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This article was published in the August 2016 edition of More Woodturning
Also see:
Whistling Top
Whistling tops of Cherry and Acrylic
Introduction
Traditionally, whistling tops are oval or acorn shaped,
have a single square hole, and are made of semi-precious materials like ivory or
at least boxwood or some other wood whose hardness is measured on the Mohs
Scale. However whistling tops are
also traditionally hard for first-timers to make work.
In an effort to avoid the latter tradition this article will avoid the
former tradition.
One of the critical things in making a whistling top that
works is the ratio between the hole area and the volume of the chamber.
On the lathe, it’s easier to actually get the volume you’re trying for if
the chamber you’re turning is a simple cylinder.
As tops with a low center of gravity are more stable and spin longer,
this article uses a short squat point.
Having experimented with various hole configurations to
measure the rpm needed to whistle (I used a Foredom handset with a 1/4” collet
and a stroboscopic tachometer) I found that two medium sized round holes would
whistle at a lower rpm than one big round hole or even one square hole (some of
my early tops looked like Swiss cheese if the tape covering the unused holes was
removed). The rpm required, by the
way, is in the range of 4000 to 8000, depending on the top diameter, hole
configuration, and pitch of the note (yes, it’s complicated, which is one of the
reasons people traditionally have trouble making them work).
So don’t expect to be able to test the top by spinning it on the lathe
(instead use a straw). Neither will you be able to make a finger spun top work.
You’ll need a top launcher and pull string.
Briefly, a tenon is turned on the shaft blank and an
optional Corian tip blank prepared.
The top body blank is turned round with a mounting tenon and then reversed.
A hole to both mount the handle and indicate hollowing depth is drilled,
then the shaft blank is glued in and shaped.
A tenon is formed on the top of the top and the top parted off.
Holes are drilled in the side of the body and then the body is hollowed.
The body is reversed and the tip turned and finally the top is glued together.
The photos follow using #1 jaws in a Oneway Stronghold
chuck, but of course you can substitute other mountings.
Dennis Daudelin and Ian Salisbury collaborated in developing this article
but bear no responsibility for my eccentricities or any mistakes in executing
it.
Preparing the Blanks
Cut a faceplate oriented piece that’s 2-7/8” on a side and
1-1/2” thick for the top body blank.
I used cherry, but any reasonably fine grained diffuse porous hardwood will do.
Use corner to corner diagonal lines to find the center, then mark the
diagonals 5/16” away from center to help center the blank when it’s mounted for
roughing on the lathe (a Oneway cup center tailstock is just under 5/8”
diameter) as shown if Figure #1.
Figure #1:
Mark the turning blanks.
Cut a maple 3/8” dowel 2” long for a shaft blank.
If you don’t have maple dowels, cut a 2” piece of decent hardwood.
Mount the shaft blank in #1 jaws in your 4-jawed chuck and turn a 5/16”
diameter tenon that’s about two parting tool width’s deep as in Figure #2.
Figure #2:
Turn a 5/16” tenon on the shaft blank.
You can just turn a point on the bottom of the top, however
wood wears quickly, at least on a basement floor, and a top with a worn point
tends to travel around a lot. Corian,
or some other hard plastic, is a reasonable compromise between a wooden point
that’s too soft and a metal point that might damage floors.
So optionally, mount a square of Corian in the #1 jaws in your 4-jawed
chuck. Create a dimple for a cone
center tailstock with your skew or a stub centering drill and bring up the
tailstock for support. Then turn the
Corian point blank to 5/16” diameter.
It only needs to be 1/4" or so long, but why not turn enough for a few
points while you’re at it as shown in Figure #3?
Figure #3:
Turn a Corian point blank to 5/16” diameter.
Preparing the Top body
Knock out the point of your cup tailstock center.
This will let you adjust the blank to center it, as well as not put a
dimple where the point should be if you choose not to use a Corian insert.
Fully closed, #1 jaws don’t provide a stable platform to pin the blank to
for roughing to round. If you keep
your chuck cleaner than mine, if the jaws are not clamping on something the
chuck may open when the lathe is on.
To prevent this clamp a small scrap wood square in the chuck.
Bring up the tailstock center to gently pin the blank to the chuck as in
Figure #4. You can tap the blank
(with a tool handle, for instance) until the cup is centered, as in the inset of
Figure #4, between the marks made earlier.
Then clamp the blank securely to the jaws with the tailstock center.
Figure #4:
Mount the Top Blank for roughing round.
Use a small bowl gouge and turn the blank round as in
Figure #5. You may wish to refine
the surface with a shear scraper.
Then use a parting tool, or bowl gouge followed by a parting tool, to form a
mounting tenon as in Figure #6. The
tenon should be about 1-3/4” in diameter (small enough that the chuck jaws will
be recessed below the side of the blank) and a parting tool width deep.
Figure #5:
Turn the blank round.
Figure #6:
Turn a mounting tenon on the blank.
Turn Shaft and Lid
Mount the top blank in your 4-jawed chuck via the tenon.
Then true up the face of the blank.
Mount a 5/16” drill bit in a drill chuck and hold it against the top
blank so that the tip is about 1/8” from the shoulder of the mounting tenon and
wrap tape around the bit to mark the drilling depth as in Figure #7.
Create a starting dimple for the 5/16” drill bit with a skew or stub
drill. Now mount the drill chuck in
your tailstock and drill to the marked depth as in Figure #8.
This hole will serve both as a mortice for the shaft and a depth
indicator when hollowing the top.
Figure #7:
Mark drilling depth.
Figure #8:
Drill to the marked depth.
Spread some wood glue in the mortice and insert the shaft
tenon. Use the cone tailstock center
(with the center still removed) to clamp the shaft in place as in Figure #9.
As the cup of the tailstock center is larger than 3/8”, if your shaft
blank is reasonably close to being cut straight across the tailstock center will
help center the shaft as well as serve as a clamp.
Figure #9:
Glue and clamp the shaft in place.
Mark the shaft for turning.
First mark a shoulder about 1/8” from the face of the body.
Then hold your launcher (if you don’t have one, a 6” piece of 3/4" I.D.
PVC pipe with a 5/32” hole drilled close to one end works well) with the side of
the launcher at the shoulder mark.
Mark the approximate center of the launcher hole for a pull string hole.
Then mark a spot about 1/4”
past the other end of the launcher.
Drill a 1/8” hole through the shaft at the middle mark for the pull string.
The result is shown in Figure #10.
Figure #10:
Mark the shaft for turning and drill a hole for the pull string.
Turn between the shoulder and end marks to a diameter of
1/4". True up the shoulder and then
part off the nub. Sand the top of
the body and shaft. Polish the top
face of the body and the shaft if you’re using a friction polish.
The result is shown in Figure #11.
Figure #11:
Turn the shaft, then sand and optionally polish the face of the
top and shaft.
Use a standard parting tool to make a cut about 3/32” to
1/8” (depending on how confident you feel about hollowing) deep about 1/16” from
the face of the top body. Then use a
1/16” parting tool to part off the lid as in Figure #12.
You will have to widen the slot so the narrow parting tool doesn’t bind
and alternate cutting at the left and right of the slot.
As a standard diamond profile parting tool is 3/16” wide this should
leave a tenon about 1/16” deep on the cap.
If you have difficulty with a deep parting cut with the 1/16” tool,
simply start the cut and then finish with a small hand saw.
It won’t show.
Figure #12:
Form the lid tenon and part off the lid.
Hollowing the Body
You can measure the diameter of the lid tenon and transfer
the measurement to the top body. But
there’s also a no-measure no-math way:
Use the tailstock center to pin the top lid to the body.
You’ll have to check visually that it’s centered.
Turn the lathe on and stick a sharp pencil into the corner formed by the
lid tenon and top body as in Figure #13.
Just remember to start checking the fit a little further inside the line.
Figure #13:
Mark the top body for hollowing.
Hollow the top body a little deeper than the lid tenon as
in Figure #14, testing until the lid fits.
As I didn’t get a clean parting cut across the shaft stub I hollowed a
little deeper in the center.
Figure #14:
Shallowly hollow the top body to fit the lid.
Align the top body in the chuck so that the side grain
lines up with the chuck jaws. Put
the lid in place. Pin it with the
tailstock center if the fit isn’t tight enough to stay by itself.
Line up a ruler with the middle of a jaw that aligns with the face grain
of the body and find the center between the mounting tenon shoulder and the top
of the lid and make a mark as in Figure #15.
This will make the hole appear centered when the top is completed.
Repeat for the other side.
Drill shallow 9/32” holes at both marks as in Figure #16.
Drilling the holes before hollowing, and locating them on face grain
makes clean holes more likely.
Figure #15:
Mark hole locations
Figure #16:
Drill tone holes.
Now hollow the body of the top to the depth of the depth
drill as in Figure #17. Use whatever
tools you like. You can remove most
of the waste with a small bowl gouge and follow up with side cutting scrapers or
shear scrapers. Be careful not to
change the fit of the lid.
Figure #17:
Hollow the top body.
Pin the lid back on the top body with the tailstock center.
Refine the side of the top (thin the side if the side walls are more than
1/10” thick at the holes). Look
ahead to Figure #23 if you want to tune the top now.
Use a straw to blow across one of the holes.
You may have to vary the angle—usually the straw should be angled down a
little. Sand the side of the top and
polish if you are using friction polish as in Figure #18.
Figure #18:
Thin, sand, and optionally polish the side of the top.
Turn the Bottom
Remove the lid and reverse mount the top body on your
4-jawed chuck in expansion mode. Be
gentle when expanding the chuck as the walls are thin—but test to make sure the
grip is secure by trying to turn the top body.
If you’re using the optional Corian tip, mark a 3/16” drill
bit for a depth of about 1/4”.
Create a dimple in the center of the top bottom with a spotting drill or with
your skew, then mount the drill bit in a tailstock mounted Jacob’s chuck and
drill in 1/4” as in Figure #19. Use CA glue to secure the Corian tip blank in
the drilled hole and briefly clamp it in place with a tailstock center as in
Figure #20.
Figure #19:
Drill for the Corian tip blank.
Figure #20:
Glue and clamp Corian tip.
Cut off the excess Corian with a narrow parting tool (or by
hand with a saw). Turn a point on
the bottom, blending the surface with the shoulder tenon.
Then sand and optionally polish the top bottom as in Figure #21.
Figure #21:
Turn a point of the bottom of the top.
Complete the Top
Remove the top body from the chuck.
Spread a thin coat of wood glue on the lid tenon and clamp the top
together as in Figure #22 until the glue cures.
If you’ve polished the top as you go, you should be able to wipe away any
glue squeeze out before it sets.
Figure #22:
Glue and clamp the top lid on the body.
Pre-test the top to see if it will whistle by blowing
across an opening with a straw as in Figure #23.
You may have change the angle of the straw—usually it has to be angled
down somewhat. Making a whistle with
the straw is necessary but not sufficient for whistling when spun, particularly
with large holes. If you’ve followed
the instructions in the article and thus have the same chamber volume as my top
it really should work. If it doesn’t
whistle, check to make sure the edges of the holes are sharp and clean.
If you want to change the tone you can make it higher in pitch by
enlarging the holes. You can usually
enlarge the hole with a hand held drill bit 1/64” inch at a time without
significant tear out. Alternately
you can use a round file, rolled up sandpaper, or a mini-sanding drum on a
rotary tool. I suggest that you not
be greedy about trying for a higher pitch, as higher pitches require a higher
rpm to work. Figure #24 shows the
completed top.
Figure #23:
Test the top with a straw.
Figure #24:
The completed top.
Variations
After you’ve gained confidence by making a basic whistling
top work you may wish to try different materials, shapes, and sizes.
For instance, the main photo shows an Acrylic top alongside the basic
cherry top. This was made from a
1-1/2”x1-1/2”x1” acrylic blank and 1/2” clear acrylic rod.
It has two 5/32” holes. The
pull string hole is 3/32”, as a 1/8” hole made the shaft too fragile.
But the top is lighter so a thinner pull string can be used.
If you attempt a different shape, I suggest you start with
holes that you know are too small, and gradually enlarge them, testing them with
the straw as you go. Testing with
the straw is a whole lot quicker than winding on a pull string and spinning the
top. If you want to try
extrapolating or predicting what hole area, chamber volume, and edge thickness
(or neck length) will work, read the Wikipedia article on Helmholtz Resonance
at:
https://en.wikipedia.org/wiki/Helmholtz_resonance