An automotive technician needs to manually cut a section of thin-walled stainless steel ex… — Armed Services Vocational Aptitude Battery (ASVAB)

An automotive technician needs to manually cut a section of thin-walled stainless steel exhaust tubing with a wall thickness of $\frac{1}{16}\text{ inch}$ ( $0.0625\text{ inch}$ ). To prevent tooth stripping and ensure proper cutting action using a standard hand hacksaw, which blade pitch and installation orientation should the technician select?

A
A 14-TPI blade installed with teeth pointing away from the handle to cut on the push stroke
B
A 32-TPI blade installed with teeth pointing toward the handle to cut on the pull stroke
A 32-TPI blade installed with teeth pointing away from the handle to cut on the push strokeAnswer
D
An 18-TPI blade installed with teeth pointing toward the handle to cut on the pull stroke

Answer

A 32-TPI blade installed with teeth pointing away from the handle to cut on the push stroke

Selecting a fine 32-TPI blade satisfies the critical shop rule that at least two to three teeth must contact the material cross-section at all times (

2 \times \frac{1}{32}\text{ inch} = \frac{1}{16}\text{ inch}

). Furthermore, standard hacksaw blades must always be installed with teeth facing forward away from the handle so that cutting takes place on the forward push stroke under controlled downward pressure.

Step-by-Step Solution

Determine the minimum tooth pitch required based on material wall thickness

The general shop rule requires at least 2 to 3 consecutive teeth in contact with the workpiece thickness at all times to prevent the teeth from straddling the edge and shearing off. For a wall thickness of

\frac{1}{16}\text{ inch}

(

0.0625\text{ inch}

), the pitch must be

\leq 0.0313\text{ inch}

, which corresponds to a

32\text{ TPI}

(

1/32\text{ inch} = 0.03125\text{ inch}

) blade.

Coarser blades (such as 14 or 18 TPI) have tooth spans larger than the material thickness, which catches on the thin metal and strips the teeth.

Identify the standard hacksaw blade mounting orientation and cutting stroke direction

Standard hand hacksaw blades must be mounted with the teeth pointing forward (away from the handle), so that cutting occurs during the forward push stroke.

The hacksaw frame is tensioned to maintain blade rigidity under forward thrust, while downward pressure is released on the return stroke to avoid dulling the teeth.

Key Concept

Hacksaw Blade Selection (TPI Rule) and Stroke Direction

Estimated Time:1m 15s

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