Manual Numeric Control Ball Turning

I know I’ve seen a link to a spreadsheet to layout cuts on my manual lathe to rough out a ball, but I’ll be dammed if I can find one!

I know Rick Sparber posted one using a graphing calculator, but I don’t have one, and this is for a one-off project, so I’m not interested in building a ball turning attachment.

Anybody got a link/idea?

Thanks in advance,
John W

a41capt,

You may have a graphing calculator on your computer and don't know it, or apps may be cheaply available. Same goes if you have a smart phone.

What kind/size of ball do you need? You can buy them. What do you need it for? Somebody needed a ball handle for a drill press one time and used a golf ball.

I built a ball turner just to practice my other making skills even though I rarely need it. It was a fun project.

--ShopShoe

ShopShoe said:

a41capt,

You may have a graphing calculator on your computer and don't know it, or apps may be cheaply available. Same goes if you have a smart phone.

What kind/size of ball do you need? You can buy them. What do you need it for? Somebody needed a ball handle for a drill press one time and used a golf ball.

I built a ball turner just to practice my other making skills even though I rarely need it. It was a fun project.

--ShopShoe

Click to expand...

Thanks for the advice! I’m just creating a 2 5/16” ball to upgrade a trailer hitch lock for a trailer parked in an unsupervised/vulnerable area and I’ve found the commercial units aren’t very tough.

There may be other needs in the future, so I’ll probably just go ahead and build myself a ball turner after my shop cools down again (summer in Arizona! ). I was just looking for a quick and simple job at present.

Thanks again,
John W

I posted this on the other forum

I made an Excel table to generate a stepover routine for an elliptical shape. An ellipse is handy because you can define the A & B lengths independently, resulting in a wide range of aspect ratios to suite the purpose. For example elongated like a bullet or stubby like the end of a propane tank. (Or if a & b are equal, it becomes a circular section). Ellipses are nice smooth shapes & the intercept will be tangent to the straight shaft segment.

Hopefully the table example & sketch makes sense. Red are input values. Parameters a & b define the X & Y segment lengths respectively. X (L to R) means the step the cutting tool from left to right, but practically you probably want to use X (R to L) Right to Left. My DRO displays diameter when I infeed so I also put Y-dia that on the table. So you make the step-overs using something like a parting blade, blue the resultant stair step surface, then finish down with file & paper until no more blue is showing.

The underlying equation is : y = [ (1- x^2/a^2) * b^2 ] ^ 0.5 Y-dia = 2 * Y

petertha said:

I posted this on the other forum

I made an Excel table to generate a stepover routine for an elliptical shape. An ellipse is handy because you can define the A & B lengths independently, resulting in a wide range of aspect ratios to suite the purpose. For example elongated like a bullet or stubby like the end of a propane tank. (Or if a & b are equal, it becomes a circular section). Ellipses are nice smooth shapes & the intercept will be tangent to the straight shaft segment.

Hopefully the table example & sketch makes sense. Red are input values. Parameters a & b define the X & Y segment lengths respectively. X (L to R) means the step the cutting tool from left to right, but practically you probably want to use X (R to L) Right to Left. My DRO displays diameter when I infeed so I also put Y-dia that on the table. So you make the step-overs using something like a parting blade, blue the resultant stair step surface, then finish down with file & paper until no more blue is showing.

The underlying equation is : y = [ (1- x^2/a^2) * b^2 ] ^ 0.5 Y-dia = 2 * Y

Click to expand...

That’s it exactly! Is there any way I can have that spreadsheet? I’ve been scouring the internet for the past couple days without success, and it’s been driving me mad!

John W

a41capt said:

That’s it exactly! Is there any way I can have that spreadsheet? I’ve been scouring the internet for the past couple days without success, and it’s been driving me mad!

John W

Click to expand...

Goggle sheets is what I use on the rare occasion that I want a spreadsheet.

John, here is the spreadsheet I made years ago. A word of explanation about how it is set up:



In the upper left corner, you can enter the diameter of the ball, the amount of crossfeed that you get with one complete revolution of your crossfeed screw, what you want to use as the start setting for X (the lathe carriage position - really this is the Z dimension on a lathe, but I found it easier to think of it as X), and what you want to use as the starting setting for Y (the crossfeed position, which is really X, but again ... easier for me to think of it as Y). As shown above, my lathe has an 8 tpi crossfeed screw, so each revolution of the dial is .125". I chose to "start" from an X setting that was roughly equal to the radius, but negative - more about this below - and with the crossfeed set to 60 when it is at the farthest-in position (no particular reason for choosing that value - not sure why I did the last time I used this spreadsheet).

You will also see a "rough" and a "smooth" setting, in the case above, .025" and .005" - this represents the amount of carriage travel (what I am incorrectly calling X) each time. This allows a roughing pass to remove the bulk of the material, followed by a finishing pass that will give very smooth results. The first column of results contains the readings using the rough settings; the next three columns contain the readings when using the smooth settings. Hopefully obvious, but just in case - when making the rough cuts, I stayed "outside" the final dimensions. Note also that for my own convenience, I translated the actual "Y" (crossfeed) position into the turns and readings needed to achieve that position - but a better approach would likely be to put a dial indicator on the crossfeed. Best yet would be to have a DRO for both the carriage and crossfeed!

To use this, I used a narrow-angled tool with a rounded-tip lathe tool and set the carriage so that the tool is in the middle of the material that will become the ball. I set up a dial indicator such that it could measure the travel to either side of the full radius of the ball; e.g., for the example above, I "loaded" the dial carriage with at least .200" or so, so that it would not run out of travel before it got to the end of the ball. I then set the dial to zero (thus needing to set the "Start" to a negative "X" setting). I then moved beyond the stock and wound in the carriage to where the tool was just at the center line, and either set the crossfeed dial to .060, or perhaps this is what it wound up at (maybe that is why I chose that as the "Y-offset").

I don't know how clear any of this is when described in words ... I'm happy to try to clarify anything as needed. A word of warning: this spreadsheet does not account for the width of the tool tip, so it will not produce a perfectly spherical result. As I recall - it's been years since I used this - it did produce very good results that were more than acceptable for my needs, and didn't take nearly as long as one might expect. I started to work up a spreadsheet that would account for the width of the tool, but never finished it; I would be happy to make it available if anyone wants to work on it.

See:



These will still work when your spreadsheet battery is flat.

BALLCUT from Marv Klotz' utilities also does this. His original site does not work tonight so see this mirror:

https://github.com/andygoulden/mklotzpy

djc said:

These will still work when your spreadsheet battery is flat.

Click to expand...

FWIW, when I used the spreadsheet I linked above, I entered my desired numbers, then printed it out. No batteries required after that!

Thanks to everyone, I’ll get to work!

John W

petertha said:

I posted this on the other forum

I made an Excel table to generate a stepover routine for an elliptical shape. An ellipse is handy because you can define the A & B lengths independently, resulting in a wide range of aspect ratios to suite the purpose. For example elongated like a bullet or stubby like the end of a propane tank. (Or if a & b are equal, it becomes a circular section). Ellipses are nice smooth shapes & the intercept will be tangent to the straight shaft segment.

Hopefully the table example & sketch makes sense. Red are input values. Parameters a & b define the X & Y segment lengths respectively. X (L to R) means the step the cutting tool from left to right, but practically you probably want to use X (R to L) Right to Left. My DRO displays diameter when I infeed so I also put Y-dia that on the table. So you make the step-overs using something like a parting blade, blue the resultant stair step surface, then finish down with file & paper until no more blue is showing.

The underlying equation is : y = [ (1- x^2/a^2) * b^2 ] ^ 0.5 Y-dia = 2 * Y

Click to expand...

Another "Etch-a-sketch" machinist Very Nice! I made a similar sheet where you'd enter (in the green cells) the large and small diameters, the span between them and the "X" increment (resolution) you wanted to cut at and it would give the depth of cut to make a circular curve tangent at the small end. Like the shapes at the top, middle and bottom of the 2nd pic.

Slooowwwwwwwwww CNC!

a41capt said:

Thanks for the advice! I’m just creating a 2 5/16” ball to upgrade a trailer hitch lock for a trailer parked in an unsupervised/vulnerable area and I’ve found the commercial units aren’t very tough.

Click to expand...

Not to spoil your fun, but an angle grinder doesn't care very much about "toughness".



Gene