Computer Controlled Machining

https://academy.cba.mit.edu/classes/electronics_design/index.html

💡 Group assignment

• Complete your lab’s safety training.

• Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine.

• Document your work to the group work page and reflect on your individual page what you learned.

About this week

Briefly describe the goal of the assignment. What are you characterizing, testing, or exploring

Carl:

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Tools and materials used

List all the machines, software and materials used in this assigment.

• Shopbot PRS Alpha

• Fusion 360

• 9mm Laser plywood

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Process and methodology

When using the CNC we are following the SOP's that have been creatied by the Fablab

Safety:

Know where your E-Stop is and when to use it

Any time you are interacting with the spindle the interlock shoud be turned off

Never place your hand on areas of the machine where the gantry or spindle car rides!

See this baggy shirt...

No allowed while operating the CNC!

Non-loose fitting clothes are ideal as there is nothing to get snagged in the machine.

Alway read the warning on the PC! This message means it's time to turn the spindle on the machine, if you ignore it your tools will break!

The key aspect to opperating the CNC safley is paying attention with all your sences, with an emphasis on your ears!

Is the machine slowly getting louder or higher pitched? - The tool may be loose

Is the tools screeching? - The feed rate may be too low for the spindle speed

Is there a burning smell? STOP the machine, and deal with any hot chips

Machine Test:

For our machine test we will be looking at how being aggressive effects out cuts and exaggerate flaws such as run out, by increasing tool pressure.

First warm up your spindle, on the shopbot that is comand C5

Secure your stock to the machine, i used wood screw in the corners, just make sure they are not near your cuts

Check your actual thickness of your material, this will always be different from your nominal so this is critical.

Measure your stock in X

and Y

Us the shopbot macro C3 to home X and. Y

We have a spreadsheet that we share with members to calculate feeds and speeds

It includes some chiploads for common materials and tooling

For our test piece we offset in so that we avoid aread of the stock that have been cut

We will do 3 tests, Agressive, normal and precice.

In the CAM workflow we create a setup and set our WCS in the settup menu

Now the axis match that of our machine

For our aggressive cut we are going full depth so i have reduced the chipload to 0.2, giving us a feedrate of 4800mm/min

We select a 6mm compression endmill and enter the speeds and feeds from our sheet.

Out first test will be an ID pocket of 50mm, we are using the 2D Pocket Toolpath.

We then duplicate this toolpath so that we can apply our other test pieces, adjusting our values as we go.

For the precice test, i leave 0.5mm stock on the part after the pocket, this this is then removed by a 2D Contour

Note: for all my roughing and finishing i rough the part in climb but i finish in conventional. I find this gives the best finish.

Same procedure for the external of the part, only this is a 2D Contour instead of a Pocket

All the toolpaths organised into folders

This was an error we went back to fix, on my stock to leave we had 0.5mm axial stock to leave which meant that when the countour was run it became a loose piece.

After our programs have been posted we are back to the machine. We use C3 to zero out X and Y

M3 moves the spindle in 3 axis, in this case it was moved to a convient location to acess it to change the tool.

We use the provided spanners to remove the tool loaded in the machine

Note: Shopbot made a very good PokeYoke where the key for disengaging the spindle is conneted to the wrench. This makes it far less likely you will be removing a tool on a potentially active spindle.

For this project we have a 6mm collet, our collet nut and a 6mm 2 flute compression endmill

When assembled make sure to shake to confirm that the collet is seated properly in the collet nut.

First hand tighten and minimise stickout, We push the endmill into the collet as far as the start of the ground flutes.

Titghten collet nut

Attached aligator clip for Z probe to something conductive

Run comand C2 on the PC and make sure that the endmill makes contact with the plate twice.

Replace the dust shoe

To confirm Z height is correct we manualy type MZ 18 into the controler to move the tip of the tool to 18mm above the workpiece

And check with a piece of 18mm stock.

We are now safe to reengage the spindle

We load our program from Fusion.

And make sure to hit the green start button on the machine before hitting ok on the program.

Cutting begins.

All ID tests complete

And the machine now does the external tests

We moved the machine to a safe location

Disengage the spindle

And inspect the parts

Before removing them i note the different setting used for each part.

and then removed the tabs with a multitool

before flushing them up with a chisel.

We now have 3 finished test pieces that we can measure and compare.

9.5mm Ply Test	1 Pass	2 Pass	3 Pass
Chipload	0.2mm	0.28mm	0.28mm
Feed Rate	4800 mm/min	6750 mm/min	6750 mm/min
RPM	12000	12000	12000
Depth Of Cut	10mm	6mm	6mm
Direction of Cut	Climb	Climb	Climb + Conventional Finish
Nominal Ext X and Y	100mm	100mm	100mm
External X	100.75mm	100.55mm	100.2mm
External Y	100.88mm	100.55mm	100.2mm
Nominal Int X an Y	50mm	50mm	50mm
Internal X	49.65mm	49.7mm	49.9mm
Internal Y	49.3mm	49.3mm	49.9mm
Surface Finish	Poor	Poor	Good

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Files

Add all files created for this group assignment

See below link to to files created this week: