Pinning Tenons

[Birdhunter]

I'm building 8 outdoor benches with Ipe. The 3 boards that make up the top are jointed using 8/40mm Sipo tenons.

I'd like to pin the tenons because I'm not sure the Titebond III is going to hold.

The boards are 1X6 so they are 3/4" thick.

What's the best method for pinning the tenons?

 

[Stephen B]

[size=11pt]

Hi,

Whilst the following link is about pinning for breadboarding it may none-the-less give you some ideas that may be adapted to your needs. In particular the slight offset between the pin holes and the pins themselves. It is beyond my experience and knowledge of timber species available to you to comment on timber selection for the pins. You could I assume make them yourself from the Ipe.

http://festoolownersgroup.com/festool-tools-accessories/domino-500-or-700-for-breadboard-table-top/msg271050/#msg271050

 

[Rick Christopherson]

I would avoid pinning the tenons as it will tend to weaken them as opposed to strengthen them. Any pin that is large enough to have any shear strength will cut into the tenon enough to reduce its strength. The exception would be a small metallic pin that has a high shear strength but a small diameter.

 

[Birdhunter]

I was thinking about using a 1/2" screw as a pin.

 

[shed9]

I can see your rationale in the extra holding capacity for an item that supports people but if you have concerns on the adhesive this is what needs to be addressed first in my opinion as opposed to doctoring the domino to compensate for it.

 

[wow]

I can see your rationale in the extra holding capacity for an item that supports people but if you have concerns on the adhesive this is what needs to be addressed first in my opinion as opposed to doctoring the domino to compensate for it.

I agree with shed9. Here's another way at look at it:

If you're pinning it because you have a concern that the glue might fail, consider building it WITHOUT glue...using only your pin to hold it. If that isn't an acceptable solution then you need to fix the glue issue. Make sense?

Now, if you're going for a 'belt AND suspenders' kind of solution, then I would think a small stainless steel pin would be fine and *might* provide some strength to the joint to help prevent a glue failure.

Just my  [2cents] [2cents] (adjusted for inflation)

 

[Kevin Stricker]

Just my $0.02, I would not use TBIII for Ipe.  While I saw your earlier post about your strength tests, you did not do the real test of checking the holding power over time.  The oils in Ipe will leach into the mortices and the joint will eventually fail, if you do enough research on the web you will come to the same conclusion.  I have seen the results first hand, it is not pretty. Epoxy is your best bet, and even that is questionable. Ipe is a tricky wood for joinery.

If you are going to pin the tenons, plan to make your own. Using the wide setting on your Domino and some home made tenons you should be able to get good results without compromising the tenon strength too much.  I would also plan to max the depth so you get the most wood behind the pin.

 

[Michael Kellough]

I would avoid pinning the tenons as it will tend to weaken them as opposed to strengthen them. Any pin that is large enough to have any shear strength will cut into the tenon enough to reduce its strength. The exception would be a small metallic pin that has a high shear strength but a small diameter.

About 30 years ago I worked with some Turkish carpenters making the Minbar and Mihrab for a new Mosque.
They remain the most skilled woodworkers I've ever worked with.

When all the parts were done and assembly began the patrons of the project came by to see the progress
and were appalled to find that the guys were using finishing nails. When a patron asked why they weren't using something
like dowels the senior carpenter held up a nail and said "steel dowel".

 

[festooltim]

My experience with Ipe is limited but I would think a small stainless finish nail would be the best kind of pin. Drill for the nail of course.

 

[mouppe]

Are you pinning both ends of the 40mm domino? If so, that's going to seriously weaken the tenon. If not, your fix for the glue problem is going to fail anyway.

I would nail a batten across the underside of the benchtop if the design permits, or use breadboard ends.

 

[Birdhunter]

Thanks for all the input.

In the absence of any definitive data on glues for Ipe, I decided to go with TB III for the Sipo 8X50 tenons that connect the 3 1X6 boards. Each tenon is pinned on each end with a screw inserted about 3/4" from the edge of the board. The screws are inserted from the underside of the bench top.

I'll use epoxy on the other glued surfaces after wiping them with alcohol. The glue will be backed up with stainless steel screws.

Every joint and every tenon will be both glued and screwed.

Lots of labor involved, but I want the benches to stay together long term.

I kind of wonder if I should not have gone with another wood, say teak.

 

[jacko9]

Thanks for all the input.

In the absence of any definitive data on glues for Ipe, I decided to go with TB III for the Sipo 8X50 tenons that connect the 3 1X6 boards. Each tenon is pinned on each end with a screw inserted about 3/4" from the edge of the board. The screws are inserted from the underside of the bench top.

I'll use epoxy on the other glued surfaces after wiping them with alcohol. The glue will be backed up with stainless steel screws.

Every joint and every tenon will be both glued and screwed.

Lots of labor involved, but I want the benches to stay together long term.

I kind of wonder if I should not have gone with another wood, say teak.

I would consider wiping with acetone instead of alcohol and Teak is just as problematic as Ipe and a lot harder on tools given the hard mineral deposits in the wood.  Just for fun try running a perfectly sharp hand plane over a board of teak and listen carefully, it sounds like your going over sandpaper after a few swipes.

Jack

 

[Birdhunter]

I'll try the acetone, but will have to go outside.

I guess outdoor durability and tough to work with go together.

In Connecticut, there were barns made totally of black walnut. They were very old with huge beams made from locally harvested trees. I wonder how walnut compares with Ipe on durability.

 

[tjbnwi]

Once you got the cost of teak, you would have gone with Ipe anyways.

Tom

 

[jacko9]

Ipe should outlast Black Walnut by generations given the same environmental conditions.  I agree that the Hardwood forests of the New England States produced some great wood but none of it was as dense as the rain forest exotics like Ipe (which comes from multiple trees).  I also agree with the cost difference between teak and Ipe where the costs of teak, genuine mahogany, rosewood, etc have gone through the roof over the past 40 years.

Jack

 

[bruegf]

Once you got the cost of teak, you would have gone with Ipe anyways.

Tom

I've got a few hundred board feet of burmese teak shorts (mostly 1x2 and 2x2 in 4' and 5' lengths) that I'd be willing to sell at a good price if anyone is interested.  I bought it for a boat project over 20 yrs ago and sold the boat before I got around to starting the project. Its been sitting in my basement since.

Fred