CNC Tooling

1
CNC Tooling

• Lab 3
• Basics Calculations

2
Vertical Mill Cutting Tools

• Identify each cutting tool found on the milling
  machine. (Attempt to be specific)
• In teams of 3, compete to find the most
  information about each cutting tool
• One person in the text book
• One person on the internet
• One person in a machinery handbook
• Limit the entire exercise to 30 minutes
• The winning team will have the most individual
  pieces of information about each cutting tool
• Winning teams will have first access to the CNC
  Vertical Mill
• Instructor Stop Here for Students

3
Carbide Inserts

• How would you characterize the carbide insert
  used on the Vertical Mill?
• In teams of 3, compete to find the most
  information about that specific carbide insert
• One person in the text book
• One person on the internet
• One person in a machinery handbook
• Limit the entire exercise to 15 minutes
• The winning team will have the most individual
  pieces of information about the carbide insert
• Winning teams will be team captains for the team
  projects
• Instructor Stop Here for Students

4
Vertical Mill Spindle Speed

• Feed rate for a cutting tool is dependent upon
  spindle speed. As 3 member teams, create lists
  to answer the following (limit time to 15
  minutes)
• In manual mode, how is spindle speed controlled
  on the VMC190xi?
• What options does the operator have for
  controlling/monitoring spindle speed?
• What are the anticipated differences in torque
  and the resulting stalling of the tool bit, with
  relation to driving horsepower of the mill?
• What do you anticipate would happen if the mill
  is in CNC automatic mode and the tool bit stalls
  while cutting?
• Instructor Stop Here for Students

5
Answers

• Spindle speed on the VMC190xi can not be
  accurately controlled by using the manual
  pushbuttons. Therefore, the only manual method
  of controlling spindle speed is through the
  Boxford software.
• Optionally, an instrument that reads out in RPM
  can be mounted to display spindle speed
• As horsepower increases, the variation in spindle
  speed due to cutter loading decreases. Also, for
  machines with geared or belt driven spindles, the
  slower spindle speeds at the same motor speed
  will have more torque and less speed variation.
• When in CNC automatic mode and the tool bit
  stalls while cutting, the table will further bind
  the tool into the work piece and may break the
  tool, damage the work piece, stall the x-y table
  movements,

6
Vertical Mill - Tapping

• When tapping using a vertical mill, how is torque
  on the tap limited to reduce breakage?
• Instructor Stop Here for Students

7
Answer

• Recommended Drill Bit size is chosen for tap
• A cutting fluid is specified for the material
• Taps are discarded when worn
• Taps are matched to the materials machined
• Spiral fluted taps help minimize the torque while
  cutting threads by keeping shavings from binding
  within the cutting edges
• A tap clutch accessory can be purchased for about
  500 which can be programmed to slip at specific
  torques
• A reversing motion is needed by some taps to
  clear metal shavings to prevent binding
• Some milling machines have torque sensors that
  allow feedback to reverse the spindle when a
  preset torque is exceeded

8
Calculating Spindle Speed

• Each material has recommended cutting speeds
  listed in sfpm.
• Sfpm 3.14 x tool diameter x RPM
  12
• Solve for RPM

9
Calculating Spindle Speed

• If a material calls for an optimal cutting rate
  of 250 feet per minute, what should the spindle
  speed be set at?
• Assume
• ¼ end mill
• Aluminum stock
• Instructor Stop Here for Students

10
Calculating Spindle Speed

• RPM SFPM x 12
  Tool Diameter 3.14
• RPM 250 x 4 x 12 1
  3.14
• RPM 3822 or about 3800 rpm

11
Calculating Spindle Speed

• Using Appendix C, what size of end mill and
  spindle speed should be used when milling
  aluminum?
• As a 3 member team, determine the appropriate
  relationships
• Limit this exercise to not more than 15 minutes
• Instructor Stop Here for Students

12
Calculating Spindle Speed

• Aluminum sfpm 250 when using HSS
• Sfpm (tool diameter) x RPM x 3.14 / 12
• Solving for variables on one side and constants
  on the other
• RPM x tool diameter SFPM x 12 / 3.14
• Therefore, for any tool diameter there is a
  unique spindle speed, but there is no ideal tool
  diameter and speed combination
• tool diameter is restricted by available power,
  clamping of the material, the smallest radius
  feature of a machined object, and other criteria

13
Calculating Tap Feed Rate

• Given the requirement to tap a ¼-20 prepared
  hole in a ½ aluminum plate what 2 pieces of
  information are necessary to manually control the
  tap operation along the z-axis?
• How many seconds will it take to tap each hole
  using spindle speed calculations?

14
Hint

• Aluminum sfpm 250
• 1/4x20 tap 1/4 diameter cutting surface
• RPM 250 x 4 x 12 4000 rpm
  1 3.14
• 20 threads per inch or 10 threads per ½
• 1 revolution per thread
• Instructor Stop Here for Students

15
Answer

• 10 revolutions x min x 60 sec 0.15 sec
  4000 rev 1 min
• Therefore, such operations can only be performed
  using CNC equipment
• Slower manual operations can be performed at a
  cost of labor
• Always check the tool manufacturers
  recommendations for determining best spindle
  speeds, appropriate cutting fluids,

16
Calculating Feed Rates

• Associated with Feed Rates are the actual table
  positions in the X and Y axis
• Using full size manual vertical mills, how are
  the actual positions of the X and Y axis
  controlled/measured?
• Go to the next page for a picture of a full size
  manual vertical mill

17
Full Size Vertical Mill
18
Manual Feed Rates

• What are the options for manual feed rate
  control/monitor of the x-y axis on the VMC190xi?
• Setup the Boxford Software to display the manual
  control of x-y axis feed rates
• Each team should be splitting the tasks
• There are 4 computers with identical software,
  hooked to different types of machines
• The Boxford manuals can be accessed on all of the
  lab computers, and also from the NSF sponsored
  Wiki website

19
Team Problems

• Youve had several opportunities thus far to
  operate as a TEAM
• List your insights as to why you believe the team
  suffers in certain areas
• Separately list what benefits you achieved by
  working as a team
• As a class, create a comprehensive list of rules
  for operating as a team
• Limit this exercise to not more than 20 minutes

20
Evolved List of Team Rules

• Every semester the class has been asked to do
  this exercise, and the following is a compiled
  list of rules that students have cited that are
  believed to contribute to team productivity
• use the Result Management tool cited earlier if
  there is a conflict

21
CNC machining from CAD Drawings

• Capturing the specific features of a design in a
  binary file provides the opportunity to machine
  parts in an automated mode
• Remove the tooling from the VMC190xi and put the
  mill in the Home Position
• See Lab 2

22
Selecting a sample CAD drawing

• Video for CAM implementation of a sample CAD
  drawing goes here

23
Run the CAM software without tooling

• For the remainder of the lab, every student
  should
• remove all tooling and work pieces from the 4 CNC
  machines
• Start each CNC machine
• Put each machine manually in the Home Position
• then mock machine a sample CAD file
• Be ready to hit the Emergency Stop Button to
  prevent a collision between the spindle, vise,
  x-y table, chuck, walls of the enclosure,
• If time permits, introduce precision orientation
  of the bench vise