Replies

1. 
   Scrit | Nov 21, 2003 07:16pm | #1

   Probably because it looks nice... <G> Before we had reliable glues joints needed to be pinned and/or wedged - there simply wasn't any other way to get them to hold together, especially in building frames (which still to this day utilise pins and wedges). As reliable glues became available the need to pin or wedge joints diminished so the only place it was needed on smaller items such as furniture was where there was a need to dismantle pieces in order to install them in (or possibly remove them from) a room with restricted access. Other than that these days they are almost pure ornament, although drawbore pinning is a useful way to pull up joints where you can't get a sash cramp onto a frame. 

   I still use pins when installing oak panelling frames, partly because it is the correct "period" look and partly because I find it easier to carry the frames and panels broken down and assemble in the client's house.

   I'll now wait to be told tht I'm completely wrong.....

   Scrit

1. 
   JBentley | Nov 21, 2003 07:29pm | #2

   Thanks you Scrit. I like your answer. Makes sense. One of those things I was wondering about.

   JeffB

2. 
   VeniciaL | Nov 21, 2003 07:34pm | #3

   Jab,

   A tenon does not "always" have to be pinned. A properly made MT joint has enormous strength if it is snug fitting, true and square and glue has not been squeezed out during clamping.

   Pinning is one of those decicions that has as much to do with style as function. A pinned joint draws attention to itself, which can be useful in exposed-joinery design. The pin can be a contrasting color.

   Pins do add strength where needed. In a design that might be subject to racking stresses, they can help resist movement and pull-out.

   Pin holes should be made nearer the tenon shoulders than the tenon end, or the end grain of the tenon can pop right out. But they should not be so close to the edge of the mortise piece as to weaken the small distance between the edge of the hole and the edge of the piece.

   A pin can help draw the joint together if the holes through the mortise cheeks are minutely offset (away from the tenon shoulder) from that through the tenon. When the pin is driven in, the shoulders of the tenon snug up against the mortise piece.

   Pins are used in unglued joinery - joints that are intended to be taken apart from time to time.

   A technique that has both functional (strength) use and visual appeal is to drive a square or hexagonal pin through a just slightly undersize, round hole in the mortise cheeks. The corners of the pin dig into the hole tissue, anchoring the pin firmly. I like to prepare my pins slightly long, leaving them just proud of the surface, and finish their end grain with a very sharp chisel, slightly chamferring the edges. This polishes the end grain and is visually interesting.

   VL

1. 
   JBentley | Nov 21, 2003 07:55pm | #4

   Venicia,

   Excellent answer. Very thorough and you have given me some good ideas in the process! I think I will like this forum a lot! I have been reading it for awhile now and have already learned many things. Thanks for sharing.

3. 
   BobSmalser | Nov 21, 2003 08:15pm | #5

   I do drawbore tenons often like in the pic below when I'm not using sliding dovetails...look for the untrimmed pointed dowel end.  Bulletproof joint.  Excellent for tool stands and tables that get a lot of racking stress in use....makes those glue joints hold up longer.

   Make and dryfit your M/T...drill the the mortise cheek until the drill bit just touches the tenon enuf to make a mark....disassemble and drill the tenon a tad offset toward the shoulder.  Finish the hole thru the mortise.  Point an overlong dowel, lube it with glue, and drive it thru your assembled joint.

   Example

   
   

   ---

   Edited 11/21/2003 4:34:34 PM ET by Bob

1. 
   JBentley | Nov 21, 2003 08:23pm | #6

   Bob,

   Thanks for the picture! It's nice to have a visual with the answer.

1. 
   BobSmalser | Nov 21, 2003 08:33pm | #7

   My pleasure.

1. 
   cft353 | Nov 22, 2003 06:24am | #8

   When I went to school in Boston I used to go over and get in trouble at the Museum of Fine Arts on a regular basis by handling the furniture in the Colonial American Furniture exhibit. (The guards seemed to understand, and while they made me stop touching the exhibits, nobody ever threw me out.)

   All the MT joints were pinned, naturally, reliable glues not being available at the time this furniture was constructed. These pieces had held together for 200+ years with no indication that the joints were about to fail any time soon.

   I'll pin joints now usually in joints that will be subject to wracking, like in chairs. My idea is that if the glue fails at least the pin will hold until the joint can be taken apart and repaired, rather than risking more damage occuring as the glue fails and the joint comes apart.

4. 
   4DThinker | Nov 23, 2003 01:45am | #9

   If you understand how wood expands and shrinks relative to the  direction of grain, then you understand why most glued-only M&Ts will eventually fail.  Wedging or pinning the tenon adds a mechanical lock to the joint which if done right will keep it together long after the glue has failed.

   I now pin almost every M&T joint I make.  But some, like the vertical post of a trestle base table tenoning into the foot, will be kept together by gravity even if the glue fails.  If a pin in these cases would distract from the look, I'll leave it out.  But since some of my projects are now 25 years old, I've started to have a few "come back" to me for repair, usually because an un-pinned M&T joint came loose.  And yes, I put a pin though them before I send them back repaired.

   4DThinker