The cut that didn't work

 I wanted to mill out some jigs to hold together pipes for Peter's Eagle Scout project, and I was using scrap plywood, so I got aggressive on the settings.  With a 1/4" bit I tried cutting out the circles with a pass 4 mm deep at a feed rate of 2526.2 mm/min, and then cutting out the edges with a pass 5 mm deep at a feed rate of 2526.2 mm/min.

The first triangle worked.

The second triangle did not, but the plywood was rotated. I'm not sure if that would make a difference or not given that only two of the cuts were aligned with the wood.

The spindle was set a 10,000 RPM. It is possible that I didn't get the speeds exactly the same between the cuts because I'm still using the dial on the controller to set the speed and haven't set up the wiring to control the RPM.

Cabinet work

 The front was largely done on the CNC, although the edging was done by hand with a router table. 

Drag chain upgrades

 I managed to get the drag chains installed today.

After failing to get the drag chains to work without support, I realized I needed to add some supports to the machine. The support along the Y-Axis would add some weight, but the alternative was having cables drag along the table. Since I'm adding a water cooled spindle, this would be a bad idea.

For the drag chain along the Y-Axis I attached a 25mm by 50mm extrusion to the Y axis, anchored a the two ends. The chain is anchored at one end with a piece of aluminum I attached to the carriage. Rather than use the CNC to mill the piece I used a hack saw and drill. The other end is attached with a zip tie.

Along the X-Axis I attached a 25mm by 75mm extrusion along the side of the table. One end is attached with another piece of aluminum, and the other end is directly attached to the extrusion through some holes I drilled.

I also upgraded to the Inventables fork of GRBL 1.1, because Fusion 360 is now producing G-code that doesn't work with GRBL 1.0.

Making a catapult

Over the summer, at the Pathway to Adventure weekend summer camp for Cub Scouts, Johnathan and I made a catapult:

I decided this would be the next project for our Bear Den. We need to make something out of wood, it doesn't involve any glue, and I've already made it.
Of course, I turned to the CNC to mill the triangles. The 1/4" dowels go all the way through the side triangles, which is a bit of a shame, because the top can be squeezed a bit. In my model the holes for the dowels don't go all the way through, so they sit more tightly against the triangles. It does make it harder to cut the dowels to the right length.
I decided to be a bit aggressive on the milling parameters, but everything worked. On 1/2" plywood I used a 1/4" bit, a feed rate of 1000mm/minute. and 1/8" depth cuts. I was surprised that it came out so with that deep and fast of a cut, but there were no skipped steps.

Milling acrylic

A friend wanted 90 silhouettes of the State of Illinois for part of a trophy:

Getting 90 of them milled was quite the learning experience. Here's what I learned along the way.

I used Easel to do the design, because milling a simple SVG doesn't require the functionality of Fusion 360. Plus, I was able to hand the design off to my friend to edit under Easel, something that would have been much more difficult with Fusion 360. The pre-set millings were helpful too.

Lessons:

• You really do want cast acrylic rather than extruded. The extruded acrylic melted, producing cuts that were a bit rough and the bit almost always pulled the acrylic up.
• Tabs are you friend if you want to mill a lot of pieces. But with acrylic the broken off tabs are nasty sharp. I put tabs on the outside of the silhouettes but not the inside, so that the visible part of the design would be clean (the outside is hidden in the final assembly).
• Getting the acrylic from a plastic distributer --- Petersen Brothers Plastic --- worked out better than getting it from a big box store. Cheaper, easier, and better selection than Home Depot.
• My machine was able to cut the 1/8" acrylic in 3 passes, but every now and then the bit would pull the acrylic up off my cutting board. I settled for 4 passes at 45 inch/min, which is 5 inch/min faster than Easel's recommended setting.

At long last

A dovetailed box.  Haven't figured out how to do the bottom yet.

More upgrades to the table

To address the bend in the table, I added another 75 by 25 mm truss that runs lengthwise under the middle of the table, and two more legs so that the X-axis doesn't span as far. The dip is gone, and the table is stiffer.

I've also added a jig for holding the wood in place while dovetailing it.

The two auto-adjust clamps don't need to be adjusted for different thickness of wood, and do an excellent job of keeping the wood in place. The clamp on the right is attached to the new truss that runs lengthwise under the middle of the table. It's also a lot easier to line up the vertical piece with the horizontal piece with the jig, because locking in in place is just a matter of closing the clamp.

The one unexpected surprise was that clamps will push the extrusion that the wood is centered on. I fixed this by attaching it to the new truss.