Solving the ‘Case of the Missing Hammers’

If you restore more than one or two square pianos it seems inevitable that one will come along with missing hammers and overhead damper arms, and if it has a Geib double action, perhaps a missing intermediate lever or hopper jack. All of these are tapered mahogany slips (in squares later than about 1780), and a quick review will show that a hammer alone requires over ten steps just to produce a finished part ready to glue down to a hammer rail.

With that in mind, I share this approach, which is not the only way to go about this job, but gives the reader a place to start. We first need to get a quantity of similarly wedge shaped pieces, and a good way to do that is as follows:

From a stock of 1 X 4 X  4.25 inch mahogany (20X75X110mm), mount the block in an angle jig for either a circular table, or band saw as below. A little tape will keep the guide and block together as the cut proceeds.


 Set the angle for what you will need, in this case we are set for 5 degrees (twice the angle of either side of an original from its center line.)The cut will start on the block such that we will have a wider tail than required, giving an end that we will remove later. Cut completely through the block, moving the jig and the block as one piece. If you need to, attach a waste strip to your jig to avoid marking it with the saw.

 You should end up with two wedge shaped blocks like this, with the tails a bit wider than the widest hammer in the bass section.

The hammers are grouped somewhat irregularly into sizes on some instruments, and while things will change with make and design, for a circa 1791 Longman and Broderip the hammers are roughly 93 mm long in the bass, and shrink to ~86 mm long in the treble. The width shrinks by about 2 mm as well over the compass. Measure adjacent hammers for best fit, but there will be a chance to make subtle adjustment of the actual strike point later. The lengths quoted may be very different on other squares, so copying the remaining hammers is the best approach. These wedges can now go to a small band saw and sliced into ~3.5 mm thick blanks. Thickness can be adjusted to the requirements of a specific make.

In the same way, dampers, hoppers, and intermediate levers can be made, adjusting the angle of the cut to perhaps a total of 3.5 to 4 degrees for the bass octave, and for the intermediate levers and hoppers.

The hinge end of the hammer is a compound angle cut at a slant and with a bevel, so that the hammer can swing up without interference. We will take a 10 inch length of 1 X 4 pine and glue on two strips to capture the blank we just made. If you are doing dampers as well and will have more than one angle to contend with, make a second base, or fit one of the two sides with slots and screw it in for an adjustable blank holding jig. Now we will mark the block at the correct hammer hinge width and angle of the cut (in this case ~6 deg.) using a remaining hammer, and with the saw at about 45 degrees, cut the blank for a proper hinge butt. The total hammer length is then cut from the thin end of the taper and we are left with a proper hammer shank.

We need to make the guide mortise for the hammer guide rod to act against, which keeps the somewhat flexible hammer hinge in line and makes sure the hammer hits the string correctly every time. Old hinges have so little side to side give it seems that this is not really needed, but a fresh hinge will show you why these were so ubiquitous!

On your drill press, chuck in a 2 mm bit, with only about 0.5 inches or so showing. As you can see, we have marked the center line of the block before gluing down the strips so the blank straddles the line. Back on the press, clamp blocks on the press table to allow the plank to travel along this center line only. Lower your drill to just penetrate the pine, set your travel stop at this point, and drill a series of very closely spaced shallow holes about 2 cm long in the area of where the thru-mortise will be, then with the drill down to the stop, move the plank from side to side to mill out a slot.

Mark on the hammer blank where the mortise limits are (mortise is about 9 mm long on most models) and seat the blank firmly in the jig. Drill your closely spaced holes in the blank and then move back and forth to mill a good slot.

Once you get started, a full set can take less than 2 hours to produce to this point.

Turn the shank over and cut the rebate underneath with an X-acto blade. A 60 deg point bit or veining  router bit can be used to make this quickly, but you lose that feel of a good authentic cut face. We just need enough of the original mortise face showing to ride on the guide pin.

Now we will set up our router table with a ½ inch straight bit, and adjusting it to stand only about 0.25-0.5 mm proud, cut the rebate on the back of each hammer at the hinge end, to receive the hinge leather. Whatever hinge leather thickness you are using, divide that by ½ and set that as the rebate depth.

There is a bottom piece for each hammer that is a mirror image of the first 20 mm or so of the butt end, complete with bevel and rebate, and these are cut as before.

The hammer core is usually of lime wood, but poplar works also. There are several basic hammer head shape variations. Copy your style for a good match. The blade form is shown, and his may or may not have beveled sides, but usually is tapered from end to end, and copying adjacent hammers can set the angle and length. These are glued on the tapered tips.

Now you are ready to leather. The subject of leather choice is long and controversial, but deferring to the gentlemen at Broadwoods, we could do worse than selecting a fine flexible skein of vegitable tanned sheep about 1.0 mm thick for the hinge, and oil tanned deer about 1.o mm thick for the hammer coverings (two layers, cut like a butterfly to image the block as above, smooth side down, and glued on the sides only.) Install the hammer on the rail, set the action in place, and hook the hammer from below to bring it in contact with the string. Mark on the leather the point between the two unisons for each hammer. Remove the action, and with a strip of buff deer leather perhaps 1.5 mm thick or so (tapered in width from bass to treble from about 6-7 mm down to 2.5-3.5 mm) wrap the hammer end to engage the unison pair, gluing again on the side but not the top. Adjustments can be made later on select hammers that don’t hit quite where they should. Vegetable or brain/oil tanned leather seems best, but the subject of thickness, type choice, tanning, and quality is far too enormous to be addressed here, so check out the page on re-leathering hammers for more information. Treat the suggested dimensions above as only the roughest guides. I’d be delighted to hear how others have approached this task!

Comments are closed.