# Fixing broken rung



## saminmn (Oct 2, 2012)

I have a 1940-ish kitchen table and chairs and one of the chairs has a broken rung. If I can add a new tenon, instead of replacing the rung, I won't need to refinish the entire set. It broke at the tenon joint and as I think of fixing it, I think this weak point would be weaker still if I just doweled a new tenon on. Is this correct?

I am thinking of using epoxy on a steel rod section instead of a wooden dowel to attach a new tenon. Would this be a good solution?

I have very limited experience so any help/advice is appreciated.


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## crank49 (Apr 7, 2010)

A new wooden tenon the same size and of similar wood should be as strong as the original.
A smaller tenon of steel or brass or similar might work, or might split the rung or the leg.


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## a1Jim (Aug 9, 2008)

Chairs are the number one item of furniture that need constant repair. Replacing just the tenon part of your rung should work fine if the area where the new tenon is to be installed is good solid wood and you are able to drill the rung out accurately . If you have a reasonable fit on the tenon just a good wood glue will do the job. A Iron pin would need to go a good 1-1 1/2" into the tenon and rung to add any measurable strength, as Crank said adding an iron pin might split the rung and the new tenon ,all depending on it's size and accuracy of drilling both pieces out for the pin,many times the drilling operation will crack one or both sides all by it self.


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## saminmn (Oct 2, 2012)

The chair has a round rungs. The break occurred at the point where the round tenon on the end of the rung enters a hole in the chair leg (round mortice). The rung is large enough to bore a hole into the end for a dowel or metal rod. I would think 3/8" dowel/rod would be the max diameter I could use for attaching a new tenon piece to the rung. I was thinking of using a 1/4" steel rod would leave me more wood reducing the chance of splitting the rung while drilling. Is splitting concern because the metal wont shrink with the wood?

I just took calibers to the rung and it is .81" (11/16"?). So I am not going to be drilling any bigger than 3/8". I should be able to manage a good hole into the rung with my Shopsmith in horizontal bore mode and the rung clamped to a v-block. So how deep into the rung will I need go if i use a 3/8" oak dowel (or cut/turn a tenon on the new tenon down to that)?

I have read that sometimes boring down the grain just won't stay straight. So…might be a bit of luck needed


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## crank49 (Apr 7, 2010)

.81" would be 13/16", that's half way between 3/4" and 7/8".

Are you sure you couldn't get at least a 1/2" bore into that.
A 1/2 " dowel will be twice as strong as a 3/8" in resistance to the bending forces at play here.

In wood to wood glue-up the glue joint is considered stronger than the wood around the joint.
So the strength of the joint is determined by the cross section of the joined materials.
Area of a 3/8" dowel is .1104 sq.in.
Area of a 1/2" dowel is .1963 sq.in.
Area of a 13/16" dowel is .5185 sq.in.
If you drill a 1/2" hole in a 13/16 tenon you have .5185 sq.in. minus .1963 sq.in. = .3222 sq.in.
So, even with a 1/2" hole through it, the 13/16" tenon has more strength than the 1/2" dowel.

The biggest concern will be the stress of drilling the hole without splitting the spindle.
And, with the horizontal boring ability of the Shop Smith you have a great tool to do this.
A good sharp brad point drill would be best for staying straight without extra stress.
I would be leery of a screw point auger or a spade bit especially.

It might help to wrap the spindle with nylon twine, very tight (think of the eye attachments on a fishing pole) and then tightly stretch a couple layers of good electrical tape over that to hold it in place.


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## saminmn (Oct 2, 2012)

Thanks for thinking this out with me. I may be able to do 1/2".

I am still worried that at the bottom of the hole I will be drilling, to add a new tenon, the only supporting material is the remaining material in the original rung. With a 1/2" hole, well centered, and we a talking 3/32" wall thickness. Of course that goes all the way around so it is not flimsy, but…it is not much and there is no wiggle room in this plan.

That is why I was leaning toward the steel rod idea going into the rung - adding strength. I did not quite understand your concern with splitting. Was this a wood movement/shrinkage concern?

I just tried take the rung out so I can see/measure the broken tenon's diameter. I think it is 5/8", but I could not get the rung out with rubber mallet tapping. I expect the chair uses hide glue. Advise on disassembling?

Thanks again,


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## LeeBarker (Aug 6, 2010)

Now we're getting somewhere.

If I didn't want to completely disassemble the chair I would epoxy the butt ends together where it broke, good epoxy, long cure time. Then I would drill through from the outside of the leg, overboring for a 3/8 dowel, maple or birch (not the dreaded "white wood"), and epoxy that in and top it off with a nice plug, and finish to match.

If that's too noticeable, I'd just do dummy plugs on all the chairs. No one will ever know.

Kindly,

Lee


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## saminmn (Oct 2, 2012)

Lee,

I had not thought of just going in from outside of leg to put in dowel. I will probably use this approach. I am not familiar with epoxy options. Will I need to go to Rockler/Woodcraft type store for long "cure time"? I have Menards or Ace locally. Other Big Box stores are the same 40 minute ride as Rockler. Also, "overboring for a 3/8 dowel" are you saying to leave room for epoxy or deep enough for a plug?


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## mtenterprises (Jan 10, 2011)

I have replaced MANY tenons on chair rungs over the years. What I do is cut the old tenon off cleanly then drill a hole as on center and straight as possible about one half the diameter of the tenon then I turn a new tenon with the step down to fit the hole. Lately I have been using Gorilla Glue to assemble the two parts making sure there is good squeeze out to have all surfaces glued then clean it up after it is hard. When I reassemble the chair it is very important to clean all the old glue from both the mortises and tenons and here I use Elmer's yellow wood glue with good success coating both surfaces with glue using an acid brush. Spread the glue evenly and not too heavily. Too much glue will cause a hydraulic lock and you may split something. Once assembled and clamped clean up the glue squeeze out with a wet rag.
MIKE


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