Making Keys for Uilleann Pipes, Part II
by D.M. Quinn
In the previous installment we took a look at the various types of keys that have been used on uilleann pipes over the years, and began an examination of the techniques involved in the forging or cold-forming of chanter keys.
As we left the process last time, the key blanks had been roughly shaped by spreading out the touch end. The technique as laid out can be summed up rather simply: one alters the shape of a piece of brass (or a similar non-ferrous alloy such as nickel silver) by hammering on it in a controlled and directed way, and reannealing the workpiece as necessary to avoid fracturing the metal.
The piece of metal as shaped by the forging process is not particularly nice to look at, and at this stage only suggests the look of a finished key. The rough forgings are quite a bit bulkier than they will be when finished. The process of forging shifts the mass of the metal into a shape from which some metal must then be cut away to yield the final shape. There is still a good bit of work left to be done.
A key, in any position on the uilleann pipes, must be of a particular size suitable for its role. The size and shape of its pad area must be determined by the nature of the hole it is to cover. Its touch end must be in a particular position to be comfortably reached by the player’s hand. The extent to which the key opens is critical to its musical performance, in that it must be possible to open the key quickly and far enough to allow the note to sound without breaking or otherwise causing undesirable acoustical artifacts. If two or more keys are mounted near each other, the actions of the keys should not interfere with each other. The opening action of the key should be such that it does not put undue stress on either the key itself or the block or other bearing in which it is mounted. These factors should all be taken into consideration in the design and plan of each key’s size and shape, and ideally there should be no surprises or ad hoc workarounds when it comes time to put the keys onto the pipes.
For many years now it has been my practice to make at least a sketch, and usually a detailed and dimensioned drawing, of everything I make before I lift a tool to make it. For me, the first tool in just about any process is a pencil. This is certainly true of keys. My drawings allow me to determine just how long a key needs to be, where the key will pivot, and how much it can rotate around the pivot. In the early days, my drawings were indeed all pencil on paper, but I have been using Computer Aided Drafting for quite a while now, and have come to depend on some features of computerized drafting. It is, for example, quite easy to rotate a drawn entity around a given point, just as a key rotates around its pivot, so one may see with some accuracy how the key is likely to perform in its place. A CAD program also allows you to determine the dimensions of a drawn entity to a very precise degree, so accurate plans can be made ahead of time.
With information about how long a key needs to be and where its pivot point is to be, we can proceed to cut or file away some to the excess metal. The first of the steps involved in shaping the key is to shape the touch. For most chanter keys, I like to use a very simple tear-drop shape, and I shape them freehand using a disc and belt sander. It may help to draw the shape you want to achieve with a pencil or Sharpie on the metal itself, or to refer to a sketch while shaping the key at the sander. Certainly, you should have a clear idea of the overall length required in order to make sure that you do not “cut yourself short.” The disc sander is a flat surface and can only be used to shape the convex parts of the curve of a touch. For the concave portions, I use the barrel at one end of the sanding belt.
At least part of the shank of every chanter key has a rectangular section where the sides of the key are parallel to agree with the parallel sides of the slot into which it will fit. The danger of using the barrel section of the belt sander is that it is all too easy to remove metal which should be left to form a smooth transition from the concave part of the curve to the straight sides of the key. Unfortunately, this is another skill that costs time and failures to learn.
The same end can of course be achieved using only files, and in any case I always touch up the shapes with a file, to try to make them as symmetrical as I can, or in the case of asymmetrical keys, to make the transitions as smooth as I can get them.
Before moving on to the next step, I want to say a few words about safety while using a power sander. Brass and nickel silver are both quite good conductors of heat, and applying a key to a sander under power will generate plenty of it. I do not think it is a smart idea to wear gloves of any kind while working with a sander, so one needs to have a plan for what to do when the key gets hot. If you are working on a large batch of keys, it is feasible to work on one piece until it becomes too hot to handle, then put it down and work on another. If you are working with just a few pieces, it may make sense to dip a hot piece in a pot of water kept nearby. You must be particularly careful with sleeves, aprons and hair, and take appropriate precautions to keep them well away from and clear of the moving parts of the sander. Never use a power sander without appropriate eye protection and a dust mask. Make sure that you understand the normal conventions of safe operation before you use any power tool.
At this stage, the shape of the key has been established “in plan,” i.e. looking down onto the key, but its shank is still the full section of the rectangular bar from which it was forged.
After the shapes of the touches have been established it is possible to determine the overall length of the key and the position of the pivot. I use my drawings as a guide, as shown, to mark the positions of the three cuts that I usually make with a bandsaw. These cuts may also be made with a conventional hacksaw, but this is obviously more time-consuming. The first cut brings the shank of the key roughly to length, and the next two remove the bulk of the excess metal. I usually leave the key shank close to its full width at the point where the pivot will fall.
Sawing an irregularly shaped piece on the bandsaw can present difficulties. Providing adequate support for the material as it is being cut and making sure that the support is as close as possible to the point at which the cut is being made can be challenging for small pieces such as key forgings. I use a piece of scrap material clamped to the saw table to support the keys as they are being sawn.
Sometimes because of the shape of the key it is only possible to provide support under a very small section of the key. The keys with curved touches are fairly easy to support well, but the straight keys require more planning: often it is only possible to support a key in the immediate area of the cutting while part of the key must extend over the edge of the support block. When sawing any key in this manner on the bandsaw, the hands are very close to the moving blade, and it is a time for serious concentration. The key should be advanced into the moving blade only by the motion of the fingers, with the heels of the hands both firmly anchored on the saw table or on the supporting block clamped to it. The process is inherently dangerous, and unless you have a clear idea of what to expect and how to go about preparing for it, I recommend that you stick to a muscle-powered hacksaw.
It may also be worth pointing out that not all bandsaw blades are appropriate for this type of work. The conventional wisdom is that there should be at least two teeth in contact with the workpiece at all times. Therefore, it would not be appropriate, for example, to attempt to saw a piece of brass 1/8” thick using a blade with only four teeth per inch. Strictly speaking, one should use a blade with 16 or more t.p.i., but a blade of 10 t.p.i. will always have at least one tooth in contact with the work, which seems to be adequate to prevent too aggressive a feed. In any case, I routinely use a 10
t.p.i. blade when doing this sort of work, and keep a separate 4 t.p.i. blade for sawing wood.
If you are sawing nickel silver, it is rather important that you organize some method of reducing blade speed to a level considerably slower than what is conventionally used for sawing wood. This can be achieved with a jackshaft or counter shaft, or by using a variable-speed motor to drive the bandsaw. My own bandsaw is fitted with a speed-reduction gearbox, a feature which has paid for itself many times over in the twelve or so years I have owned the machine. It is possible to saw brass using the same speed as for wood, but blade life is increased dramatically by slowing down the cutting speed, thereby reducing the amount of heat generated in cutting. If you attempt to saw nickel silver without reducing blade speed, you will very quickly blunt the teeth of your bandsaw blade. I keep a block of beeswax on the saw table when I am sawing nickel silver or large quantities of brass, and lubricate the blade with it frequently while sawing.
After the rough cuts on the bandsaw (or with a hacksaw) I use hand files to continue the shaping process, and to even out the curves under the touches of the keys. This involves holding the key forgings in a vise, projecting so as to allow access with the various files.
Most workshop vises are fitted with steel jaws, usually with some sort of striations to “improve” the grip. Even if the jaws of your vise are perfectly smooth, they will leave marks on the relatively softer brass or nickel silver if they are clamped with enough force to hold them steady. Some kind of padding is essential to prevent this. I have fitted the jaws of my favorite vise with smooth brass faces, but even this precaution is insufficient for some of the smaller keys, where the clamping force is concentrated on a very small portion of the key. If I am going to be doing any quantity of this sort of work, I will line the vise jaws with strips of wood (cut from what are essentially large tongue-depressors or popsicle sticks) held in place with masking tape. These are meant to be sacrificial, and I do not expect them to last for more than a couple dozen keys. (Please see Fig. 04 above.)
Once the keys have been shaped to my satisfaction, I refer again to the drawing to determine the finished length of the shank, according to my plans. I make a mark on the side of each key to represent the length to which it will be milled. The next step is to cut a concave curve on the end of the shank to mate with a disc to be soldered in place which will serve as the pad of the key. The discs are cut from rod of the appropriate diameter. I prepare as many discs as required by facing the two ends of a rod on the lathe, and then slicing off discs of suitable thickness from both ends. This results in a number of discs all of a consistent diameter and with one side perfectly flat and square to the sense of the rod. Again, if working with nickel silver, a slow blade speed is necessary to avoid excess heat and potential damage to the saw blade.
I use a milling machine for the step of making the concave cut on the end of the key shank. The same warning about marring the workpiece with vise jaws is applicable here. I do not believe wooden jaw linings would be appropriate for this purpose, so I have worked up a pair of brass blocks which I use to hold keys for milling processes. Wooden linings such as I use when holding keys for filing would not be appropriate here because the force required to securely hold a piece for milling would be great enough to compress the wood in a way that could make accurate centering unreliable. The brass holding blocks were designed to allow for two different settings, and I prefer to use the longer setting whenever possible.
I use a conventional edge finder to position the workpiece in line with the center of the machine spindle. Fig. 11 shows a key in position for finding its location with an edge finder, but to mill the cove on the end of the piece, it should be positioned with less material projecting from the blocks, i.e., with only enough sticking out that the milling cutter can complete its job without touching the blocks or the vise. Using a simple milling cutter (end mill) of the same nominal diameter as the disc I expect to use as the key pad, I nibble away at the end until a suitable cove is cut in the shank. In other words, I advance the workpiece until it just contacts the rotating cutter, lift the cutter out of the way, advance the piece another 0.002” or so, and bring the cutter down slowly through the workpiece, and repeat these steps until the cove is cut to its full depth. Each pass removes no more than about 0.002” of metal.
Using the same clamping setup and with the machine still in the same alignment, the end mill can be used to skim the underside of the key to make sure it is square with respect to the parallel sides, a feature which will come in handy later when it is time to drill and tap a hole for the screw that will hold the spring to the key. Likewise, if a riveted spring is to be used, a flat and square underside of the key will make for easier going.
Before I acquired a milling machine, I used the lathe to make these coves. I would clamp a block of wood (maple for preference) in the vertical slide, and put a small end mill in the lathe chuck, of the same diameter as the thickness of the key shank. I would then mill a slot in the wooden block, which would therefore automatically be of the correct height with respect to spindle. Then I would chuck a cylindrical hand reamer of the same diameter as the pad disc, and support this with the tailstock. With the key held in the slot in the block of wood, I would then advance the end of the shank against the slowly rotating reamer until the cove was cut. I do not regard this as a particularly good practice, and present it only as an example of the lengths to which we must prepared to go if the “right” tool is not available.
Once the coves have been cut, I will take a fine hand file and make one pass only on each of the two straight edges of the cove, to remove any hint of a bur, and to create a tiny facet.
At this stage, the parts are ready to be soldered together to form recognizable keys. It is a good idea to avoid touching with the bare fingers any surface which will form part of the soldered joint. I use a number of simple holding jigs to make sure that the shank and the pad disc are aligned properly. These jigs were all made from brass bar, which material I chose only because it is easy to machine. If you intend to make something similar, I would recommend annealing the metal fully before doing any machining. Steel would probably have been a better choice, but the brass jigs have given well over ten years of satisfactory service, and so far I have never soldered a key to a jig, which is one of the hazards of which I need to remain mindful.
I use a piece of 400-girt paper to “freshen up” one side of edge of the disc, then place it flat-side down into the jig. The cleaned area of the edge of the disc should be pointing toward the slot which will hold the key shank. I then apply a touch of flux to the disc where the shank will meet it. I then apply a bit of flux to the cove on the end of the key shank, and put the shank into position in the jig, making sure that the shank is pressed firmly up against the disc. Because of the way the jigs and the shanks have been machined, I can be sure that the alignment of the shank to the disc is correct. Then I place the jig on my soldering hearth and apply heat with a torch. The jig, being brass, will soak up quite a bit of heat, and the entire assembly of shank, disc and jig will begin to glow red when it is time to apply the solder. If the joint was properly cleaned and fluxed, and the correct heat is achieved, the solder will flow neatly into the joint and form fillets all around the joint. The solder may ball up upon contact with the joint if the heat is still insufficient to make it flow, so it is important to watch carefully. As soon as the solder flows, remove the heat and allow the assembly to cool. After a jig has been used once, its surfaces will have heavy oxidation, and this is desirable in that the oxidation will help keep solder from flowing where it is not wanted. Still, it is advisable to avoid getting any flux on the jig itself, and to take special care that no flux is present where the disc or the shank touch the holding jig.
When the assembly is cool enough to touch, the key can be safely removed from the jig and pickled in the usual way to remove flux glass and oxidation. If I am doing large batches of keys (the usual condition) I will sometimes quench the key and jig after they have stopped glowing, to speed things up a bit, but I believe it is preferable to allow things to cool down slowly.
When the key comes out of the pickle pot, the top surface of the pad can be formed. My own approach these days is to curve the top surface of the pad using the disc sander, and to leave its top surface slightly proud from the key shank. This is a personal design consideration, and other workers may prefer to have a flush surface. If the top of the pad is flush with the shank, a solder joint line will always be present and noticeable, whereas if the pad is left proud, the solder joint is less likely to be noticed. (This process of rationalization is also known as “making a virtue of a necessity.”) Regardless of whether the pad is flush or proud, there will still be some fillets of solder around the joint which should be removed. A good solder joint depends on there being a microscopic gap between the pieces to be joined, and an absolutely perfectly fitting joint would not allow the solder to flow fully between the pieces. This may be a consideration to be dealt with in other types of joints, but in this case the failure to achieve a perfect mating fit is a good thing and can pretty much be banked upon. If there are fillets around the edges of the joint, it is safe to assume that the solder has flowed adequately between the two pieces, and that the joint is sound and permanent.
I use a small warding file to remove the solder fillets. This is one of my favorites and most frequently-used tools. It is a standard smooth-cut 4-inch warding file, of which one edge has been made “safe,” that is to say, its teeth have been ground away leaving an edge that cannot cut. The handle in which it is mounted has one flat side so I can always know from the feel of the handle which is the safe edge.
After the keys have been brought to this stage, they are ready to be put into place on a chanter or other pipe. There is still considerable work left to be done to finish the key, but the remaining steps must wait until after the pivot holes have been drilled (which I always do with the key in place on the chanter or other pipe) and the springs have been fitted, either by riveting or using a small screw. These operations will throw up burs, require filing on the touch, or entail the risk of marring from clamping in a vise, so it is best to wait until after a key is mounted and its spring has been regulated to go ahead with the finishing steps. We will examine the processes of filing, sanding and polishing in some detail later on in the series.
In the next installment, I propose to have a look at the method of fabrication I have been using for making regulator keys since 1998, and at some processes similar or related to those already presented which can be used for making forged regulator keys.
For a complete PDF of the original Autumn2012 Pipers Review this article is from, click here.
