Reciprocating Saw

Revision as of 09:47, 22 March 2007

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

<embed src="http://www.youtube.com/v/yfjMW4G0INM" type="application/x-shockwave-flash" width="425" height="350"></embed>

Right-click here and select "Save Link As" to download the video of the disassembly of the camera (.wmv)

3D Models

3D Models as Alibre Design AD_PRT