# Reciprocating Saw

(Difference between revisions)

Figure 1: Fully dissected product

## Description

This product is a produced by Black and Decker. The product is used to grind down metal.

## How It Works

Inside the grinder there is an electric motor that spins a shaft connected to a bevel gear. The bevel gear is then attached to another driving shaft. A grinding wheel is clamped onto the driving shaft, causing the grinding wheel to spin.

Because of constant friction and the forces acting on each component there is a certain life expency. This varries for individual parts based on the force acting on the part and the design of the part.

For the bearing, an assumed torque of 0.315 Nm was applied to the shaft. Assuming the grinder is being used constantly the bearing would last 1.83 years before failure. If the grinder was being used six hours every day, 365 days a year then the bearing would last 7.33 years. If the grinder was being used six hours a day, five days a week, the bearing would last 10.26 years.

For the force requirement on the gears to rotate the grind wheel at 10,000 RPM, the power consumption of the grinder was looked up. From the power consumption the torque was calculated to be 0.315 Nm, which equates to about 2.61 lbs of force on the workpeice from the grind wheel. This calculates to 12.4626 N of force at the gears to rotate the grind wheel at 10,000 RPM.

To calculate the stress in the gears, a stress equation was used from the Fundamentals of Machine Compoents Design by Robert C. Juvinall. The velocity factor was caluated with the assumption that the gears were precision shaved and ground. The overload factor was calculated with the assumption that the source of power is uniform and the driven machinery is assumed to have moderate shock. Both gears were overhung, which gave a mounting factor of 1.25. The calculated stress in the smaller gear was 613.601 PSI and the stress in the larger gear was 442.438 PSI.

## Parts

The table belows lists the Bill of Materials for the Reciprocating Saw:

Table 3.1: Reciprocating Saw Bill of Materials
Part # Part Name Category # Function Material Picture
1 Trigger Switch Control electrical signal Plastic, copper wires
2 Variable speed control Speed control Control speed of blade Plastic, copper wires
3 Insulated Bearing Support Element Allows rotation of motor Steel
4 Motor Input Turns to drive gears Copper wire, steel wire
5 Fan Structural Cools motor Plastic
6 Bearing Support element Allows motor and spiral bevel gear to rotate Steel
7 Spiral bevel gear Transmission motion conversion Changes direction of rotation from motor Steel
8 Brushes Input Electric signal causes motor rotation Nickel, iron, cobalt
9 Shaft Support element, motion conversion Convert circular movement to linear Stainless steel
10 Blade Output Cut Stainless steel