                          Shopcost 2.1 for DOS
John Scheldroup - 406 E. 9th St. - Superior, WI 54880 - jschel@execpc.com
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Table of contents

Overview
     Introduction

        o What is Shopcost?
        o Material hardness
        o Feed rate
        o Rake angle of the cutting tool
        o Tool wear factor
        o Chip breakers
        o Cutting fluid
        o Actual capacity
        o Available capacity
        o Metal removal rates
        o Machining time
        o Notes

     Overview
     Introduction

        o What is Shopcost?
          Shopcost is based on a mathematical model to
          help determine the performance of machinery
          found in machining and manufacturing.
          The energy required to cut a material is a
          product of cutting speed and cutting force.
          By determining how much cutting energy is
          required to remove material, it can be
          determined at what horsepower level the
          machine is functioning. The method for
          determining the horsepower level is the
          power constant for various materials and
          conditions. The power constant alone does not
          determine the cutting energy, but provides a
          proven method for computing the power at the motor.


* Some factors that do not influence the power constant are:

             + The cutting speed.
             + The depth of cut.
             + The cutting tool material.






* Some factors that do influence the power constant are:

             + The material hardness.
             + The feed rate.
             + The rake angle of the cutting tool.
             + Tool wear or the condition of the cutting edge.
             + Chip breaker.
             + Cutting fluid at lower cutting speeds.


* Material hardness

        o Plain Carbon Steel-Low, Medium and High carbon content from 80 to
          360 Brinell hardness.
        
        o Free Machining Steel-American Iron and Steel Institute values are
          given from 1108 to 1151.
        
        o Alloy Steels- American Iron and Steel Institute values are given
          from 1330 to 8740.
        
        o Gray Cast Iron-100 to 240 Brinell Hardness.
        
        o Alloy Cast Iron-150 to 250 Brinell Hardness.
        
        o Tool Steel-175 to 400 Brinell Hardness.
        
        o Stainless Steel- 150 to 250 Brinell Hardness.


* Feed rate

          Feed rates from .001 to .060 are given, and reflect the feed in
          inches per revolution for turning or chipload per tooth for
          milling.

          Example: A turning operation of .018 inches per revolution,
          requires the cutting tool to move .018 thousandths of one inch
          per one revolution of the part.

          Example: A milling operation of .005 chipload per tooth, will
          produce a chip of that given thickness, taking into account the
          feedrate in inches per minute. Chip thickness effects the life of
          the milling cutter.











* Rake angle of the cutting tool

          The rake angle can be disregarded, but with this model, the rake
          angle of the tool is based on a positive 14 degrees. Using a rake
          angle that is more positive will reduce the power required by one
          percent per degree. Using a rake angle that is more negative
          increases the power required at the cutting tool by one percent
          per degree.


* Tool wear factor

          The tool wear factor shows up in the applet as one of the
          following prompts during a turning or milling Op:

               What type of turning operation is it. ?

                       + Finish Turning(lightcuts)
                       + Normal rough and semi-finish turning
                       + Extra-heavy duty rough turning

               or

               What type of milling operation is it. ?

                       + Slab milling
                       + End milling
                       + Light and medium face milling
                       + Extra-heavy duty face milling

          In either case or selection, the cutting speed will decrease and
          the horsepower will increase as you go from a Normal or Medium
          operation to an Extra-heavy duty operation. The operation that
          you choose, is really fine-tuning the model to allow a condition
          for sharp tooling or expected tool wear; as would be expected in
          an extra-heavy duty application. Try to experiment.

        o Behind the scenes

          In planning your turning operation, if your
          inserts have been indexed or your tooling is
          sharp, you might select Finish turning(Lightcuts).
          In selecting this operation, you have set-up
          the best possible condition for your tooling.
          You will see the cutting speed increase slightly,
          but the required horsepower will stay the same.









* Chip breakers

          Chip breakers may reduce the power needed while machining the
          same material, but has not shown to be true or false. Try to
          experiment.

* Cutting fluid

          Some cutting fluids may reduce the power needed at lower cutting
          speeds, but could be counter- productive for high-speed
          applications. As a rule, high-speed, high-temperature cutting,
          does promote better shear flow and might reduce the cutting force
          and thus the power needed.


* Actual capacity

          Based on the attributes of feed, depth of cut and cutting speed
          for starting conditions, the model will show how much cutting
          energy is needed at the tool, and how much horsepower is
          required, with the following efficiency rating:

        o 90% efficiency rating for a direct belt drive
        o 75% efficiency rating for a back gear drive.
        o 75% efficiency rating for a geared head drive.
        o 70% efficiency rating for a oil-hydraulic drive.
        
        o Behind the scenes

          If you have a gear driven machine that you feel is higher than
          75 percent, and closer to 90% efficient, then go with the belt
          drive. These values are based on averages only and may not
          reflect the rating of your machine, but usually their close.

          Actual capacity is the required HP needed to machine the part,
          with the values that you gave.

* Available capacity

          Based on how much horsepower is actually needed to produce the
          part, the model will show a relationship between actual and
          potential capacities. The range between what's needed, and what
          your machine has to offer are the available capacities.

          Available capacity is usually the max. machining performance,
          that your machines motor will permit.









* Metal removal rates

          From the actual and available capacities, we can determine the
          rate of metal removal in cubic inches per minute. Keep in mind
          that actual MRR, the blue bar, is not always a minimum value for
          MRR, because you could over-shoot the capability of your machine.
          The result of an actual MRR which is greater than the available
          MRR, proves that the values you gave are really more than the
          horsepower you specified.

* Machining time

          Based on the capacities our model has produced, we can take a
          look at time as a relationship with actual and available
          capacity. The purpose of Machining time for Shopcost, has been
          constructed to use our capacities as an estimate for heavy chip
          removal or a roughing operation. Please note that no estimate is
          given for tool changes as might be found in a finish turning
          operation, however the amount of material to be left for
          finishing is your option.

        o What machining time does not consider in the model:
             + The finish cycle, which might include a tool change on a
               manual, or indexing the tool changer on CNC.
             + The time required to index the insert, sharpen the tool or
               take a coffee break and eat a donut.
             + Drills, Taps, Boring bars or other tooling which would
               require changeover time from our turning or milling
               operations.
             + The time to load and unload parts.

* Notes

          The first version of this program came in 1994, and the
          latest version today uses Java with JDK 1.02.
          
          The Java version of this program is stored on my web site
          over here:  http://www.execpc.com/~jschel/shop22.html

          It's an applet that needs a version of Netscape Navigator
          between 2.0 and 3.01 to run. The 4.0 browsers will not work.

          I'm working on converting the program with Java Development
          Kit 1.1 that will allow the applet to run in Navigator 4.0
          or Explorer 4.0. At least I hope it will run, but thank you
          for trying it if it doesn't.
                    
          
          Cheers!
