FA 7 - Machine Controlled Cutting

Fab Academy 7

Computer Controlled Machine

Make Something Big

For this week assignment, we had to make something big on wood, using the CNC. For this it was required to have Dog Bone Joints, since the CNC drill cuts a little bit rounded, so it doesn't makes straight cuts, so that makes this difficult to fit.

In the beginning (during lockdown) I designed a table and stool... but was never able to CNC it because of Covid. So when we went back to the lab, I has already designed the box of my project POWAR, and that was the one I finally cut on the CNC.

CNC stands for Computer Numeric Control,

Dog Bone Joints

The Dog Bone joints, are called like that because they look like a dog bone, and the need of this in the design is because the CNC tool is rounded and not squared, so it will never reach a corner completely if not adjusted for that, so that will give you a bit of trouble if you are going to fit two pieces together because... they wont fit correctly.

I found a very nice explanation about how to make Dog Bone Joints manually that I will share below.

Basically what I did was to create a cylinder with the diameter of the tool, and snap one of the borders to the corner of the object I'm cutting and then extrude it.

As it says here, you should also snap the center of the cylinder to the corner, but that will create a bigger unnecessary joint, compared to the smaller one I'm telling you which is much cleaner in the design.

After creating the cylinder, you can also mirror it to do exactly the same cut in the other side.

There are a lot more kind of press-fit joints, like doing them on top or in the side, but this are the ones I used.

*After I learned this I discovered that there was a plug-in in Fusion 360, that is basically a python code that does these joints for you. It kind of does the work, but it is not that good in the end. I will leave the link to the documentation and a youtube tutorial of how to use it in here.

http://tapnair.github.io/Dogbone/

Youtube Tutorial

I could sincerely say, that this was the most difficult assignment for me, but not because of the assignment itself, but because the Rhino Cam software does not works on PC, reason why I had to learn it directly in the lab computers and I have only done it twice. That is why I will try to document it step by step, so that I don't forget anything for the next time I use it.

***IN RHINO***
1. Open file in Rhino.
2. COMMAND> Rhino CAM.
3. Rhino "Origin" is the same as the machine origin in this case: "X" is always the longest side.
4. MOVE> take the corner to the origin (lower left)
a. Select the whole material and press ENTER
b. PRESS: 0 > ENTER > 0 > ENTER

***IN RHINO CAM***
1. Choose between MILL (cnc) & TURN (torno)
2. In the "Program" tab you adjust, in the "Simulate" you can simulate the work before doing it.
3. In stock, I define the Stock material > BOX STOCK
          a. The material origin is the top (lower left corner).
            b. That is point 0, 0, 0.
          c. When you define the Stock, it turns yellow.
          d. Habilitate "stock visibility."

***TO CREATE THE SCREWS***
1.  OFFSET:
        a. Select the outer part of the image.
        b. Create an offset of 20mm to the inside.
        c. COMMAND > offset > 20 > ENTER
        d. A Yellow line will appear.
2.    POINT CREATION:
        a. First create a layer called screws.
        b. The screws will be painted like dots because the material is not attached.
        c. Check twice that you are working in the screws layer.
        d. The point 0,0,0 usually is pretty worn in the CNC bed because everyone uses it... (DON'T USE IT TO ADD SCREWS)
        e. With ENTER you finalize the action.
3. MACHINE OPERATIONS:
a. Select "2 axis".
With 2.5D, the machine will move X and Y and then Z, not the 3 at the time.

CONTROL GEOMETRY:

TOOL:

FEEDS AND SPEEDS

CLEARANCE PLAIN:

CUT PARAMETERS:

ENTRY EXIT:

SORTING:

CUT PARAMETERS:

CUT LEVELS:

Fab Academy 7

Computer Controlled Machine

Make Something Big

Dog Bone Joints

Stove (LINK)

Z Desk (LINK)

Project Parameters

Setting the CAM Files

CONTROL GEOMETRY:

Spindle RPM, feed rate, chip rate:

Spindle RPM and Feed Rate Calculations:

A precondition to obtain maximum machine performance, tool life and chipping efficiency is to balance the optimum chip removal, cutting speed and feed rate of a machine. The following article provides valuable information on how to maximize the machining performance.

Spindle speed

Feed rate

Chip Rate

The chip load is a term used to describe the thickness of a chip removed perpendicular to the cutting direction, measured vertically to the cutting direction. The chip load is sometimes also referred to as "feed per tooth" and is calculated as follows:

MY SETINGS:

TOOL:

PROPERTIES: Feeds & Speeds

FEEDS AND SPEEDS

CLEARANCE PLAIN:

CUT PARAMETERS:

ENTRY EXIT:

SORTING:

POCKETING SETTINGS:

After I created the settings for the engraving of the holes, now I'm going to duplicate the settings file and modify some settings for the pocketing.

CUT PARAMETERS:

CUT LEVELS:

Small parts Pocketing and Profiling:

Saving G-Codes:

Machining with RaptorX-SL:

Safety Advices:

The CNC is one of the most dangerous machines in the lab, because it can Kill You! This doesn't means you should be afraid of it, but it means you should follow always two safety recommendations:

Wear Safety Glasses!

Never leave the machine alone!