How to Flare Copper Tubing Perfectly: Mastercool Tool Technique
A leaking flare joint is one of those problems that looks like a refrigerant issue until you trace it back to the connection itself. Bad flares are the single most common cause of joint leaks on split system and refrigeration installs — and almost every bad flare comes down to either poor tube preparation or inconsistent tool technique. Neither of those is a difficult fix once you understand what a good flare actually requires.
This guide covers the complete flaring procedure using Mastercool flaring tools: how to prepare your tube correctly before the flare starts, how to operate the tool to produce a consistent 45-degree cone, how to inspect the result, and how to diagnose and correct the most common flare defects. Whether you're working on a residential split system in coastal Queensland, a VRF install in a Melbourne high-rise plant room, or a cold-storage refrigeration circuit on a regional NSW farm, the technique is the same. Get the preparation right, use the tool correctly, and the connection will hold.
Written by Rica Francia Macaspac, HVAC Shop content writer, in consultation with Aussie HVAC tradies and industry experts. Published: June 2026 · Last reviewed: June 2026.
Tube Preparation and Cutting
The quality of your flare is determined before the flaring tool touches the tube. Every defect that shows up in the finished flare — cracking, ovality, surface tears, uneven cone angles — traces back to something that went wrong during tube preparation. Taking an extra minute at the prep stage saves you the time of re-flaring and the frustration of a connection that seeps refrigerant after commissioning.
Tube benders and associated preparation tools are available through the tube and pipe benders collection at HVAC Shop — the right bending and prep equipment is as important to a quality flare as the flaring tool itself.
Achieving a Square Cut
The cut must be perfectly square — 90 degrees to the tube centreline, with no angle, burr, or crush. Use a proper tube cutter, not a hacksaw. A hacksaw cut is rarely square and leaves metal filings in the tube that will end up in the refrigerant circuit if not completely removed. A quality tube cutter produces a clean, controlled cut with minimal deformation of the tube wall.
Tighten the cutter wheel gradually as you rotate — overtightening in a single pass crushes the tube wall and creates an oval cut end that will produce an oval flare. Two or three gradual passes with light tightening between each rotation gives you a clean, round cut with minimal burr. The cut end should look perfectly circular when viewed from the end of the tube.
On larger diameter tube — 5/8 inch and above — take particular care not to rush the cut. Larger tube has more wall area for the cutter to work through, and impatient overtightening is more likely to cause crush deformation on bigger sizes. A slow, methodical approach produces a cleaner result every time.
Tube Straightening
The section of tube entering the flaring block must be straight. If the tube has a bend or curve within 100mm of the cut end, the tube won't sit squarely in the flaring block and the flaring cone will apply uneven pressure across the face of the tube. The result is a flare that's thicker on one side and thinner on the other — a consistent source of leaks under pressure cycling.
Straighten the tube by hand before cutting wherever possible, using a gentle rolling motion rather than sharp bending. If the tube has a tight bend from being coiled on the reel, work it straight over a longer length — 300mm or more — rather than trying to straighten just the last 50mm. Trying to flatten a tight curve in a short section creates kinks, which create oval cross-sections, which create bad flares.
Deburring and Chamfering
After cutting, deburr the inside edge of the tube with the reamer on the back of the tube cutter or with a dedicated deburring tool. The internal burr left by even a good tube cutter cut is enough to catch copper particles and create turbulence in the refrigerant circuit. On R32 systems, cleanliness in the refrigerant circuit is even more important than with older refrigerants, as R32's different molecular properties mean contaminants have more potential to interact with lubricating oil.
Deburr with a light touch — the goal is to remove the burr, not to chamfer the tube end into a funnel. Aggressive reaming removes wall thickness at the cut end and can affect how the flare forms. Two or three light passes of the reamer, rotating as you go, is sufficient. Point the tube downward while reaming to let the copper filings fall away from the tube rather than into it.
A light external chamfer on the tube's outer edge isn't strictly required on most flaring tools, but it helps the tube enter the flaring block cleanly on tools with tight tolerances. If you're finding the tube end catching on the block entry, a light chamfer pass on the outside edge with the deburring tool resolves it.
Tube Cleanliness
Wipe the tube end with a clean, lint-free cloth before inserting it into the flaring block. On job sites in dusty conditions — WA mining infrastructure, regional farm sheds, or construction sites — fine particles on the tube surface get rolled into the flare face during the forming process and leave pits in the sealing surface. A single wipe takes two seconds and removes this risk entirely.
Keep tube ends capped or protected until you're ready to prepare and flare. Refrigerant-grade copper tube that has been sitting open in a dusty environment or exposed to humidity for an extended period can have surface oxidation or contamination that affects both the quality of the flare and the cleanliness of the refrigerant circuit.
Tradie Pro Tip: Always slide the flare nut onto the tube before you flare — it sounds obvious, but it's the most common single mistake apprentices make on their first few jobs. Once the flare is formed, the nut won't pass over it. You'll need to cut off the flare and start the prep sequence again, which is a waste of tube length and time.
Using Mastercool Flaring Tools
Mastercool produces flaring tools across different operating principles — eccentric cam-action tools and hydraulic tools for different application needs. Both produce 45-degree flares to the industry standard required for HVAC-R connections in Australia. The technique differs between tool types, but the quality standard for the finished flare is the same.
Setting Up the Flaring Block
With the Mastercool eccentric flaring tool, begin by selecting the correct hole size in the flaring block for your tube diameter. The standard sizes encountered in HVAC-R work are 1/4 inch, 3/8 inch, 1/2 inch, 5/8 inch, and 3/4 inch. The block hole must match the tube's outer diameter exactly — inserting an undersized tube into a larger hole produces a flare that's too small for the fitting and won't seal correctly.
Insert the prepared tube end into the correct hole from the underside of the block. The tube end should protrude above the block face by the correct amount — typically one tube wall thickness, or approximately 1–1.5mm for standard HVAC-R copper. Too little protrusion produces a thin, fragile flare. Too much produces an oversized flare that won't fit the flare nut correctly and may crack under tightening torque.
Many experienced techs use the chamfer on the back of the flaring cone as a guide: place the cone lightly against the tube end before tightening the block, adjust until the tube protrudes level with the first step of the cone, then tighten the block. This gives consistent protrusion across all tube sizes without needing to measure.
Tighten the block clamping screws firmly and evenly. Uneven clamping torque allows the tube to rotate or shift slightly during the flaring operation, which produces asymmetrical flares. On the Mastercool eccentric tool, tighten both clamp screws alternately in small increments rather than fully tightening one before the other.
Cone Alignment and Initial Engagement
Position the flaring yoke over the block with the cone centred over the tube end. On the Mastercool eccentric tool, the cone doesn't advance straight into the tube — it uses an eccentric cam action that rolls the cone in a controlled orbital pattern as it advances. This orbital action produces a more uniform flare surface than straight-in tools, which can produce flat spots if the cone contacts unevenly.
Make sure the yoke is fully seated on the block rails before applying any forming pressure. A yoke that's not fully engaged can tip slightly under load, introducing angle error that produces a tilted flare face. On Mastercool tools, the yoke clicks or seats positively — if there's any play in the yoke-to-block engagement, check that it's fully seated before proceeding.
Applying Forming Pressure
Begin turning the forming handle clockwise, applying gradual, even pressure. The initial resistance is light as the cone contacts the tube end and begins spreading the material outward. Resistance increases steadily as the flare forms and the copper work-hardens under the cone pressure. The pressure curve should feel smooth and progressive — a sudden hard stop indicates either full flare formation or the cone bottoming out on the block face.
On the Mastercool eccentric tool, continue turning until you feel firm, consistent resistance and the handle requires noticeably more effort to continue. At this point, the flare is fully formed. Do not attempt to force further advancement — over-forming thins the flare wall, can crack the copper at the flare edge, and creates a brittle connection that may fail under the vibration of a running system.
For the Mastercool hydraulic flaring kit, the pressure application is controlled by the hydraulic mechanism rather than by feel. Follow the tool's recommended pressure setting for the tube diameter you're working with — the hydraulic tool removes the variability of hand pressure and produces highly consistent results across repeated flares, which is its main advantage on high-volume commercial work.
Tech Specs: The 45-degree flare angle is the Australian and international HVAC-R industry standard for refrigerant connections. Some plumbing applications use 37-degree flares — these are not interchangeable. A 37-degree flare in a 45-degree fitting will contact only at the outer edge of the cone, producing a line contact seal rather than a face seal, which will leak under refrigerant pressure. Always confirm you're using a 45-degree tool for HVAC-R refrigerant connections.
Cone Removal and Block Release
Once the flare is formed, reverse the handle direction to retract the cone. Back it out smoothly — jerking the cone out quickly can drag across the fresh flare surface and leave marks that compromise the sealing face. On the eccentric tool, the cone retracts through the same orbital path it advanced through, so the retraction should feel as smooth as the advance.
Once the cone is fully retracted, loosen the block clamping screws and remove the tube. Support the tube as you withdraw it from the block rather than pulling it straight out, which can damage the fresh flare edge on the block face. With the tube free, inspect the flare before assembling the connection.
Quality Verification and Troubleshooting
Inspecting the flare before assembly is a professional habit that separates techs who never have flare leak callbacks from those who do. A bad flare takes thirty seconds to identify visually and another two minutes to re-do correctly. A leaking flare joint on a commissioned system costs far more in time, refrigerant, and professional reputation.
Inspecting the Flare Cone Angle
A correctly formed 45-degree flare should be symmetrical when viewed from the end of the tube. The cone should be centred on the tube axis with an even angle around the full circumference. If one side of the cone is steeper than the other, or if the cone appears off-centre relative to the tube, the tube wasn't sitting squarely in the block when the flare was formed.
The outer diameter of the flare should be consistent around the full circumference. Measure across the flare face with a calliper if you're unsure — the diameter should match the flare nut's seating surface closely. An undersized flare won't seat against the fitting face. An oversized flare will compress unevenly when the nut is tightened and may crack at the edge.
Surface Finish Assessment
The sealing surface of the flare — the face of the cone that contacts the fitting — must be smooth, shiny, and free of pits, cracks, or tool marks. Run a finger or a thumbnail lightly across the sealing surface. It should feel uniformly smooth with no ridges, roughness, or steps. Any surface irregularity is a potential leak path under refrigerant pressure.
A dull or slightly rough surface indicates either dirty tube, a worn flaring cone, or contamination between the cone and the tube during forming. A surface with visible pits indicates grit or particles rolled into the surface during forming. Both of these require re-flaring. A smooth but slightly swirled surface — the orbital pattern from an eccentric tool — is normal and not a defect.
Common Defects and Causes
| Defect | Likely Cause | Action |
|---|---|---|
| Cracked flare edge | Over-forming pressure; work-hardened tube from repeated bending; too much tube protrusion | Cut off and re-flare. Check tube protrusion and reduce forming pressure slightly on next attempt. |
| Asymmetrical cone (one side higher) | Tube not square in block; block not fully clamped; bent tube entering block | Re-flare. Straighten tube end, ensure square cut, clamp block evenly before forming. |
| Rough or pitted sealing surface | Grit or debris on tube or cone; worn flaring cone; oxidised tube surface | Re-flare. Clean tube end and cone before retry. Inspect cone for wear. |
| Undersized flare diameter | Insufficient tube protrusion; under-forming (stopped too early) | Re-flare with correct protrusion and full forming cycle. |
| Oversized or split flare | Excessive tube protrusion; over-forming | Re-flare with reduced protrusion. Stop forming at correct resistance point. |
| Oval flare (not circular) | Crushed tube from over-tight cutter; tube not round at cut end | Re-cut with lighter cutter pressure. Re-flare from fresh tube end. |
| Burr or fold at flare edge | Insufficient deburring before forming; internal burr folded outward by cone | Re-flare after thorough deburring of cut end. |
When to Re-Flare
The decision to re-flare should be straightforward: if the flare has any visible defect — cracking, pitting, asymmetry, or surface roughness — re-flare. The cost of cutting off 20mm of tube and forming a new flare is negligible compared to the cost of a refrigerant leak callback after commissioning. There is no defect category where "it'll probably be fine" is the right call on a sealed refrigerant system.
On jobs where tube length is tight and you're working close to the minimum length needed to reach the fitting, the discipline is to plan tube lengths with enough margin for one re-flare attempt. If you're cutting tube to the exact minimum length, you've created a situation where you can't correct a bad flare without replumbing the run. That's avoidable with a small amount of planning at the installation stage.
Assembly, Tightening, and Leak Testing
Once the flare passes visual inspection, assemble the connection. Apply a very light film of clean refrigeration oil to the sealing face of the flare — this aids in seating and provides lubrication during the initial tightening that prevents the flare face from galling against the fitting seat. Do not use thread sealant, PTFE tape, or other compounds on a refrigerant flare joint.
Tighten the flare nut by hand until it seats, then use a torque wrench or calibrated flare nut spanner to apply the correct tightening torque for the tube diameter. Under-tightening leaves the connection loose enough to leak under pressure cycling. Over-tightening compresses and distorts the flare face, creating stress cracks that may not leak immediately but will develop into leaks under vibration and thermal cycling over time.
Before pressurising with refrigerant, pressure-test all new flare connections with dry nitrogen and verify with a quality leak detector. Under ARCtick licensing requirements, refrigerant must not be released unnecessarily, and pressurising a system with refrigerant before confirming connection integrity is both a compliance issue and a waste of refrigerant. The leak test with nitrogen is the final quality gate before commissioning. Browse the full range of flaring and swaging kits at HVAC Shop to ensure your tube work kit covers every size you need on the job.
Did You Know? Work health and safety obligations under Safe Work Australia guidelines require that refrigerant handling procedures minimise the risk of uncontrolled release. Verifying flare integrity with nitrogen before introducing refrigerant is both a best-practice quality step and a practical WHS measure — a nitrogen release from a failed flare is a manageable event; a refrigerant release from the same failure on an R32 system is an A2L safety incident.
Frequently Asked Questions: Flaring Copper Tubing