Practice chanters

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Six Great Highland bagpipe practice chanters in 3mm plywood, alike except for their bores. One has a triangular bore, the others square, pentagonal, hexagonal, heptagonal and octagonal. Two more are built differently, from four long strips round a square bore: the strip chanter, whose holes come from the model, and the standard strip chanter, whose holes are a real practice chanter's. Each is a stack of thin cross-section plates with the bore cut through every one, clamped on two threaded rods, under a stacked cap and mouthpiece. The only part you buy is a plastic practice-chanter reed.

Output is millimetre-true — 1 user unit = 1mm with a physical width/height — so it prints and cuts at real size.

None has been cut or played yet. The holes come from an acoustic model that has not been checked against a real chanter, and the reed's length inside the cap is a guess. Before you cut says what that costs, and Tuning how to take it up.

the pentagonal chanter: every plate on one sheet

Built for LaserMadeMusic.

The rest of the build files — every instrument, generator and tool, indexed.

Download everything as a ZIP

Where the cut-off is

Built as stacked plates, there is no cut-off between three sides and eight. Every shape builds, fits one sheet and tunes in the model. What a bore's cross-section needs is the right area. Its shape matters far less: a square-bored chanter was built on exactly that principle, a square of the round bore's area at every point. Here every bore is the area of a 4mm circle, 12.57mm², the bore most practice-chanter makers drill. A plate is a slice across the chanter, so the polygon is simply cut out of it, and any polygon can be.

Two things change with the number of sides, and neither stops the build:

• The faces shrink. Each face of the bore is 5.39mm wide on the triangle, 3.54mm on the square, 2.70mm on the pentagon, 2.20mm on the hexagon, 1.86mm on the heptagon and 1.61mm on the octagon. By eight sides the laser's own kerf rounds the corners and the bore is all but round, so eight is where adding sides stops meaning anything, not where it stops working.
• The triangle has the most wall. For the same area it has 29% more wall than a round bore, against 13% for the square and 3% for the octagon. More wall means more friction losses, so the triangle's notes should be a little less bright and responsive. The model counts that loss.

There is a cut-off if the bore is built the other way, from long strips jointed round it as the octagonal flute is. Each strip is a face of the bore, and its finger joints need ply between them. In 3mm ply at a 4mm bore, only the square works. The pentagon leaves 1.36mm between joints where 3mm is needed. The hexagon and up leave less, and the octagon none. The triangle cannot be finger-jointed at all, since its corners are too sharp for the joint. Thinner 1.5mm stock buys the pentagon. A wider bore would buy more shapes, but then it is no longer a practice chanter. That is why these are stacks.

The chanters

Low G is left out of the worst note: it sounds from the whole bore, and the bore is a whole number of plates, so it lands up to a few cents out. The generator prints how far for each shape.

The holes are not all the same size. Each is the width that puts its note in tune, in a fixed hand layout: the lower hand's four holes 27mm apart, the upper hand's three 27mm and then 21mm apart, the thumb 9mm above G. A hole is a slot cut across one plate, 3mm tall and as wide as it needs. A slot under 1mm wide is too narrow to cut cleanly. Such a hole is drilled through instead, after assembly, at a small V cut into its plate's edge. The drill is the slot's area as a circle, so it tunes the same. On every shape that is G, about 1.3mm; on the square, pentagon and hexagon also D, about 1.9mm.

On the pentagon to the octagon the thumb's slot wants to be wider than 5mm. It is held at 5mm and moved up the chanter until 5mm is right, to the nearest plate, which is why those four are a few cents out. A slot wider than the bore runs in to the bore's middle and ends square there.

The strip chanter

The second design builds the square bore from four long strips of 3mm ply, front, back and two sides, glued round it. The strips run from the sole to just above the high A hole. Above that the chanter is stacked plates, the cookies, up to the reed's seat.

Finger joints do work. The strips are 3mm thick round a 3.54mm bore. At each corner one strip has a finger 3mm deep and its neighbour a notch. Each strip has fingers along one edge or the other in turn, so it is seldom only its 3.54mm middle. Round each hole its own strip has fingers along both edges, 1.5mm past the hole, so the ply beside a hole is never a notch. The strip across from it then has none, for 4 to 10mm: the back strip opposite each front hole, and the front opposite the thumb's. Glued into the square, those stretches are held on all four sides. The fingers also line the strips up as they go together, which butt joints leave to you. With --joint=butt the front and back are 9.54mm wide and the sides 3.54mm, glued between them.

Why the holes are small. The holes are spaced for the hands, 27mm apart in each hand, but the scale's steps are not equal, so each hole is whatever size puts its note in tune where it stands. A hole for a small step, such as D or G, comes out small. The largest is limited by the bore: a hole wider than the bore's 3.54mm face would cut into the side strips, so 3.2mm is the most. The hand's layout is set by C and E, which are solved at 2.5mm and pull every other hole along with them. The wall's thickness matters little: with an 8mm wall the holes are within 0.4mm of these. It does matter for G. F to high G is the scale's smallest step, so G must sit 16mm above F instead of 21mm. Any further and high G would be sharp even at a 1mm hole.

The thumb has room. The cookies stand 5mm proud of the strips. The high A hole's centre is 10.5mm below that shoulder, so the thumb can seal it. Pass --switch=0.8 to put the change 4/5 of the way up instead.

The staple stops on its hemp. The round bore under the seat is 4mm, the size of the smallest staple, so a 4mm staple could slide on into it. A larger one stops on the bore.

What is glued. The strips to each other, and the strips into the cookies' socket. The cookies are clamped on rods, and the cap press-fits as on the plate chanters.

Building it:

1. Cut the sheet. Dry-fit the four strips first: each strip's two edges have different finger patterns, so it goes in only one way.
2. Glue the strips round a length of 3.5mm rod or a waxed drill bit, to keep glue out of the bore. Clamp lightly and wipe off any glue that squeezes out.
3. Thread the cookies onto the two rods, from the seat down to the socket, with a nut and washer at the seat end. Brush shellac on each face as it goes on.
4. Glue the strips' top 15mm into the socket. Put the bottom washers and nuts on and tighten them. Cut the rods flush with the top nuts.
5. Seal the bore with shellac on a pipe cleaner, and fit the cap and reed as on the plate chanters.

The standard strip chanter

This one takes its holes from a real practice chanter: aero1016's model of the practice chanter they own, measured from its 3D file. That chanter has a 4.87mm round bore, 238.5mm from the sole to the reed's seat, its front holes 25mm apart, and a collar 10mm under the seat that the top rests on.

Every hole is where the reference's is, measured from the reed's seat, which is what the notes depend on. The sizes differ because a hole here goes through a 3mm strip, where the reference's walls are 5 to 7mm. A hole through a thinner wall sounds sharper, so it has to be smaller for the same note. A 4.5mm bore, the smallest that takes the reference's 4.15mm hole, would need holes of 2.5 to 3.2mm. The 5.5mm bore is the size at which they come back to the reference's, 3.2 to 4.1mm. Each is solved so its note sounds where the reference's does, in the model, and the bore is 3.8mm longer at the sole to bring low G there too.

The model is used only for the difference, not the pitch. It cannot reproduce the reference's own scale: at the reed allowance that fits best, 130mm, it is still about 40 cents out across the scale, low A at about 255Hz. So it is asked only how far the square bore and the thin wall move each note from where the reference's is. That is a much smaller question, and it plays at whatever pitch the reference plays. The reference's maker had not yet printed it, so that pitch is the real chanter's they measured, not one anyone has checked on the print.

Shellac barely moves the pitch. Dipping the chanter four times in 3 to 5 lb cut leaves perhaps 50 to 100µm of shellac on each surface. That is an estimate, not a measurement: the first coat soaks into the ply, and the film depends on the cut and how it drains. It narrows the bore from 5.5mm to between 5.4 and 5.3mm, and every hole by the same 0.1 to 0.2mm. In the model that flattens the notes by 1 to 3 cents, the high notes most. Watch for shellac pooling in the bore's corners and bridging the finger holes: blow through the chanter after each dip, and clear each hole with a toothpick. The seat narrows the same way, to about 5.4mm, still over the largest staple.

High A has room. The thumb reaches up past its hole, so the band leaves the back bare. The side pieces of the band are cut away along a quarter circle where they meet the back, so they slope up to the collar rather than ending square beside the thumb. Nothing stands proud of the back strip until the collar, 22.1mm above the hole's centre. On the reference chanter, its collar is 20.6mm above.

Cut the sheet, and glue the strips as in the strip chanter's first two steps, round a 5.5mm rod or waxed drill bit. Then:

1. Press the jig's base and two rings together on two 2mm pins, and line the cup with packing tape or wax so the glue cannot stick to it. Stand the chanter in it on its sole. Glue the foot's layers in round the strips one at a time, the circle centring each. Each piece runs round one corner of the circle to the inner corner beyond. Each layer turns the other way from the one below, so no seam runs through.
2. Glue the band round the strips' top 10mm: the wide piece across the front, the two narrow ones on the sides, flush with the back, their curved corners at the back and down, away from the collar.
3. Glue the strips' top 3mm into the collar's socket plate, and that plate to the collar's round plates above it.
4. Press the collar's round plates and the tenon together on two 2mm pins. Cut the pins flush with the collar's bottom face. Their ends land on the strips' top corners, inside the socket plate.
5. Glue the cap's 40 rings and its top plate together, top plate last. Lay them in the inside corner of two straight boards while the glue sets, which lines up their outsides. Then glue the mouthpiece on as for the other chanters.
6. Seal the bore with shellac on a pipe cleaner, and brush the inside of the cap.
7. Push the reed's staple into the seat. Wrap the tenon with hemp or tape until the cap slides on snugly and rests on the collar.

How it is built

From the top down:

• The mouthpiece, 24 round plates with a 4.5mm blowing hole, shaped as the measured practice chanter's top piece is: a 45° shoulder off the cap, a step to 16.5mm, a step to 14.3mm, then a long taper from 12.4 to 11.0mm and a rounded lip. It is 72mm long, the reference's 71.5mm. Each plate is cut to the reference's diameter at its own mid-height, so the long taper goes down in steps of under 0.1mm. The plates are too narrow for pins, so they are glued, lined up on a rod through the blowing hole.
• The cap: two top plates, twelve plates round a 14mm chamber for the reed's blades, and five plates whose hole is the body's own polygon, 0.3mm larger, to slide over the top of the body. It is the body's shape grown 6.3mm outward, pressed together on two pins in its corners.
• The seat: six plates with a 5.5mm round hole that takes the reed's staple. Practice-chanter staples run 4 to 4.8mm across. The bore below is narrower than any of them, so the staple stops on it.
• The bore: one plate for every 3mm, the polygon through each, down to the open sole. Eight of them carry the finger holes.

Every body plate has the same two rod holes, placed so that turning or flipping the plate puts them somewhere else: a plate threads on only one way, so no slot can end up facing the wrong way. The rods are clamped by a nut and washer at each end. A pin pressed through 130 plates would never go in, and nothing is glued. The cap is not on the rods, since it comes off to set the reed. It slides over the top five plates of the body and rests on the two top nuts.

Turn them in 3D

Before you cut

Measure the ply. The stack multiplies the stock's error by every plate in it. 2.9mm ply makes the bore 13mm short, and every note 50 to 57 cents sharp in the model, which is a quarter-tone. Measure a few places on the sheet with calipers, then pass the average as --plate=. The generator re-solves every hole on that grid, and the plate count follows.

The reed's length is a guess. The model treats the reed and staple as 20mm of extra closed bore, which is not a measured figure. A reed pushed deeper into its seat plays sharper, and one pulled out plays flatter. That is how every practice chanter is pitched, and it shifts the whole scale together, but it cannot fix one note against another. --reed= sets the figure if you measure your own.

The model does not match a real chanter. It is a transfer-matrix model with textbook tone-hole and end corrections. Given the measured chanter that the standard strip chanter copies, it cannot reproduce that chanter's scale at any reed allowance. The closest, at 130mm, is still about 40 cents out, and at the 20mm the six plate chanters and the strip chanter were designed with, the reference's scale comes out stretched by hundreds of cents. So the model's own designs may play well out of tune, with the upper notes sharpest, until a real chanter has been played and the model fitted to it. The standard strip chanter avoids most of this by copying a real chanter and using the model only for the difference. For the others, expect to do the Tuning in earnest.

The slots are cut exactly to width, so a kerf other than the default 0.13mm changes every hole. Pass yours with --kerf=.

Building it

You need two lengths of M2 threaded rod, four M2 nuts and washers, a few centimetres of 2mm brass rod for the pins, high-cut shellac, and a plastic practice-chanter reed.

1. Cut the sheet. The generator prints the stacking order for its shape. For the square it is: 6 seat, 51 bore, hA, 2 bore, G, 6 bore, F, 8 bore, E, 5 bore, D, 8 bore, C, 8 bore, B, 8 bore, A, 22 bore. Here "seat" and "bore" are runs of the plain plates, and the letters are the hole plates.
2. Cut the rods to the length the generator prints: 403mm, or 406mm for the triangle. Put a nut and washer on one end of each.
3. Thread the plates on from the sole up, in the reverse of that order. Brush thin shellac on each face as it goes on. The slots all face the same way because the rods only let them.
4. Put the top washers and nuts on and tighten them evenly, just enough to close every seam. Cut the rods off flush with the top nuts, or the cap will rest on the rods instead of the nuts. Let the shellac dry.
5. Drill the small holes at their V marks, starting a size under the printed figure. Then seal the bore: draw a pipe cleaner wet with shellac through it a few times, and let it dry. Brush the inside of the cap the same way.
6. Press the cap's plates together on two pins through its corners. Stack the mouthpiece's plates, widest first, on a 4.5mm drill shank pushed down through the cap's top, gluing each one, and pull the shank out before the glue sets. Sand the steps of the long taper smooth if you like.
7. Push the reed's staple into the seat. Wrap it with hemp if it is loose. Put the cap on.

Tuning

Tune low A first, by moving the reed in or out of its seat. Then go up the scale:

• A note that is flat wants its hole bigger. File the slot wider a little at a time, or open the drill up a size.
• A note that is sharp wants its hole smaller. Line part of the slot with tape, or with a sliver of veneer and shellac.
• Low G has no hole. Tape across part of the open sole flattens it.

Widening a hole moves its own note most, about 10 cents for a fifth wider in the model. The notes either side of it move a cent or two, so go up the scale once, then check every note again and touch up.

Regenerating it

python3 practice_chanters.py --sides=5 --no-write          # the checks, writing nothing
python3 practice_chanters.py --sides=5 --out=cut-files     # its sheet
python3 practice_chanters.py --sides=5 --plate=2.9 --no-write   # for ply as measured
python3 practice_chanters.py --sides=5 --reed=24 --no-write     # a different reed allowance
python3 practice_chanters.py --sides=5 --low-a=233 --no-write   # a different pitch
python3 practice_chanters.py --sides=5 --kerf=0.18 --out=mine   # for a laser with a 0.18mm kerf
python3 strip_chanter.py --out=cut-files                   # the strip chanter, finger-jointed
python3 strip_chanter.py --joint=butt --out=cut-files      # the strip chanter, butt-jointed
python3 standard_chanter.py --out=cut-files                # the standard strip chanter
python3 standard_chanter.py --joint=butt --out=cut-files   # the same, butt-jointed
python3 practice_chanters.py --page-to=turn.html           # the 3D view, every design
python3 chanter_model.py --sides=5                         # the acoustic model alone

practice_chanters.py draws nothing until every check passes:

• every note is in tune in the model, and low G is as near as whole plates allow;
• the bore is a 4mm round bore's area;
• the bore is whole plates, down to the sole;
• every finger hole is in its own plate, at its centre;
• every hole is cuttable or drillable;
• every slot runs the width it is tuned for;
• every rod and pin keeps ply between it and every cut;
• the nuts sit on the end plates, inside the body;
• every body plate goes on only one way;
• the seat holds a staple, and the bore stops it;
• the cap slides over the body and stops on its nuts;
• every sheet fits the bed;
• no two parts on a sheet come closer than the gap;
• every part is on a sheet.

practice_chanters.py imports the kerf and the Part class from the square flute's square_flute.py, the mitred offset from the four-hole ocarinas' four_hole_ocarinas.py, the path writer from swept-curve and the 3D page from lasermade-tools. So square-flute, four-hole-ocarinas, swept-curve and lasermade-tools must be checked out beside this repository.

Files

Every chanter is one sheet of 3mm ply.

Released under CC0 1.0.