Cast Aluminum Tooling Plate (MIC-6)
Mic-6 aluminum tooling plate is the best material for your build plate, period. It’s extremely flat and conducts heat really well. Also, it’s pretty. Let's get into some crunch before you guys revoke my man card for calling something pretty.
Each side is machined to a maximum of 20 microinches or 0.50-micron smoothness. The tolerance for any thickness is ±0.005” /±0.127mm.
Specified plate thickness maximum variation:
3/4” and over: .005” / 19mm and over: .127mm
1/4” to 5/8”: .015” / 6mm and over: .381mm
I love me some crunchy data. You don't have to understand the data. Suffice it to say MIC-6 is very, very flat. It doesn't get any better than this for a build plate on a 3d printer.
The best way I've found to cut aluminum tooling plate is with a jigsaw. You can clamp a bar or straight-edge to it to make a fence to keep your cut straight. One note: Don't lift the saw off your material until the blade stops or it will break your blade. Don't ask me how I know that. I buy Bosch jigsaw and bandsaw blades.
If you need to mill your aluminum, use two-flute endmills. Aluminum is kind of "gummy" and tends to stick to a four-flute end mill so you end up cutting through your chips. Two-flute end mills are much better for chip clearance. For keeping your cutter cool, a lot of machinists use kerosene when cutting aluminum. Mineral spirits work fairly well, in my experience but I'm no machinist so I'm sure someone will come along and tell me how wrong I am. For endmills, Niagara Cutter makes some of the best cutting tools on the market.
Where to Buy
Hopefully, you didn't go and google where to buy MIC-6 before you finished this article. If you did that you probably saw the high price tag and closed my website. We just need relatively small pieces of it for our 3d printers. There's a lot of sellers on eBay selling remnants for ~$20 or so. I've bought several pieces from eBay seller USA Metal Online. I highly recommend them.
If you're like me, go ahead and order two plates so you don't have to wait on a new to be delivered when you wreck the first one. Also, I covered my MIC-6 plates with painter's tape to protect the surface while I was cutting them out. Aluminum is soft so be careful with clamps.
Practical Machinist Forum -- a Great resource to learn how to machine your own parts
USA Metals Online -- Where I buy MIC-6 aluminum
Metal Remnants Inc -- Good for aluminum angle, flat bar, etc
Industrial Metal Sales -- Another good source for aluminum and other metal stock
Linear rails are far superior to smooth rods for linear motion. They're more precisely machined, less prone to warpage, and far more accurate. Since 3d printing is a growing hobby, you can find tons of cheap, China-made linear rails on Amazon and eBay. These knock-offs were cranked out as quickly and cheaply as possible to cash in on the growth of 3d printing as a hobby. Often, these are stiff and don't operate freely out of the box. Some folks find the cheap ones work fine if you take them apart, clean and lubricate both parts, then reinstall the carriages to the rails. One thing I want to point out, be very careful when removing the carriages from the rails. The tiny ball-bearings can come out and get lost. Ask me how I know.
However, I highly recommend industrial name-brand linear rails over the knock-offs. Lightly-used, industrial linear rails/carriages can be found on eBay for close to the same price as the knock-offs. The industrial brands, (such as HIWINN, THK, NSK) have been making linear rails for industrial use for years. These are companies that know everything there is to know about linear motion. Also, rails designed and manufactured for industrial use will NEVER wear out on a home 3d printer. They will literally outlast every other part of your 3d printer. Install them correctly, keep them lubricated and "forgot headache" as one of my Ukrainian co-workers likes to say (hey, Pavel). Also, you can often find "new-old-stock" name-brand linear rails on eBay. These are rails that sat on a shelf in a companies' parts/supply room and never got used. I bought most of the linear rails for the Wildbot as new-old-stock. I got the two 470mm rails for the Wildbot's Z-axis for less than $100 still sealed in the manufacturer's packaging. Two comparable rails from "Iverntech" on Amazon would cost ~$70 at the time of this writing. A small difference in price, HUGE difference in quality.
On lubrication, I use Tri-Flow PTFE lubricant for the THK linear rails on the Wildbot. I purchased it because it's the lubricant that THK recommends. However, it smells exactly like Remington Gun Oil and I suspect it's the same thing. So if you're having trouble finding Tri-Flow (it's available on Amazon) and you happen to have some RemOil on hand, it will probably suffice. The Tri-flow comes in a little squeeze bottle with a straw that fits into the groove on the linear rails. The oil will sit in the groove so I just put a little on each side and then move the carriage through it allowing it to carry the lubricant over the length of the rail.
One more note on the advantage of linear rails. The carriages have threaded mounting holes. This makes it so easy to design good, rigid mounts for your carriages. Linear bearings for smooth rods, on the other hand, are often used without a housing (bad idea) and simply zip-tied to a carriage. This is not rigid at all and will lead to problems with your print quality. Also, linear bearings are meant to be pressed into a housing to bring them into tolerance.
Another option for linear motion is vee wheels. There are industrial machines that use vee wheels and they can be as accurate as linear rails when used correctly. However, they are bulkier and require more maintenance/adjustment than linear rails. It's vital you use concentric vee wheels and that they are adjusted perfectly. If you're an industrial mechanic (as I am), then you'll have no problem with vee wheels. Otherwise, I recommend linear rails for most folks as they require no continual adjustment once they're installed.
Best Industrial Supply -- "New old stock" THK linear rails