LumberJocks

Help with through tenons

  • Advertise with us

« back to Woodworking Skill Share forum

Forum topic by Jack_Isidore posted 03-09-2011 01:36 AM 846 views 0 times favorited 10 replies Add to Favorites Watch
View Jack_Isidore's profile

Jack_Isidore

89 posts in 1604 days


03-09-2011 01:36 AM

Topic tags/keywords: tenon mortise jig router

I’m making a pair of night tables (model view attached), and am to the point of cutting the through mortises for the legs. I have a question about shoulder width, and a request for general advise. First of all, the legs are 1-1/8×1-1/8, and I wasn’t sure what would be a good shoulder width. As it is now, I plan on having shoulders 3/16” wide, leaving 3/4” of the end grain to remain exposed. I guess ideally, I would have more end grain showing through, but I’m afraid of making the shoulders too thin, and running into structural issues. I’m also open to other suggestions, including not using through mortise and tenon at all.

So, I’m wondering how best to go about cutting these through mortises. The table is made of walnut, and I don’t want to ruin or otherwise screw up some valuable boards I’ve put a lot of time into. I have a powerful plunge router (3.25 HP) and a 3/4 straight carbide bit (not helical, i.e. up cutting). I was going to cut pilot holes (not sure if router bit is center cutting) then 3/4” through holes and then square up with a chisel. However, I feel nervous about squaring up the mortises by hand without an original flat reference surface. The plus side to this method is, I wouldn’t need a template, I could simply clamp fences to the board in the x and y direction. If I use a smaller diameter bit, I still have to square the edges, but this might be easier. In that case, I’ll need to make a template of some sort. As far as templates go, I was thinking something simple like 3/4” MDF with a square cutout, and I’d have to find a bit with a bearing on the shank end. Then I could screw stops on the MDF template so I butt it up against the board and clamp it down. Thoughts? Advise? Prayers for success?

I did pick up a bit of wisdom somewhere, to set my plunge depth limit to slightly shallow, as to avoid tear out, and then punch the hole out with a chisel. I also think I’d clamp some boards around the mortise as I square it with chisels, to give something of a guide for the chisel to stay vertical.

I’m having trouble embedding the photos from imgur.com, so I’m just going to put the links here.

http://imgur.com/L0eT3
http://imgur.com/JUjJ0


10 replies so far

View Jack_Isidore's profile

Jack_Isidore

89 posts in 1604 days


#1 posted 03-09-2011 01:37 AM

Maybe I should point out, in my hand drawn diagram, the top sketch was before I decided to thin the tenon shoulder, the bottom sketch is the only one with the correct dimensions.

View Loren's profile

Loren

7825 posts in 2398 days


#2 posted 03-09-2011 02:44 AM

View Loren's profile

Loren

7825 posts in 2398 days


#3 posted 03-09-2011 02:51 AM

3/16” is wide enough for a tenon shoulder going all the way around
but may not provide great wracking resistance. You should try to
make the joints fit precisely if using 1.125” square stock.

While a lot of woodworkers overbuild furniture, I’m a little nervous
about your design. Put a stretcher across the bottom and I’d be
more confident in your plan to use such a small square section
to support a table.

There’s no huge benefit to using through tenons here unless you
like the way they look.

-- http://lawoodworking.com

View Jack_Isidore's profile

Jack_Isidore

89 posts in 1604 days


#4 posted 03-09-2011 03:03 AM

Thanks for the input. What exactly do you mean by wracking though?

View patron's profile

patron

13181 posts in 2092 days


#5 posted 03-09-2011 03:09 AM

like dominoes collapsing
the only thing keeping it stable is the thickness of the top
and the tenon length

kind of like putting a post in the ground
the shalow ones fall over
the deeper they are
the stronger

why spreaders help
more overall holding the legs

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View Jack_Isidore's profile

Jack_Isidore

89 posts in 1604 days


#6 posted 03-09-2011 03:15 AM

Ah, I see. Point taken. The legs are only about 6” tall, so I didn’t think it would be much of a stability issue. I’ll give it some serious thought though.

View patron's profile

patron

13181 posts in 2092 days


#7 posted 03-09-2011 03:24 AM

at 6” it probably isn’t an issue just don’t let someone sit on it
and wiggle around

the wood will have lots to do with the strength too
soft may weaken with time and motion
hardwoods will stay stronger longer
and good tight tenons a must either way

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View Jack_Isidore's profile

Jack_Isidore

89 posts in 1604 days


#8 posted 03-09-2011 03:38 AM

Hah! A few times I’ve looked at the design, and thought, how will I politely tell everyone who comes into contact with it, not to sit on it. Also, if/when I have kids, it might need to be replaced.

I’m considering running FEA structural analysis on it just to see what it’s limits might be. That’s surely overkill, but for a while now, I’ve been meaning to try and get some wood species properties into my CAD program and seeing how well I can optimize a design.

View Jack_Isidore's profile

Jack_Isidore

89 posts in 1604 days


#9 posted 03-12-2011 01:17 AM

I decided to cut these on the mill. This way, I can easily make multiple passes using a large end mill and then go to a smaller one so I only have to remove a small amount of material with the chisel. Being able to make them very precise is a nice advantage too. They’ll be clamped down on top of sacrificial MDF, which should avoid tearout on the bottom. Sometimes (often) it is nice having access to shop tools at work…

For anyone who is interested, I’ll post my setup and results in a couple of days.

View jsheaney's profile

jsheaney

141 posts in 2739 days


#10 posted 03-13-2011 03:13 AM

As for actually cutting the mortises, these are pretty small and there’s only four of them. I think templates and jigs aren’t really necessary. Just mark the four mortises top and bottom with a knife. Drill your holes from the top to waste out the material. Square up with a chisel; half the depth from the bottom up and then finish top down. The marking knife leaves a nice reference for your chisels. Just go slow with the chisel when starting from the top because that’s the show right there. Be careful for the first 1/32” of depth and then you can start whaling away once you have a cheek started. You can use a machinist square to keep your chisel vertical, if you want.

-- Disappointment is an empty box full of expectation.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com

Latest Projects | Latest Blog Entries | Latest Forum Topics

GardenTenders.com :: gardening showcase