Week 10

Individual Assignment

Design a 3D mold around the stock and tooling that you'll be using, machine it, and use it to cast parts.

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Designing the Mold

Once again I chose Fusion 360 for this assignment. And was ready to try my hand at the Reuleaux Tetrahedron.

From this R.Tetra, I want to try and make it a Solid Of Constant Width.

So let's fire up Fusion and get to work!

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Trying to grasp the math of the R.Tetrahedron.

Oooh boy...

The Reuleaux Tatrehedron in a three dimnsional state, is akin to a pyramid with 3 sides of equal length. It is then rounded off by a circumscribed sphere.

Meaning, it will have to pass through all the vertices or points of the triangle.

My first attempt will be to draw a triangle of equal sides and then to find the center, in order to find the 0 point in the axes of Fusion 360.

Find the Center of the Triangle

Center the trianlge and then move it downward.

Centered.

Now we need to extrude the triangle and create a tetrahedron/pyramid from it. We use the square root of 2/3.a . And this can be typed into Fusion.

My sides are equal sides of 50mm meaning the formula is going to be : 50*sqrt(2/3). Now that we have our height, we need to bring the edges together.

This can be done with the Draft function in Fusion 360. It rotates the faces around the axes.

We select Draft, and then select the bottom face, and then the left and right side faces. We leave the top face alone, as we want to rotate the other faces in order to make our pyramid.

Editor's note: as you can see, I lost all my pictures in the making of this process.

Now we look at the Face-Edge-Face Angle in the wiki page for the formula. Arcus(inverted) Cosinus(1/3)=arctan(2.sqrt2)

Alright, let's do it....or rather not. In Fusion the formula was making the edges go outward instead of inward as expected. So in order to bring them closer I tried with negative 90 (trail and error(s) got me to -90).

I was struggeling quite a bit, but the formula that finally made it to a pyramid was: -90+ atan(2*sqrt(2))

I have my pyramid. Now this is where things started to go wrong for me. Most likely a math problem. But whenever I tried to draw the arcs, I noticed that the pyramid was not adhering to the center of the triangle. Meaning the arcs would not be of equal lengts.

The K.I.S.S. for Troubleshooting.

After going back to back, with the redrawing and trying to understand where I went wrong with the formulas, I finally said OK!, back to basics.

The Visual Cue, which reminded me.

I'll take this chance, so call me blind... SO I went to zero and started with a simple skecth of a triangle.

Draw a trianlge with equal sides.

Draw circles starting from each point of the traingle

Trim the outer arcs.

Now we have arcs of equal lengths.

Now we revolve our Triangle

We Select the face we want to revolve and then the plane. Just select the opposite plane/direction.

Make it revolve 360 degrees and voila! we have our Solid of Constant Width.

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CAM process.

I will be using a lot of the same strategies for the CAM process as I did in week 8. Instead of a 2D cut however I will be using 3D pocket clearing and Parallel cutting.

The setup will be practically the same as week 8's assignment, the only difference is the 0 point. This time around I selected the Box Point as my 0 point

And used the models for my orientation.

Main setup.

I then proceed to creat the stock it's real life dimensions, which are:

• Width = 70mm
• Height = 26mm
• Depth = 30 mm

Stock Settings.

3D Pocket Clearing.

I left the post processing tab, alone for now. I can do that in a more advanced post processing window later on.

No I want to create a setup for 3D Pocket Clearing, which can be found under the 3D tool on the toolbar.

The setup for the "1/8" (3.175mm) Flat Endmill is as following:

• Spinde Speed = 1600 rpm
• Feedrate = 1000 mm/min
• Lead-Out & Ramp Feedrate = 20 mm/min

Tool settings.

Here I was having some issues, with the simulation, as it was cutting away at my pegs. So I came to the conclusion that my Geometry was off.

I had a better simulation once i Selecte the Machining Boundry to be bound to the box and the Tool Containment to stay inside the boundaries of the cutting area.

The working Geometry settings.

The heights seemed OK, especially once the simulation ran, without any errors.

I am going to run just one pass, so this I left at default.

I also left the linking on default, as it is calculated beforehand, depending on your tool settings and geo.

Parallel Cut

For the parrallel cut, I used the same tool parameters, but only for a Ball Endmill, with a cutting diameter of 3.175 mm.

Tool settings for the Parallel cut.

For the geo. parameters, I selected Silhoute of the main setup. This will ensure for a clean-up of the rough cut.

Finished mold.

Again, the heights seemed fine, so left at default.

During simulation, of the parallel cut, I was not satisfied with the cleanliness of the mold. So I went back lowered the stepover to 0.5875 mm (I just subtracted 1 mm) and added a Perpendicular pass.

The simulation resulted in a cleaner cut, due to the smaller stepover.

Added Perpendicular pass and smaller stepover.

I left the linking on default settings.

Creating the .NC files.

Because we created to seperete jobs, we need to create individual .nc jobs for the milling. In Fusion 360 this is called Post Processing and can be found either in the toolbar, or by right clicking your setup.

The first mill job was cutting horribly. The plunge was waaay to slow (took about 1 min helixing around before cutting) and the Z axis looked inverted.

The issue with the .nc file was that it indeed started with a -Z, which was making the Stepcraft 840 confused(? no just cutting with the wrong params.)

In order to fix this, you will require the correct post processing library, for the correct software. I for example am using Stpecraft's UCCNC

I looked up the post library for UCCNC and if you are using any different kind of CNC machine, that does not show up in the Fusion post library, you can try your luck here AutoDesk HRM Post Libraries

Once dowloaded, you will need to place the .cps file in the post library folder. This can be opened at the Post Processing window here:

Open The Post Configuration Folder.

Be sure to add them to the post library folder.

We now save the jobs into seperate .nc files.

After selecting the correct posts configuration, you can name adn comment your post before creating your .nc file

Note*: If you do not see the added library, close the window and re-open it.

Now we do the same for the parrallel cut.

You can download the .NC for Pocket Cut here:Download

You can download the .NC for Parallel Cut here:Download

Milling the Mold

Now it is time to mill the mold. I am using the Stepcraft D840 with the MM-1000 spindle

The software is UCCNC by Stepcraft. With this piece of software I can position the 0 point and start the milling job.

Once the .nc file is uploaded, you can click on the tartget icons to set your axes, and jog it manually to see if your mill goes out of bounds of your stock or not.

If it does, you can always stack on your previous 0 position to calibrate the mill to your design. Once correctly calibrated you can press Cycle Start to run the job.

The Pocket Clearing job.

My mistake was not to have the right feed rate for the helix operation, taking more than 1 min to lower the bit for the cut. Once the mill has reached the right depth, however it cuts it fairly fast.

The proccess for the parallel cut is the same.

And this is the result:

The negative mold complete.

Nice and clean, although I did leave the Plunge Feedrate at auto calculation, which made the helix operation unbearably slow.

Next time , I will alter for a quicker job.