Most of my photos aren't present, because I somehow left timesnapper off for the entire week.

Design
This week I decided to design a crate for my robotics team next season. The crate will have a compartment to store the robot and a compartment to store tools and snacks. The exterior dimenstons of the box will be 20 inches (a little less than 2 subway sandwhiches) by 20 inches by 40 inches (a little less than 4 subway sandwhiches). I chose these measurements because the maximum size every year for the robot is 18 inches (1.5 subway sandwiches) cubed, and I wanted half an inch (about one centi-whatever) of extra space around the robot.
I designed the box in Aspire, which allowed precise design and was easy to export to the shopbot files. To design the box I used the process decribe on the CAD page, but this time I was assisted by a calculator that I threw together in google sheets.

The calculator calculates the dimensions of a press fit box with a hinge, including tab lengths. The calculator works with all measurement systems (yes, including the sandwich system), just remember to keep your units consistent.This has helped me design a prototype box out of cardboard on the lasercutter.

After I confirmed that my method worked, I proceeded to scale that model so that I could cut it out of scrap plywood as a test using the CNC mill. The test cut would be larger than the actual box, but it was helpful to know that my design would work on the CNC mill. I found out that I would have to file down the interior corners, because of the limitations posed by a circular bit cutting straight corners. the test piece was easily assembled with a rubber mallet.

After that, I measured my final material with a pair of calipers, and inserted the value into my calculator. With the calculated values, I was able to design the entire box within several hours. However, this took a bit of mentally adding and subtracting decimals, so your milage may vary. Make sure the spacing between your parts is at least twice the width of the bit you are using.

Loading the file onto the CNC machine (in this case a ShopBot) is a several step process that has to be followed carefully. First you select the parts in Aspire. navigate to File>Export>Export Selected Vectors to DXF and select the option. If you designed your object at the computer you control the ShopBot from you can skip the export. It is a good idea to have the individual vectors welded together.

Move the DXF to the ShopBot computer and open aspire. Start a new file and make sure your material size is the size you are using and that the origin is at the top of the material and at the lower left corner. The correct settings for a 4' by 8' (4 sanwiches by 8 sandwiches) board are shown below.
I ran into problems with the correct X-Y origin. If you set it to the top left, the shopbot will attempt to go out of bounds. I can only imagine what horrors would result if the Z origin was set to the bottom of the material.

Import your DXF into the new aspire file using File>Import>Import Vectors You can also use Ctrl+I. The vectors may not appear inside the workspace, so move and rearrage until it works. This is a good time to double check that the spacing between parts is at least twice the diameter of the bit you are using. Try fitting as many projects into one sheet as you can, because half inch (one centi-whatever) plywood sheets can be as much as [insert large monetary value here].

After arranging your parts, open the toolpaths tab found at the right of the screen. Select the Profile Toolpath option. In the Profile Toolpath menu, check the start and cut depths. Make sure the start depth is 0.0 and the cut depth is 0.01 to 0.05 inches greater than your measured material thickness. This prevents the machine from cutting too shallow, but too deep ruins the tabs.
Next, check that the setting for your cutting bit are correct. Set the diameter to the exact diameter of your cutting bit and the spindle speed to 18000, or a comparable speed for your machine, which can be found on a sticker on the spindle, which should still be there. Set the number of passes to 6, because less passes = less depth = less friction = less fire (and fire = bad). Theres probably a few other parameters worth looking at, bit I didn't bother looking.
Now you need to determine if you need tabs. Small objects definitely need tabs, but anything about 20 inches square (about 2 sanwiches square) also need tabs, like the ends and the divider of my box. The correct settings for tabs shoud be about [see photo below]. Add the tabs, and make sure that you don't get way too many tabs, if you do, try re-welding the vectors or joining open vectors.

Now press calculate and check that everything is correct. Now close the preview and re-open the toolpaths tab. Select the Save option, which looks like a floppy disk. Select the .sbp option for your choice of measurement units. Name and locate your file somewhere you will remember.

Cutting
First you want to attach your material to the shopbot. You can use clamps or screws. If you are using clamps, make sure you have enough space for the bit. If you are using screws be especially careful about where you put them, because if the bit hits the, the bit will shatter. you can avoid this by using some plastic screws, but try not to screw them in too tight, because their heads break off easily.

After you install the material, you can set the shopbot up with the following steps.

1. First turn the machine on. If you are installing a new bit, do that beforehand.
2. Open the ShopBot controller and begin warming up the spindle. To do this, use the command C5. the spindle should be warmed up in about 2 to 5 minutes.
3. Afterwards, use the command C3 (double check first that this is the right one) to zero the X and Y axii. This might take awhile, and the program won't let you move the mouse outside the stop button area for safety reasons.
4. Now start zeroing the Z axis. attach the provided clamp to the spindle somewhere and place the provided plate under the bit. you may have to use the control pannel to do this. Now use the command C2 to begin zeroing. This will take only about a minute.

After you have set the ShopBot up you can load the .sbp file. You may also want to open the spindle RPM controller with TR because the shopbot rarely obeys the RPM settings in the .sbp. Press the Cut Part button and select the .sbp. A dialog box will appear asking you to press the start button on the physical ShopBot controller. After doing that and pressing ok on the dialog box, the program will once again lock your cursor inside the stop button box. The machine maight take awhile, but stick around, because the machine needs to be watched.
[no insert photo here, screenshots of the dialog boxes are hard to get]
After the machine is done cutting you can break the tabs with the tool of your choice, but I've found that the wrench that comes with the shopbot works well. After removing your parts there will be burrs along the edge, and the tabs will be hard to remove.

It is easy to remove those burrs if you rub the edge with some sandpaper a few times, and a file will quickly remove the tabs. Be careful removing the tabs, because the file might also peel back the outer plywood layers.

If you designed your piece without considering the curved inner corners, I suggest using a sqare file to square out the inner corners so that the piece fits together correctly. You can now mallet the pieces together. Be gentle, because the malleting might peel the layers of the plywood. If you use two different sheets of plywood like I did, the thicknesses might be different, so you may need to file the slots and put some strength into it.

If you wish to attach hardware, now is the time to do it. Be careful with the length of your fasteners (I did not use fasteners to hold the box together, only to attach the hardware to the box), if they are too long, they may go through and blow the plywood out. If all of the avalible fasteners are too long, you can use rivets, like I did. To use rivets, pre-drill a hole the size of the wider shank, and at the depth of the length of the wider shank. then, position the rivet inside the hole, on top of the hardware you wish to attach.

Then, take the riveting tool and attach the right size bit. The longer, skinnier shank should fit smoothly into the hole in the bit. Place the tool on the rivet and squeeze the tool. This might take some effort. Repeat the process until the long shank snaps off. Dispose of the shank.

To use bolts, like I did to attach the casters, first select a bit that is the diameter of the threads of the bolt. This differs from a screw pre-drilling because the bolt will easily fit in the hole. Drill the holes and attach the hardware with nuts and lock-washers if you prefer.I did not use lock-washers because the bolts I bought were too short to use them. An impact wernch comes in handy here, because it will securely attach nuts to the point where they won't come off easily.

Your object should be finished. You can stain or paint the object as you wish. I chose not to paint the box, because I am usnure of what the team I will be on will choose.

Files
First Part Here
KiBox2.crv3d - Second part of the box
kiCrateProto.crv3d - Cardboard prototype
kiCrateProto.ai - Adobe Illustrator file for the cardboard prototype