For me it was a fantastic first project on the Tormach CNC Mill at the TechShop: http://www.TechShop.ws
In this instructable you will learn how to make a Turner's Cube and in the process practice your skills and precision needed to tackle much more difficult projects and open the doors of all the incredible things you can make using a metal mill.
Metal Bandsaw (horizontal and/or vertical)
Square or Center Finder (ruler works fine too)
CNC Mill (Such as the Tormach 1100 at the TechShop)
1/2" End Mill bit
2"x2" cube of aluminum
For my tutorial on designing the cube in AutoDesk Inventor 2012 go here: http://www.instructables.com/id/Turners-Cube-Designing-in-AutoDesk-Inventor-Pro/
Step 1: Step 1 - Creating a perfect cube
The tolerance for the cube must be within .01 inches or it will be visibly off.
Cutting the blank
First get yourself a chunk of aluminum. It can be just about any shape but you will need to get it roughly to 2"x2". This can be done with a horizontal and or vertical bandsaw. I started with a 4"x8"x2" blank and made one cut on the horizontal band saw and then again in half on the vertical band saw.
The more care you take in getting it cut at straight right angles the better for later on.
Measure the blank with calipers and get a rough idea of how long each side is.
Facing the cube
This was the trickiest part for me; measure twice cut once!
I started off spending a lot of time learning how to zero all the axis of the Tormach. This should be included in the introductory class from the TechShop and you should already be somewhat familiar with this process. Be sure to check both ends of the vise for being at Y0.00 I try to get within .003 inches to be sure my precision is good enough. Don't forget to account for the width of the edge finder when finding zero (0,0).
Find the two surfaces that are the most parallel and put them against the faces of the vice. Below the piece I used a set of 1/2" parallels. At this point it wont make much difference and just about none of your faces are square yet.
Find your Z zero by starting the spindle and lowering it close then jump stepping till the bit cuts in. I used .002 steps here. Zero out your Z axis. Remember EVERY time you reset your piece in the vise you need to find your Z axis zero again. If your face is closer to finished you can lower the bit without the spindle moving till a piece of paper no longer slides between your piece and the bit, then set it at .003 (the thickness of a piece of paper)
Using the jump step settings on your CNC Mill bring your spindle about .05 below z0 and start to face the top of the cube. I would usually bring the bit left and away from my piece, use the Gcode g0z0x-1y0 to bring the bit to z0 then I would set the jump step to about .05 and jump down one step so you are at z-0.05 then set the jump step to .25 and the spindle speed to 7. Start slow and use the override at 50% and work up from there as you get comfortable. I would manually move the bit back and forth across the face with my stepover never exceeding .25
Once my top is machined flat, measure the top to bottom and using the same faces that were against the vice, orient the piece bottom up.
Calculate how much you need to take off to get to 1.875 inches (the final thickness of the cube), find zero again and face the surface down at about .05-.1 thickness max depth at a time. Measure twice and be sure you have your math right. Better to face it in a few paths than screw it up now. There is no shame in leaving the cube roughly at 1.925 inches and doing the final dimensions when you are sure you have your cube faces all perpendicular and clean.
Repeat this process until you have a perfectly square cube at 1.875 in choosing the most square sides to put against the vice sides and bottom you can with each face.
Congrats, one of the most challenging parts is over!
-Use some compressed air each time you reorient the cube to be sure there are no metal chips between the vise and parallels and your cube. Once chip can screw up the entire precision.
-Remember to wack the top of the piece with a mallet after you tighten the vice to be sure the parallels below are held firmly and snug the vise one more time. Several of my mistakes came from the piece moving slightly in the vice when machining.