How many dowels do I use?

DustinS

Dustin
Senior User
I am partially through my first major build using rough(ish) lumber and milling it all myself. My major goal is to build the entire table with no screws and so far it has gone pretty well but I have started second guessing myself now that i have to actually make the joint. Just curious to hear from some people who have done this before.

The entire table is built from some reclaimed 6/4 red oak I got for cheap. It will be a 48" trestle table. Here are the sketchup plans:
SketchupImage.png


I have everything cut and now am second guessing how to connect the trestles. My original plan was to use dowels. I would love to have made these mortise and tenon joints but I didn't trust my skills for this large of a project. I have a Jessem dowelling jig (#8350) so I can make pretty accurate dowel joints but I have only used these for 3/4" joint shop furniture so far and haven't tried a joint like this. My worry is that since I can only put the dowels flat on the mitered butt end, I am shifting to a more shear stress than direct stress and losing some strength. The trestles are 2.75" square solid red oak and the center column is 3.25" square solid red oak.

I only have a 3/8 dowelling jig. Has anyone made this joint before? Roughly how many dowels would be strong enough? The actual face of the joint is 2.75" x 4".

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golfdad

Co-director of Outreach
Dirk
Corporate Member
Your dowels are like biscuits. There is no strength they just aid in alignment
 

cpw

Charles
Corporate Member
It appears that you have tight joints with lots of surface contact, so if your planning to use a good wood glue I would thing that a couple of hardwood dowels for alignment purposes should be sufficient. I would be more concerned with how I was going to clamp it while the glue dries.
 

DustinS

Dustin
Senior User
I was under the assumption that a biscuit was only to aid in alignment and gave no added strength, but a hardwood dowel worked similar to a floating mortise and tenon and could add strength to a butt joint. Maybe this was incorrect but I saw it as similar to a festool domino if I used multiple. My worry is that the end joint wont hold unless I add a few dowels. I was thinking at least 5 but i cant find any documentation to help gauge what is needed.

Yeah, the clamping is another issue. I am between using the cutoff blocks (about 4 inches from the glue up with 45 deg miters on the end) or trying to make a small plywood frame to support the clamps on a miter. Any suggestions here would be appreciated as well.
 

DustinS

Dustin
Senior User
Yeah, but unfortunately I blew all of my new tool money on a jointer and planer earlier this year. If you were going to use dominos, how many would you use?
 

cpw

Charles
Corporate Member
Do you have a router? Or a drill and some decent chisels? you could make loose tenons the old-fashioned way, if you want to go that route.


 

DustinS

Dustin
Senior User
Is there that much of an advantage of floating tenon over dowel? It doesn't seem that much different to me to have a single larger floating tenon vs multiple dowels. From what I have seen on the web, the failure rate is pretty close and both far surpass general usage, especially in this case where force will be close to the direction of the dowel, not drawing against it. But again, I am pretty new to joinery that isn't pocket holes or 3" wood screws.

Whatever joint I use it has to be pretty accurate and I have to cut it 16 times, so I think I'm too afraid on this project to try the router loose tenon method and I was too intimidated to try and hand cut them from the start. I wasn't sure how to keep the mortise on the proper miter angle and align everything when doing by hand. Or to be more proper, I had a clue how I thought I could do it, but was pretty sure I couldn't do it 16 times and keep tight joints.
 

Oka

Casey
Corporate Member
Besides helping with alignment, dowels can improve shear resistance. Just depends whether this piece really needs it or not. Anything that attaches and secures perpendicular to a connection will, whether it be a nail screw or bolt. The Japanese have done quite a bit of research on this and you can find their engineering testing results on the web showing their means and methods....... and of course comparing different types of dowels and even the orientation of the grain performance. That is if you are in to the "mechanical math-ie" analysis... ;)
 

cpw

Charles
Corporate Member
Alignment is a major function of both dowels and loose tenons, and both provide more glue surface, but if you're looking for a mechanical joint that offers strength, a loose tenon CAN be the better option.
The advantages I can think of right now:
A loose tenon can be whatever size you deem appropriate, so it can be much thicker, hence much stronger. A dowel joint is based on the size holes you can drill and your dowels fitting that hole appropriately.
With loose tenons, usually only the fit of the width of the tenon is important, so you can have some room to fidget with the length of the mortises.
Again, though, if you use a good wood glue, have tight joints and can clamp them well while the glue dries, dowels vs. tenons is almost moot. A good glue joint will outlast you and your children.
 

cyclopentadiene

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I have used Mortise & tennon, Dowels, loose tennons and more recently Dominos. I typically use 1 true tennon, two large dowels loose tennons or Dominos if using 8/4 stock (2 will not fit easily with 4/4). I
The only joint tat ever failed was a desk that I built for my daughter. It was a unique design (posted in my gallery). It worked fine for about 1 year and she purchased a 36” curved screen monitor which was really heavy. Due to the weight and all of the stress on the back two legs, the joint failed. I also used system 3 structural epoxy in the winter so it may not have cured properly.
the fix was to add a butterfly joint on each side of the attachment. That repair was 3 years ago

based on tge design you posted, i do not think tgere will be a lot of stress on the Joinery and you should ve fine with Dowels. Worst case you have to make a repair later. Good reason to use Waterlox finish!
 

DustinS

Dustin
Senior User
Okay, so it seems like I should make sure my joints are tight, drill a few dowels (maybe 5 to be safe) and stop overthinking things. Thanks for everyone's help.
 

llucas

luke
Senior User
Well, this is an interesting discussion, and I am inclined to agree with Fred regarding the value of dowels....but I think I would use the biggest ones that would fit easily and prolly use at least 4 on each joint (more if its easy to do).
My opinion (and it is only that) is based on having used lots of dowels without problems and a review of a few "studies" seen on-line.
Here is a typical video that may give you confidence that your plan to use dowels is a solid one.
 

Pop Golden

Pop
Corporate Member
Hi Fred, Here's some more horsepucky! I don't understand the bit about biscuits not having strength I have used them for years as have the furniture industry. They are compressed so they swell with glue and a very tight joint is obtained. They do a whole lot more than Alignment.

Pop
 

cyclopentadiene

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Design is the key factor. The table that Dustin has designed would have very little stress on the angled supports. I am assuming the base is a lap joint which is very strong. Dowels, glue and screws will hold the vertical support in the center post stable and the angles pieces just add additional support. There should be limited stress on these pieces. The support supports are similar as it appears the center support goes to the top. This design should be structurally strong and biscuits, dowels, dominos or M&T would all work fune for the joinery.
Maloof style tables use a 45 degree for theupper and lower legs and dowels. I have switched to dominos because it is much easier to align and the process is so fast.
I have made several pieces using dowels with no issues. However, i am on my third Dowel max as over time these seem to lose center making alignment difficult. My second one out of the box required a puece of duct tape on one side to make the dowel fit exactly in the center. I find it really time consuming to set up the drill press at angles and use Dowel centers. The process takes an hour per joint versus 5 minutes with a Domino. This is especially useful with complex angles. My Esherick music stand would have been very difficult without a Domino.
Noone ever sees the magic behind the joint (hopefully) so why spend hours on it.
My one failure was a very unusual design which should have been a M&T joint and pegged. Due to the weight distribution, it may still have failed.
 

FredP

Fred
Corporate Member
Hi Fred, Here's some more horsepucky! I don't understand the bit about biscuits not having strength I have used them for years as have the furniture industry. They are compressed so they swell with glue and a very tight joint is obtained. They do a whole lot more than Alignment.

Pop
Agree'd It started as a sales pitch to sell fussy tools. :p
 

marinosr

Richard
Senior User
Is there a reason you're not going to have cross members that join the central pillar to the slanted cantilever supports? That sure would negate any potential problems with dowels. You're not planning on attaching the top to the angled supports, are you? If so, you're going to split those dowel joints wide open with wood expansion and contraction, no matter how many dowels you use.
 

drw

Donn
Corporate Member
 

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