View Full Version : Cutting a spiral shaped hole with a mill

05-23-2012, 04:47 PM
Cutting a spiral shaped hole with a mill.
For a tesla turbine for pumping water using hard drive disk.




Rich Carlstedt
05-23-2012, 04:57 PM
My ignorance, sorry...What is a teals turbine ?
Nothing comes up showing one on Google
Do you have a Bridgeport ?


05-23-2012, 05:09 PM
What is a spiral shaped hole? Do you mean cutting a spiral slot or ... ?

The Artful Bodger
05-23-2012, 05:25 PM
If you need to cut something like a scroll I assume that requires a rotary table and some sort of gearing between that and the table X or Y feed.

It does not have to be mechanical gearing and could be electronic using stepper motors for example.

If you need to cut a spiral as in a helix, then a lathe is the machine to do that (I would think).

05-23-2012, 05:32 PM
My ignorance, sorry...What is a teals turbine ?
Nothing comes up showing one on Google
Do you have a Bridgeport ?


Dyslexia strikes again! ;)

Try tesla turbine.


05-23-2012, 06:00 PM
a spiral shaped groove....or a helical shaped hole....both difficult but at least not impossible....a sprial shaped hole? on that my brain quits

05-23-2012, 06:24 PM
Sorry typo. tesla

Spiral shaped hole from a round stock


Trying posting picture first time


05-23-2012, 06:27 PM

05-23-2012, 06:33 PM

was not shareing

05-23-2012, 06:44 PM
That is not a spiral shaped hole, that is a tear-drop shaped hole.

05-23-2012, 06:54 PM
I'm thinking more Yin-Yang than teardrop... :rolleyes:

05-23-2012, 07:42 PM
looks like a slot to me :).....Bill it looks to me like a round cavity with the set of disks offset to one side....are you sure the outer curving is a change radius? If it is you have to either couple (electronically would be easiest) a rotary table to a mill's table axis....or manually cut it as a whole bunch of facets by move the rotary a degree then the x(or y) axis so many thou, ie make up a table. I've done cams that way, a bit tedious but doable....but my impression from that image is that if it's a spiral at all its very slight??

05-23-2012, 07:47 PM
Since you've got stacked disks for the Tesla turbine already, I always assumed the way to do it was to rotate the disks relative to each other as they're assembled on the spindle to get the spiral path. Barmen do this trick all the time with napkin stacks. Or to reverse the process if you're drilling all the holes relative to a key position, move the keyway successively in rotation as you're drilling each disk. Worst case I suppose you could fashion a helical EDM electrode and spiral it down through the workpiece - rather like EDMing a thread with a hollow tap.

05-23-2012, 10:21 PM
Maybe way, way off base here but it puts me in mind of some tri-lobe blower set-ups...


certain designs do spiral/twist helix (could be just me but I find some drawings, like the one shown confusing...which part is spiral and which is not and which part is lobe and which part is "space"...just saying since one or the other could be vastly more difficult to machine)

05-24-2012, 12:24 AM
From the drawing it's kind of hard to determine exactly what the groove is like, but whatever it needs to be a CNC mill can do it.

Here's a picture of a spiral groove cut in plastic on a CNC vertical mill.

The groove is a semi-circular pocket of varying width with a varying groove radius. I had trouble drawing and programming this to cut efficiently with CAD/CAM. I ended up writing a macro program to do it in the CNC controller. The macro allows varying all the features of the spiral and groove by altering parameters, groove radius, groove width, etc, etc. The cutter was a ball end mill. The mill controller has the axis rotation option.

I have no idea how this could be done only with a manual mill and rotary table.

This test was cut in plastic to verify the mold cavity was right before cutting in metal.


05-24-2012, 03:44 AM
Perhaps the OP would like to scan these links and tell us how that turbine looks and works.

Does he have a good pic from a hand-book or manual?



05-24-2012, 04:02 AM
If you want a shape like the one in the drawing your best solution is probably to get it laser cut...

05-24-2012, 04:57 AM
Here is the OP's pic.


That is not a spiral shaped hole, that is a tear-drop shaped hole.

I seem to agree with flathead that it seems to be a stack of off-set discs with three "tear-drop" shaped holes.

If each of those plates were off-set a pre-determined angular amount around the spindle/axis, the three cavities would be spirals. You can see it in the laminations in some electric motor rotors.

Cutting those "tear-drops" is a simple excercise in marking out and using a drill and an end-mill cutter with the discs stacked on a rotary table.

Its not a lot different to some modellers without a a CNC-ed mill who make straight or curved spokes on wheels (and fly-wheels) for model machines.

05-24-2012, 10:49 AM
Sorry for not being clearer its the ever widening hole around the disk I am trying to get.
Will just cut round holes in the disk the total size of disk holes should = 3 to 4 times the hole # 11 in drawing will use 4 disk from 5-1/4 inch hard drive with .02 to .03 spaceing.


05-24-2012, 10:54 AM
Make a wooden pattern and cast it in aluminum. The original was cast,wasn't it?

05-24-2012, 11:39 AM
Sorry for not being clearer its the ever widening hole around the disk I am trying to get.

That shape is called a Volute and you should be able to find information on how to draw it online.

Weston Bye
05-24-2012, 12:37 PM
Back in the Jan-Feb 2003 issue of HSM, I presented Machining a Spiral Cam. I didn't have a rotary table at the time, but the cam was small so I mounted it directly on the shaft of a stepper motor to use for indexing. I chose to grind, taking very light cuts, rather than mill the profile and everything worked out. Photos later, on request, if anyone is interested.

To the question at hand: working inside is usually harder than working outside, but the principle remains the same. I would mount the workpiece on the rotary table, and after hogging out the material down to the minimum diameter of the spiral, begin taking successive cuts of suitable depth, each starting at successive degrees around the profile. This might leave a "rippled" surface that would have to be cleaned up with an additional operation - a drum sander or such.

A spiral of constant rate will have the successive cuts and successive starting points all equal and uniform throughout the process. A volute will be something else, as Paul suggests.

05-24-2012, 01:14 PM
There was a thread on Tesla turbines not so long ago: http://bbs.homeshopmachinist.net/showthread.php?t=46331&highlight=tesla+turbine.
Perhaps the OP there can help you out.