8. Computer controlled machining

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

Preparation for this week work

• Selection of wood to work with

  We selected JAS-certified Lumber Core Plywood Panel used mainly for interior furniture and cabinetry. (following information was searched by ChatGPT Auto)
  • Type: Lumber core plywood (blockboard)
  • Standard: JAS certified
  • Grade: Type II adhesive / Grade 1 surface
  • Formaldehyde emission: F☆☆☆☆ (lowest emission class)
  • Size: approximately 15 mm × 915 mm × 1830 mm

  The panel has a core made of solid wood strips sandwiched between veneer layers.
  Compared with ordinary plywood, it is lighter and stiffer in bending, which makes it suitable for shelves, furniture panels, and interior woodworking.

  However, because it is labeled “ordinary plywood (普通合板)” rather than structural plywood, it is not intended for structural construction such as load-bearing walls or floors.

  Typical characteristics:
  Good bending stiffness along the panel length
  Lighter weight than solid wood panels
  Good dimensional stability
  Commonly used in cabinetry, shelving, furniture panels, and architectural millwork
  * Adhesive classification Type II indicates suitability for interior use with moderate humidity exposure.

Cross section of Lumber Core Plywood Panel

• Book CNC Facility

  We booked FABLAB MinatoMirai which owns ShopBot.
  

In order to use this ShopBot, you need to have Safety and User lecture which is being held every month by booking the session in advance.

Lab’s Safety Training

At Fab Lab Minato Mirai, special training is required for using the ShopBot, held on specific lab days. Upon completion, your membership card will be stamped and you will be authorized to use the ShopBot from your next visit.

Issued Stamp Card for FABLAB Minatomirai user

The training included learning how to create paths using Vcarve for design data, how to operate the ShopBot, and important safety tips.

Here is the Dress Code for ShopBot usage;
Long sleave shirt
Long Pants
Gloves
Shoes
Tie the long hair if you have
Ear Plug
Better to wear glasses
Better to wear a mask at CNC operation
* Remove jewelry such as necklaces. * Avoid wearing towels or other items that may easily get caught in the equipment.

Read through the Safety Rule and follow them;

• Follow the operation manual.

• When the ShopBot is milling, always use a partition curtain to prevent flying material from flying around.

• When milling, always keep the vacuum system on with a brush on the end mill to prevent chips from building up and causing a fire.

• Always stay away from the machine while milling to prevent unexpected accidents.

• Stay within easy reach of the emergency stop switch to power down the ShopBot at any time.

• Avoid working alone, in case of an emergency.

Emergency Button to stop the machine

This time, we had a special instructor!

Thanks to our special instructor Asako, we could have fruitful CNC experiment with decent agenda to experience.

Tool paths trial

• Measure the wood board thickness

  

1st corner thickness was 14.9mm

2nd corner thickness was 15.0mm

3rd corner thickness was 15.1mm

4th corner thickness was 15.0mm

The size of Long Side length was 1830mm.

The size of Short Side length was 915mm.

Based on the measurement result, we used following values as the size of the board;
Thickness 15.0mm
Length 1830mm
Width 915mm

• Design a tool path

For the Group work, we decided to use the “Kerf Check Parts Generator” program which was made by Daisuke Doyo in Fab Academy 2018 which we used for Computer controlled cutting week.
The Kerf Check Parts Generator

Knowing the thickness of Lumber COre Board as 15.0mm, we decided to design the tool 14.8mm as the base with 0.1mm pitch.

Transport the data into “VCarve”.

Thanks to Asako’s suggestion, we added big square (700mm X 700mm) to test the accuracy of ShopBot that we use this time. After CNC trace path surface cut, measure the depth several part, measure the distance of each corner to corner to see how much distance difference.

Set “Cut Depth” as 15.3mm which will cut under 0.3mm of sacrifice bed surface.
Add 3 “Tabs” each for the test pieces’ end-milling trace path.
Set tab length as 10mm and thickness as 3.0mm.

Set “End-Mill” specification, Cutting Parameters, and Feeds and Speeds.

Select “Square” to design milling trace for confirm the accuracy.

Set Cut depth as “5mm” for this accuracy checking square which will not completely cut the shape but carve 5mm depth to measure by caliper.

Select tool paths to see the preview tool path.

Preview tool paths

Saving tool paths

After transporting the tool path G-Code into ShopBot, Asako instructed us to “Set the Z Zero Position at Machine Bed” not Material Surface which we were told from the MinatoMirai CNC lecture.

Strong Suggestion from our instructor Asako

It is highly recommended “Set the Z Zero Position at Machine Bed” for following reasons;

Reason 1: Easy to check how much depth will be carved below the Sacrifice Board by checking G-Code before operation

Reason 2: Can definitely cut the material(If the test bed is totally flat without wavy surface)

Then we decided to follow this instruction.
Open “Set Job Dimmentions and Origin” in Drawing menu.

Got following message, and click “Yes” to proceed.

Turn ShopBot main switch to On.

Operate Ten Key in the ShopBot application display to move the spindle to the place where the surface seems lowest for our cutting area.

Move end-mill to Z position calibration area.

Z Zero Calibration by following the manual;

Set board at the right corner edge.

Open G-Code to check the path depth at certain part… which is as follows;

Check the last part of G-Code by focusing “M3” the Z-height of end-mill point if the value is same as your set (in this case -0.3mm depth cut from the bed surface).
If this shows the same value as your design, then at least the cut will not destroy the machine significantly.

Air Path trial <– this can be skipped if you are sure about the path programming
Click following button in the display.

Off-set selection –? Select 3D Offset

3D Offset was selected for Air Path check.

Manually set End-mill height as high enough not to cut the material.
In this case, 40mm was set by position control key.

If you want to directly check the path at certain position in your cut design, Open File menu to go to the line in G-Code manually.

Goto line column

Input line number where you want to start the Air Path.

Start Air Path by pressing “GoTo” button in display.

Machine operation can also be done by pressing “Run from Here” button.

After checking there is no problem such as cutting path hits the screw, prepare the actual cut as follows;
Set Brush with Vacuuming hole at the End-mill part.

Check Brush position.

Switch on the Vacuuming Machine.

For actual cut, Select “No Offset” at machine start.

Start cutting by pressing “OK” button.

CNC Cutting

CNC Cut done

Check the Milling Dust size.

If the Dust Size is too small like power, it is not good for health such as lung. In this case, the dust size is goog.

The “Big Square” was designed as 700mm X 700mm and depth of 5.0mm to test the accuracy of ShopBot.

Depth measurement by caliper at point right corner


Measurement result 5.25mm

Depth measurement by caliper at top center


Measurement result 5.15mm

Depth measurement by caliper at top right corner


Measurement result 5.25mm

In depth wise, the accuracy of this ShopBot seems good.

Vertical length at right side measurement by scale


Measurement result 700mm

Measurement result 700mm

Measurement result 700mm (measured from 100mm at scale)

Measurement result 700mm (measured from 100mm at scale)

In XY length wise, the accuracy of this ShopBot seems good.

Next, Cut off the “Gap testing parts” with a saw.

Cut off the parts for gap testing.

Gap connection test

We could confirm that the Gap 0.0mm can be well connected.

Based on our test, we decided to design our products with 0.0mm Gap with this ShopBot.

As a further trial, we tried pocket milling size test.
Design circles by changing sizes by 0.1mm in Diameter.

In order to reduce time, pocket test design was made as follows;

Design pocket circles as the diameter of 40.0, 40.1, 40.2, 40.3, 40.4, 40.5, 40.6, 40.7, 40.8, 40.9

Also designed the 40.0mm diameter circle cut part as the size checker.

Pocket milling depth set as 3.0mm

Pocket milling condition

Cut path for diameter checking part

Cut path simulation in VCarve

CNC milling for the Pocket size test

MIlling done for pocket size test

Cut the circle size checking part by a saw.

Circle size checking part

Pocket size checking parts

The result of Pocket size ended up as;

Pocket was milled 0.4mm smaller in diameter.

When you design Pocket, it is necessary to design the pocket 0.4mm bigger than your actual design size.