Level 1, Unit 5, Section 3 – 3.1 Joint Preparation, Measuring & Torch Setup

3.1.1 — Joint Cleaning and Preparation

Cleaning and preparation remove oxides, oils, and debris that prevent wetting. Solder cannot bond reliably to contaminated surfaces — no amount of heat or flux will compensate for a poorly prepared joint. A clean, properly fitted joint is the single most important factor in producing a leak-proof solder connection.

Why Surface Preparation Matters

Copper oxidizes rapidly when exposed to air, and the oxide layer is chemically inert to solder. Even new copper tube has a thin oxide film that must be removed before flux is applied. Oil from handling, cutting fluids, and storage contamination all repel the molten solder and create voids in the finished joint.

Cleaning Tools and Materials

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Emery Cloth / Abrasive Strip

Used to clean the outside of the tube end. Select a fine-grit emery cloth (120–150 grit) and sand the tube end with a circular motion until the copper is bright and uniformly shiny. Do not use steel wool — steel fibres left on the copper surface can contaminate the joint and cause premature corrosion.

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Fitting Brush (Internal Brush)

A round wire brush sized to the fitting bore is used to clean the inside of the fitting cup. Insert, rotate several times, and withdraw. The inside of the fitting cup must be bright and uniformly clean before flux is applied. Do not use emery cloth inside a fitting — it is difficult to control and can leave abrasive particles in the joint.

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Clean Dry Cloth

After abrasive cleaning, wipe both the tube end and fitting cup with a clean, dry, lint-free cloth to remove all abrasive dust and loose oxide particles. Apply flux immediately after wiping — the bare copper surface begins to re-oxidize within minutes at room temperature.

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What Not to Use

Never use files, grinding discs, or power tools to clean tube ends — they remove too much material and can oval or thin the tube wall. Never use petroleum-based solvents that leave a residue. Do not touch the cleaned surfaces with bare hands; skin oils contaminate copper immediately and will cause wetting failures.

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Fit-Up Check Before Assembly

The tube end must slide smoothly into the fitting cup with light hand pressure — it should not require forcing and should not be loose enough to rattle
Standard solder joint clearance is 0.05–0.15 mm (0.002–0.006 in); this gap is what capillary action fills with solder
If the tube is oval or the fitting cup is out of round, correct before assembly — an out-of-round joint will not fill uniformly and is likely to have voids
The tube should seat fully at the bottom of the fitting cup — confirm depth by marking the insertion depth on the tube before final assembly

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Clean, Flux, and Assemble Immediately

The cleaning, fluxing, and assembly sequence should be completed without delay. Cleaned copper surfaces begin to re-oxidize within minutes at room temperature and much faster in humid conditions. If a joint has been sitting assembled and unsoldered for more than 15–20 minutes in normal conditions, disassemble, clean again, and re-flux before applying heat.

3.1.2 — Pipe Measuring and Cutting

Accurate measuring reduces unnecessary joints and avoids stress from forced alignment. Pipe runs forced into position by miscut lengths put mechanical stress on solder joints and on fittings, which can lead to vibration cracking and long-term leakage. Cutting should produce square ends and minimal burr so the tube seats correctly in the fitting cup and solder can flow uniformly around the joint.

Measuring Procedure

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Face-to-Face and Face-to-Centre Measurement

Two common dimensioning methods are used when laying out copper piping runs:

Face-to-face (F–F): the distance between the face of one fitting cup and the face of the next; the tube cut length equals F–F plus the insertion depth at both ends
Face-to-centre (F–C): the distance from a fitting face to the centreline of a branch or tee; requires knowledge of the fitting centre-to-face dimension for the second fitting
Mark the tube with a felt-tip marker or scratch awl at the cut point; double-check the measurement before cutting
Account for fitting make-up depth (insertion depth): measure with a short scrap piece inserted into the fitting to determine the actual socket depth for the size being used

Cutting Procedure

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Using a Tubing Cutter

Position the cutter wheel on the cut mark; align the cutter wheel exactly on the mark — not beside it. The wheel must be perpendicular to the tube axis to produce a square end.
Snug the feed screw so the wheel contacts the tube with light pressure — not so tight that it deforms the tube before cutting begins.
Rotate the cutter around the tube in the direction that tightens the feed screw. After each full rotation, advance the feed screw one-quarter turn. Continue until the tube separates cleanly.
Do not over-tighten the feed screw on each pass — advancing too aggressively collapses the tube wall, creates a large internal burr, and can oval soft copper tubing.
Deburr the cut end immediately using the reaming blade on the cutter or a dedicated deburring tool. Rotate the reamer inside the tube end to remove the rolled-in burr completely. Hold the tube pointing downward when reaming so metal chips fall out rather than into the tube.

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Always Deburr — Internal Burrs Reduce Flow and Trap Debris

The internal burr left by a tubing cutter reduces the inside diameter at the cut end, restricts flow, and provides a ledge where scale and debris can accumulate. In refrigeration systems, metal chips that enter the system can score compressor valve seats and cause premature failure. Deburr every cut end before cleaning and assembly.

3.1.3 — Torch Setup and Lighting

Correct torch setup ensures you can deliver heat smoothly and predictably, which reduces overheating of the flux and prevents localized burning of the joint surfaces. For soldering copper with lead-free 95/5 solder, an air-fuel torch (propane or MAPP) is sufficient for most tube sizes up to 50 mm (2 in) diameter. An oxy-fuel torch may be used for larger diameters but requires additional care to avoid overheating thin-wall tube.

Torch Setup for Soldering

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Tip Selection and Pressure Setting

Select a tip size appropriate to the tube diameter: a larger tip for larger diameter tube so heat can be applied evenly around the full circumference; a smaller tip for small-bore tube where a large flame would overheat the fitting before the tube is up to temperature
For propane air-fuel torches, working pressure is typically 70–140 kPa (10–20 psi) depending on tip size — follow the torch manufacturer’s specifications
Assemble the outfit and perform a leak check before lighting
Set the tip at the correct angle relative to the joint before lighting — repositioning a lit torch with the other hand occupied by solder is a burn risk

Lighting Procedure

Confirm the work area is clear of combustibles, heat shields are in place where needed, and fire-watch materials are accessible.
Open the cylinder valve and confirm the regulator is set to working pressure. The torch valve should be closed.
Hold a friction (flint) lighter at the tip, slightly in front of the tip orifice. Never use matches, a cigarette lighter, or an open flame held in the hand.
Open the torch valve approximately one-quarter turn and strike the lighter immediately. The flame should catch within one to two strikes.
Adjust the torch valve for a soft to medium working flame — a small, well-defined inner cone with no harsh roaring. For soldering, a softer flame than for brazing is preferred; the lower heat input gives more control and reduces the risk of burning the flux.
Allow the tip to warm briefly (10–15 seconds) for a stable flame before approaching the joint.