Reciprocating Saw

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{{disassembly}}
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[[Image:saw4.jpg|right|thumb|300px|Figure 1: Skil Reciprocating Saw]]
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{{CAD_Models}}
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{{Scanned}}
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[[Image:internalworkingsofgrinder.JPG|right|thumb|300px|Figure 1: Fully dissected product]]
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==Description==
 
==Description==
  
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This product is a produced by Black and Decker.  The product is used to grind down metal.
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The Skil Reciprocating Saw has removeable blades to cut materials ranging from wood to metal.
  
 
== How It Works ==
 
== How It Works ==
  
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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.   
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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.
  
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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.   
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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.
  
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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. 
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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.
  
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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.
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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.  
  
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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==
 
==Parts==
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|align="center"|Control speed of blade  
 
|align="center"|Control speed of blade  
 
| align="center"|Plastic, copper wires  
 
| align="center"|Plastic, copper wires  
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| align="center"|[[Image:speedcontrol.JPG|center|thumb|50px]]
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| align="center"|[[Image:SpeedControl.JPG|center|thumb|50px]]
 
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| align="center"|Turns to drive gears
 
| align="center"|Turns to drive gears
 
| align="center"|Copper wire, steel wire  
 
| align="center"|Copper wire, steel wire  
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| [[Image:badwasher.JPG |center|thumb|50px]]
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| [[Image:motor1.JPG |center|thumb|50px]]
 
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| align="center"|Cools motor
 
| align="center"|Cools motor
 
| align="center"|Plastic
 
| align="center"|Plastic
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| [[Image:Blackanddeckerhandle.JPG |center|thumb|50px]]
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| [[Image:fan.JPG |center|thumb|50px]]
 
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| align="center"|Allows motor and spiral bevel gear to rotate
 
| align="center"|Allows motor and spiral bevel gear to rotate
 
| align="center"|Steel
 
| align="center"|Steel
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| [[Image:blackanddeckerguard.JPG|center|thumb|50px]]
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| [[Image:bearing2.JPG|center|thumb|50px]]
 
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|-
 
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| align="center"|Changes direction of rotation from motor
 
| align="center"|Changes direction of rotation from motor
 
| align="center"|Steel
 
| align="center"|Steel
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| [[Image:blackanddeckertransmission.JPG |center|thumb|50px]]
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| [[Image:bearing2.JPG |center|thumb|50px]]
 
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| align="center"|Electric signal causes motor rotation
 
| align="center"|Electric signal causes motor rotation
 
| align="center"|Nickel, iron, cobalt
 
| align="center"|Nickel, iron, cobalt
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| [[Image:Camera Spindle.JPG  |center|thumb|50px]]
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| [[Image:brushes.JPG  |center|thumb|50px]]
 
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| align="center"|Convert circular movement to linear
 
| align="center"|Convert circular movement to linear
 
| align="center"|Stainless steel
 
| align="center"|Stainless steel
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| [[Image:badmotoroutput.JPG |center|thumb|50px]]
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| [[Image:shaft.JPG |center|thumb|50px]]
 
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| align="center"|Cut  
 
| align="center"|Cut  
 
| align="center"|Stainless steel
 
| align="center"|Stainless steel
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| [[Image:badtranscase.JPG  |center|thumb|50px]]
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| [[Image:blade1.JPG  |center|thumb|50px]]
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| [[Image:Dissectedblackanddeckergrinder.JPG  |center|thumb|50px]]
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<embed src="http://www.youtube.com/v/yfjMW4G0INM" type="application/x-shockwave-flash" width="425" height="350"></embed>
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==View Saw in Motion==
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[[Media:saw.avi]]
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[[media:Camera_Dissection.wmv|Right-click here and select "Save Link As" to download the video of the disassembly of the camera (.wmv)]]
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===3D Models===
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[[media:Kodak Camera 3D Models - Alibre Parts Only.zip|3D Models as Alibre Design AD_PRT]]
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Latest revision as of 18:06, 22 March 2007

Figure 1: Skil Reciprocating Saw

Contents

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
Trigger1.JPG
2 Variable speed control Speed control Control speed of blade Plastic, copper wires
SpeedControl.JPG
3 Insulated Bearing Support Element Allows rotation of motor Steel
Bearing.JPG
4 Motor Input Turns to drive gears Copper wire, steel wire
Motor1.JPG
5 Fan Structural Cools motor Plastic
Fan.JPG
6 Bearing Support element Allows motor and spiral bevel gear to rotate Steel
Bearing2.JPG
7 Spiral bevel gear Transmission motion conversion Changes direction of rotation from motor Steel
Bearing2.JPG
8 Brushes Input Electric signal causes motor rotation Nickel, iron, cobalt
Brushes.JPG
9 Shaft Support element, motion conversion Convert circular movement to linear Stainless steel
Shaft.JPG
10 Blade Output Cut Stainless steel
Blade1.JPG


View Saw in Motion

Media:saw.avi

Retrieved from "http://gicl.cs.drexel.edu/wiki-data/index.php?title=Reciprocating_Saw&oldid=8142"
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