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A 90" 'V' shaped groove must be prepared along the crack to accept the welding rod
Begin by removing any paint from the repair area with a body file or D/A sander an area 10 to 15mm around the damage should be sufficient. If sections of the material have been impacted and become trapped the application of heat up to 200 degrees C will help to free them. A screwdriver blade can also be used to free trapped sections.
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The 'V' groove can be formed with careful use of a square edged file but the best tool is a rotary burring bit with a cutting edge on its circumference and end face. This creates the 90 degree groove in one operation even following the most erratic of crack courses.
Begin the groove up to 10mm beyond the start of the crack and increase the depth progressively to maximum by the time the start of the crack is reached. The depth of the groove should be no more than 2/3 of the thickness of the material.
Best results are obtained when a high speed drill is employed. A slow drill or the use of a single cutting face burring tool may lead to it jumping from the groove.
During the burring operations always wear eye protectors and a dust mask to prevent irritation from fine particles of plastic.
When the groove is finished the welding rod for the material should rest neatly in it, the upper curve face of the rod protruding 1 to 2 mm above the surface of the repair. This allows for weld dressing operations, eliminating the need for fillers and ensuring enough depth of penetration for the rod.
This test relates to larger components such as bumpers where 5mm profile welding rod should be used. If 3mm welding rod is used more than one run may be necessary. For small or thin walled components one run of 3mm rod may be sufficient.
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Crack Prevention
After removing decorative trims and adhesive, the end of each crack or split should be drilled with a maximum 3mm diameter drill to prevent further lengthening of the crack. Remember, plastic swarf can be as abrasive to the eyes as metal. Wear eye protectors.
Missing Material
Where small sections of plastic are lost, a piece can be used from a spare unsalvageable part of the same material. This can be shaped and inserted, though success will depend on the availability of spare plastic, the intricacy of the design and the experience of the operator.
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