Domino Glue-Up Tutorial?

[Matthew Schenker]

Everyone,
Would any of you Domino experts be willing to create a text/visual tutorial about good general practices for Domino glue-ups?

In several discussions, we've talked about various Domino joints.  But I'm wondering about addressing the following points (or any other relevant points) that apply to all Domino joints:

• How much glue to apply to the Domino itself (show what it looks like)
• Where to apply the glue (on the Domino, in the mortise)
• Whether to spread the glue
• What the squeeze out from a proper Domino joint should look like

When using the Domino, I've asked myself these questions.  I know there are people here who could put these questions to rest!

Thanks,
Matthew

 

[Dave Ronyak]

I have not tried this yet, but use of a brush corresponding to the width of the domino should speed up applicaton of the glue.
Dave R.

 

[Matthew Schenker]

Dave,
Good point about the glue brush.  My idea here is to illustrate the "best practices" with Domino glue-ups.

Anyone else have general suggestions on the points mentioned?

Thanks,
Matthew

 

[Jerry Work]

Hi Matthew,

No great secrets here.  Use a solder brush (rolled metal handle with black bristles), dip it in glue and roll it around inside both mortises.  The "trick" is to fully coat the sides of the mortises.  Now swipe the brush on both sides of the Domino up half its length holding it by the half without glue.  Insert into one mortise and drive the Domino all the way to the bottom of that mortise.  Use a hammer or mallet if you need to.  That will cause glue to squeeze up the groves insuring a really good glue joint on that side.  Use the brush to pick up the puddle of glue around the base of the domino and spread that on the other half of its length and on the mating faces of the work piece.  Now make the joint and clamp it so the mating faces are nice and tight together.  You can remove the clamps after about five minutes or so as long as you do not stress the joint for at least an hour.  As you make the joint the glue on the mortise walls and on the edges of the Domino will get sticky very quickly holding the joint together without spring back.  If there is a back side to the piece that will never be seen shoot a micro pin that penetrates the outside edge of the joint into the mortise and through the Domino by half of the other wall thickness.  That pin will make sure the joint stays tight while the glue dries as it prevents the Domino from pulling out of the mortise even if you inadvertently apply stress to the joint too quickly.  On soft woods let the first application of glue in the mortises soak in for about five minutes and reapply glue before pushing the Domino all the way home in one side of the joint.  Whatever you do, do not try to make the joint by pushing the Domino part way into one mortise and then putting the other end into the other mortise and expect to clamp your way to success.  What will happen most often is glue will be scraped off the edges of the Domino and puddle around the base on both sides and will puddle up at the bottom of the mortises.  As the mating faces come together these two puddles at the base of the mortises and around the base on the mating faces will act like a hydraulic lock and the joint likely will not go all the way together even if it looks like it did.  That hydraulic action may also cause spring back pushing the joint apart while the glue dries.  So, rule of thumb is make one half of the joint first by fully seating the Domino in that mortise, then make the other side of the joint.  Since the Domino is shorter than the nominal mortise depth marked on the Domino machine, fully seating the Domino in one mortise will create a large enough reservoir area at the bottom of the other mortise to prevent the puddle from causing the hydraulic lock.  On the issue of which width of Domino to use I find a Domino half the thickness of the wood to work well for most hard woods.  That creates a joint with roughly the same total wall thickness on the work piece as on the Domino.  On soft woods that do not have the wall strength of hard woods the more traditional one third will usually work a bit better.  On thicker work pieces two thinner Dominos placed side by side I find stronger than one thicker Domino - same for any other M&T or loose tenon joint.  Hope this addresses your question.

Jerry

Everyone,
Would any of you Domino experts be willing to create a text/visual tutorial about good general practices for Domino glue-ups?

In several discussions, we've talked about various Domino joints.  But I'm wondering about addressing the following points (or any other relevant points) that apply to all Domino joints:

• How much glue to apply to the Domino itself (show what it looks like)
• Where to apply the glue (on the Domino, in the mortise)
• Whether to spread the glue
• What the squeeze out from a proper Domino joint should look like

When using the Domino, I've asked myself these questions.  I know there are people here who could put these questions to rest!

Thanks,
Matthew

 

[bruegf]

Jerry,

I've found that a small, thin, narrow stick is quicker and easier than a brush to spread glue inside the mortise.  My father just showed me that trick this last week (right after a bought a large bag of solder brushes).

Fred

 

[Lou Miller]

On the issue of which width of Domino to use I find a Domino half the thickness of the wood to work well for most hard woods.  That creates a joint with roughly the same total wall thickness on the work piece as on the Domino.  On soft woods that do not have the wall strength of hard woods the more traditional one third will usually work a bit better.  On thicker work pieces two thinner Dominos placed side by side I find stronger than one thicker Domino - same for any other M&T or loose tenon joint.  Hope this addresses your question.

Jerry

I'm not trying to be a smart @$$ with this question, I'm just really curious. Jerry, did you happen to advise the people who did the testing on joint strength for that magazine about how to use the Domino?

I've been wondering about that since that test came out, and I can't help but think the Domino scored as poorly as it did because they used too thick of a domino. You say to use 1/2 the thickness, but my own experiments are proving that to be a bad idea. In the case of a 3/4" work piece, 1/2 the thickness would be 3/8" or roughly a 10mm tenon. Using that thickness is going to leave the sidewalls of your mortises at 3/16". When that joint starts to have stress put on it, by far the weakest part will be the 3/16" sidewalls.

In all of the testing done on the Domino in the magazine article, it was never the joints that failed, it was the wood just outside the joints. However, the other joints (dowels, and M&T) tested had the wood surrounding the joints hold under a lot more force. Its my belief that using a thinner Domino would have made an enormous difference in those tests because a larger domino weakens the surrounding wood too much.

I've been making a bunch of frame and panel wainscoting over the last few months, as well as a good bit of cabinetry. I've been using dominos for all the joints and I've been using it almost every day. What I'm finding is that joints made with 8mm and 10mm tenons in 3/4" stock end up being fairly weak. I discovered this when I realized I had to rip out a frame that I goofed on. I used 10 mm tenons and the joints were ridiculous easy to break while ripping it out. I decided to start using 6mm tenons instead and did quite a bit of tests on them. Granted, nothing scientific, just stupid things like standing on top of things that I assembled to see if they would hold.  Joints with 6mm and 5mm tenons hold very well, but the joints with 8mm and 10mm break quite easily in 3/4" stock. Most often, its the sidewalls of the mortises, or the wood just beyond the end of the mortise when I see failures.

I'm just curious where you are coming up with your 1/2 thickness theory and whether you'd care to elaborate on how you came to that conclusion? No disrespect is intended with this post, I just simply disagree with you.

 

[Jerry Work]

Hi Fred,

My only issue with using a stick instead of a brush is that with a stick the glue may just roll down the inside walls of the mortise instead of really being distributed evenly over those critical surfaces.  At least when I have tried a stick in the past I found myself needing to be more observant and therefore taking longer than when I just roll the brush around inside the mortise.  Six of one, half a dozen of the other I guess.

Jerry

Jerry,

I've found that a small, thin, narrow stick is quicker and easier than a brush to spread glue inside the mortise.  My father just showed me that trick this last week (right after a bought a large bag of solder brushes).

Fred

 

[Jerry Work]

Thanks Lou,

No disrespect taken.  My experience is that the wood and the way it was milled makes more difference in resulting strength than the other factors.  For example, red or white oak is often used for such tests.  In most cases the long grain wood fibers along side and even with the bottom of the mortise will separate as the point of failure if the joint is at the end of one piece.  If the joint is in the center of that same piece of wood the point of failure may well shift to the long grain of the mating piece.  In both cases the loose tenon stays firmly attached to the walls of the mortise but the surrounding grain gives way as it is relatively weak on woods like red and white oak.  Shift to Oregon Black oak, Tan oak, Chinquapin, or Australian silky oak and the same joints will behave very differently as the strength of the long grain bond in the wood itself is much higher.  Any of the dense resinous hard woods will likely stay together and fail only when the glue bond is sheered between the mortise wall and the sides of the loose tenon.  Usually, the failure is the bond on the mortise wall side since it is so slick and the wood pours are crushed by the machining of the mortise.  If you need extreme strength in such cases take the time to use a Dremel tool or such to abrade the sides of the mortise and assemble those joints with epoxy.  Now the failure, when it finally does occur, will take place by tearing the long grain fibers of the loose tenon, not the wall of the mortise.  So, my experience says one size does not fit all.  In most cases whether you use a one third or one half width loose tenon the assembled piece (made up of multiple such M&T joints) will be more than strong enough for nearly any furiture application.  I did talk with the editors of that mag before they published their results.  They said they applied the glue as I suggested and still found failure with the 5mm Dominos.  They attributed the failure to the tight fit of the Domino scraping the glue off the walls of the mortise.  I suggested they test that hypothesis by abrading the walls of the mortise first and then applying the same test.  They did not do that as far as I know and simply reported the pull out/glue failure issue.  I also noted in the published article that they show assembling the joint by inserting the Domino partially in both mortises and then trying to clamp the joint.  As I posted earlier, that in my experience leads to hydraulic lock issues often with a joint that never did properly make and which may well have hydraulic stress trying to push the joint apart.  I do not know how they actually assembled the joints used for the university testing.  The university testing that followed showed failure in the work pieces near the bottom of the mortise and not failure in the glue joint between the mortise wall and the loose tenon (aka Domino) but the pics did not show the reservoir at the bottom of the mortise so we don't know if one side was fully seated before the joint was pulled togehter.  I noticed that the first batches of Dominos I received before the introduction of the device into the US market did not have stamped ridges, they were just slick.  If the magazine used those, part of the issue might have been the glue slipping on those slick faces.  Hard to tell in a telephone conversation.  Anyway, all the theoretical testing aside, loose tenons make very, very strong joints partially because the shoulders are always "perfectly" formed, unlike a conventional M&T where the shoulders may or may not be a good fit with the mating work piece.  A final point on the tenon thickness vs wall thickness issue.  Once a good glue bond is formed between the walls of a well cut mortise and the faces of a well fit loose tenon the two act as a single piece and something other than the glue line gives first - usually the long grain bond on the work pieces themselves.  Using the one half thickness size on hard woods means the two walls collectively and the tenon are the same overall thickness and hence should (all things being equal - which they never are) have similar strength.  Using the one third size means the two walls collectively are twice the thickness of the mortise and helps overcome the difference in long grain strength of soft woods vs hard woods (other than red/white oak and many of the woods now sold as "mahogany" which both have relatively weak long grain strength). 

Jerry

On the issue of which width of Domino to use I find a Domino half the thickness of the wood to work well for most hard woods.  That creates a joint with roughly the same total wall thickness on the work piece as on the Domino.  On soft woods that do not have the wall strength of hard woods the more traditional one third will usually work a bit better.  On thicker work pieces two thinner Dominos placed side by side I find stronger than one thicker Domino - same for any other M&T or loose tenon joint.  Hope this addresses your question.

Jerry

I'm not trying to be a smart @$$ with this question, I'm just really curious. Jerry, did you happen to advise the people who did the testing on joint strength for that magazine about how to use the Domino?

I've been wondering about that since that test came out, and I can't help but think the Domino scored as poorly as it did because they used too thick of a domino. You say to use 1/2 the thickness, but my own experiments are proving that to be a bad idea. In the case of a 3/4" work piece, 1/2 the thickness would be 3/8" or roughly a 10mm tenon. Using that thickness is going to leave the sidewalls of your mortises at 3/16". When that joint starts to have stress put on it, by far the weakest part will be the 3/16" sidewalls.

In all of the testing done on the Domino in the magazine article, it was never the joints that failed, it was the wood just outside the joints. However, the other joints (dowels, and M&T) tested had the wood surrounding the joints hold under a lot more force. Its my belief that using a thinner Domino would have made an enormous difference in those tests because a larger domino weakens the surrounding wood too much.

I've been making a bunch of frame and panel wainscoting over the last few months, as well as a good bit of cabinetry. I've been using dominos for all the joints and I've been using it almost every day. What I'm finding is that joints made with 8mm and 10mm tenons in 3/4" stock end up being fairly weak. I discovered this when I realized I had to rip out a frame that I goofed on. I used 10 mm tenons and the joints were ridiculous easy to break while ripping it out. I decided to start using 6mm tenons instead and did quite a bit of tests on them. Granted, nothing scientific, just stupid things like standing on top of things that I assembled to see if they would hold.  Joints with 6mm and 5mm tenons hold very well, but the joints with 8mm and 10mm break quite easily in 3/4" stock. Most often, its the sidewalls of the mortises, or the wood just beyond the end of the mortise when I see failures.

I'm just curious where you are coming up with your 1/2 thickness theory and whether you'd care to elaborate on how you came to that conclusion? No disrespect is intended with this post, I just simply disagree with you.

 

[Mike_Chrest]

For applying glue to the inside of the mortise, and joint strength isn't critical, I like using the Fastcap Glue-bot(cool name) ;D It also works at any angle, for joining stuff up on a wall or overhead.
http://www.amazon.com/FastCap-Glu-B...0-4449650?ie=UTF8&s=hi&qid=1187562564&sr=8-13

The "Yorker" tips allow you to accurately run a bead along the inside edge of the mortise really quick.
http://www.amazon.com/FastCap-Glu-B...4004470-4449650?ie=UTF8&qid=1187562849&sr=8-1

Want more strength(takes longer), acid brush the Domino, more still, what Jerry says.

 

[Brice Burrell]

I agree with Mike. 
  I have a few glue-bots, great product. Squeeze the bottle and the right amount of glue comes out, a vacuum pulls the glue out. No more turning the bottle upside down and shaking to get the glut to the tip. If you see them a store or if you are ordering something from Amazon, make sure you buy one or more. Worth the $6 USD. They also sell a smaller glue-bot, get it too.

 

[Dave Ronyak]

... No disrespect taken.  My experience is that the wood and the way it was milled makes more difference in resulting strength than the other factors.  For example, red or white oak is often used for such tests.  In most cases the long grain wood fibers along side and even with the bottom of the mortise will separate as the point of failure if the joint is at the end of one piece. If the joint is in the center of that same piece of wood the point of failure may well shift to the long grain of the mating piece.  In both cases the loose tenon stays firmly attached to the walls of the mortise but the surrounding grain gives way as it is relatively weak on woods like red and white oak.  Shift to Oregon Black oak, Tan oak, Chinquapin, or Australian silky oak and the same joints will behave very differently as the strength of the long grain bond in the wood itself is much higher.  Any of the dense resinous hard woods will likely stay together and fail only when the glue bond is sheered between the mortise wall and the sides of the loose tenon.  Usually, the failure is the bond on the mortise wall side since it is so slick and the wood pours are crushed by the machining of the mortise.  If you need extreme strength in such cases take the time to use a Dremel tool or such to abrade the sides of the mortise and assemble those joints with epoxy.  Now the failure, when it finally does occur, will take place by tearing the long grain fibers of the loose tenon, not the wall of the mortise.  So, my experience says one size does not fit all.

Jerry ]

Jerry,

I am seeking clarification of your reference in the quote above to failure or weakness of the long grain bond.  What do you mean by "long grain bond strength?"  Are you talking about the resistance of the wood fibers to transverse tensile shear loading?  In a typical M&T joint connecting an apron of a table to a corner leg of that table, the lengthwise grain or fibers of the wood used for the apron and the tenon (whether a domino or integrally formed of the wood of the apron) will be oriented parallel to the length of the apron (horizontal when the table is in use)), whereas the lengthwise grain or fibers of the leg will be oriented parallel to the length of the leg (vertical when the table is in use), and thus the fibers of the leg will be oriented at right angles to the fibers of the tenon.  As a result, when a vertical load is placed on the apron away from the M&T joint, or force is applied to pull the apron straight out of the mortise in the leg, the fibers of the sides of the mortise in the leg will be subjected to a shearing stress that is oriented perpendicular (at right angles to) the lengthwise direction of the leg and wood fibers of the leg, effectively trying to split the wood of the leg with the force concentrated at the ends of the tenon (assuming the sides of the tenon are securely gripping the sides of the mortise).  So, is weakness of failure of the long grain bond simply another way of characterizing the relatively low resistance of the wood to splitting?

To me, the observed improvement upon use of a pair of smaller tenons spaced across the thickness of the apron makes sense because the total load applied to the joint is less per unit area, i.e.. it is distributed over a greater area of wood fibers associated with the mortise in the leg, especially those at the base of the mortise.  Also, with such a pair of spaced tenons, any side bending loading, e.g. caused by pushing the table frame by one of its legs without any top being attached, helps to convert some of the bending loading that would be experienced by a single centered tenon into tension and compression loading in the pair of spaced tenons.

I think this discussion also leads to confirmation that the strongest joints probably are through M&T joints in which the protruding part of the tenon is wedged or pinned.  The resistance to pull out of such a joint does not rely on the resistance to splitting of the piece forming the mortise.

Dave R.