What is a double flaring tool used for? A double flaring tool is used to create a strong, leak-proof seal on the end of metal tubing, most commonly for brake lines or fuel lines. This process creates a flared edge that resists high pressure and vibration, ensuring a safe connection.
Why Double Flaring is Essential
Metal lines carry fluids under pressure. If a line leaks, it can cause serious problems, especially with brakes. A single flare might work for low-pressure tasks. However, for critical systems, a double flare is the standard.
A single flare creates a 45-degree angle at the tube end. This is okay for some low-pressure uses. A double flare is stronger. It creates a folded-over lip. This lip sits securely against the flare nut. This design stops leaks much better than a single flare. Many hydraulic systems, like automotive brake systems, demand this secure connection.
Setting Up Your Double Flaring Tool
Proper setup is key to success. If you skip steps here, your flare will fail. This section covers setting up a double flaring tool correctly.
Inspecting Your Components
Before starting, check all parts. Look at the yokes, the die blocks, and the flaring cone.
- Cleanliness is Vital: Make sure the tubing and the tool parts are clean. Any dirt or oil can cause a weak seal.
- Check the Die Blocks: The die blocks hold the tubing steady. They must match the size of your tubing. You cannot use a 3/16 inch die block for 1/4 inch tubing.
Choosing the Right Die Block
The die block is crucial. It has a hole where the tube goes. The hole size must match your tubing exactly.
| Tubing Outer Diameter | Recommended Die Block Size | Common Application |
|---|---|---|
| 3/16 inch | 3/16 inch | Most automotive brake lines |
| 1/4 inch | 1/4 inch | Larger hydraulic lines |
| 5/16 inch | 5/16 inch | Some fuel or transmission lines |
Securing the Tubing
This step needs precision. The amount of tubing sticking out matters a lot.
- Measure the Stick-Out: You need to know how far the tube sticks out past the die block. This distance changes based on the type of flare you are making (single vs. double). For a standard double flare, the measurement must be exact. Refer to the manual for your specific kit for the exact measurement.
- Insert into the Block: Slide the tubing through the die block. Tighten the clamping screws evenly. The tube must not move at all when you work the tool. If the tube slips, the flare will be ruined.
Using a Double Flaring Kit: Step-by-Step Guide
Double flare tool instructions can seem complex, but the process is logical. We will walk through using a double flaring kit step by step. This detailed double flare tutorial focuses on creating robust flares, perfect for double flaring brake lines.
Phase 1: Creating the Initial Flare (The Single Flare)
The first step in making a double flare is actually making a single flare shape.
Inserting the Flaring Cone
The flaring cone is the wedge shape that spreads the metal.
- Lubricate: Put a small amount of cutting oil or high-pressure grease on the end of the tube. This helps the cone turn smoothly and prevents the metal from cracking.
- Position the Cone: Place the flaring cone into the opening of the tube. Make sure it sits centered.
- Engage the Yoke: Attach the yoke assembly over the die block and cone. The yoke draws the cone down into the tube.
Making the First Pass
You must turn the main screw slowly. This drives the cone deeper into the tubing.
- Slow Turning: Turn the flaring screw a little bit at a time. You will feel resistance increase. This is normal.
- Stop and Check: After each turn or two, stop. Check the flare shape on top of the tube. You are aiming for a 45-degree angle spread.
- Do Not Overtighten: If you force the cone too far too fast, you can crack the tube end. This ruins the piece.
Removing the Cone
Once the initial 45-degree flare is formed, back the flaring screw out. Remove the cone. You now have a standard flare shape on your tube end. This is the base for the final double flare.
Phase 2: Creating the Double Flare (The Fold Over)
This phase is where the magic happens. We need to fold that 45-degree edge back over itself. This is the core of making double flares on tubing.
Swapping to the Spreader Adapter
Some kits require you to remove the initial flaring cone and insert a different, usually flatter, adapter or spreader. This adapter is designed to press the flared edge back into a 180-degree seat.
- Clean the Area: Wipe away any excess oil or metal shavings from the first flare.
- Insert the Adapter: Place the specific double flare adapter over the existing 45-degree flare.
Compressing for the Double Flare
Now you use the yoke again, but the goal is different.
- Re-engage the Yoke: Screw the yoke down slowly, pressing the adapter into the tube end.
- The Folding Action: The adapter forces the metal edge to fold sharply back against the tubing wall. This creates the strong double lip.
- Check the Appearance: A perfect double flare will look like a smooth, rounded lip where the flare nut will seat. It should look thicker and symmetrical.
Phase 3: Finalizing and Inspecting the Flare
A good flare is smooth and flawless. Poor flaring copper tubing double flare results in leaks.
- Visual Check: Look closely at the flare. Are there any cracks, wrinkles, or signs of metal tearing? If yes, the piece is bad. Start over with new tubing.
- Seating Test: Take the flare nut and slide it onto the finished flare. The nut should slide down easily over the flare and sit flat against the double fold. If it catches or seems loose, the flare is wrong.
Best Practices for Double Flaring
Achieving consistent, reliable results requires more than just following steps. Mastering the hydraulic line flaring technique means adopting best practices for double flaring.
Tubing Material Matters
Not all tubing flares the same way.
- Soft Copper Tubing: Copper is very soft. It flares easily but is prone to cracking if over-worked. Use lots of lubricant and make very small turns during the compression steps.
- Steel/NiCopp Tubing: Modern brake lines are often made of steel or NiCopp (nickel-copper alloy). These materials are harder. They require more pressure and patience. Ensure your tool is rated for the material you are using. A weak tool will fail when trying to flare steel.
Lubrication Strategy
Do not skip oiling the tool or the tube end.
- Purpose of Oil: Oil reduces friction between the cone and the metal. Friction creates heat. Heat hardens the metal temporarily and increases the chance of splitting the tube wall.
- Where to Apply: Apply a thin coat to the threads of the flaring screw and the sides of the flaring cone before use.
Torque Control: The Gentle Approach
The most common mistake is applying too much force too soon.
- The Rule of Quarters: When in doubt, turn the screw only a quarter turn at a time, especially during the second flare-forming pass.
- Listen to the Tool: You will feel a distinct change in resistance when the metal has fully formed the desired shape. Pushing past this point usually leads to failure.
Utilizing the Double Flare Wrench
Many double flaring kits come with a specialized wrench. This is often called a double flare wrench usage tool, though it serves several functions in the kit.
Wrench Functions
This tool is usually multi-purpose:
- Holding the Die Block: It often has an open end designed to hold the die block steady while you turn the main flaring screw.
- Sizing/Gapping: Some wrenches include slots or notches that help you measure the correct overhang of the tubing before you start flaring.
- Nut Tightening: In some kits, the wrench is used to ensure the flare nut is seated properly, though standard wrenches are usually better for final torque.
When you are tightening the yoke screws or holding the assembly, use the supplied wrench. This prevents the entire assembly from spinning, which could damage the tubing or your workbench surface.
Maintenance of Your Flaring Tool
A quality tool lasts years if cared for properly. Good maintenance ensures consistent results every time you are making double flares on tubing.
Cleaning After Use
Metal shavings are the enemy of good flaring.
- Brush Away Debris: Use a small nylon brush to clean metal dust from the die block grooves and the threads of the main screw.
- Check the Cone: Inspect the flaring cone for burrs or scratches. Even a small scratch can transfer to your next flare, causing a weak spot. If the cone is damaged, replace it.
Storage Considerations
- Keep it Dry: Store the tool in a dry place. Rust on the threads makes turning the screw difficult and uneven.
- Protect the Components: Keep all small parts, especially the different size die blocks, together in their case. Losing a die block means you cannot properly flare lines of that specific size.
Comparison: Double Flare vs. Single Flare
Why go through the extra effort for a double flare? This table shows the key differences when deciding between flaring copper tubing double flare or a single flare.
| Feature | Single Flare (45°) | Double Flare (90° Fold) |
|---|---|---|
| Strength | Moderate | Very High |
| Pressure Handling | Low to Medium Pressure | High Pressure (Standard for Brakes) |
| Seal Integrity | Good, but prone to weeping under vibration | Excellent, highly resistant to leaks |
| Formation Process | One pressing step | Two distinct pressing steps |
| Application Example | Some low-pressure fuel lines (older cars) | All modern brake lines, high-pressure hydraulics |
Troubleshooting Common Double Flare Issues
Even with careful attention, problems can arise. Knowing how to fix a bad flare saves time and material.
Problem 1: Tube Splitting or Cracking
This usually happens during the first pass (creating the 45° angle).
- Cause: Too much pressure applied too fast, or lack of lubrication.
- Fix: Cut off the cracked end. Re-measure and start again. Apply oil to the cone. Turn the screw only a quarter turn between checks.
Problem 2: Flare Not Symmetrical (Wobbly Flare)
The finished flare looks uneven or lopsided.
- Cause: The tube was not held perfectly straight or tight in the die block. Alternatively, the die block itself might be worn or damaged.
- Fix: Ensure the clamp screws on the die block are tightened fully and evenly on both sides before starting. If the tube slips even slightly, the flare will be ruined.
Problem 3: Flare Too Loose or Too Tight
The flare nut does not seat correctly—it either won’t thread down or it bottoms out too easily.
- Cause (Too Loose): The second pass (the double fold) was not completed fully.
- Cause (Too Tight): The initial 45-degree flare was made too wide, or the final seating pass was over-compressed.
- Fix: If loose, gently re-engage the yoke for the second pass, applying slight additional pressure. If too tight, you must cut the tube and start over, as trying to correct an overly compressed flare rarely works.
Frequently Asked Questions (FAQ)
Can I use a double flaring tool on rigid plastic lines?
No. Double flaring tools are designed specifically for soft, malleable metals like copper, aluminum, or steel/NiCopp tubing used in pressurized fluid systems. Plastic lines require different fittings, often push-to-connect types, and should never be flared with a metal flaring tool.
Is flaring copper tubing with a double flare harder than steel?
Yes, in a way. Copper is softer, meaning it forms the initial angle very easily. However, because it is so soft, it is much easier to over-work or tear the material during the second folding step if you apply too much force. Patience is more important with copper.
How much tubing should stick out of the die block?
The exact measurement depends on your tubing size and the specific tool manufacturer’s guide. Generally, for a standard double flare, you need a specific length protruding to allow the metal to fold completely over itself without running out of material or cracking against the block face. Always consult your kit’s double flare tool instructions for the precise “stick-out” measurement.
Do I need a special tool for every brake line size?
Most quality double flaring kits come with interchangeable die blocks and cones to handle common sizes (like 3/16 inch and 1/4 inch). You need the matching die block for every line size you intend to flare.
What is the difference between a flare nut and a coupling nut?
A flare nut screws directly onto the flared end of the tube, creating the seal against the mating fitting (like a brake caliper inlet). A coupling nut is used to join two separate pieces of flared tubing together using a double-ended fitting (a union). Both require a properly formed double flare to seal correctly.