Mini Hacksaw

Selecting the correct blade

Blades eventually wear or break and need replacing. The blade can be replaced by loosening the wing nut adjuster until it comes off the two ‘studs’ that normally hold it in tension in the frame. A blade should always be positioned with its teeth pointing away from the handle. Two types of hacksaw blade are generally available. High Carbon Steel blades are used for general cutting/sawing. They do not last as long a High Speed Steel blades. These are much more expensive but keep their cutting edge for longer and are suitable for cutting hard materials such as stainless steel and alloys. Selecting the correct blade for the material to be cut is important when setting up a hacksaw. High Speed Steel (HSS) blades are used for tough, resistant materials whilst High Carbon Steel blades are for general cutting.

Technique

Selecting the correct number of teeth per inch (25mm) is also important. The general rule is that at least three teeth should extend across the surface of the material to be cut. One hand holds the hacksaw handle with the index finger pointing in the direction of cutting (pistol grip). The other hand holds the frame, near the wing nut. Cutting/sawing should be carried out close to the jaws of the vice. This ensures that the metal does not flex or bend under the force of the hacksaw and the sawing motion.  When the metal has been cut, it will need filing. This removes sharp ‘burrs’ so that the metal can be handled safely, without the possibility of cuts to the hands.

What are treatments?

Hardening and tempering of engineering steels is performed to provide components with mechanical properties suitable for their intended service. Steels are heated to their appropriate hardening temperature (usually between 800-900°C), held at temperature, then "quenched" (rapidly cooled), often in oil or water. This is followed by tempering (a soak at a lower temperature) which develops the final mechanical properties and relieves stresses. The actual conditions used for all three steps are determined by steel composition, component size and the properties required.

Hardening and tempering can be carried out in "open" furnaces (in air or combustion products), or in a protective environment (gaseous atmosphere, molten salt or vacuum) if a surface free from scale and decarburisation (carbon loss) is required ("neutral hardening", also referred to as "clean hardening").

All tool and die steels must be treated to develop optimum properties in terms of hardness, strength, toughness and wear resistance. Almost all are hardened and tempered.

• Hardening involves controlled heating to a critical temperature dictated by the type of steel (in the range 760-1300 C) followed by controlled cooling. Dependant on the type of material, appropiate cooling rates vary from very fast (water quench) to very slow (air cool). 

• Tempering involves reheating the hardened tool/die to a temperature between 150-657 C, depending on the steel type. A process which controls the final properties whilst relieving stresses after hardening, tempering can be complex; some steels must be subjected to multiple tempering operations.

What are the benefits?

Hardening and tempering develops the optimum combination of hardness, strength and toughness in an engineering steel and offers savings in weight and material. Components can be machined or formed in a soft state and then hardened and tempered to a high level of mechanical properties without having t pay for more expensive heavier materials.

What are the limitations?

The response of a steel component to hardening and tempering depends on steel composition, component size, and method of treatment. Every steel has a "limiting" section size above which full hardening cannot be achieved. A higher grade of steel will be required to ensure optimum properties in a larger section. It may be possible to harden larger components in lower-grade steels by using non-standard treatments such as faster quench rates or lower-temperature tempers. Faster quench rates always increase the risk of distortion or cracking, and low-temperature tempers can seriously impair mechanical properties such as toughness. Serious consideration should be given to these facts before asking for non-standard treatments to be carried out. Almost all engineering steels containing over 0.3% carbon will respond to hardening and tempering.

Other limiting factors include the presence of other alloy metals such as aluminium, nickel and chromium; and the steel conditions, shape, size and availability of suitable equipment.

Material required 

- 12 x 12mm Mild Steel Bar - 6mm dia’ Bright Mild Steel rod - 18mm dia’ Brass bar 

Tension Bracket 

1. Mark out and cut 12mm x 12mm Mild Steel Bar to a length of 57mm 

(this allows 2mm for inaccurate cutting out). 

2. File both ends square so that the steel is now the correct length. 

3. Mark out, centre punch and drill the 2, 6mm holes 

4. File 2mm chamfers on the top end of the bracket. 

5. Mark out and file the 2 tapers on the bottom end of the bracket. 

6. Mark out and cut with a hacksaw the recess for the blade. 

7. File the recess so that both sides are flat and smooth. 

8. Using a hacksaw cut the slot for the mini blade, so that the blade is just below the end of the tension bracket. 

9. Using a hacksaw cut the small indent for the small blade pins. 

10.Finally draw file and polish all surfaces. 

Tension Knob 

1. DO NOT CUT brass to the correct length. 

2. Mount the 18mm brass stock in lathe so that 40mm is protruding from the chuck. 

3. Face off exposed end (no more than 1mm). 

4. Set up and knurl (use the same settings as the centre punch) 10mm from the faced end. 

5. Leave the brass in the lathe. 

6. Set up and drill (use the same setting as the tack hammer handle) a 5mm hole 20mm deep. 

7. Replace knurling tool with a parting tool, carefully machine the 5mm section down to 10mm in diameter. 

8. File any burrs off the edges of the knurl. 

9. Finally using a parting tool part-off the 15mm knob from the brass stock. 

10.Place the knob in a vice with soft jaws. 

11.Using a M6 x 1mm tap and Treflex cut the screw thread through the 5mm hole. 

Frame 

1. Cut the Bright steel 2mm longer than required. 

2. File both ends square (DO NOT round over ends). 

3. Using the M6 x 1mm Die and Treflex cut the external screw thread. 

4. Using a jig or mandrel Bend at “A”. 

5. It may be necessary to gently squeeze the handle together in a vice in order for the tension bracket to slide on easily. 

6. Fit the tension bracket to the frame. (ensure it is on correct as it cannot be removed once “B” is bent) 

7. Using a smaller jig or mandrel bend the frame at “B” 

8. It may be necessary to heat the bend slightly with LPG set-up in order to achieve a neat bend. 

9. Hold the end of the frame in a vice. 

10.Using a hacksaw cut the slot for the blade. (ensure you use a spare blade to check that the slot is deep enough). 

Finish & Assembly 

- Polish all surfaces and lightly oil. 

- Fit blade and tension with tension knob. 

Extra Notes 

- when 6.3mm rod is used

- 6mm holes will need to be drill at 6.5mm. 

- A 35mm section at the end of the frame will need to be put on the lathe and machined down 

to 5.9mm in order to tap the screw thread. 

A critical aspect of project management is to manage effectively the time taken to produce the project.  Time management is the management of the time spent, and progress made, on project tasks and activities. Excellent time management requires the planning, scheduling, monitoring, and controlling of all project activities to ensure the project is completed on time and to a high-quality standard.  A project, has an official due date and in order to meet this deadline, every project needs a schedule and to manage the production of the project. When some people refer to project time management, they’re also referring to the tools and techniques used for managing time.