RDG Ball-turning attachment

[Allen Smithee]

I was browsing through some pages looking for cheap stuff people can give me for xmas presents when I came across this item. I know that there are many similar ones, and they can be a bit naff and tricky to get to work well, but it fills the bill of finding something I may actually want (rather than something someone else wants to give me that just clutters upo the house).

But looking at it I'm a bit mystified:



One of its features is that it has a graduated scale that could be more than sufficient for non-precision work and the scale is double-ended implying that it could be used for both convex and concave cutting. But as far as I can see the geometry of the vertically-supported insert (which probably makes it reasonably stiff) surely prevents cutting internal concave surfaces? Is this feature to allow cutting a radiused fillet or something?

AS

[Jasonb]

Not unlike my homemade one. Pictute looks like a neutral TNMT insert where mine uses a TCMT or TCGT with 7deg side clearance. You could probably fit either. Mine works well for concave jobs as well as the usual convex.

[uuu]

I've used one of those at the PumpHouse.  A challenge is that the base can foul the chuck jaws if you want to turn anything close up.  So putting a ball end on a handrail stanchion, for example, has too much material sticking out, and it bends.   So for small diameters we put a small secondary chuck on an arbour, e.g. a drill chuck, into the main chuck and this provides more support.

I'm attracted to the ball turners that use a vertically pivoting frame, but I've not tried one.  Like this: https://www.ebay.co.uk/itm/357556237346

Wilf

[Jasonb]

For small balls like handrails, acorn nuts and decorative beads you are better off just making a form tool out of gauge plate or silver steel.

[Sanjay F]

I'd like to know how to make the tools shown on the last 3 images especially the 1st one;the result looks great! 

[Jasonb]

Drill a hole to the chosen size of your ball.

If using silver steel mill away half the diameter. Gauge plate has a flat top so nothing to do at th etop.

Tilt the plate/rod 5-7degrees in the vice and mill the end away so you have a half a hole with a bit of a clearance angle on teh tool.

Use a needle file to put similar clearance around the half hole stopping just short of filing the actual half circle.

heat to red heat and quench in water. Some people temper the tool but I tend to use them just hardened.

You can use a small oil stone or diamond lap to touch them up if needed.

The second image is actually a tool that was made for a 9/16" ball being reused with a bit of modification.

Here it is drilled and a cut out of the final profile used to mark it out for sawing and filing to shape.



In action



Nice swarf from the brass



Finished items

[Sanjay F]

That's great, seems very straightforward the way you have described it, I'll give it a go; I have a project in mind where I need just such a tool 

[jcge]

Jason you've achieved some great results there with the O1 tools - very nice!
Regards
John

[Allen Smithee]

Thanks Jason - I've now added both the RDG one and the Hemmingway kit for a vertical-axis one to my Xmas list. I think the Hemmingway one will probably work better for most uses, but the horizontal-axis RDG one can cut "Ogive" cones (part arc) curves for things like spinner-nuts and radiused corners which the vertical axis one can't because it can be set with the pivot axis away from the lathe spindle axis - the vertical axis one essentially has the pivot axis nailed firmly to the lathe centreline.

We'll have to see what (if anything) santa delivers. I'm just hoping he doesn't use Evri...

AS

[Jasonb]

As the Hemmingway one just mounts in the tool post you can raise and lower the axis just as you would to set a tool on Ctr height. Might need to get a bit inventive if it is offset a lot but just having some additional holes in the body so the clamping block can be positioned further up or down would cover most cases.

The best one I have seen for getting in close and leaving the ball on a very small stick is the one from Eccentric Engineering.

<a href="https://www.youtube.com/watch?v=Xs8XZ8X1I-g" target="_blank">http://www.youtube.com/watch?v=Xs8XZ8X1I-g</a>

[Zephyrin]

For me, using form tools with the lathe is the most pleasing moment of a workshop session...
I have lots of brass blanks for taps or other fittings left over because I always make more than I need.
you also make your own desired and personal profile, and be certain to have all the same parts.

https://photos.app.goo.gl/Wer5KkTknrEZjdxp6
https://photos.app.goo.gl/HCzF5pnjENWHTa9G9

[Allen Smithee]

As the Hemmingway one just mounts in the tool post you can raise and lower the axis just as you would to set a tool on Ctr height. Might need to get a bit inventive if it is offset a lot but just having some additional holes in the body so the clamping block can be positioned further up or down would cover most cases.

You can, but only over a limited range. A horizontal axis tool can allow much greater offset and I'm often want to do ogival shapes like this which are easily done with a vertical axis tool but more of a faff to do by raising the toolpost:



So I probably have a use for both options because for most other uses the horizontal axis one is much easier/quicker to set up (especially when mounted in a QCTP holder!).

AS