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 2025 · Last reviewed: June 2025.
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.
Step-by-Step Flaring Procedure
The following sequence applies to the Mastercool eccentric flaring tool. Complete all tube preparation steps before beginning this sequence.
- Select the correct block hole size. Match the hole in the flaring block to your tube's outer diameter exactly. The standard sizes in HVAC-R work are 1/4 inch, 3/8 inch, 1/2 inch, 5/8 inch, and 3/4 inch. An undersized tube in a larger hole produces a flare too small for the fitting.
- Slide the flare nut onto the tube. Do this before inserting the tube in the block. Once the flare is formed, the nut cannot pass over it.
- Insert the tube into the block from the underside. The tube end should protrude above the block face by approximately one tube wall thickness — typically 1 to 1.5mm. Too little protrusion produces a thin, fragile flare. Too much produces an oversized flare that may crack under tightening torque. Use the chamfer on the back of the flaring cone as a protrusion guide: place the cone lightly against the tube end, adjust until the tube protrudes level with the first step of the cone, then clamp.
- Clamp the block firmly and evenly. Tighten both clamping screws alternately in small increments rather than fully tightening one before the other. Uneven clamping torque allows the tube to shift during forming, producing asymmetrical flares.
- Position the yoke over the block. Centre the cone over the tube end and ensure the yoke is fully seated on the block rails before applying any pressure. On Mastercool tools the yoke seats positively — if there is any play in the yoke-to-block engagement, check seating before proceeding.
- Apply forming pressure gradually. Begin turning the handle clockwise with smooth, even force. The eccentric cam action rolls the cone in a controlled orbital pattern as it advances, spreading the tube material outward progressively. Resistance will increase steadily as the flare forms and the copper work-hardens under the cone.
- Stop at full formation. Continue turning until you feel firm, consistent resistance requiring noticeably more effort. This indicates the flare is fully formed. Do not force further advancement — over-forming thins the flare wall and can crack the copper at the flare edge.
- Retract the cone smoothly. Reverse the handle direction to withdraw the cone through the same orbital path it advanced through. Back it out without jerking — dragging across the fresh flare surface leaves marks that compromise the sealing face.
- Release the block and remove the tube. Loosen the clamping screws and support the tube as you withdraw it. Do not pull it straight out against the block face, which can damage the fresh flare edge.
- Inspect the flare before assembly. Check cone symmetry, outer diameter consistency, and sealing surface finish before fitting the connection. See the Quality Verification section below for what to look for.
For the Mastercool hydraulic flaring kit, follow the same setup sequence for block selection, tube insertion, and protrusion, but 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.
Safety Considerations
Flaring is a low-risk mechanical task in normal circumstances, but a few practical safety points apply on site. The clamping block applies significant clamping force to the tube — keep fingers clear of the block jaws during clamping and unclamping, particularly on larger tube sizes where the screws require more torque to tighten fully.
Copper filings from the deburring step are sharp and can cause skin irritation. Point the tube downward when reaming and wash hands before handling other equipment. On site in confined spaces or elevated positions — roof cavities, plant room mezzanines, scissor lifts — secure the flaring block and tube before forming so neither can fall if released unexpectedly during the operation.
If working on a system that has not been fully recovered and isolated, confirm the system is at zero pressure before cutting any tube. Never flare on a tube section connected to a live refrigerant circuit. Safe Work Australia's guidance on working with tools in elevated and confined positions applies to flaring work carried out in non-standard conditions — refer to Safe Work Australia for current guidance relevant to your site conditions.
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 / lopsided flare | 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. |
| Trumpet flare (flared end too wide, funnel-shaped) | Excessive tube protrusion combined with over-forming; tube material pushed outward past the correct cone angle, producing a wide bell rather than a 45-degree face | Cut off and re-flare with correct protrusion. The trumpet shape prevents proper seating against the fitting face and will leak regardless of tightening torque. |
| Rough or pitted sealing surface (micro-cracks) | Grit or debris on tube or cone; worn flaring cone; oxidised tube surface; micro-cracks from work-hardened material | Re-flare. Clean tube end and cone before retry. Inspect cone for wear. If tube is work-hardened, cut back to fresh material. |
| 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. |
Reworking Defective Flares
Every defect in the table above requires the same corrective action: cut off the flared end and re-flare from fresh tube. There is no way to rework a formed flare in place — the copper has already been work-hardened and deformed by the forming process, and attempting to re-form the same flare end produces a worse result than the original. The only correct procedure is to start from scratch.
The reworking sequence is:
- Cut off the defective flare end with the tube cutter, removing at least 10–15mm back from the flare face to ensure you're working with undamaged, un-work-hardened tube.
- Inspect the freshly cut tube end. If the tube shows signs of kinking, ovality, or work-hardening from repeated bending at that point, cut back further until the tube cross-section is round and the wall is uniform.
- Deburr and clean the fresh cut end as described in the preparation section.
- Diagnose and correct the cause of the original defect before forming the new flare — adjust tube protrusion, check block clamping, clean the cone, or straighten the tube as the defect diagnosis indicates.
- Form the new flare following the full step-by-step procedure above.
On jobs where tube length is tight, the discipline is to plan tube lengths with enough margin for at least one re-flare attempt — typically 30–40mm of additional length per connection. Cutting tube to the exact minimum length means a single bad flare requires replumbing the entire run, which is avoidable with a small amount of planning at the installation stage.
When to Re-Flare vs Accept
The decision threshold should be simple: any visible defect means re-flare. There is no category of flare defect where "it'll probably be fine" is the right call on a sealed refrigerant system. 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.
The only flares that should proceed to assembly are those that pass all three checks: symmetrical cone angle, smooth sealing surface free of pits or cracks, and correct outer diameter consistent around the full circumference. A flare that passes two of the three checks does not pass.
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.
For guidance on selecting the right Mastercool flaring tool for your work — including the comparison between manual eccentric and hydraulic kits — refer to the Mastercool Flaring Tools: Selection & How-to Guide.