Loose tenons! Aaaargh! Um, Fixable?

[Bill Brehme]

Hey guys, I've been lurking this site for a couple weeks and this is one helpful tool! I am in the transitional stage of going from power tool, slap/hack together 'function over form' woodworker, to 'wanting to do something more hand crafted/transcendental...
Heres my dilemma. i am building a 'pair' of stile and rail panel doors (entrance to my shop). I'm using mortise and tenons to connect my rails to my stiles. My mistake was cutting my tenons first, and then chopped out my mortises after. I hogged out my tenons on my tablesaw w/ a dado blade(s). The mortises was where I decided to go neanderthal and chopped and pared them out. I'm out of wood and money for the time being and really need to find a cheap/quick fix. Is this fixable or am I deep in the drink? Any help would highly be appreciated...

[Aaron Beaver]

Um, so are the mortises to wide, to long, both. I could be missing it in your first post.

[Wilbur Pan]

All you have to do is get a shim into the gap. This can be a thin piece of wood, wood shavings, or even paper.

Another approach is to just glue a piece of wood to the tenon, and recut the tenon.

[Bill Brehme]

The mortises are too wide/tenon cheeks too thin.

[Wiley Horne]

Bill,

It's fixable, as long as the tenons have enough meat on them at their existing (thin) width. The fix is to glue shims on the existing tenon cheeks. Exactly how you do this depends on the details: How loose are they? Are the tenons offset to the mortise, or dead center? Are the mortises themselves OK, or are they going to have to be pared?

First thing to do is get the mortises the way you want them. If they're raggedy or wandering, pare them true so they will accept a good tenon. Now hold the tenons up to the mortises, and find out how thick a shim will be needed, and whether on both sides, or just one side, of the tenon. You might need to shim both sides of the tenon, in order to get the rail and stile flush with each other.

How to make shims? Saw them. Use band saw or hand saw. Take a likely stick, at least as wide as the tenon, and plane one side flat (that'll be the glue side of the shim). Saw a thin slice off this stick, and that should make plenty of shim material. You'll either need to glue a shim on one side of the tenon, or both, depending on the details of the problem. It's a trivial glue job. You're gluing the smooth side of the shim to the smooth tenon cheek, and this will make a good bond. Ordinary yellow glue.

When the glue dries, you get a second try on the tenons. Trim off the shim's excess with a sharp chisel. Then plane or chisel or rasp the shimmed cheeks down til they fit your mortises--and leave the rails and stiles flush with each other!

What you give up by fixing your tenons, rather than starting over, is that the strength of the tenons is set by their original width--the shims do not restore actual width to the tenon, they just give a good fit to the mortise.

Wiley

[Bill Brehme]

Thanks for the replies. How would I go about the wood shaving method?

[Bill Brehme]

Awesome! Thanks Wiley and Wilbur! I have alot of fitting and jimmying to get these square. I think I'm going to try the 'shim and retrim' method. Hopefully I'll get it right on the second shot. I really want to have these babies done and the shop secure by the end of this weekend.
Does anyone think doweling the joints would be worth the effort? If so, what size dowels for 5 1/2" wide stiles and rails w/ tenons running 2 1/2" deep? Thanks again fellas!

[Pam Niedermayer]

You could peg the M&T joints, couple or three pegs each, excellent idea to strengthen the joints.

To avoid these problems in the future, cut the mortise to the width of a chisel, measure the width of that chisel to mark the tenons. It doesn't really matter which you cut first, except that if you insist on checking the fit you can if the mortise is already cut.

Pam

[Randy Klein]

If I'm not mistaken, if you are using loose tenons, then you should have 2 mortises and not 1. By your description it sounds like an integral mortise and tenon.

If that's the case, just cut your tenon off, chisel a mortise on the other piece and mill up a loose tenon. This is a loose mortise and tenon technique.

[Sean Hamblett]

I have an article, I can't remember from which wood working magazie, that showed that the dowels in a M&T joint, actually weaken the joint. The joint gets its strength from the surface area, and when you punch holes it it, you reduce the surface area of the joint. This mostly applies to either shear or torsion forces, I can't recall which. I will try to find the article and post it.





You could peg the M&T joints, couple or three pegs each, excellent idea to strengthen the joints.

To avoid these problems in the future, cut the mortise to the width of a chisel, measure the width of that chisel to mark the tenons. It doesn't really matter which you cut first, except that if you insist on checking the fit you can if the mortise is already cut.

Pam

[Bill Brehme]

Thanks again Sean & Pam... Yes, I would be most interested in reading that article Sean. Depending if I decide to go w/ the pegs, what size pegs would be appropriate for an entry sized door? (by the way - I'm using pine and the door is 1 1/2" thick, tenons are 1/2" thick).

[Bill Brehme]

[quote=Randy Klein;620139]If I'm not mistaken, if you are using loose tenons, then you should have 2 mortises and not 1. By your description it sounds like an integral mortise and tenon.

Sorry Randy, I used poor choice of wording... Yes, the tenons are indeed integral. What I meant was that the tenons had too much slop inside the mortises. Oooops!:o

[Pam Niedermayer]

I have an article, I can't remember from which wood working magazie, that showed that the dowels in a M&T joint, actually weaken the joint. The joint gets its strength from the surface area, and when you punch holes it it, you reduce the surface area of the joint. This mostly applies to either shear or torsion forces, I can't recall which. I will try to find the article and post it.

Sure, I'd love to see the article; but from an engineering standpoint, using pegs is an intuitively obvious good thing to do. Among other things, drawbored pegs take on most of the job of holding things together, thus allowing the tenon/mortise to do less of the job. Also, I don't recommend dowels, rather hand shaped pegs made using long grain.

Pam

[John Goodridge]

I believe the article being referenced is the Nov 2006 Wood magazine. The difference in strength for both shear and tension tests is rather slight comparing a 1.75" x 1.5" tenon with and without two dowels. It does not seem to specify whether the dowels were drawbored or not. The shear strength dropped from about 1100 lbs to 1000 lbs. The tensile strength dropped from about 2500 lbs to 2400 lbs. The dowelled case was weaker in both tests.

[Randy Klein]

What I meant was that the tenons had too much slop inside the mortises. Oooops!:o

Oh I get it - Loose tenon in your mortise, not a loose mortise and tenon. Oh I feel silly.

Well, you can still convert your joint into a loose mortise and tenon and not worry about any other fixes...

[Sean Hamblett]

[quote=Randy Klein;620139]If I'm not mistaken, if you are using loose tenons, then you should have 2 mortises and not 1. By your description it sounds like an integral mortise and tenon.

Sorry Randy, I used poor choice of wording... Yes, the tenons are indeed integral. What I meant was that the tenons had too much slop inside the mortises. Oooops!:o

The article is from the November 2006 issue of WOOD, #173, and being a newbie to this I am not sure about the 'drawboarding', but I have to say that it looks like the holes made for, and/or the dowels is where the failure happened. The article also goes on to show that increasing the width of the tenon had a great affect on improving the strength of the joint.

Thanks,

Sean

[Sean Hamblett]

I believe the article being referenced is the Nov 2006 Wood magazine. The difference in strength for both shear and tension tests is rather slight comparing a 1.75" x 1.5" tenon with and without two dowels. It does not seem to specify whether the dowels were drawbored or not. The shear strength dropped from about 1100 lbs to 1000 lbs. The tensile strength dropped from about 2500 lbs to 2400 lbs. The dowelled case was weaker in both tests.


Whoops quoted the wrong post, yes John is correct. The other thing to note is wider is better...

Sean

[Sean Hamblett]

From the article... they may not be the best quality, but a the picture says it all....

Sean

[John Goodridge]

Sean:

Drawboring is when you drill the hole in the tenon slightly closer to the shoulder than the hole in the mortise, so when you put the tenon in the mortise the holes do not quite line up. When you drive the pins in, the holes are pulled in line, "drawing" the tenon deeper into the mortise.

John

[Sean Hamblett]

Thanks John! I would like to see a test on the difference in that, and just some dowels, and without on the strength of those joints.

[Raymond Stanley]

Sorry to jump in here late, but...
Bill --
If you don't want to make shims, you can always use veneer, depending on how "off" your tenons are. I think this is recommended by Tage Frid in his books.

[John Goodridge]

One thing to keep in mind regarding these tests is that it is not really representative of how joints fail. The tests load the joint until failure, often with the wood itself tearing apart. While the structural limit of a joint can be reached in a short time frame, more often the joint fails over time and repeated stress cycles. The glue gives way and the wood moves weakening the joint. Having it pegged pretty much guarantees that the wood needs to tear apart for that joint to fail.

[glenn bradley]

The standard fix I've read about is to laminate some thin wood to the tenon and re-work it down to the size to fit your mortise. On the bright side, I bet you always cut your mortise first from now on ;-)

I have a real love/hate relationship with the painful lessons . . . .

Update - Oops, just read Wiley's reply . . . he's got it.

[Sean Hamblett]

Good point, it actually looks like the the dowels assist in the failure of the wood, and not the joint.