CNC Tooling Lab 3: Basics & Calculations

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

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

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

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, …

Vertical Mill - Tapping When tapping using a vertical mill, how is torque on the tap limited to reduce breakage? Instructor: Stop Here for Students

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

Calculating Spindle Speed Each material has recommended cutting speeds listed in sfpm. Sfpm = 3.14 x tool diameter x RPM 12 Solve for RPM

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

Calculating Spindle Speed RPM = SFPM x 12 Tool Diameter 3.14 RPM = 250 x 4 x RPM = 3822 or about 3800 rpm

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

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

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?

Hint Aluminum sfpm = 250 1/4”x20 tap ~1/4” diameter cutting surface RPM = 250 x 4 x 12 = 4000 rpm threads per inch or 10 threads per ½” 1 revolution per thread Instructor: Stop Here for Students

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, …

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

Full Size Vertical Mill

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

Team Problems You’ve 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

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

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

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

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