newbie question about tennons

[stryped]

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How long, deep and wide should a tennon be on a 1/2 inch thick slat like on a mission style headboard? What if it was 3/4 inch?

[Stephen M]

That depends:

For me, I try to standardize as much as possible, to minize setups, and math errors. Sometimes aesthetic concerns override this system, but I can generally make these work.

Also, always measure, or register you work from the same face of your stock, That way, if you are a little off, it will always be consistent.

When I design, I sometimes have both "structural" and "non-structural" tennons. If I have a frame with slats in the middle, I generally consider the slats to be non-structual (they do add significat ridgidity but the main work is done at the corners of the pannel.

Depth:

1/2" deep for nonstructural, I like 1-1/4 for structural.

Thickness.

There's a couple of considerations, pretty much in this order:

1. Tennon should be inset from sides of the slat so as to hide the edges of the mortise.
2. Tennon should not me much thicker than 1/3 of the thickness of the stock into which it is inserted (not to be confused with the thickness of the tennon stock)
3. All dimensions are in even 1/8th's to mitigate brain cramps.
4. Adequately beefy, bigger is generally better, 1/4 is fine for a cabinet door. 3/8 is prefeerable for a carcass.
5. All tennons in a project, if possible, should be the same thickness to minimize setups.

Width,

Just as a convention to keep things simple:

I put a 1/4" shoulder on all tennons (tennon is 1/2" less wide then tennon stock). Unless....

The corresponding mortise is at the end of a board, then shoulder is 3/4"

or

The tennon stock is > 3" I'll inset the shoulders 3/4" and only glue the center of the tennon if it's really big.

-steve

[Frank Ketchum]

[Dave Jackson]

I'd suggest cutting the mortices at 1/2", then cut the slat to fit in the mortice, thus using the slat as the tenon. Generally on 3/4 "stock, I make the tenons at 3/8". --dave

[stryped]

[Swingman]

What size mortising bit/chisel do you have? Most folks (the smart ones) let their tools determine the mortise and tenon widths.

Otherwise, make the tenons 1/4". You will have an 1/8" shoulder, but that is fine for slats and it makes them easy to cut on a table saw using a dado set. Use a 1/4" mortise bit/chisel to cut the mortises.

NOTE: If you use the optional "slat" solution that I mentioned to you in my last post, just use the slat itself as the "tenon", and a groove, running the length of the rails as the "mortise", then fill in between your regular spacing.

[Dave Jackson]

Yes, I'm suggesting making the mortise the size of the whole slat. It will require the same level of accuracy as cutting a tenon to fit in the mortise, but you will save the time of actually cutting tenons. If one of the mortises ends up slightly large, and a gap is seen, simply cut the slat a few thous larger. One of my first projects was a mission style buffet that had slats on the sides of the case. I cut the mortises with an attachment for the drill press I had at the time, cleaned them up with a chisel, then cut the slats so they fit snugly into the mortises. It worked well, and I'd do it again. If the slats are cut tightly enough, the edges of the mortise are very close to invisible. You can always try this method on scrap pieces to determine if it'll work for you. --dave

[stryped]

[Teamcasa]

Don't make a mortise for the slats. Using your router table with a straight bit, cut a 1/2"x1/2" slot in the rails. Fill the gaps with 1/2"x1/2"x 1" blocks.

Simple and does not require accurate mortising.

Dave

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[George Shouse]

Why x-no-archive:yes when it comes from google?

Isn't that antithetical to usenet?

[stryped]

[Teamcasa]

You would only glue the blocks. The slats would float. I posted an illustration in A.B.P.W Make the blocks out of the same wood as the rails. It will be very hard to tell they are not real mortises. Dave

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[Swingman]

That is the same method I've been repeating to you. The filler "blocks" will look just fine if you use the same wood, just try to match the grain on the two pieces before you cut your groove.

[Andy Dingley]

I don't know. I've been doing this for years now and I still couldn't give you a simple answer to this - it's just not an easily answered question. Even just for cabinetry, without getting into green timber-framing tenons.

First of all, they should fit your mortices. To me this means making them a size that matches a chisel in my morticing machine. It also means cutting them afterwards, to exactly fit the mortices. I bandsaw my tenons, which is easily and accurately adjustable, to fit mortices I have much less control over.

Secondly they should be the full width of the timber. Use two shoulders, not four. Run this long width along the grain of the mortice, not across it. Sometimes haunching is good too. Read Tage Frid's book.

For rough width on the short axis, somewhere between 1/3rd and 1/2th of the timber thickness, usually tending towards the thicker measurement..

if the slats are big wide cross-grain things, then start to worry about moisture movement. Breadboard-end techniques start to make sense, not simple tenons.

[C&S]

Hmmm. I always use four because I always make my mortise a little longer then the tennon so that I can wiggle a joint back apart after a dry-fit. The extra two shoulders cover the intentional < 1/8" gap.

How do you disasseble a dry fit with no wiggle?

-Steve

[Australopithecus scobis]

Mallet. I use the ugly black rubber one for this. Scrap of pine against the work, tenon piece held in the bench vise. Whack (gently but firmly) the mortice piece on alternate sides of the tenon piece. If I've done a sloppy job of making either piece, I clamp the mortice piece in the bench vise and just haul on the tenon piece bare-handed.

[Andy Dingley]

I don't see why wiggle-room depends on how many shoulders you laid the tenon out for ?

If you're concerned about visible gaps, then that's carelessness, not just wiggle. You'd also be bringing in the problem of cutting the shoulders neatly enough that you don't get any unevenness where the four shoulders meet (and thus a gap at the end of the tenoned member).

Something I forgot to mention was that the length of tenons should be at least as long as their minimum thickness. Unless they're shorter than this, in which case it's a "stub tenon" and don't expect it to be so strong. Pegged tenons (with a drawnail through them) need to be even longer, so that the shortest length of unsupported short-grain timber is as long as the thickness and there isn't a risk of it breaking out, The thinnest part of long-grain timber (side of the mortice, where the nail is going) can be a bit thinner than this, depending on species.

Incidentally, to disassemble a Wiggle you find the Australian parent of multiple small children, then give them a Wiggle and a big mallet. They'll do the job for you....

[C&S]

No it's intentional... I have made them tight and have stopped doing so because it gave me too much greif.

...Sippage...

I'm not talking about stub tennons. A recent project is representative of my typical aproach:

1"x2.5" stock give me tennons 3/8" x 1-1/4" x 1-3/4" or 2-1/4" (end or middle). I think you would have a tough time pulling apart a frame with a single interior rail (6 joints) of that depth and no wiggle without the aid of a reversed cabinet master clamp..

Have you ever had a glue up have a problem, where you say "Oh sh*t I have to back that out" as you are just pulling the joint together and you realize something doesnt work (if you're like me it's probably the last time you neglected to dry-fit something) and you can barely get it apart? I think to myself, boy is this going to be strong when there is cured glue in there rather than wet glop.

It's my contention that, if the joint is approriately snug on the thuckness dimension, the should shoulder of the tennon, in conjuction with the sheer strength of the glue on both faces of the tennon (4-3/8 square inches of glue area per joint), is way more than enough to resist racking forces placed in the frame. (compressive forces, just push the joint together and simple pulling forces are a bit unusual for a furniture carcass and not largely effected by tennon width)

Perhaps, it's modern glues that give me comfort ing taking this liberty.

-Steve

[Andy Dingley]

No - not since I abandoned PU glue! Now I use hide glue for nearly everything and rarely have trouble. I can abandon a job 20 minutes after gluing it, pull it all apart by hand and just leave it on the bench in disgust. Clean up for a later attempt is easy.

Most of my tenons are dry-fitted anyway. These days I'm inclined to a fairly "rustic" approach, either big timber framing or medieval oak repro. Although I may well glue this too, it's designed to be dry assembled and often is held purely by the treeenails.

Resisting racking, IMHE, relies on adequately wide tenons and in getting some good compression onto the ends of the tenon member. I do this by pegging my tenons with some draw on the pegs to pull them tight. Gluing is certainly possible - plenty manage it, but it needs good flat shoulders and some decent clamping during glue-up.