CNC Acrylic

Today I tested out machining acrylic with my CNC. I used a 1/8" end mill and machined out my home's street number in 1/4" clear acrylic at a depth of 1/8". It turned out pretty well for a first attempt but the bottom of each pocket wasn't very smooth. There was also tiny "islands" of plastic that weren't cut out in several pockets. I painted the numbers black and will check tomorrow how well that turned out.

Bulb-ramping project still on-going. I got the encoder to switch between states and display the current selection on an LCD.

Finite State Machine

I've spent the last weekend learning how finite state machines (FSM) work and how I could implement one. I plan to use one to keep track of the state of a menu system for my bulb-ramper project. After browsing stackoverflow.com and Google, I found that it's actually fairly easy to implement. My code is based off of the code here. I have a list of possible states (e.g. menu1, menu1_entered, menu2, menu2_entered, ...) and a list of possible actions (e.g. button press, encoder turn, ...). I then create an array that contains the action that should be performed when a certain event has happened and what state to transition to based on the current state.

I also wanted to test SyntaxHighlighter (for any code I post here; 2020 Update: SyntaxHighlighter is now replaced with prism):

int test = 0;

Table Clamps and Rockets

Today I had the machine drill holes into the table for table clamps. This would allow me to securely hold down material that wasn't very big. However, my calculations were off and half the holes (the outermost two columns) were unusable because they intersected the bracing below. Still, there should still be enough usable ones for most projects. I still need to cut out clamps to use with the holes.

Afterwards, I cut out two new fin designs for the Team America Rocketry Challenge (TARC) rocket my team is using. I used my new 1/8" end mill and cut at 10 ipm. I was not in a rush and wanted to make sure the fins were as accurate as possible. They came out very nicely.

Alignment

Today I took a little time to level the spindle to the base. I did this by making sure the height of the spindle to the table was the same at all four corners of the table. Beginning near the origin, I lowered the spindle until the end mill was just above a piece of wood. Then I jogged the spindle to all four corners and adjusted the bearing pipe supports as needed. If the bit dragged into the wood, I would raise that corner up.

While adjusting a corner, the screw in the adjustment block stripped its threads out and broke off a piece of the super-glued wood (which was supposed to harden the wood so the threads would hold better). My dad and I made a new block by using a scrap piece of wood from cutting out router clamps. We took the center circle and made it into an adjustment block.

Old vs. New

New adjustment block.

I did get the machine reasonably level but since the center of the machine has a little sag (I would say ~1/50 of an inch) from the unsupported rails the alignment isn't perfect.

I hope to test the accuracy and precision of the machine with some simple shapes. I also intend to use a slower feed rate.

On another note, my 1/4" end mill and 1/8" ball mills from eBay came in a couple days ago. I should soon get the 1/8" end mill. I also received some plastic drawer cabinets for sorting my haphazard electronics workbench.

Waste

Today my dad and I cut out the back of the gantry so it would line up with the sides and have a hole in middle (like the original plans). This wasn't as easy as we expected. Only on our third attempt did we finally get the exact shape we wanted.

Back of gantry. 1/8' too short.

The first time went very smoothly, except that the length of the back was 1/8 of an inch short. The wobble from the only partially-tightened bearing rails cause this. Every other axis didn't have this issue.

To compensate for the 1/8 inch, I made the gantry CAD file 1/8 of an inch longer and updated the tool paths. After I installed the new back I would re-tighten all the axis to remove the wobble.

The second time was going along fine until... everything shut down. I opened the shed door to find everything shut off and the gantry stuck on a cable. The motor shaft caught onto the power cable of the overhead lamp and cut through the insulation. This caused a short circuit that blew the surge protector in the extension socket (I couldn't reset it anymore). I was just relieved that all the expensive electronics survived.

Uh oh.

After cleaning up the dust and fixing the lamp cord, we began cutting the back for the third time. This went off without a hitch and we were able to install the new back.

Today was definitely a day of learning and a warning to pay more attention to the machine. The torque of the motors aren't meant to be joked with.

I just need to tighten up all the bearing pipes and create a dust boot with vacuum attachment for the router. The dust is really getting out of hand.

Precision

With the start of school, I won't be able to do as much with my CNC, but I'll still be able to do less time consuming projects on the weekend. This labor day weekend I decided to redo the walls of the gantry so the router didn't stick so far forward.

Yesterday I attempted to cut out the new sides but failed all three times I tried. The first one looked fine but when I cut out a second, I noticed they didn't line up. The back of the second one was missing about a 1/8 on an inch. I tried a third time (and failed) before realizing that the wood I thought was 12 inches wide — the width of the gantry sides— was actually 11 and 7/8 inches. I would not be able to get identical sides without perfect alignment of the cutting material. I decided to stop there and get some wider planks of wood the next day.

Today, my dad and I went to Home Depot and got 4'x8'x3/4" piece of fairly nice plywood. We also picked up a wet/dry vacuum that attached to a bucket (used for the dust collection). The plywood was cut into 16 inch wide planks, which is wide enough for the gantry sides.

A little tweaking to the CAD drawing (to fix the upper corners; I forgot to readjust the diameter of the bearing mount but I don't use it anyways) and several dusty minutes later, the two new sides were cut out. They were a 1/8" short but I expected that. The entire gantry bends back as the router plunges into the wood and the cutting forces push and pull the bit off center. It's relatively accurate for now, but I'll definitely need to tighten up the y-axis or rebuild the lower axis to use supported bearings.

Old CAD drawing

New drawing.

It was fairly easy to disassemble the gantry and drill the holes into the new sides because we could use the old sides as templates. We did have a little confusion when we forgot which pipe mounting block went where but with a little trial and error and looking at pictures we got all of them in the right place.

Old.

New.

Vacuum is pretty good for the price; just need a way to mount it and to add a dust boot.

Now the gantry looks a lot cleaner and cooler. I tightened up the y-axis and added super glue to the thread to keep them from stripping. Tomorrow I'll cut out the back of the gantry as the old one doesn't line up anymore.

Router Clamps

It turns out that my initial tool paths for the router clamp were calculated incorrectly because I accidentally doubled the width of my end mill in VCarve (5/8 instead of 5/16). After adding a line in the CAD file where the clamp tightens and recalculating the tool paths, I was ready to cut out two new router clamps. The first one went rather smoothly but when cutting out the second one, the z-axis coupler slipped off. A slight re-tightening fixed the problem and the second clamp came out nicely.

You can see a partially completed clamp on the left (the one where the z-axis fell).