# Reciprocating Saw

Figure 1: Skil Reciprocating Saw

## Description

The Skil Reciprocating Saw has removeable blades to cut materials ranging from wood to metal.

## How It Works

The reciprocating saw runs off a 120 Volt, 8.5 Amp motor. At the end of the motor is a spiral bevel gear that is attached to a scotch yoke mechanism. The scotch yoke mechanism converts circular motion to linear motion. Referring to the avi file below, the mechanism involves a circular gear with a pin connected to a shaft. The linear motion is what moves the saw back and forth in its reciprocating motion.

The radial ball bearings on the motor were analyzed as medium bearings with a phi of 20 degrees and alpha of zero. At first the power from the motor was calculated in ansys however the power seemed to be too small so it was decided to assume that the power was the voltage multiplied by the current to give us 540 Watts. From this the force on the tip could be calculated and was found to be 99.6 N. Through force and moment calculations the normal forces were calculated and plugged into the lifetime equation for medium bearings. The results were that the bearing closest to the tip would fail first at 121446 hours. The major assumption that forces this number to be so large is that the shock was not taken into account. If this were calculated the time would be even more realistic.

Analysis in Adams yields a power output of about ¼ horsepower when cutting a medium sized log. As far as the power output is concerned there is not much as far as improvements. If a larger stoke was implemented, the time required to cut would be reduced significantly. However, a larger stoke implies a larger device which will increase material costs.

The shaft connecting to the saw blade runs between 800 and 2700 strokes per minute when it is not cutting. The shaft's motion is controlled by a scotch yoke mechanism that is connected to a gear by a pin in a slot. Using an Adams analysis, the net force acting on the shaft at an average motor speed was 22.02 pounds. This force results in a maximum deflection of the slot connected to the pin of 4.65e-4 inches. Such a deflection shows that the scotch yoke mechanism will be stable when running at very high speeds.

## 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
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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