[pianotech] unusual lyre joint

[Mike Spalding]

William,

I'm also quite familiar with pegged mortise and tenon joints using an 
offset hole to draw the joint together.  But the dowel used in that type 
of joint is straight, not tapered.  The leading end might be chamfered 
for ease of assembly, but the dowel itself is straight.

The holes in this lyre taper from 9/16 to 5/16, or about 6 degrees.  
That's what is so unusual in this joint.  It's as if the intent was to 
make it easy to disassemble and reassemble the joint in order to remove 
the lyre from the piano while leaving the top block (ok, capital) in place.

Mike



On 12/12/2011 4:20 PM, William Monroe wrote:
> Hi Mike,
>
> Sure.  A pegged mortise and tenon is a pretty cool joint.  Can't say 
> I've seen it in a piano before, but elsewhere.  The design is to 
> offset the hole in the tenon just slightly, so that when the peg is 
> driven in, it tightens the joint fully.  Prior to drilling, the two 
> pieces can be clamped together, then using an undersized transfer 
> punch, hold it to the bottom of the hole in the capital (top piece of 
> the lyre) and mark for drilling.  Then after you have drilled, a new 
> tapered dowel should pull the assembly together nicely.
>
> It's likely that whomever installed the machine screws enlarged both 
> holes and goofed up the otherwise elegant design.
>
> William R. Monroe
>
>
>
> On Mon, Dec 12, 2011 at 3:39 PM, Mike Spalding 
> <mike.spalding1 at frontier.com <mailto:mike.spalding1 at frontier.com>> wrote:
>
>     I brought home a Kimball lyre to repair:  loose joints, top and
>     bottom.  The lower joints (post to pedal box) were more or less
>     conventional round tenons, on which the epoxy is currently curing.
>      The top joint is one I've never seen in a piano before.  Did I
>     mention the piano is a former player?  Anyway, the post has a
>     square tenon which fits very loosely into a 3-sided mortice in the
>     top block, and is secured with a tapered dowel.  Well, it was at
>     one time.  The tapered dowels had been replaced with steel machine
>     screws, so the whole thing was really floppy.  I roughed out a
>     couple of tapered dowels and fitted them in the holes, and I'm not
>     satisfied with the way the joint fits together.  The main problem
>     is that with the dowels in place, the top block is held almost 2mm
>     above the shoulders of the posts.  I'm considering whether to plug
>     and re-drill the dowel holes in the posts, or build up the block
>     to meet the shoulders.  I'm also considering drilling out the
>     tapered holes and using a straight dowel.  Anybody ever seen this
>     joint before?  Any insights or free advice?
>
>     thanks
>
>     Mike
>
>
>
>