7. Computer-controlled Machining¶

This week I learned about CNC machining, designed a shelf for my vinyl collection in Autodesk Fusion and actually built it in our lab.

I teamed up with Anna, Kerstin and Lars, the other students from HRW FabLab, to find out more about our machine’s runout, alignment, fixturing, speeds, feeds, materials and toolpaths.

You can find our group work page right here.

Designing a vinyl tree¶

I recently started collecting vinyl records when Worlds by Porter Robinson was reissued on vinyl for its 10th anniversary and I never really had a proper place to store them in.

With this week’s project I want to change that by building a tree-like shelf, that was heavily inspired by Shara from Woodshop Diaries.

Her shelf, while awesome and inspiring, was completely built with manual tools and is held together with dowels and a wood glue, so to make the whole idea fit into this week’s assignment I redesigned it for CNC machining and applied joints that should hold it together without any fasteners or glue.

Of course my design is also going to be in metric instead of imperial units which as we all know are objectively better.

Since I covered CAD in earlier assignments such as week 2 and week 5 I am going to keep the design portion of this quite short.

The shelf consists of long and short branches, that are connected via through finger tenon joints and come together at the bottom with a regular finger joint.

Most of the joints in this design have the same T-bone cutout features, meaning the slots are not only rectangular but also have additional circular cutouts in the corners.

This is necessary because round cutting tools such as the ones found on a CNC machine cannot cut sharp inside corners and the little bits that are not removed would interfere with any part that is inserted there.

T-bone cutouts are actually a more or less invisible variation of dog-bone cutouts which I also make use of.

A part of the branches gets pushed through the backboard so that they can be locked in place with a wedge joint.

All of the joints come equipped with an additional 0,1mm clearance as that showed the best results in the test we did for our group assignment.

With more through finger tenon joints, the backboard is slotted into a base board which the lowest part of the branches also rests on so it hopefully doesn’t fall over.

If you want to learn more about wood joinery, here are some links with great examples, that I drew inspiration from:

You can find my Vinyl Tree Fusion file in the Download section at the bottom of this page

Preparing a setup for CNC machining¶

The first step to set all of the parts up for CNC machining is to start an Arrange command from the MODIFY menu.

make sure that all the parts are organized in their own component, even if you have a component with multiple copies of the same body, these need to be organized into individual sub-components
once in the Arrange command, select the XY-plane as well as all the components you want to machine from one sheet, in my case the branches, which are going to be cut out of 12mm plywood
in the Envelopes tab of the Arrange command set up the width and length of your sheet, then make sure to uncheck Allow Partial Arrange

I set the object spacing to 26mm because the tool to do the rough outline cuts is an 8mm end mill and I want there to be at least 10mm of material left over for the tabs to adhere to, so my parts don’t go flying off to the moon

after repeating those steps for the backboard and base, I switched over to the MANUFACTURE workspace

in there I first hid the components so I could only see the 12mm arrangement

then I opened the Tool Library from the MANAGE menu
I right clicked on Local and imported the .tools file that I got from the manufacturer

after importing the tools I had to import the postprocessor for the CNC machine, which is done the same way in the Post Library which is also found in the MANAGE menu

next I created a new setup

with the setup command open I first selected all the components from the 12mm arrangement, which projects a bounding box around them
I then set the origin point at the lower leftmost corner

I switched over to the Stock tab to set the Mode to Relative size box and the offsets to 0mm

the first thing to do in the setup is a drilling operation

I selected a 4mm drill from the CNC machine’s tool library which is slotted into the 6th tool position

the default settings looked good so I headed over to the Geometry tab where I selected the surface of one hole and checked the Select Same Diameter box

with all the holes selected I switched over to the Heights tab
to save a little bit of time I reduced the Clearance Height offset from 10mm to 5mm and set Retract Height and Top Height to Highest of...
another important setting was to check the Drill Tip Through Bottom box

the Multi-Axis , Cycle and Linking tabs can be left alone
this is what the current toolpath looks like

to clear out the joint holes I added a 2D Contour command and selected the 8mm flat end mill in tool slot 1

the default settings came with Coolant enabled, which I disabled because our machine simply doesn’t have such a feature
in the Geometry tab I selected the bottom edges of the cutouts

the settings for the Heights tab essentially stayed the same to the ones for the drill operation, except for a -0,3mm offset to make sure the end-mill goes all the way through the wood

the Passes tab needed some changes as well

I checked the box for Multiple Depths and set the Maximum Roughing Stepdown to 4mm
a genereal rule of thumb is to set the milling depth to roughly half of the mill’s diameter
I then checked the boxes for Stock to Leave and Feed Optimization
after that I set Radial Stock to Leave to 0,75mm and Axial Stock to Leave to 0mm which means that this operation leaves 0,75mm of material around the edges that are going to be removed with a different tool
in the Linking tab I only enabled Keep Tool Down which is simply an efficiency setting that removes unnecessary travel paths

the next operation is another 2D Contour that removes the leftover 0,75mm of material with a 3mm finishing end mill in the 5th tool slot
the settings are exactly the same as the ones from the previous command with the only difference being that I unchecked the Stock to Leave

next order of business: cutting the outlines of the branches
I started yet another 2D Contour command with the 8mm flat end mill in slot 1 and selected the bottom edges of the parts
this time I checked the Tabs box in the Geometry tab though
the purpose of tabs is to keep the cut parts connected to the sheet so they stay in place during later operations
8mm Tab Width , 2,3mm Tab Height and 45mm Tab Distance have worked quite well for me, I just had to set the Positioning Method to Segment because otherwise the tabs would be all over the place

the settings for the Heights tab are the same as in the finishing operation from before

Passes and Linking also pretty much stayed the same

finishing the outlines posed a question: which tool do I use?
the 6mm finishing mill would not be able to finish all the small holes for the t-bones and the 3mm finishing mill would probably not be done before next christmas
the solution was in the Geometry tab of the next 2D Contour
instead of selecting the entire bottom contour, you can select an open chain
I used this to let the 6mm tool finish the simple outlines without any t-bones

after that I set up another 2D Contour with the 3mm finishing end mill that takes care of the rest

with that the setup was pretty much done so I rightclicked it and selected Post Process

in the post processing menu I gave the setup a name, selected a location to save the file in and clicked on Post

of course the vinyl tree does not only consist of branches so I went through the same process again for the backboard, base and the wedges, which are all cut from a sheet of 18mm thick plywood
feel free to take a look at the setups in the Vinyl_Tree.f3d file from the Download section at the bottom of this page
with all that done I loaded the files onto a flash drive and headed over to the machine

Cutting and assembly¶

Cutting and assembly are not the whole story.

The actual steps went more like this:

clean the sacrificial board of any dust and debris

load up material

secure the material with M5 wood screws

load the .nc file into NC-EAS(Y)

enable the dust collection via an M8 command directly next to the first tool call and reposition the parts in the software so the cutting tool doesn’t run into a screw, then start the cutting job

wait for like an eternity, constantly stressing out about things that could go wrong

if things went well and the job finished successfully, cut through the billions of little tabs that hold the parts in place

try to remove the leftover bits of the tabs with a flush trim router

realize that some parts are really small and you kind of want to keep all your fingers

quickly design and print a part that protects you from losing any fingers

load up a new sheet of plywood and start the second job, then repeat tab removal steps

do a quick test fit, that has you questioning the 6 hours you put into the setup in Fusion

get cramps in your hands from sanding all the edges and joints and decide to print some helpful tools

do another test fit that actually works, restoring your faith in your mental capactiy

prop up the backboard on some pieces of wood so that the wedge joints can go through without being blocked

assemble the branches next to the joints in the backboard, then carefully slot them in as one piece

flip the whole thing and put in the wedges

slot the backboard into the base and hope it doesn’t fall over

admire the thing you just created

To end this week’s assignment I want to thank Lars who taught me a lot about the different types of end mills and their functions as well as how to set up everything in Fusion and around the machine.

And my brother, who helped a lot with sanding, assembly and transportation.

This would not have been possible without you!

Downloads¶

Vinyl_Tree.f3d

Wedge_Holder.f3d