Lessons learned from milling aluminum

• No manual steps for the g-code generation.  The workflow that I came up with for the top brackets is:
  •   Draw in Inkscape
  •   Export to SVG
  •   SVG into makercad
  •   Manually adjust the vertical position for the SVG
  •   Add profile operations
  •   Export g-code
  The problem is that the manual positioning made the process impossible to reproduce.  In my case, I wanted to change the feed rates in the middle of the first run, but have it mill the same workpiece. 
• If the piece around the spindle's collet starts to shake, stop things before it falls off.
• The settings from Inventables for milling aluminum work.
• Mill in the center if you want to avoid getting aluminum dust on the y-axis rails and carriage. 

Drawing the top bracket mounts

To mount my 80/20 25-5010 extrusion to my two Makerslides, I need to mill some brackets for the top.  Doing the design has been a bit harder than I thought it would be.
My first thought was to use Easel, but it doesn't let you specify locations in absolute terms with numeric input. Since the top bracket has to line up with the T-slots in the three extrusions, that rules out Easel, at least for the design.
Since the top bracket is a simple milling it seemed like it would be worthwhile to dive into generating the SVG for it by hand, and then import the SVG into Easel.
The first complication was spending a lot of time looking at the SVG arc, which seems to lack a clear explanation, although there is this excellent demo.  Having had some difficulty working with SVG's arc, I decided to use a Bezier curve instead.  You don't have to figure out the style for the curve on your own; there is a nice page right here that lets you dynamically adjust things.
Or, I could just edit things in Inkscape, which turns out to be much easier.  The only complication is that I have to specify the drill locations for the holes via bounding box, instead of center point.  This is painful when you want to adjust the hole's diameter.
But here are the calculations for the top bracket.
An extrusion bracket for Makerslide is 14mm wide, which means we want to have 3mm of clearance from the Makerslide's v portion, meaning we'll want the section of our bracket over the Makerslide to be 17mm.  The 25-5010 extrusion takes up another 50mm, and then the other Makerslide takes up another 17mm, for a total of 50mm + (17mm*2) = 84mm.
The T-slots for the Makerslide are centered, but our bracket section isn't, which means that the holes need to be centered 7mm from the edges of our bracket.  The 25-5010's T-slots for the  25-5010 are 12.5mm in from the edge of the 25-5010.  That would give us drill holes centered at Y=7mm, 29.5mm, 54.5mm, 77mm.
But Inkscape won't let us put in center coordinates.  If our drill holes are to be 6mm in diameter, we need to subtract 3mm from each Y position, for 3mm, 26.5mm, 51.5mm, and 74mm.