of wood still attached to the glue (I've seen this in failed joints).

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

I think you reached a conclusion that is not always correct. The wood failed, not the glue. So you propose to add more glue area. The glue area was obviously large enough that the wood itself broke somewhere. When you make a mortise and tenon joint in wood, you reach a point where the tenon is so large that it weakens the joint because the walls of the mortise are too thin. Conversely, you can make a mortise and tenon joint where the walls of the mortise are quite strong but the tenon is not strong enough. Since wood is not a homogenous material and since different loads will cause vastly different breaking strenghts depending on load type and direction, there is a lot of variability in what makes a given joint the strongest. Proportions and wood grain can cause unexpected results.
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In general, Mortise and tenon are quite strong joints. However, Dowel joints are easy to make with the new jigs from Jessem and Dowelmax. I've made cabinets with strings of dowels several feet long and every single one of them fit perfectly. Dowel joints are very useful in casework where the alignment they provide is a huge benefit. Dowelmax and Jessem can be used to position the dowel holes in both directions to extreme accuracy due to repeater bars and positioning the next set of dowel holes incrementally off the last set. You can use these jigs to replicate the work of a multi-spindle drilling machine used to make cabinet case work.

As a young man, I learned the importance of roundness and precision location. My boss had designed a metal stamping die that did not use dowels to locate the parts of the die. Instead it used the outside of the die parts which were sort of trapezoidal to fit in a trapezoidal mortise to high precision. It was damn near impossible to assemble. Had it been made with dowel positions, it would be much easier to align the parts of the die and press them together with a lower likelihood of cocking the parts.

Dowels add a mechanical lock due to the swelling of the compressed material while mortise and tenons have clearance and no compression as cut. So a straight mathematical calculation of glue joint surface area doesn't tell you the complete picture.

So as far as joints go, dowels, loose tenons, and M&T all have their place and dowels may surprise you in strength compared to loose tenons and M&T depending on the joint and the particular pieces of wood being joined. I can definitely see a well designed dowel joint beating loose tenons and M&T joints at least occasionaly depending on the joint and wood involved.

[John Lankers]

Mike, Art, I think you both are raising valid points here. A m/t joint is usually laid out and executed with great care and a dowel joint, which can also be very strong when done properly, is often chosen to save time and it is easier to do for lesser skilled workers in a factory setting.
However, when I picture a 2 x 4 and a 2" dowel, which could be compared to a tenon and a dowel in furniture construction, the 2 x 4 would be much stronger than the 2" dowel when used as a lever.

[jack duren]

I started using dowels in a cabinet shop in 83. Love em, but I know better in certain situations. Anyone can argue but experience tells you whether this or that is appropriate especially when it comes to keeping a roof overhead.

I still to this day, use my trusty Craftsman dowel jig. It was used when I bought it from an old woodworker when he died in 83 and his family sold off his shop. If you want one on the cheap these work fine. I use to use the doweling machine in the day. Like to have one...
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[Mike Henderson]

I think you reached a conclusion that is not always correct. The wood failed, not the glue. So you propose to add more glue area. The glue area was obviously large enough that the wood itself broke somewhere. When you make a mortise and tenon joint in wood, you reach a point where the tenon is so large that it weakens the joint because the walls of the mortise are too thin. Conversely, you can make a mortise and tenon joint where the walls of the mortise are quite strong but the tenon is not strong enough. Since wood is not a homogenous material and since different loads will cause vastly different breaking strenghts depending on load type and direction, there is a lot of variability in what makes a given joint the strongest. Proportions and wood grain can cause unexpected results.
l
In general, Mortise and tenon are quite strong joints. However, Dowel joints are easy to make with the new jigs from Jessem and Dowelmax. I've made cabinets with strings of dowels several feet long and every single one of them fit perfectly. Dowel joints are very useful in casework where the alignment they provide is a huge benefit. Dowelmax and Jessem can be used to position the dowel holes in both directions to extreme accuracy due to repeater bars and positioning the next set of dowel holes incrementally off the last set. You can use these jigs to replicate the work of a multi-spindle drilling machine used to make cabinet case work.

As a young man, I learned the importance of roundness and precision location. My boss had designed a metal stamping die that did not use dowels to locate the parts of the die. Instead it used the outside of the die parts which were sort of trapezoidal to fit in a trapezoidal mortise to high precision. It was damn near impossible to assemble. Had it been made with dowel positions, it would be much easier to align the parts of the die and press them together with a lower likelihood of cocking the parts.

Dowels add a mechanical lock due to the swelling of the compressed material while mortise and tenons have clearance and no compression as cut. So a straight mathematical calculation of glue joint surface area doesn't tell you the complete picture.

So as far as joints go, dowels, loose tenons, and M&T all have their place and dowels may surprise you in strength compared to loose tenons and M&T depending on the joint and the particular pieces of wood being joined. I can definitely see a well designed dowel joint beating loose tenons and M&T joints at least occasionaly depending on the joint and wood involved.

Well, you can believe what you want but on chairs, in that back joint, doweled joints fail on a regular basis, and loose tenon (or full M&T) joints rarely fail. I haven't had to repair a chair with a M&T joint in that location but part of the reason is that there are few commercial chairs that are made with M&T joinery there.

As I've said many times earlier in this thread, dowel joints can be used quite successfully in many places in furniture making - but M&T joints are stronger and should be chosen for high stress locations. Specifically, the back joint on a chair and the attachment of the legs to the apron on a table (people grab a table and drag it to a new location. The length of the leg causes great stress to the joint where the leg joins the apron.)

Mike

[It's unlikely that you would "weaken" the joinery members by putting in a M&T. In a chair, for example, the back member will be over an inch wide and we usually put in a 3/8" thick tenon. Additionally, for most M&T joinery, we do not go completely through the member. And, in any case, we do not see joinery failure in chairs and tables where the joinery member breaks. For chairs with dowels, we see the dowels pull out of the back member. For chairs with M&T, I haven't seen any failures in that joint but neither have I seen a chair back break off, leaving a stool.

For tables, the legs are generally much larger, perhaps as much as 4" at the top. The apron is generally 3/4" material and the tenon is again generally 3/8" thick. I've never seen a leg break off from the mortise "weakening" the leg, but I have seen dowels pulled out of the leg.

Your concept of a mortise "weakening" a joint by putting a mortise into it simply does not hold water. We just don't see joinery members breaking because of well made M&T joinery.]

[Brian Brightwell]

Good write up Sean.

[jack duren]

Good write up Sean.

Really....I'll side with Mike on this one..

Let the party begin..............
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[Glenn de Souza]

When you make a mortise and tenon joint in wood, you reach a point where the tenon is so large that it weakens the joint because the walls of the mortise are too thin. Conversely, you can make a mortise and tenon joint where the walls of the mortise are quite strong but the tenon is not strong enough. Since wood is not a homogenous material and since different loads will cause vastly different breaking strengths depending on load type and direction, there is a lot of variability in what makes a given joint the strongest. Proportions and wood grain can cause unexpected results.

You've touched on an interesting and valid point. When joining two members, there is a balancing act between the size of the joint and the weakening consequence of removing wood to make way for the joint. This doesn't have to do with the dowel vs. M&T debate that is going on here but has to do with optimal joint design using either approach, or any joinery method for that matter. The 1/3 thickness tenon rule was mentioned earlier in this thread which is a good rule for M&T.

I enjoy seeing these tests that measure the lever force exerted on a right angle joint to see where the breaking point occurs. However it's important to remember that a properly designed piece of furniture will create an assembly that should not be exposed to bare levered force like that. Even a table apron without a stretcher is secured in two directions (planes) so it would need to break in two places at least, and maybe three or more. This is not to mention the incidental racking support of the top which is secured to the apron/leg assembly using your attachment method of choice (although I will agree, the chair back situation that Mike is referencing is a particularly stressful joint).

This is why both joinery methods if well made and properly glued should be more than adequate for most appropriate applications. This is also why I believe design has more to do with failure than joinery method unless the joinery method really violates rules and good sense. Otherwise we are probably splitting hairs between each other in terms of strength.

I like using conventional M&T, loose tenon M&T,and I happen to have a Jessem Dowel jig which I think is unbelievably accurate and efficient to use. I've never seen one of my dowel joints fail, but then I've never seen one of my own M&T joints fail either. Everyone is entitled to their personal favorite method. Some prefer Ferraris, some prefer Corvettes. They're both pretty fast.

Since the original post has to do with dowels and dowel jigs, here's a question that I've always wondered about - Which situation would be better/stronger? Using fewer longer or larger dowels, or using more smaller dowels? For example, in a joining two 3/4" thick pieces, if you had the choice of four 3/8" diameter dowels in a row vs seven 1/4" diameter dowels staggered in two rows like Jessem shows, which would be your choice?

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[Jerome Stanek]

I have the one like the Wood Craft one and when was out of town I needed it but left it home. I went to Harbor Freight and they had the same kind but for about $15 instead of the $66 that works just as good. That is the one I carried when I traveled