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A copper tubing flaring tool forms the tube end into a precise cone so it can seal against a matching flare fitting. For the common copper-tube connection, that means selecting a tool for the tube’s outside diameter and a 45-degree flare, cutting and reaming the tube square, putting the flare nut on before forming the cone, and tightening the tool only enough to make a smooth, round flare. The finished flare must sit evenly on the fitting face; a crooked, cracked, or overworked flare can leak.
The Ask the Builder copper tubing flaring tool video identifies Tim Carter and embeds a visual demonstration. Use it as a supplement to the written procedure below, while following the instructions supplied with your specific tool and fitting. The exact cone height, supported sizes, and tightening method vary by tool design.
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What does a copper tubing flaring tool do?
A flaring tool clamps the end of copper tube in a sized opening and presses a cone into the tube. That pressure spreads the copper into a tapered sealing face. When the flare nut is tightened onto a flare fitting, the two conical faces meet and create the seal; the threads provide clamping force but are not the sealing surface.
Most copper flare work uses a 45-degree cone, but 37-degree systems also exist. A 37-degree flare and a 45-degree flare are different geometries and are not interchangeable. McMaster-Carr lists 45-degree tools for one class of applications and 37-degree tools for another, but the fitting and equipment manufacturer’s specified angle is the authority. Do not choose an angle based only on a general pressure label.
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A bar-type tool normally has openings for several tube outside diameters, a yoke, a cone, and a clamp or screw. Other tools use one-hand clamps, a depth gauge, or a vise-mounted body. Those features change ease of setup, not the fundamental requirement: the opening, cone angle, and tube must match.
How do I choose the right flaring tool?
Choose compatibility before convenience. A tool that clamps the tube securely but has the wrong opening or cone angle cannot make a fitting-compatible joint.
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| Check | What to verify | Why it matters |
|---|---|---|
| Tube outside diameter | The tool opening is marked for the exact tube size. | A loose opening lets the tube slip; a wrong size can crush or distort it. |
| Flare angle | Use the angle specified by the fitting or equipment maker, commonly 45 degrees for copper flare fittings. | 37-degree and 45-degree mating faces do not seal together. |
| Tube material and temper | Confirm that the tool is intended for soft copper and the tube you have. | Soft, annealed tube forms readily; hard temper may split unless its end is annealed. |
| Positioning method | Look for a depth gauge, marked bar, or manufacturer’s height dimension. | Consistent protrusion controls the flare’s diameter and length. |
| Clamping stability | Check whether the bar, yoke, or vise mount holds the tube without slipping. | Movement while the cone is tightened produces an eccentric or uneven flare. |
The Copper Development Association’s Copper Tube Handbook is explicit that the tool must match both the tube outside diameter and the flare angle. A catalog listing from S-Ks Tools Corp. gives the CT-275 as a 45-degree flaring and swaging kit for soft copper, brass, and aluminum, with listed sizes from 1/8 inch through 3/4 inch outside diameter. That is the seller’s specification for that model, not a universal range or an independent recommendation.
What materials and accessories do I need?
Before clamping the tube, gather the flaring tool, a tubing cutter, a deburring or reaming tool, the correct flare nut and fitting, and a wrench sized for the connection. A vise can stabilize a bar-type tool if the manufacturer permits it. Keep the tube clean and free of grit; particles caught on the conical faces can prevent a seal.
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Use annealed (soft-temper) Type K or Type L copper for ordinary flaring work. The Copper Tube Handbook notes that hard-temper Types K, L, or M may require annealing at the end before flaring. Do not assume that a rigid, hard-temper length will flare safely just because its outside diameter matches the tool. Follow the tube and fitting manufacturer’s instructions for any heating, cleaning, and cooling operation.
How do I flare copper tubing step by step?
Set up on a stable surface and read the tool maker’s instructions first. In particular, use its specified tube height rather than treating a protrusion dimension from another guide as universal.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →- Confirm the fitting and angle. Identify the tube outside diameter and the mating flare angle. Verify that the flare nut, fitting, and tool belong to the same system. If the equipment documentation calls for 37 degrees, a 45-degree tool is the wrong tool even if it accepts the tube.
- Cut the tube square. Put the cutter around the tube and tighten it gradually as you rotate it. A square cut gives the cone an even wall to form. Avoid crushing the tube by tightening the cutter aggressively in one turn.
- Ream the inside and remove the burr. Run a deburring tool or reamer around the cut edge until the internal burr is gone and the bore is restored to its full inside diameter. Remove loose chips. An inside burr can thin or split the flare and can restrict the passage.
- Round the tube if it was distorted. Cutting or handling can leave the end oval. Gently resize it with an appropriate round-forming tool or by careful corrective work before clamping. The handbook calls for resizing out-of-round tube; do not expect the flare cone to repair an oval end reliably.
- Slide on the flare nut. Put the nut over the tube before forming the flare, with its threaded end facing the fitting. Once the cone is made, a nut left on the bench cannot be added without cutting off the finished flare.
- Place the tube in the matching opening. Open the bar, select the exact outside-diameter mark, and seat the tube straight. Set the tube’s protrusion to the height directed by the tool manufacturer. Some tools provide a depth gauge; others use a marked bar or a separate gauge.
- Clamp without crushing. Tighten the bar or clamp enough that the tube cannot slide when the cone enters. The tube should remain centered and round below the forming area. If the tool has a yoke, align the cone with the tube axis before applying force.
- Form the cone gradually. Turn the cone screw smoothly until it contacts the tube, then continue only as the instructions direct. Keep the yoke square and watch that the tube does not rotate or pull through the bar. The Copper Tube Handbook warns: “Care should be taken not to over-tighten the cone and cause cracking or deformation of the tube and/or the tool.”
- Release and inspect. Back off the cone, loosen the clamp, and remove the tube without prying against the new edge. The flare should be smooth, even, and round, with no radial cracks, folds, deep tool marks, or thin spots. Its length must fully contact the mating face but must not extend into the fitting’s threads.
- Assemble and tighten carefully. Bring the flare squarely against the fitting face, thread the nut by hand to avoid cross-threading, and tighten with a wrench according to the equipment or fitting instructions. Do not apply pipe-joint compound to the mating flare surfaces; the metal-to-metal conical faces are intended to seal directly.
How should the finished flare look?
Look for a continuous annular cone that is centered on the tube and has the same thickness around its circumference. The mouth should be round rather than oval, and the cut edge should not show a split or a sharp crack. The cone should be long enough to bear on the fitting’s sealing face, but it should stop before the threaded area.
A flare that is tilted, lopsided, wrinkled, or visibly cracked should be rejected. Cut it off, prepare a fresh square end, and repeat the process with a new nut. Reusing a nut on a shortened tube can leave insufficient length for a proper flare, so check the available straight section before recutting.
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What causes a leaking or damaged flare?
| Symptom | Likely cause | Correction |
|---|---|---|
| Crack at the cone or mouth | Hard-temper tube, excessive cone force, or an internal burr. | Use annealed tube or anneal the end as specified; ream fully; tighten only to the tool maker’s limit. |
| Flare is oval or one side is thin | Tube was out of round, cut at an angle, or clamped off-center. | Resize the tube, recut square, center it in the exact opening, and reset the height. |
| Flare pulls into the bar | Clamp was loose or the tube protruded too far. | Use the correct opening, set the specified height, and secure the bar before turning the cone. |
| Nut will not reach the fitting | The nut was omitted before flaring or installed backward. | Cut off the flare, install a correctly oriented nut, and form a new flare. |
| Joint seeps after tightening | Mismatched angle, dirt on the conical faces, damaged flare, or cross-threaded/insufficient tightening. | Disassemble, verify the angle and sizes, clean and inspect both faces, then remake the flare if necessary. Follow the fitting maker’s torque or tightening guidance. |
Do not try to cure a damaged flare by coating the cone with sealant or by forcing the nut tighter. Over-tightening can deform the tube and fitting, while compound on the flare faces can interfere with the intended metal-to-metal seal.
What is the difference between flaring and swaging?
Flaring makes a tapered sealing face for a flare fitting. Swaging expands the tube end so another tube can slide inside it for a soldered or brazed joint. The operations require different forms and serve different joint designs; one is not a substitute for the other.
Some kits combine a flaring cone with swaging punches or dies. A combined kit can be convenient, but select the component for the joint you are actually making. The Home Depot guide to swaging and flaring tools illustrates the distinction and covers the same core preparation steps: square cutting, deburring, nut placement, clamping, and cone tightening.
Can I use a 45-degree tool on every copper connection?
No. A 45-degree tool is appropriate only when the mating fitting is designed for a 45-degree flare. Equipment may specify a 37-degree flare or another connection method, and those geometries cannot be mixed. Read the fitting, appliance, or equipment documentation and check the angle marking on the tool before cutting the tube.
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For fuel-gas flare-joint work, the Copper Tube Handbook advises checking local authority requirements. Current code, permit, and manufacturer instructions take precedence over a general how-to description.
How does the video fit into the learning process?
The Ask the Builder page is a useful visual reference for identifying the tool and the basic sequence, but an embedded video does not replace the dimensions and limits for your particular model. Pause to compare the tool’s markings, cone angle, and tube-height instruction with your hardware. If the video’s tool differs from yours, follow your tool manufacturer’s setup and tightening directions.
How should I decide between tool designs?
For occasional repairs, a bar-and-yoke tool that clearly marks common tube sizes may be adequate. A depth gauge can make repeatable positioning easier, while a one-hand clamp or vise-mounted body may improve stability when access is awkward. None of these features compensates for a wrong angle, wrong size, or unsuitable tube temper.
Use this order when comparing catalogs: first confirm the fitting angle and tube outside-diameter range; next confirm soft-copper or material compatibility; then assess clamping stability and positioning aids. Treat a listed size range—such as 1/8 through 3/4 inch on a particular seller’s kit—as model-specific. Availability and included accessories can change, so verify the current listing and package contents before purchase.
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Safety and workmanship checklist
- Depressurize, isolate, and drain the system before cutting an installed tube.
- Wear eye protection when cutting, reaming, or handling copper chips.
- Keep the flare faces clean and protect the finished cone from scratches.
- Support the tube so the new flare is not bent while the nut is tightened.
- Never force a nut that cross-threads; remove it and start again by hand.
- Use the fitting or equipment maker’s tightening instructions rather than guessing from feel.
- After assembly, inspect for movement or seepage using the procedure required for that system. Do not introduce an ignition source around a fuel-gas connection.
The reliable result comes from matching the tool, preparing the tube, forming the cone with controlled force, and rejecting any flare that is not smooth and concentric. A careful setup is faster than trying to rescue a cracked or uneven flare after the fitting has been installed.
Frequently Asked Questions
Can I flare copper tubing without annealing it?
Use annealed or soft-temper Type K or L copper whenever possible. Hard-temper K, L, or M may need its end annealed first, and the tube manufacturer’s heating procedure should be followed; forcing hard copper through the cone can cause cracking.
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There is no single universal protrusion dimension. Set the height specified by your tool maker or use the tool’s depth gauge, because bar thickness, cone design, and tube size change the required amount.
Should I use thread sealant on a copper flare fitting?
No sealant belongs on the mating conical faces. The flare seals by metal-to-metal contact; compound can prevent full seating. Thread treatment, if any, is a separate matter governed by the fitting and equipment instructions.
What should I do if I forgot the flare nut?
Cut off the existing flare and prepare a new end. The nut must slide onto the straight tube before the cone is formed, and forcing or splitting a nut will not produce a reliable connection.
