[pianotech] unusual lyre joint

[William Monroe]

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>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
>
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