Introduction: Turner's Cube - a Beginner CNC Milling Project

The Turner's Cube we are going to make is an interesting little project that originally came from beginners learning to work in the metal shop. The seasoned old veteran or shop owner would hand one of these to a new apprentice and tell him to figure out how to make it and reproduce it.

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.

Tools Needed:

CAD program
CAM Program
Metal Bandsaw (horizontal and/or vertical)
Drill Press
Metal Scribe
Square or Center Finder (ruler works fine too)
Calipers
CNC Mill (Such as the Tormach 1100 at the TechShop)
1/2" End Mill bit
1/2" Parallels
2"x2" cube of aluminum




For my tutorial on designing the cube in AutoDesk Inventor 2012 go here: https://www.instructables.com/id/Turners-Cube-Designing-in-AutoDesk-Inventor-Pro/

Step 1: Step 1 - Creating a Perfect Cube

The most important and often most challenging step of this process is milling 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!

Tips

-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.





Step 2: Step 2 - Drilling Center

Use a center finder or a square like the one pictured above and scribe an x in the very center of the piece.

Use a 1/4" drill bit and the drill press to drill a hole through the three axis.

Be sure to use liquid coolant and move the bit up and down throughout to not damage the bit or your piece.

Pretty simple step but take your time.

Step 3: Step 3 - Milling the Piece

Upload the stl file i included  into the CAM program (I used Cut 3D)

The settings I used in Cut 3D were:

.5in End Mill
Speed 5000 rpm
Feed 7 inches/min
Stepover: .2in
Plunge depth .1in  (to ensure three passes)
Plunge rate 2 in/min
Origin to xyz at top left corner

I only used a roughing pass and set the machining tolerance to .0001  The fine tool-pathing is unsuitable for this project.

Start off slow, find your z0 using the paper method and begin with an airpass. Go to z+4.0 (Gcode is g0z4) and set z to zero. Then run your program once all the way through to be sure you have everything correct. This will run your program 4 inches above your piece.

Bring it back to z0 and set it to the proper z value as z4 again.

You are ready to run your first toolpath. Start it off slow at 50% override and as things look good you can slowly raise it back up to 100%.

If you have managed to make it through all 6 faces and did not mess up congrats! You have achieved the basic machining skills to be very successful in future projects!


Step 4: TroubleShooting

Well if you screwed up join the crowd. This was a very challenging first project for me.

My first mistakes include:

Not starting with a perfect cube.
Having to make my cube smaller than planned because I went too deep on the manual facing several times.
A couple divots in my piece when it moved in the vise.
Forgetting to change the machine tolerance to 0 or .001 so the cube needed another pass on each face.

Tips for avoiding and fixing errors

GO SLOW and measure everything twice!!

If you end up with a smaller cube than expected you can figure out based on the current dimensions where x,y,z should be and set zeros in space to there.

For example. If your cube ended up being 1.85in on each face instead of 1.875in, find your actual x,y,z  zero and  add .0125 to each (gcode g0x-.0125y.0125z.0125 and then zeroing all axis assuming you are starting at the top left corner for zeros, the x axis is minus in that case). This is because the difference is .025 and the cube is half that thickness less on each side. (1.875-1.85=.025, .025/2=.0125)

If you get done and the cubes are not distinct enough with the corners being attached with too much material you can add additional thickness to the z axis and run your program again on each face. For example I wanted to make mine a bit more defined so I needed to take off an additional .05 thickness of each face. I found my z zero and then set it so it was actually z0.053 (my added thickness and the thickness of the paper i was using to set it to zero). I ran the program again on all the surfaces, scribing marks on the surfaces I hadn't done to keep track.

If your piece jumped out of place in the vice don't fret. Just finish the piece as you should and then reface the entire cube again afterwards below the ding in it.

Comments

author
space123 (author)2013-12-05

Thanks for posting. This is likely a dumb question, but I have yet to do my first project. Why did you need to use the drill press for the centre hole, rather than centre finding on the piece, and manually jogging the z-axis down in small steps? Thanks!

author
ravenquest (author)space1232013-12-05

Honestly it was just easier to do on a manual drill press as the center block can become somewhat fragile if you drill those holes last. I wanted to be sure how much pressure I was applying.

It can be done just as easily on the CNC mill though. In the end it came down to how much time I had left on my appointment at the mill.

author
space123 (author)space1232013-12-05

Sorry, I mean using the CNC mill rather than the drill press for the centre hole.

author
rog8811 (author)2012-05-07

As I have been offered a 3d print for my instructables, I thought of you and this instructable.

I wonder if your files are usable for 3D printing and if so would you mind if I used them please?

author
ravenquest (author)rog88112012-05-07

The STL would work fine for 3D printing. The only problem is you may need a support structure to make it work.

author
ironsmiter (author)2012-01-23

not to put TOO big a dent in your machining ego(though it is a neat piece of work)

but the turners cubes are nested, FREE MOVING cubes!
http://1stclass.mylargescale.com/abernat/turners%20cube.jpg

It makes for a MUCH more challenging project, thought the techniques used to produce it is nearly identicle.

author
ravenquest (author)ironsmiter2012-01-23

I've seen them made lots of different ways, free moving and not. I chose to make them solid for my first project since I wasn't prepared for what to do if it broke loose while machining it.

This was the original source I was inspired by:
http://www.cnccookbook.com/CCTurnersCube.html

You can see there are plenty of other cubes there that are not free moving.

As you said, it makes for a much more challenging project. You should post an instructable on how you made your's free moving. I've not really seen any info on how to do that.

author
ironsmiter (author)ravenquest2012-01-23

powerglitch while posting... hopefully this isn't a doublepost.

Anyhow.
There's really no way to give a hint, without giving the whole thing away.

And since this is instructables, not frustratables...

The trick involves making the stepped plugs BEFORE beginning on the cube.
These plugs hold the inner cubes while you do the undercutting to free them from the outer cube.
A tight fit is needed, but not a pressed fit. 1-2 thousandths should be more than enough clearance.

author
canida (author)ironsmiter2012-01-25

Sounds like you need to post this one yourself!

author
Xyver (author)canida2012-04-30

Gotcha covered :)

https://www.instructables.com/id/Turners-Cube-Manual-Machine/

author
TheITSystem (author)2012-01-30

I'm inspired. I'm taking the class a week from Monday and looking forward to taking on this project as it is. I have half a mind to print one on the 3D printer just to blow off steam while I'm waiting for the class. I watched ravenquest work through this and like I said, inspired. Great work!

author
Ambermile (author)2012-01-29

Well, free-moving or otherwise, (and I don't see anyone stepping up to do an ible on the "completed" option - plugs or whatever), for a first-off project I think it's a great result and you should be well proud of it.

author
Skymeat (author)2012-01-26

I've been trying to make one of these on my lathe. Getting closer each time. I never thought of making one on a mill. Great looking piece.

author
Kyling Zhang (author)2012-01-26

very professional! really appreciate your great job!

author
awoodcarver (author)2012-01-26

Wow ...We use to do these in wood when showing at local county fairs with the cubes free inside the others , people would always ask if we made them in 2, 3, or 4 parts and look for a glue joint .... I never would have thought of doing one in metal .....Very nice work

author
keefo54 (author)2012-01-26

Stepped plugs ...ha ha ha no contest ...when you make the thing on a conventional lathe by hand ...ooooh just like the old days ....you pack the cubes with hard wax or wet tissue and then undercut to release the cubes I'm sorry but you have only done half the work .
If your having trouble about getting it square then leave it 1/2 longer in one plane ,hold it in vice and mill the top and 4 sides let the cnc do the work , then flip it over and remove the surplus 1/2 inch hey presto a cube
stick at it as its far more impressive with loose cubes but your doing well

author
ravenquest (author)keefo542012-01-26

Well I'd love to see an instructable on that!

author
Hephaestus (author)2012-01-26

I made one of these during my apprenticeship in the early 70s. I used a conventional vertical mill plus a boring and facing head., along with a variety of slot drills etc.. I concurr it is an excellent project and lends itself to CNC very well. Highschool tech teachers should look at the above article..
Roy Maybery

author
whenu (author)2012-01-26

Nicely done but probably more of a test if the whole thing was machined by hand.

author
twimh (author)2012-01-26

interesante proyecto,,,,,,,,,jejeje,,, tu tambien tienes una tormach PCNC,,,,que chido

author
jeffrey4283 (author)2012-01-25

That's a cool little machining project. I wish we had something in Tampa like TechShop so I could have access to that type of equipment.

author
mikeasaurus (author)2012-01-22

What a neat metal machine project!