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Tenon length, will this work?

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Forum topic by Eric_S posted 03-21-2010 09:35 PM 3204 views 0 times favorited 14 replies Add to Favorites Watch
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Eric_S

1521 posts in 1950 days


03-21-2010 09:35 PM

Please forgive my noob status.

So I made all the tenons yesterday for the nightstands on the bandsaw. This went really well, much easier than the tenon jig I made for my innacurate table saw fence. Anyways, I really hope these nightstands will be sturdy when assembled but I’m starting to worry, here is the deal:

I’ve read tenons are supposed to be 5 times as long as they are wide. Well if thats true I’m really screwed. My legs are going to only be 1 1/4” wide squared at the top and ~2” at the bottom. All of the mortises though are aligned 1/2” inward from the edge, so the max depth they can actually be is 7/8”. I thought I plunged them to that depth, nope, they are only 6/8” really. So I made all the tenons 7/8” and I haven’t decided yet if I want to take the time to replunge and resquare all the mortises by 1/8” or just trim off 1/8” from the tenons. Either way though, I’m worried they wont be long enough. They also have to be rabbetted or mitered since the sides and back share mortise holes. Any suggestions? Do you think I’ll be ok? At this point I’ve spent way to much time and money so starting over is NOT an option.

If possible, I’d rather trim the tenons to 6/8 then plunge the mortises another 1/8” since it will be much quicker. Will 6/8” tenon be strong enough? I was thinking I could add extra strength by pinning the tenons, but I’m afraid at only 6/8” that the pins would have to be 1/4” or so and not sure if thats really strong enough. Can I actually pin a 6/8” tenon that has the mortise 1/2” offset from the edge of the legs? Any suggestions would be great. Thanks. I’ll try to get pics up by tomorrow evening of an updated status.

-- - Eric Indianapolis, IN


14 replies so far

View Peter Oxley's profile

Peter Oxley

1426 posts in 2629 days


#1 posted 03-21-2010 09:52 PM

I would cut them to 3/4” (6/8) and miter the ends. 5 times as long is a rule of thumb, but any tenon increases the strength of the joint. If the joints are relatively snug, you’ll do fine. If you were putting a huge amount of weight on the joint, I’d suggest finding a way to increase the tenon length, but for a nightstand you could almost get away with a butt joint. An example – cabinet door frames usually have a 3/8” long tenon in an open mortise . The door gets a lot of stress in it’s lifetime, but the joint rarely fails.

-- http://www.peteroxley.com -- http://north40studios.etsy.com --

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Peter Oxley

1426 posts in 2629 days


#2 posted 03-21-2010 09:53 PM

By the way, it’s a good question. I’m glad you didn’t let your self-proclaimed status as a noob stop you from asking.

-- http://www.peteroxley.com -- http://north40studios.etsy.com --

View teenagewoodworker's profile

teenagewoodworker

2727 posts in 2523 days


#3 posted 03-21-2010 09:54 PM

don’t worry that will be plenty strong. I’m not sure where you heard that they should be 5 times as long as the are wide… that’s impossible in about 99 percent of cases. you’re right on as far as the depth for a nightstand goes. also if you pen them that will make them stronger. two pegs probably in this case (one doesn’t look right). but a 1/4” peg will give it ton’s of strength. if you’re doing cope and stick doors with the router bits you can use a toothpick to peg them and even that adds a considerable amount of strength.

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Eric_S

1521 posts in 1950 days


#4 posted 03-21-2010 10:05 PM

WOOHOO! Thanks guys. I was getting really worried. I’m glad they will work. Yes, the tenons are nice and snug (not too snug though where all the glue will squeeze out).

-- - Eric Indianapolis, IN

View CharlieM1958's profile

CharlieM1958

15822 posts in 2973 days


#5 posted 03-21-2010 11:53 PM

Random thought about a “rules of thumb’:

If a woodworker cuts off his thumb in a table saw accident, is he forever after exempt from the rules?

-- Charlie M. "Woodworking - patience = firewood"

View Jim's profile

Jim

142 posts in 2077 days


#6 posted 03-21-2010 11:59 PM

Well I just took a good chunk out of my thumb with a router… can I be exempt a chunk of the time? :)

-- -- Jim - Kokomo, Indiana

View grumpycarp's profile

grumpycarp

257 posts in 2500 days


#7 posted 03-22-2010 12:50 AM

I think you might be misremembering. 4-5 times long as they are THICK. i.e. a 1/4 thick tenon in 3/4 thick stock would net a tenon of 1 to 1 1\4 long utilizing division of thirds for tenon thickness. Or you might be confusing width of stock, (like a wide table apron) with width of tenon, i.e. 5” apron nets 4 1/4” tenon width and using the above mentioned formula would also have a tenon length of 1to 1 1/4”. And a tenon that wide might well be more properly be split or doubled. I might also be misremembering ;-)

Charlie . . . while thumbless carpenters may or may not be exempt from rules of thumb, he almost certainly would be exempt from thumbing his nose at the rules . . .

View Eric_S's profile

Eric_S

1521 posts in 1950 days


#8 posted 03-22-2010 02:13 AM

Aprons are 3/4” thick, tenon is 3/8” thick.

-- - Eric Indianapolis, IN

View grizzman's profile

grizzman

7193 posts in 2058 days


#9 posted 03-22-2010 04:52 AM

eric …what is a noob status mean…

-- GRIZZMAN ...[''''']

View Eric_S's profile

Eric_S

1521 posts in 1950 days


#10 posted 03-22-2010 05:00 AM

Sorry its video game slang. It just means I’m noobie. These are my first tenons and I’ve only been woodworking for about 8 months now.

-- - Eric Indianapolis, IN

View Peter Oxley's profile

Peter Oxley

1426 posts in 2629 days


#11 posted 03-22-2010 05:02 AM

As a rule of thumb, tenons are 1/3 the thickness of the material. There’s nothing wrong with making them thicker unless the mortised part is also the same thickness, because then there isn’t much material surrounding the mortise. This isn’t a problem in this case because your legs are thicker than your apron. However, the five times rule of thumb is based on the 1/3 rule of thumb. Ideally your tenons would be 1” or 1¼” long, but they will be just fine at ¾” long.

-- http://www.peteroxley.com -- http://north40studios.etsy.com --

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Eric_S

1521 posts in 1950 days


#12 posted 03-22-2010 05:12 AM

Glad to hear peter :) thank you.

-- - Eric Indianapolis, IN

View bobkberg's profile

bobkberg

375 posts in 1828 days


#13 posted 03-22-2010 09:14 PM

Eric, one other factor that hasn’t been mentioned is that rule of thumb was developed long before modern glues.

The primary reason for that is that a table leg (for example) has a lot of leverage considering its length, compared to any tenon, and that can put an enormous amount of torque on the joint, which can cause the joint to fail.

Someone else mentioned cabinet door frames – which not being open are not subject to that sort of torque in daily use.

-- Bob www.singularengineering.com - A sideline, not how I earn a living

View Peter Oxley's profile

Peter Oxley

1426 posts in 2629 days


#14 posted 03-22-2010 10:26 PM

@bobkberg – I definately agree that the rules of thumb (I was going to say “rule of thumbs” but that sounds like some kind of tyranical system of government) came about before modern glue. But I’m sticking by my cabinet door analogy: most cabinets are constructed with overlay doors now, so they don’t have the benefit of any support from the face frame when they are closed – the entire weight of the door is always hanging on the hinge side stile. The doors are opened and closed repeatedy in daily use, and occasionally ridden or hung from by children, creating significant torque … and yet they rarely fail. This from a comparably weak 3/8” cope and stick joint (which is weak cousin of an open mortise and tenon).

-- http://www.peteroxley.com -- http://north40studios.etsy.com --

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