Leather strap with a freshly cut buckle slot at the folded end, beside a brass buckle, an oblong punch and a rawhide mallet on a workbench.
| |

Cutting Slots for Straps and Buckles

ByPeter Joeseph 'Briefcase Maker' Kalafatis

A slot is a hole with two ends, and the ends are where it fails.

The slot is the long hole a buckle tongue swings in, or the opening a strap runs through, and it gets cut with less care than any other hole on a piece of leather. Round holes forgive you. A slot won’t, because its two ends take the pull every time the strap is cinched, and a ragged end is a tear that hasn’t happened yet. These are the questions people ask before they put a punch to a strap they already spent an afternoon cutting.

Video: Basic Tips for Working with the Oblong Punch, from Weaver Leather Supply on YouTube.

I build briefcases, and on a briefcase every strap ends at a buckle, a keeper, a latch or a slot. My buckles get stitched on by hand. No rivets. That’s my bias, and you’ll see it, but most of what follows comes from the toolmakers and the working leatherworkers who have argued about slots in public for years, and each of them gets named where the point is theirs.

What the slot is doing

Two jobs from one hole: let the tongue swing, or let a strap pass.

Hands positioning an oblong punch on a leather strap to cut a buckle slot.

Weaver Leather Supply sells its oblong punch as the tool for holes “ideal for buckle tongues, strap slots, and hardware placement.” That covers it. The same long hole does two different kinds of work, and you size it differently for each.

The first is the tongue slot at the buckle end. The tongue comes up through it and the leather folds back over the bar. Weaver’s page on assembling a belt from a blank puts it plainly: insert the tongue at the oblong hole and fold over. Tandy’s dog collar project does the same at the end, weaving the punched leather through the buckle and folding the tail underneath.

The second is the pass-through. A strap goes in one side and out the other, through a flap, a holster back, a case wall. Nothing swings. The leather has to grip without choking.

Names get mixed up, so here they are. The Montana Leather Company’s guide to punching holes in leather calls the slot punch “an incredibly precise tool meant to cut narrow oblong holes into your leather,” and says it also goes by oblong or bag punch. On leatherworker.net, the member zuludog adds crew punch to the list in a thread on oval punch sizes for dog collars. Same tool. Four names.

My opinion: the tongue slot is a hinge more than a hole. The tongue rocks in it every time the strap opens and closes, and a hinge cut short binds.

How long and how wide

Measure the buckle on the inside, then the tongue, then cut.

Start with the buckle, not the strap. The harness supplier IVC Carriage, writing on measuring harness parts and hardware, says buckles are measured by the inside width, because the outside changes with the style while the inside stays put. Its sizes run in steps to match strap widths. A smaller strap in a bigger buckle works, it says, with a lot of slop. A bigger strap in a smaller buckle doesn’t go at all.

The tongue slot is where nobody hands you a formula. In that same dog collar thread, the member Geneva says her 1-inch roller buckles “require a 1″ bag punch for the center bar.” The poster, JulieP, had been looking at oval punches no longer than 21mm, which by Geneva’s numbers would come up short. That’s one maker and one buckle. I couldn’t find a general rule that ties tongue-slot length to strap width, and I’m not going to invent one.

Pass-through slots get argued harder. In a leatherworker.net thread on belt slot size, the member JLSleather says to cut the slot to the belt’s width so it passes “without fighting it” and without room left over. The member Lobo points out the catch nobody draws on the pattern: a strap that enters at an angle needs a longer slot, and a slot cut to the strap’s width will not take it at thirty degrees. Mocivnik says a 40mm punch for a 40mm belt would be far too large.

So there are three numbers. The buckle’s inside, the tongue’s thickness, the angle the strap comes in at.

My opinion: cut a test slot in scrap of the same thickness and push the real buckle through it before the good strap sees a punch. Paper is cheap. A strap cut from the best part of a bend is not.

Punch it or cut it by hand

A stock punch for stock sizes. Two round holes and a knife for the rest.

Macro view of the rounded, beveled end of a buckle slot in thick vegetable-tanned leather.

The punches come in fixed lengths. Tandy’s Craftool oblong punches run 1/2, 3/4 and 1 inch, sold to “Create clean, professional buckle slots,” and the page says to use them on a proper cutting surface with a non-metallic mallet. Weaver’s oblong punch goes from 1/2 inch to 1-1/2 inches in hand-forged carbon steel. For small work, the saddlery supplier Abbey England lists the Osborne 158 oval drive punch in a size for tiny oblong holes in fine straps and buckle slots, used on a cutting pad with a rawhide mallet. The Montana Leather guide wants the leather on granite, which takes the blow so the bench doesn’t.

A punch is only as good as its edge. The one buyer review on Weaver’s page says the punch arrived too dull for a 4-5 oz veg-tan strap. The member oldhat, in the dog collar thread, keeps cheap punches working by touching them up on fine sandpaper and stropping them on scrap.

When the size you need isn’t made, you build the slot from parts. zuludog’s method: two small round holes for the ends, then two straight cuts to join them. Michael Magnus, writing how to make a leather belt for The Art of Manliness, punches holes at 2.5 and 3.5 inches from the tip, then runs a utility knife from the left side of one hole to the left side of the other, and repeats on the right. In a leatherworker.net thread on cutting belt slots, the member gregintenn does the same with 3/8-inch holes, two pencil lines and a hobby knife.

The hand method fits any size. It also gives you two chances to wander off the line, and the place it shows is where a straight cut meets a round end. A step there is small. Your thumbnail finds it anyway.

Where it sits on the strap

Fold the end in your head first, then measure from the fold.

The slot lives on the fold, so the fold comes first. Magnus thins about two inches of the strap’s flesh side to roughly half its thickness, centered on a mark three inches from the end, then folds it and soaks it so it holds the bend. The slot goes in the middle of that thinned section. Tandy’s collar instructions skive the last seven inches to about half thickness, round the end, then center a 1-inch oblong punch on a mark 3.5 inches in from the end.

Thinning matters because a full-thickness strap folded back on itself is two straps thick at the buckle. It stands proud. It fights the bar. My earlier post on beveling and creasing a leather strap gets into finishing the edges of that same strap, and the fold shows every sloppy pass you made on them.

Then check which way the buckle faces. Magnus warns that a buckle set upside down won’t work with the holes at the other end of the strap. It sounds too dumb to say. It isn’t, and you find out after the fold is fixed for good.

How the fold gets closed is where makers split. Magnus says you could sew the flap but most people rivet it. Weaver’s belt-blank page closes it with Chicago screws and slides the keeper between the folded layers before the last screw goes in. I stitch mine, and the straps on my cases are double-lined in bridle, so the fold is thick work before the needle ever touches it. The case for brass and leather closures in general is in the post on why the strap-and-buckle closure outlasted every alternative.

Not every closure wants a buckle at all. The Marcellino Latch was designed for attorney clients as an alternative to traditional buckles, for easier opening and closing.

Why slot ends tear

The end of a slot is a crack waiting for a reason.

Bridle leather briefcase strap fastened through a brass buckle with the tongue seated in a hand-cut slot and a stitched fold.

Pull on a strap and the load runs down the leather to the tongue, and the tongue bears on the end of the slot. All of it. A clean, round end spreads that push. A notch, a nick, a little split in the grain gives it one place to start.

Tools cause most of it. In the belt slots thread, the member particle (Eric Adams) warns that one brand of die punch will “stretch the leather too much and will tear the ends of the slot,” and points people to Weaver’s oblong punch instead. Another member, Denster, wets the leather every time he punches, to stop the top grain splitting at the ends. Haystacker, in the same thread, doesn’t wet it at all. troop punches right after the leather comes out of the water and before it’s molded. Three makers. Three habits. Nobody in that thread settles it, and I won’t pretend to.

Here’s the part that cuts against my own bias. I’ve been talking as if the knife is the craftsman’s tool and the punch the shortcut, because doing it by hand is the way I like to work. A sharp punch struck once, square, on a hard surface, cuts both ends and both sides in the same instant. No step where a cut meets a hole. No second chance to drift. On a stock size, that’s cleaner than most hand cuts will ever be, and the hand method earns its place only when the size you need isn’t sold.

My opinion: if the slot ends look torn, it’s the tool, the strike or the leather’s moisture, in about that order. Check the edge on the punch first. It’s the cheapest fix.

Finishing the inside of a slot

Nobody finishes what they can’t reach, which is why it frays first.

A slot has edges like any other cut, and the inside of it takes the same water and friction the outside does, plus a steel tongue rubbing on it all day. In the belt slots thread, gregintenn bevels the cut edges of his slots. RobDude30 cleans them up with a Dremel and a small drum sander. Haystacker, punching through layers already stitched together, says only the bottom layer has to be beveled.

None of them makes a ceremony of it. A slot is narrow and the tools are wide, so most of the work is getting anything in there at all. A strip of fine sandpaper folded over a thin stick reaches. So does patience.

My opinion: a slot edge is still an edge, and an edge left raw darkens and fuzzes where the tongue rides. It won’t sink the strap this year. It will be the first thing that looks tired on it.

OWDEN 9 Pieces Leather Hollow Punch Set: A nine-piece hollow punch set for round holes. See it on Amazon (affiliate link).

WORKPRO 18mm Retractable Utility Knife: An 18 mm retractable utility knife with snap-off blades. See it on Amazon (affiliate link).

WUTA Rawhide Mallet: A rawhide-head mallet for striking chisels and punches. See it on Amazon (affiliate link).

Farberware 12 x 18 Inch Reversible Plastic Cutting Board: A reversible plastic cutting board, 12 by 18 inches, usable as a cheap cutting surface under a knife. See it on Amazon (affiliate link).

Heavy Duty Brass Belt Buckle, 1.5 inch: A heavy-duty brass belt buckle for 38 to 40 mm straps. See it on Amazon (affiliate link).

304 Stainless Steel Chicago Screws Leather Assorted Kit: A kit of 90 stainless steel Chicago screw sets in seven sizes. 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

You Might Also Like

Similar Posts

Leave a Reply