Difference between revisions of "KraftTech Power Sander"

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Latest revision as of 10:37, 7 February 2008

Bucknell Mechanical Design


Figure 1: KraftTech Power Sander

Contents

Group

Christopher Shake

Mark Steinhauer

Joseph Valickus

Description

The KraftTech Power Sander is a light duty orbital sander. It is used to sand small to medium sized wooden items and accepts various grits of sandpaper. The sanding pad oscillates in a small circle, constantly moving even when the user isn't, allowing for much faster sanding than with just paper.

Specifications

This sander was most likely designed to meet these customer specifications:

  • Fast sanding
    • Able to remove material quickly
  • Comfortable to hold
    • Doesn't hurt to use even with constant vibration against hand
  • Removes dust from surface
    • Reduces possible particulate in air
  • AC Power Connection
    • Can be plugged into wall outlet instead of battery


In addition to customer requests, engineering specifications might have also been provided:

  • Accepts 60Hz 120VAC
    • Runs on standard wall current
  • Uses standard 1/4 sheets of sandpaper
    • Won't require hard to find consumables
  • Minimal internal losses
    • More efficient power usage - correlates to Fast Sanding
  • Minimal vibration felt by user
    • Similar to Comfortable to hold, this also is a part of mechanical efficiency by requiring that more power go to the movement of the sanding plate than the user

Parts

List of parts

Table 1: Power Sander Component List
Part # Part Name Category Function Material Picture Model
1 Power Cord Input Provides power to the Power Sander Insulated Wires
Pspowercord.jpg
2 Switch Input Allows user to toggle power on and off Plastic with metal contacts
Onoffswitch.jpg
3 Feathers Input Provides power to the motor Carbon
Feathers.jpg
4 Motor Input Spins the driveshaft Copper, Steel
Psmotor.jpg
5 Sanding Platform Output Performs the base for the sanding function of the tool Plastic/rubber
Sandingplatform.jpg
PSplatformModel.jpg
6 Fan Output Moves dust from surface into the dust collector, cools the motor Plastic
Fan2.jpg
7 Dust Director Output Directs the dust into the dust collector Plastic
Dustdirector.jpg
8 Offset Weight Motor Conversion Provides vibration and non-uniform motion within Power Sander Steel
Offsetweight.jpg
PSOffsetWeightModel.jpg
9 Bearings Support Element Allow smooth, rotational motion Steel
Bearings.jpg
PSbearingModel.jpg
10 Flexible Legs Structural Component Attaches the Sanding Platform to the body, allowing for a balance of rigidity and a small amount of motion ABS Plastic
Legs.jpg
FlexLegsModel.jpg
11 Casing Structural Component Shields the user from electrical contact, gives the device its shape, provides support to the entire tool ABS Plastic
IMG 3457.jpg
12 Sandpaper Clips Other Components Hold the sandpaper in place Steel
Sandingplatform.jpg

Details on Modeled Parts

Table 2.1: Offset Weight
PSOffsetWeightModel.jpg

1 What decisions were made in the design of this component/module? The dimensions of this part directly control the vast majority of vibration in the sander, so the designer had to decide the radius of rotation for the pad. The weight and moment of this part also directly correspond to the possible weight and sanding friction that the pad can provide.
2 What are the critical features and dimensions? The most critical aspect of this part is the distance that the hub is offset from the input shaft and its relation to the weight distribution of the part. The weight distribution is designed to be exactly opposite to the weight of the sanding pad when it is moving around in the offset circle, and any imbalance of these two moments would cause the entire sander to vibrate much more and cause more wear on internal components.
3 What kind of loading do we expect to be on the component? This part will take the output torque and power from the motor and push the sanding pad around. The offset hub will be inside the bearing on the pad and will take all the lateral forces from the sandpaper against the surface and any other resistances to the motion. The offset weight will exert a large force in the outward radial direction in the opposite direction of the force from the sanding pad, hopefully with the same magnitude.
4 What measures can we use to evaluate performance? The vibration of the sander body and motor can be measured, where less vibration shows better performance of this part. This is similar to balancing a tire, and a similar measurement device can be used to show what side needs more weight and how much.


Table 2.2: Bearing
PSbearingModel.jpg

1 What Decisions were made in the design of this component/module? When designing this bearing, the inner diameter, outer diameter, and thickness had to be decided on. The other main factor that varies between bearings is the resistance to rotation between the different rings. That probably wasn't a big decision in choosing a bearing because the sander is made to be as cheap as possible.
2 What are the critical features and dimensions? The critical dimensions are the inner diameter, the outer diameter, and the thickness. The critical feature is the ease of rotation between the inner and outer walls of the bearing.
3 What kind of loading do we expect to be on the component? The loads applied to this bearing will be in the form of rotation between the inside and the outside of the bearing. There will also be forces applied outward from the inner part of the bearing because shaft entering the bearing is offset.
4 What measures can we use to evaluate performance? To measure the performance of the bearing a shaft can be placed in the bearing, spun, and then the number of rotations before the shaft stops spinning will quantify the performance. The more rotations after the load is released, the higher the quality of the bearing.


Table 2.3: Sanding Platform
PSplatformModel.jpg

1 What Decisions were made in the design of this component/module? The size, material of the top part and the material of the pad on the bottom.
2 What are the critical features and dimensions? The critical dimensions are that the part that holds the bearing in the middle isn't too tall and that the holes for the flexible legs to be screwed in are the right distance apart. The overall size is also a critical dimension because it shouldn't extend past the rest of the body of the sander so that the whole tool is one compact unit. A critical feature is that the bottom surface must be soft enough that when pressure is applied, the sand paper provide a smooth sanding of the surface and not scratch the surface.
3 What kind of loading do we expect to be on the component? The sanding platform will undergo lots of vibrations as it is jolted around from side to side to perform the sanding task. There will also be a force applied to the bottom of the sanding platform as pressure is applied while sanding objects.
4 What measures can we use to evaluate performance? The performance of this part is directly related to the performance of most other parts of the tool. The vibrations are a result of the motor, flexible legs, and offset weight. The softness of the bottom can be measured by sanding corners and evaluating how clean the sanding finish is.


Table 2.4: Flexible Legs
FlexLegsModel.jpg

1 What Decisions were made in the design of this component/module? Due to the nature of the legs and their function within the sander, the strength of the material and rigidity of the design were primary decisions for the design. The weight and cost of the material entered the decision-making process because of the sander's purpose and desired cost.
2 What are the critical features and dimensions? The size of the "legs" is ultimately constrained to the requirement that the device fit in one hand. The most critical features of the legs is that each can withstand the continuous vibration, the stress due to the force applied through the tool against the surface, and the balance between structural support and stability, and its allowance and absorption of small movement and vibration. The legs are required to meet dimensional specification such that they are the appropriate length to attach the sanding platform to the device and are the correct width to allow for proper fitting within the plastic casing of the sander.
3 What kind of loading do we expect to be on the component? This part ultimately receives the applied force and distributes it to the sanding pad. There are two sets of the flexible legs, totaling four contact points to transfer the load primarily along the axis of the legs' cylinders. The motion of the sander along the surface also creates a lateral force, though of a lesser value. In addition, these ABS plastic legs must be capable of adequately supporting the sanding pad while undergoing the constant vibration.
4 What measures can we use to evaluate performance? Due to the inexpensive nature of the flexible legs, it is worthwhile to experimentally test the strength of the legs under "normal" conditions, assisting in measuring the device's probable lifetime. Due to a variance in the user base and thus the user's applied force, a maximum downward force can be applied to acquire the yield strength. The balance of strength, rigidity, and vibrational dampening could also be measured by analyzing the change in vibration between the surface and the user's hand. In all, a failed or collapsed leg would reflect failure and poor performance of the flexible legs.

Links

Bucknell Mechanical Design

KraftTech Power Tools Website

Palm Sander User Manual