Hacksaw Components and Functionality

Hacksaws

• Hacksaw frames are adjustable in length to accommodate blades of different lengths.
• Rectangular section steel tube is often used to make hacksaw frames.
• Handles can be of the pistol grip type or straight handled like a file.
• Blade tension is adjusted by turning the wingnut at one of the blade attachment points.
• Blade must be under tension when the saw is in use to ensure a straight cut and lengthen the life of the blade.
• Attachment points are of square section and mounted in square holes, allowing the blade to be mounted in line with the frame or at right angles to it.

Types of Hacksaws

• Junior hacksaw: used for general light work where a standard hacksaw is too clumsy, with 6-in. blades with pinned ends and flexible, 6 in. × 32 TPI blades.
• Coping saw: used for shaping soft materials like wood, with pinned blades 6.25 in. long, with 14 TPI.
• Piercing saw: used for fine sawing of intricate shapes in thin sheet, with 5 in. long blades with TPI from 32 to 80, and serrated and hardened clamps ensuring a firm grip on the blades.

Tension Files

• Tension files (e.g., Abrafiles) are made from specially heat-treated flexible steel wire.
• They do not clog and will cut in any direction, making them very useful for cutting intricate shapes or irregular holes in thin metal.
• Links enable the blades to be used in a standard hacksaw frame.
• Blades are available in three grades: fine, medium, and coarse, and are 8 in. long.

Hacksaw Blades

• The choice of blade depends on the type of material to be cut, with soft metals (e.g., brass, aluminum) requiring coarse-pitch blades and hard metals (e.g., iron and steel) requiring fine-pitch blades.
• The shape and thickness of the material must also be considered, with at least three teeth must be in contact with the material at any time.

Drill Speed and Feed Rates

• Drill speed and feed rates depend on the material being cut, the size of the drill, and the type of drill.
• The harder the material being cut and the larger the drill, the lower the cutting speed.
• The harder the drill material, the higher the cutting speed.

Centre Punching and Centre Drilling

• Centre punching is used to guide the drill until it is established in the metal.
• The standard countersink bit can be used for small jobs, but is not suitable for large jobs or pressurized skins.
• The stop countersink tool can be used for large jobs, providing a consistent depth and accuracy.

Press Countersinking

• Press countersinking (or dimpling) is used where the aircraft skin is too thin to countersink.
• It forms the edges of the hole to accommodate the head of the rivet using a set of dimpling dies.
• There are two methods: coin dimpling and radius dimpling.

Cutting External Threads

• Cutting external threads using a circular die requires securing the work in the vice, tapering the rod end, and slackening the two outer screws in the stock.
• The die and stock must be placed squarely on the rod, and the thread cut using the same technique as for taps.

Die Nuts

• Die nuts are made of high-quality chromium tool steel to exacting specifications.
• They are similar in shape to normal hexagon or square nuts, but are not intended for cutting threads.
• They are used for easing or restoring damaged threads on studs or bolts, and are turned by a suitably sized spanner.

Test your knowledge of hacksaw frames, handles, blade tension, and attachment points. Learn about the features and adjustments of hacksaws. Explore the importance of blade tension for a straight cut and longer blade life.