Tools for cutting thick leather, a round knife, utility knife, rotary cutter and strap cutter, beside a bridle leather bend and a safety ruler.
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Cutting Straight Lines in Thick Leather

ByPeter Joeseph 'Briefcase Maker' Kalafatis

A straight line through heavy bridle is a ruler problem first and a knife problem second.

Cutting a straight line through thick leather means pushing a blade through a quarter inch of packed fiber without letting it lean, wander or stretch the hide, and the tool that decides most of that isn’t the blade. It’s the thing the blade rides against. I cut briefcase panels by hand from English bridle bends, and the video on my channel is one of those cuts. Below are the tools in the order you’d reach for them, what each one is good at, and where each one lets you down.

Video: Hand Cutting Bridle Leather Briefcase Pattern, from Marcellino NY Briefcase Maker on YouTube.

A word on where this comes from. I learned most of this trade by trial and error, out of books and from pulling apart how other bags were made, back when there were almost no good tutorials. The tool details here belong to the toolmakers and to the makers on the leatherworker.net forum who cut heavy leather for a living, and they get credit by name. Where I’m judging, it says “my opinion.”

The straight edge, before anything sharp

Buy the ruler first. The knife only follows it.

Hands cutting a straight line through thick bridle leather with a round knife against a steel straight edge.

Tandy’s article on cutting leather with clean edges lists a steel ruler as essential for guiding straight cuts and says to press it down firmly on the line. That sounds obvious until a stiff bend of bridle pushes back against it. In a leatherworker.net thread on cutting straight lines, battlemunky says holding the straightedge down through the whole cut is imperative. Let it creep a sixteenth and the line has a kink in it you’ll be burnishing forever.

Thickness of the guide matters on thick leather. In a thread on preparing a straight edge before strap cutting, jasonsmith argues for a thick straight edge so the blade stays vertical, where a thin ruler lets it lean. Dwight glues cork under an aluminum ruler so it won’t slip, and Gawdzilla uses bar stock that he checks against a level. Tree Reaper clamps leather that curls and runs a steel framing square. RockyAussie, back in the first thread, screws a flat steel strip to the table at one end and slides the leather under it, so the weight of the steel holds the hide still.

Weaver sells a safety cutting ruler in 12 and 36 inch lengths, anodized aluminum with a raised flange handle and a weighted, non-slip bottom. The flange is the point. Your fingers sit up and away from the blade’s path.

My opinion: a straight edge is the one tool here I’d never cheap out on. A dull knife cuts slow. A ruler that slides cuts crooked, and you won’t see it until the panel is stitched.

The utility knife, the honest first buy

Cheap, sharp out of the pack, and good at exactly one thing.

Tandy’s article rates the utility knife as “Perfect for straight cuts.” The forum agrees, with a catch. In a thread comparing the round knife and the box cutter, JLSleather keeps a utility knife for long straight cuts because it needs no sharpening, and says it’s poor on curves. SooperJake hones even his utility blades and likes one for long straight cuts. The original poster in that thread complained the blades didn’t stay sharp for long.

I believe both of them. A fresh blade is very sharp and goes off fast in heavy veg-tan. In the strap cutting thread, RobDude30 runs a heavy-duty snap-off knife and snaps to a fresh section before a cut that matters, then holds a long ruler steady with his hand and his knee. Dwight, in the same thread, strops a new drywall blade before use and says it cuts most leather up to about 9 ounces in one pass.

The weakness is the blade’s thinness. On a thick bend it can flex, and a flexing blade cuts a wall that isn’t square to the face. In the keeping edges vertical thread, RandyScott says body position is what keeps the blade upright, and that it comes with practice.

My opinion: a utility knife is the right first buy for a beginner who wants straight lines, and the wrong last word on a briefcase panel. It gets you a clean line. It doesn’t always get you a square one.

The round knife, the one that pays you back

Hard to learn, hard to sharpen, and the tool the heavy-leather makers keep coming back to.

Macro view of a square cut edge on thick bridle leather beside an offcut with a leaning, angled cut.

Weaver’s No. 70 round knife is a forged blade of 1075 high carbon steel, 5 inches point to point, and the page calls it the knife of choice for many leatherworkers. Read the reviews on that page, though. One buyer found it dull out of the box and sharpened it in a few minutes. Another had to regrind the primary bevel. That’s the round knife in a sentence: the steel is good, and the edge is your job.

In the round knife thread, TwinOaks says that for long cuts, or cuts on thick leather, “the round knife wins out.” BondoBobCustomSaddles says it becomes the most used tool in the shop. Shooter McGavin gave up on it because he couldn’t sharpen one well. In the cutting straight lines thread, bikermutt07 rolls the round knife through the end of a cut so the leather doesn’t stretch at the corner, and RockyAussie prefers it because the edge holds up for most of a job.

Safety is the other price. In a thread on cutting heavy leather, the original poster had heard round knives are dangerous for a novice, and Johanna’s rule, learned from a saddlemaker, was to always cut away from yourself. A round knife has no handle guard and a lot of edge.

Bridle adds one more thing. I cut only from the bend, where the fiber is tightest, and that tight fiber is exactly what drags on a knife going a little dull. The post on why bridle is a hard first leather goes into the wax and the stiffness. My opinion: on that leather, an edge that was fine an hour ago starts pushing instead of cutting, and the push is where the line goes wrong.

The rotary cutter, better at scoring than finishing

Fast and vertical on a long line, out of its depth in a thick bend.

Tandy’s article puts the rotary cutter down as a tool for thin leathers and repetitive cuts. The heavy-leather makers use it anyway, with a different job in mind. In the heavy leather thread, bruce johnson describes running 45 mm rotary cutters along a 48 inch straight edge on skirting up to 16 ounces, making a partial cut with the wheel and finishing with the round knife. Gregory B. Moody puts the cutter’s limit at about 3/8 inch deep and holds his wrist parallel to the table.

The wheel’s strength is that it can’t lean the way a pushed blade can. In the strap thread, Gawdzilla says he always uses a roller blade for a true vertical cut, and bruce johnson scores with a 45 mm roller along a 6 foot ruler, then makes a quick pass with a round knife.

My opinion: on bridle, think of the rotary cutter as a scoring tool. It lays down a clean, upright groove for the round knife or utility blade to follow, so the second pass has a track to run in. Asking it to go all the way through a heavy bend in one pass is asking for a wheel that skates off line.

Strap cutters, draw gauges and plough gauges

Repeatable width, as long as the first edge is true.

Evenly cut chestnut bridle leather straps laid side by side on a workbench with a wooden strap cutter.

Straps are where a fixed-width tool earns its keep. Weaver’s wooden strap cutter cuts straps up to 4 inches wide, comes with five replaceable blades and has an adjustable thickness bar. Its Master Tool draw gauge also cuts straps up to 4 inches, with a handle that twists to set the width.

In the cutting very thick leather thread, JET4 runs a strap cutter every day on latigo around 13 to 14 ounces, and celticleather says his has cut heavy oak-tanned hide for thirty years. bruce johnson explains the practical difference between the gauges: a draw gauge needs the leather lifted off the table, while a plough gauge keeps it flat. Art, a moderator, uses aluminum strap cutters for belt-sized pieces and prefers a plough for anything over about an inch and a half.

Every one of these tools rides an edge you already cut. In the strap thread, Kevin marks a line with a straight edge, hangs the leather off the table and cuts it with a round knife before the strap cutter ever comes out. My opinion: the gauge copies whatever you give it, so a wobble in that first edge comes back in every strap you pull.

My own straps take another step after the cut. I thin the strap leather on an old hand-crank splitter and stitch two thinned pieces together, so the strap shows a good face on both sides. The post on skiving and splitting covers that machine, and the one on beveling and creasing a strap picks up where the cut edge leaves off.

One pass or three

Every source says sharpen. They don’t agree on how hard to push.

Here’s where the buyer guide falls apart a little. I’ve spent five sections telling you what to buy, and the makers who know most about this disagree on how to use any of it.

Tandy says to make several light passes to cut down on drag, instead of forcing the blade through in one stroke. In the cutting straight lines thread, Stetson912 says to use multiple passes on thicker leather and to press down, chopping rather than slicing. bikermutt07, in the same thread, says knives sharp enough for one pass work best. In the round knife thread, IngleGunLeather’s advice is never to try to cut all the way through on the first pass. Gregory B. Moody, in the heavy leather thread, says multiple passes on thick leather are close to unavoidable.

My opinion: those aren’t really opposite camps. One pass is what a perfect edge and a perfect ruler buy you, and several light passes are what you do when either one is a little off, which on thick bridle is most days. The danger is the second pass that doesn’t land in the first groove. Then you have two cuts and a sliver between them.

Tandy’s article gives the body advice that ties it together: lock your wrist and move your whole arm. That costs nothing. It’s also the hardest thing here to buy.

Panels and gussets don’t come off the bend the same thickness either. I cut gussets thinner than panels so the case bends without creasing on the outside, which means every straight line on a briefcase is cut through a different depth of leather, with the same knife and the same arm.

The tools help. My arm still has to hold the line.

Victor 18-Inch Professional Aluminum Safety Ruler: An 18-inch aluminum safety ruler for guiding a blade. See it on Amazon (affiliate link).

IRWIN Carpenter Square, Steel, 8-Inch by 12-Inch: A steel carpenter square, 8 by 12 inches, for checking right angles. 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).

OLFA 45mm Ergonomic Squeeze-Handle Rotary Cutter: A 45 mm rotary cutter with an auto-retracting blade. See it on Amazon (affiliate link).

Leather Round Knife with Wooden Handle: A round knife with a wooden handle for cutting leather. See it on Amazon (affiliate link).

BeaverCraft Stropping Compound Kit: A stropping compound kit for sharpening and polishing edges. See it on Amazon (affiliate link).

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