What is a flaring tool? A flaring tool is a device used to create a smooth, flared, bell-shaped end on metal tubing. This flared end allows the tube to seal tightly against a corresponding fitting, ensuring a leak-proof connection, especially in high-pressure systems like those found in HVAC or automotive applications.
Can I use a flaring tool on any metal? Generally, flaring tools are best suited for flaring soft metal tubing such as copper, aluminum, and some types of annealed steel. Harder metals often require specialized hydraulic flaring tools or professional swaging equipment.
Who is this guide for? This guide is for DIY enthusiasts, mechanics, and technicians who need to make secure connections using flared fittings. We will walk you through the process clearly, step by step.
Why We Flare Tubing
Making a good flare is vital for system integrity. A proper flare acts as the sealing surface when mated with a flare nut. If the flare is cracked, uneven, or too thin, the connection will leak. Leaks lead to system failure, whether it’s refrigerant loss in an AC unit or brake fluid escaping in a car. Creating professional flares is a skill worth mastering.
We primarily use flares for:
- Refrigeration and air conditioning lines.
- Brake lines (often requiring a double flare making process).
- Fuel lines.
- Hydraulic systems.
Essential Tools and Materials
Before starting, gather everything you need. Having the right tools makes the job much easier and safer.
Required Equipment
- Flaring Tool Set: This typically includes a yoke (the clamping mechanism), flaring bars (dies), and a flaring cone (the forcing element).
- Tubing Cutter: A clean, square cut is essential. Do not use a hacksaw, as it leaves burrs and an uneven edge.
- Deburring Tool or Reamer: To remove sharp edges inside and outside the tube.
- Appropriate Flare Nuts: These must match the tubing size and type of flare you are making.
- Abrasive Cloth or Emery Paper: For cleaning the tubing surface.
- Safety Glasses: Always wear protection.
- Measuring Tape or Ruler.
Tubing Types and Considerations
The material affects how you approach the job. Flaring copper tubing is generally straightforward because copper is soft. Aluminum is also relatively easy. Steel tubing, especially for brake lines, is much harder and usually requires specific tools designed for it.
| Tubing Material | Common Uses | Flaring Difficulty | Recommended Flare Type |
|---|---|---|---|
| Soft Copper | HVAC, Refrigeration | Easy | Single Flare |
| Aluminum | Low-pressure lines | Medium | Single Flare |
| Soft Steel (Annealed) | Low-pressure hydraulics | Medium/Hard | Single or Double Flare |
| Hard Steel | Brake Lines | Hard (Requires specific tools) | Double Flare |
Flaring Tool Setup: Preparing for Success
Proper flaring tool setup is the first step toward achieving a perfect seal. A poorly set up tool will ruin the tube every time.
Step 1: Cutting the Tubing
First, measure the required length for your line. Use a dedicated tubing cutter.
- Place the tubing into the cutter jaws.
- Tighten the cutter just enough so the cutting wheel bites the metal.
- Slowly rotate the cutter around the tube, applying steady pressure. Do not force it. Let the tool do the work.
- Continue rotating and tightening until you cut completely through.
Step 2: Deburring and Cleaning
Burrs are metal shavings left behind by the cutting process. They prevent the flare from sealing correctly.
- Use the internal reamer (or deburring tool) to scrape away the inside burr. Spin it gently.
- Use the external scraper or fine emery cloth to smooth the outside edge.
- Wipe the entire area clean with a dry cloth. No oil or debris should remain.
Step 3: Sliding on the Flare Nut
This is a step many beginners forget! Slide the flare nut onto the tubing before you start flaring.
- Make sure the flared end of the nut faces away from the tube end you are working on.
- Slide it far enough up the tube so it stays out of the way of the clamping process. If you forget this, you have to cut the tube and start over.
Step 4: Clamping the Tubing in the Flaring Bar
The flaring bar (or die block) holds the tube steady and sets the height of the flare.
- Select the hole in the flaring bar that perfectly matches the outside diameter (OD) of your tubing. Using the wrong size hole will deform the tube.
- Insert the tube into the selected hole.
- Position the bar so that the end of the tubing sticks up slightly above the bar’s surface. The amount sticking out determines the flare size.
Setting the Projection Height
The height the tube sticks out is crucial for tubing flaring techniques. For most single flare tool use, the tubing should protrude about 1/16 inch to 1/8 inch (about 1.5mm to 3mm) above the bar. Consult your tool’s manual for exact specifications, as this varies by tool design.
Step 5: Securing the Clamping Bar
Place the clamping bar over the flaring bar, aligning the holes. Tighten the screws firmly. The tube must not move when the flaring cone hits it.
Performing the Flare: Applying Pressure
Now you move to the yoke assembly, which holds the flaring cone that forces the metal outward.
Step 6: Positioning the Yoke
- Place the yoke over the clamped flaring bar.
- Thread the flaring cone (or adapter) into the yoke.
- Screw the cone down until it just touches the top of the tubing.
Step 7: Applying Initial Pressure (First Pass)
This is where the actual flaring copper tubing or other metal begins.
- Turn the screw on the yoke slowly and steadily. You will feel resistance as the cone pushes the metal outward into the shape of the flare seat in the bar.
- Turn the screw until you feel firm resistance. Stop immediately. Do not over-tighten on the first pass. Over-tightening can crack the metal, especially with harder alloys.
Step 8: Back Off and Re-lubricate
- Back the flaring cone out completely.
- Remove the yoke.
- Inspect the top of the tube. It should look slightly rounded over.
- If you are using a standard flaring tool (not a specialized hydraulic unit), apply a tiny drop of light oil (like 3-in-1 oil) onto the newly formed lip. This helps the final pass form smoothly.
Step 9: Final Compression Pass
- Reassemble the yoke over the flaring bar.
- Slowly turn the cone down again. Apply slightly more pressure than the first time. You are finalizing the shape and smoothing out any wrinkles.
- Keep turning until the flare is fully formed and the resistance lessens slightly, or you reach the limit set by the tool’s stop mechanism.
Important Note on Hydraulic Flaring Tools: Hydraulic flaring tools apply far more force than manual tools. When using hydraulic units, follow the manufacturer’s instructions precisely regarding pressure limits, as it is very easy to over-flare or break the tubing instantly.
Making a Double Flare
For applications requiring higher pressure, like brake lines, a double flare making technique is mandatory. This creates two lips, providing extra strength and sealing assurance.
Steps for Double Flaring
The double flare process requires specific dies and typically uses a different yoke setup than a simple single flare.
- Make the Single Flare First: Complete Steps 1 through 9 above to create a standard, well-formed single flare.
- Remove the Yoke and Bar: Carefully unclamp the tube. You now have a single flared end.
- Remove the Flare Nut (Temporarily): Slide the flare nut back down past the newly formed flare, just enough to access the flared end.
- Use the Double Flare Adapter: Most double-flaring kits come with a special adapter or punch that fits into the center of the single flare.
- Re-clamp: Re-clamp the tube and bar, ensuring the tube is seated correctly for the second operation.
- Second Press: Reinstall the yoke, but this time, insert the specialized double flare adapter/punch. Turn the screw down firmly. This action folds the outer edge of the single flare inward, creating a tight, 45-degree double seal surface.
- Final Inspection: Back off the cone and remove the assembly. The resulting flare should look like a smooth, sharp, double-angled lip.
Inspection and Final Connection
A perfect flare doesn’t help if you don’t check it or connect it correctly.
Inspecting Your Flare
Examine the flared end closely. Look for these signs of a good flare:
- Smooth Surface: The flare must be smooth all the way around. No cracks, wrinkles, or ripples should be visible.
- Even Lip: The outside edge (the lip) should be uniform in thickness and angle.
- Correct Angle: For most standard fittings (like those used in refrigeration), the flare angle should match the seat of the mating fitting (usually 45 degrees). Brake line flares are also typically 45 degrees.
If the flare looks poor, you must cut the tube back past the damaged area, deburr, and start the process again. Never attempt to use a cracked or uneven flare.
Making the Flared Fitting Connection
- Slide the flare nut completely over the flared tube end.
- Insert the tube into the female port of the mating component (valve, line splice, etc.).
- Thread the flare nut onto the port by hand. It should spin easily for several turns. If it binds immediately, the flare is likely crooked, or you are cross-threading the nut. Never force the thread.
- Once hand-tight, use a wrench to tighten the nut further. The required torque is specific to the application (check specs for brake lines or HVAC units). Tighten until snug, then usually about a quarter to a half turn more. The goal is to compress the flare tightly against the seat without deforming the tube beyond its designed limits.
Flaring Tool Maintenance
Taking care of your tool ensures it works well for years. Proper flaring tool maintenance prevents rust and sticking.
Cleaning After Use
- After every job, especially when flaring soft metal tubing like copper, clean off any metal shavings or oil residue from the yoke, cone, and flaring bar.
- Use a dry cloth. Do not use harsh solvents that might damage the metal finish or threads.
Storage
- Store the components in their original case if possible. Keep all dies (flaring bars) together.
- If you live in a humid area, consider applying a very light coating of machine oil to the steel components of the yoke and cone to prevent rust. Wipe this off before the next use.
- Ensure the threads on the yoke screw are clean. A little graphite lubricant can help keep them turning smoothly, but avoid getting lubricant on the cone tip that contacts the tube.
Checking for Wear
Periodically inspect the flaring cone. If the tip becomes nicked or rounded, it will not press the metal evenly. Worn cones must be replaced to ensure high-quality flares.
Advanced Tubing Flaring Techniques and Troubleshooting
Even with practice, issues can arise. Knowing how to fix common problems saves time.
Problem 1: Cracking or Splitting at the Flare Edge
Cause: Too much pressure applied too quickly, or the material is too hard for the tool. This is common when trying to flare thick-walled or high-strength steel without hydraulic flaring tools.
Solution:
- Reduce the pressure applied on each pass.
- Apply more passes with less force.
- Ensure you are using the correct size die hole.
- For brittle materials, ensure you anneal (soften) the metal slightly before starting, if applicable to the material specifications.
Problem 2: Uneven or Lopsided Flare
Cause: The tubing was not perfectly perpendicular to the flaring bar, or the bar itself was not tight enough.
Solution:
- Double-check your cut to ensure it is square (90 degrees).
- When clamping the tube in the bar, ensure the top surface of the tube is perfectly level with the top surface of the flaring bar before tightening the screws.
- Ensure the yoke is centered directly over the tube before you begin turning the cone.
Problem 3: The Tube Pulls Up into the Yoke
Cause: The tube was not extended far enough above the flaring bar, or the initial clamping was too loose.
Solution:
- Extend the tubing slightly more above the bar for the initial pass (maybe 1/8 inch).
- Tighten the bar screws much more firmly. The tube must be locked in place.
Flaring Soft Metal Tubing Tips
When flaring copper tubing, you have more forgiveness, but you must be careful not to create “ears” or excessive thin spots.
- Annealing: If the copper tube feels stiff, gently heat the area to be flared with a torch until it glows dull red, then let it air cool. This makes it softer and easier to work without splitting.
- Use Proper Flare Nuts: Ensure the flare nut you use is the correct type (e.g., SAE 45-degree or Metric 45-degree) for the system you are working on. Mismatched nuts cause poor sealing even with a perfect flare.
Summary of Key Practices for Success
To consistently achieve the highest quality results and master creating professional flares, remember these core rules:
- Cut Square: Use a tube cutter, not a saw.
- Deburr Everything: Inside and out. Cleanliness is next to godliness in sealing systems.
- Nut First: Always slide the flare nut on before flaring.
- Correct Protrusion: Set the height the tube sticks out of the bar precisely according to your tool’s specifications.
- Patience Over Power: Use steady, gradual pressure. Let the tool work the metal slowly. Avoid sudden, strong turns, especially on the final pass.
Frequently Asked Questions (FAQ)
Q1: Can I reuse a flared fitting?
A: Generally, no. A flare is a deformation of the metal designed for one-time compression. If you loosen the nut, you should cut the tube back, remove the old flare, and make a new one to ensure a reliable seal. Reusing an old flare risks a slow leak.
Q2: What is the difference between single and double flares?
A: A single flare creates one outward-facing lip, suitable for lower-pressure copper and aluminum lines (like many refrigeration systems). A double flare folds that single lip inward using a second pressing stage, resulting in a much stronger seal designed to handle the high pressures of hydraulic systems, such as automotive brake lines.
Q3: Why do I need to clean the tubing before flaring?
A: Dirt, oil, or burrs prevent the metal from pressing evenly against the mold in the flaring bar. Any impurity acts as a lump, causing stress risers that lead to cracks when you apply pressure, resulting in a faulty flare.
Q4: My flare nut won’t thread on after flaring. What went wrong?
A: This almost always means the flare is crooked or severely damaged. If the flare isn’t perfectly centered, the nut cannot start threading straight onto the fitting. Back off, inspect the flare for wobble or unevenness, and remake it, paying close attention to clamping alignment.
Q5: Can I use a standard flaring tool kit on my steel brake lines?
A: You might be able to make a very careful single flare on thin, annealed steel tubing, but for standard automotive brake lines, you must use a dedicated double flaring tool kit or hydraulic flaring tools designed specifically for steel lines. Standard kits often lack the strength needed for hard steel and will likely fail to create the required double flare.