Thursday, March 7, 2013

Updates, random bits.

Here are some things in the works for future posts.

  • My Zen Toolworks CNC is nearly complete for CNC functionality. I have all the parts and materials for 3D printing, I just haven't tired to do it yet, I'm still mastering CNC functionality, and tweaking my Marlin based firmware as I realize I want particular functionality.
  • I have a complete failed project started and scrapped in the space of two weeks, a record for me. I'll write it up later, but one of my goals was "to succeed, or else fail fast", mission accomplished. I did learn *a lot* though, so it was not wasted time at all.

Here are some things I learned recently:

Aluminum flashing can be very useful in projects, it's relatively cheap, found at your local hardware store, and is sort of like extra-thick aluminum foil. I've used it on previous projects. Aluminum has excellent electrical conductivity   though it does not make a great "contact" connection. Aluminum is very corrosion resistant, but ironically it is because it rapidly oxidizes to form a protective layer. The oxide does not conduct electricity, so it makes aluminum somewhat "self-insulating".  

They make foil out of stainless steel, you can find it at some "mom and pops" hardware stores, as well as craft stores. Stainless steel is not generally a great electrical conductor, but it's oxide layer is much thinner and does not seem to interfere with passing small currents. So this seems to work better for using "high impedance  signal passing. Your mileage may vary: I'm not a metallurgist  though I did a little material science study in college.

The downside to the steel foil was that although much thinner than the aluminum, it does not mill well, at least with carbide bits.

This was the nail in the coffin for my recent failed project (I had set a limit of 5 design iterations, and I technically had 6). 

On the left, Aluminum flashing, measuring roughly 0.26 mm, cut's very
cleanly. On the right, stainless steel foil, about 0.05mm. My router just shredded the edges.
Hopefully, it didn't cause too much distress to by bit. The tow pices are different sizes because
they are from different points in my design iteration.

More random milling/material science nuggets learned recently:
  • PVC trim, found typically with lumber, in 1/2" and 3/4" thick boards, cuts like butter. I'm still experimenting with higher mill rates, and so far I can cut 1000mm/minute without even breaking a sweat.
  • Never mill things that have been glued together. I industrial spay-glued aluminium flashing to a thin sheet of polycarbinate(aka by the trade name "Lexan", at least in the USA) and tried to mill it. It was a mess.
  • Acrylic("Plexiglas") can easily melt when cut. I cut a 1/4 inch thick sheet of acrylic with a reciprocating saw, only to find that the "cut" had sealed back up behind the blade! 
  • When milling, faster feed rates mean cooler chips, if you mill acrylic at too slow of a rate, the chips can accumulate and stick to places you don't want them. 
  • Digital calipers are essential. Mill something large and measure. I just yesterday realized I have some error in the output of all my work so far. I hadn't noticed at first because the error seems proportional to the size, and I initially cut pretty small parts. It seems repeatable and predictable, so if I can't isolate the root cause (I strongly suspect a hardware or firmware issue), I will calibrate and account for it in my firmware.

No comments:

Post a Comment

I welcome you're thoughts. Keep it classy, think of the children.