Screw

What it is

The screw is the mechanism at the end of the bow that adjusts hair tension. The part the player turns is properly called the button, and the threaded shaft running inside the stick is the screw. More of this kind of thing is in the anatomy section.

Turning it clockwise draws the frog toward the button, tightening the hair. Counter-clockwise loosens it.

How it works

The button is fixed to a threaded metal shaft that runs forward inside a channel bored into the stick.

The shaft engages an eyelet, a small threaded metal insert set into the underside of the frog.

Turning the button rotates the shaft, which drives the eyelet forward or back, sliding the frog along the stick. Since the hair is anchored at the frog and at the tip, moving the frog changes the tension.

The whole assembly is small, precise, and does its job under constant load.

How tight is right

The common guideline is that a pencil should fit between the hair and the stick at the middle of the bow.

It is a rough guide rather than a rule. What matters is that the stick retains its curve. If the stick has been pulled straight, the hair is too tight.

Under-tightening produces a bow that feels sloppy and where the stick contacts the hair under pressure.

Over-tightening is worse. It stresses the camber, makes the bow feel stiff and unresponsive, and reduces the natural bounce that off-string strokes depend on.

Humidity changes the required tension day to day. Hair stretches in damp weather and contracts in dry weather, so the same number of turns does not give the same tension all year.

Always loosen after playing

The most important habit in bow care.

Hair left under tension pulls against the stick's camber continuously. Over months this flattens the curve, and a bow that has lost its camber does not bounce.

This single habit does more to preserve a bow than anything else, and it takes five seconds.

Loosen enough that the hair is slack but not so much that the frog is loose on the stick or the hair can slip off.

What can go wrong

Stripped eyelet. The most common failure. The button turns freely and the frog does not move, or moves erratically.

Usually caused by cross-threading, by forcing the screw, or simply by wear. The eyelet is soft metal and the screw is harder, so the eyelet gives first.

This is a routine repair. A luthier replaces the eyelet, usually quickly and inexpensively. Ignoring it risks damage to the frog or the stick.

Bent screw. Usually from a fall with the bow tightened. The button turns stiffly or binds. Repairable.

Loose button. The button spins on the shaft without turning it. Needs attention.

Seized screw. Corrosion or debris. Do not force it; a luthier can free it without damage.

Cross-threading. Turning the button while the frog is misaligned. Damages the eyelet, sometimes immediately.

Handling

Turn the button gently. It should move smoothly. Resistance means something is wrong and forcing it will make it worse.

When loosening fully, stop before the frog becomes loose on the stick.

When the bow is in the case, it should be loose. A tightened bow in a closed case is under load for however long it stays there.

What it is made of

The button is usually ebony with metal fittings, matching the frog, often with a decorative pearl or metal end.

The screw shaft is steel or another hard metal.

The eyelet is brass or a similar softer metal, deliberately, so that it wears in preference to the more expensive screw.

On fine bows the button may be silver or gold mounted. On carbon fibre bows the whole assembly is often synthetic and metal.

Where it comes up in playing

Only in preparation and care, never during playing.

The relevance to sound is real but indirect: a bow at the wrong tension plays differently, and a player who tightens inconsistently gets inconsistent results without knowing why.

How it is taught

In the first lessons, as part of basic instrument care.

Students are shown how to tighten, how much, and above all to loosen afterward. Many beginners forget for weeks, and a teacher checking the bow at the start of each lesson is how the habit forms.

The consequence is worth explaining rather than just instructing. A student who understands that leaving the bow tight will eventually ruin its bounce is more likely to remember than one who was simply told to do it.

The habit that matters most

Every bow care instruction ultimately reduces to one thing: loosen the hair after playing.

It takes five seconds. It is the difference between a bow that keeps its bounce for decades and one that goes dead in a few years.

The reason is mechanical rather than mystical. Tightened hair pulls continuously against the stick's camber. Wood under sustained load creeps, slowly and permanently. A bow left tight for a year has spent a year being straightened.

Students forget for weeks at a time, which is why teachers check at the start of lessons and why it is worth explaining the reason rather than just giving the instruction.

A student who understands that leaving the bow tight will eventually make spiccato impossible tends to remember.

Understanding how the instrument is built on paper and producing it on the instrument are different skills. We teach both, in private and group violin lessons, in Cumming, Sugar Hill and Dunwoody. Call 470-789-2422 or book a no-commitment evaluation lesson.