Two bridle leather strap ends skived to long tapers for a scarf joint on a workbench.
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Skiving a Scarf Joint

ByPeter Joeseph 'Briefcase Maker' Kalafatis

Two ends, two long tapers, one strap that never gets thicker.

A scarf joint joins two pieces of leather end to end by thinning each one on a long slope and laying the slopes together, so the overlap comes out no thicker than the strap on either side of it. Lay two flat ends on top of each other and you get a step, double thick, that catches on every keeper and buckle it meets. Skive the ends first and the step goes away. I have skived bridle loops for a briefcase flap pivot bar and run strips through an old hand-crank splitter, and both jobs taught the same lesson the scarf teaches: leather does not like to be made thinner, and it tells you where you overdid it later, under load.

Video: Skiving Bridle Leather Loops for my Briefcase Flap Pivot Bar, from Marcellino NY Briefcase Maker on YouTube.

Why a strap needs a join

The bend is only so long, and the strap wants to be longer.

Hands skiving a long taper into the end of a leather strap.

I cut from the bend, the butt of the hide, where the fiber runs tightest. The belly goes in the trash and the shoulder goes to small parts. That rule keeps a briefcase honest. It also means the good leather comes in a fixed length, and a long shoulder strap, a leash or a trace can run past it.

That is the job a scarf exists for. The Leather Dictionary’s skiving entry names it directly: when a belt gets lengthened, the ends are thinned to a point so the overlapping surface that takes the glue is larger. More surface, more grip. Same principle a carpenter uses. Wikipedia’s article on the scarf joint describes the woodworking version, two matching tapers joined end to end when the stock is too short, and says those tapers are usually cut somewhere between 1:8 and 1:10. That is wood. Leather stretches, compresses and holds stitches, so the wood ratio is a picture of the idea, not a rule for a strap.

Some makers would rather not join at all. In a leatherworker.net thread on splicing a strap, Dwight Hitchcock suggests cutting one long spiral strip from a large hide so the problem never comes up. In an older thread on splicing, busted would cut a leash from a big oval of hide, the way long draft-horse reins are cut. Both work if the hide is big enough and you can live with the parts of it you end up using.

Marking the slope

Long and shallow beats short and steep, and both ends get thinned on opposite faces.

Decide the length of the overlap first, because everything else follows it. The forum makers do not agree on a number, and that is worth knowing before you trust any one of them.

In the 2011 splicing thread, UKRay suggests a tapered overlap of two to three inches. In a thread on a single-layer splice, Northmount says he aims for about an inch and that a quarter inch does not give enough surface for a strong splice. In the strap thread, toxo wants a long, slanted scarf, glued and stitched, and adds that the method needs leather thick enough and wide enough to take it.

The other mark matters as much. Tom Gregory, in the same strap thread, skives the two ends on opposite sides, one on the grain and one on the flesh, so they lie together with the slopes facing each other. Get that wrong and you have two tapers on the same face that meet like two hands clapping, with nothing to fill the gap.

Mark the start of each taper with a square line across the strap. Mark which face gets cut. Then mark it again, because the first time you skive the wrong side of a good piece of bridle is the last time you skip that step.

Cutting the taper

Many thin passes, a sharp blade, a clean surface underneath.

Side view of a leather scarf joint showing two tapers glued at even thickness.

The slope is cut, not split. A splitter takes a strip down to one even thickness along its whole length; that is useful, but it makes a thinner strap, not a ramp. The ramp is knife work, or tool work that behaves like a knife.

Jeff Peachey’s overview of paring tools sorts the options. English-style knives with a straight blade are the usual choice for edge paring and are comparatively easy to sharpen. Rounded French knives can thin larger areas but are harder to control. For long, gradual bevels, the kind bookbinders cut for rebacking, he turns to a modified spokeshave, and he notes that razor-blade paring machines struggle with bevels. A scarf in a strap is a long gradual bevel. That is a useful thing to know before you buy anything.

His paring guide adds the method. Build the slope with a series of cuts at lower and lower blade angles, not one heavy stroke, and keep the surface clean, because a scrap under the leather lifts it into the blade and cuts a hole. Glass or stone under the strap, nothing soft.

There are rougher ways. The machinery site lathes.co.uk writes up scarfing round leather belts for small machine drives and gives two methods: grind the leather against a strip of wood with a flap wheel in a rotary tool, or clamp the belt at an angle and slice it with a craft knife. A drive belt is not a briefcase strap. The clamp-and-slice idea still holds wherever the piece wants to wander under the blade.

Check the taper by laying the two ends together dry. Any step you can feel with a thumb, you will feel in the finished strap.

Gluing and pressing

Thin coats, let them dry, then press hard and leave it alone.

Most of the makers on these threads glue with contact cement. Tom Gregory names it in the strap thread. Jason Austin and the original poster in the 2011 thread chose Barge cement. UKRay says glue is optional if the stitching is strong enough, and then gives the real reason to use it anyway: it holds the pieces still while you stitch.

The lathes.co.uk page gives the method plainly for its belts. Use an impact-type adhesive, put it on in thin coats, let them dry, then press the overlap in a vice overnight. It gives no length for the scarf, only that enough of it should be clamped.

A different shop shows how glue can be undone. Andrae Covington, building leather straps for a woodworking project at zeugmatic.com, glued a skived strap end with hide glue, found it out of place, and steamed it loose with a warm iron and a wet rag before gluing and clamping it again. Hide glue lets you change your mind. Contact cement does not.

Press across the whole slope, not only the middle. The feathered tips are where the bond is thinnest and where the joint will start to open if it opens at all.

Stitching the overlap

Stitch along the strap, not across it.

A hand-stitched bridle leather strap with a scarf joint beside a brass buckle.

The glue holds the slope still. Stitching holds the strap together.

Tom Gregory runs a stitch line up each side of the splice and recommends stitching the full length of the strap for looks and strength. UKRay, in the 2011 thread, stitches down each edge of the overlap with a two-needle saddle stitch, and he is blunt about the alternative: “Try to avoid stitching across the strap as this weakens the leather considerably.” He compares a row of holes across a strap to the perforations on a sheet of stamps. Ramrod agrees in the same thread, X patterns included. Jason Austin, on the other side of the argument, boxed his overlap and put an X through it and called the result strong.

I sit with UKRay on this. The saddle stitch is what I trust, two needles on one thread, the stitch that holds tack together under a 2,000-pound horse, and I sew in the air with the work in my hands. A line of holes running across a strap is a tear line drawn in advance. Run the stitches down the length and they share the pull with the leather instead of fighting it.

There is also the back of the strap to think about. On a scarf, both faces are show faces. “The side nobody sees is where a weak stitch gets found out,” as I put it on The Maker page, and on a strap the side nobody sees rubs against a coat every day.

RiverCity, in the strap thread, goes further and buries thin nylon inside a strap that has to take heavy tension, so the nylon carries the load and the leather is support. That is a real answer for a working strap. It is a different object.

Where the scarf gives out

The thin tips are the joint, and the thin tips are what fail.

Here is the case against everything above. In 1872 George E. Burt of Harvard, Massachusetts, patented an improvement in belt splices, and his complaint about the ordinary splice is the scarf’s weak spot laid bare. The common joint was a beveled lap, cemented, riveted, pegged or sewn, with the ends tapered to thin edges. Running over pulleys, those thin outer edges peeled up, and sewing or riveting at the tips could not hold them down. The joint weakened and gave out long before the belt itself wore out.

A strap on a briefcase does not run over a pulley. It does bend at a ring every time it gets slung over a shoulder, and a keeper slides over the joint every time the length changes. Same peel, slower.

So here is where I land against myself. I have argued for the long slope, the opposite faces, the glue and the edge stitch. All of that is right. And still, the scarf is a repair dressed as a part. When I need a strap with a good face on both sides, I split two strips on the crank machine and stitch them together flesh to flesh along their whole length, which is a lamination, not a scarf, and it has no feathered tip anywhere to lift. When a strap has to carry a hard-used briefcase full of files, I want it thick and in one piece, cut from the bend, even if that means the strap comes out shorter than I wanted and the design has to bend around it.

The scarf earns its place on a leash, a trace, a long belt, anywhere the length matters more than the look and the hide is too short to give it. On a case I build, it is the last answer, and I would rather argue with the pattern than with a joint.

More on the knives and machines behind this work is under Tools & Leather.

Leather Skiving Knife Set, 2 Pieces: A two-piece metal skiving knife set for thinning leather edges. See it on Amazon (affiliate link).

Barge All Purpose Cement, Quart: A quart of solvent-based contact cement. See it on Amazon (affiliate link).

John James Saddlers Harness Blunt Point Needles: A set of blunt-point harness needles, five sizes with five needles of each. See it on Amazon (affiliate link).

RITZA Tiger Thread, Brown: A braided waxed polyester thread for hand-stitching leather. See it on Amazon (affiliate link).

YaeTek 6-Inch Manual Leather Skiver Splitter: A manual skiving and splitting machine for thinning leather. See it on Amazon (affiliate link).

As an Amazon Associate I earn from qualifying purchases. A commission may be earned if you buy through this link, at no extra cost to you.

Sources

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