# Radius Turning Tool From Scrap 'N' Stuff



## Nick Hulme (Mar 31, 2016)

Not my idea, just my take on it. 
I had a few 3mm diameter parts which required hemispherical ends and remembered seeing a boring head used for radius turning. 
My boring head sees regular use so permanently or even semi-permanently fixing it to something else isn't an option. 
I pulled a 1" parallel shank OD to internal MT2 adapter off the tool rack, dug through the bearing drawer for a couple of 1" ID bearings, profiled a couple of bearing mounts and a connecting plate from some ally plate offcuts, drilled, tapped, added some locktite and a couple of bolts and came up with this. 
I need to make a cutter seat with the cutting point at the centre of rotation for the bar mount but it works very well using a double sided triangular cutter. 
My boring head is still my boring head but has an extra use ;-) 

The first photo shows it assembled on the lathe, the second photo is a titanium bolt handle I made with the cutter. 

 - Nick


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## 10K Pete (Mar 31, 2016)

And an ER collet for a handle!! Excellent!!!

Pete


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## Nick Hulme (Mar 31, 2016)

Well spotted Pete! 
I forgot to mention that when I use it on the front tool post I use my Stevenson's hexagonal ER40 Collet block as a handle. 
When it sits on the tool rack it does so tidily and empty, no handle or head fitted ;-)


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## bazmak (Mar 31, 2016)

Do you rotate the cutter by hand or under power ??


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## Nick Hulme (Mar 31, 2016)

bazmak said:


> Do you rotate the cutter by hand or under power ??



By hand, you'd be surprised how low the forces are, it's possible to operate with finger and thumb on the collet block, it definitely doesn't need a big lever.


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## petertha (Mar 31, 2016)

Can you show me the business end of the cutter in a bit more detail? I've always been curious about how people grind the profile for this orientation application & what the cutter is made of etc. Also do you get the sense the cutter is being pushed up into the boring head during ball turning? (its not quite the same mostly radial force like a mill boring operation is it?). What is a typical in-feed amount per pass when you are cutting like this?


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## Nick Hulme (Apr 1, 2016)

I'm not sure how much help this will be, it's a side view of the insert mounting, note that rather than angling the tapped hole I'm using an angled washer, this allows me to play with the rake, note the worn tip closest? that's what happened with no rake ;-) I think the rake would stand increasing further to allow heavier cuts. 
The mounting has rake because the insert, being double sided, has none and experiment showed that it would rub, not cut without rake, the insert has a very nice chip breaker groove making it cut  nicely with rake. 
This tool cuts in the Y-Z plane so a large component of the force is along the axis of the boring head , there is of course a component of the cutting force at right angles to the tool surface contact. 
Unless you're doing the job with CNC you suck it and see, set the speed for a typical roughing cut on your lathe, with your work material, diameter and with your choice of tooling, start with light cuts and see when the the setup complains, you can often get further faster with lots of small, light cuts than with big ones, you can sweep 90 degrees with a ball cutter in under a second  when taking light cuts. 
HTH ;-)


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## goldstar31 (Apr 1, 2016)

Initially, might I tick a like and mention that the hss tool is described in GH Thomas's Model Engineer's Workshop Manual.

Why GHT never linked his small boring tool to do ball handles still baffles me as GHT and Jack Radcliffe shared lots of ideas. JAR was responsible for the ball turning tool and both items were part of Neil Hemmingway's business Hemmingwaykits but getting my friend Dr Bill Bennett to edit GHT's contributions to form the posthumous 'Manual.

Anyone else with guess?

Regards

Norman


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## dennisa49 (Apr 1, 2016)

Hello,
Also check the late Steve Bedair's 9 X20 lathe site.
He has a simple to build ball turner on the site with drawings.

Always happy to see the wonderful projects on HMEM.
Thanks and regards, 
Dennis


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## Nick Hulme (Apr 1, 2016)

dennisa49 said:


> Hello,
> Also check the late Steve Bedair's 9 X20 lathe site.
> He has a simple to build ball turner on the site with drawings.



I have a commercial version of Steve's design (?) which I bought around 15 years ago, it's great when I'm using a small collet chuck but the work protrusion required when using a chuck can be a pain.


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## petertha (Apr 1, 2016)

Nick Hulme said:


> I'm not sure how much help this will be, it's a side view of the insert mounting, note that rather than angling the tapped hole I'm using an angled washer, this allows me to play with the rake,...


 
Perfect thanks. The angled washer is a smart idea.


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## rodw (Apr 6, 2016)

This thread about my ball turning design using a boring head has a bit of info on the cutter design. Brian Rupnow's contribution was invaluable.
http://www.homemodelenginemachinist.com/showthread.php?t=23019


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## Wizard69 (Apr 7, 2016)

rodw said:


> This thread about my ball turning design using a boring head has a bit of info on the cutter design. Brian Rupnow's contribution was invaluable.
> 
> http://www.homemodelenginemachinist.com/showthread.php?t=23019




Excellent thread for anybody making a ball turning tool.   My biggest concern is that there is no way to feed the tool in like you can with vertical turners.  The use of the Z to feed might not work too well on short shafted ball handles.  

Otherwise the boring head based units in that thread are really slick, one of these days I may make one.


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## Nick Hulme (Apr 7, 2016)

Wizard69 said:


> The use of the Z to feed might not work too well on short shafted ball handles.



How short? 
That's an M5 thread on the bolt handle in my initial post, I wouldn't have been able to get close enough to the chuck to make it with the type that bolts down to the cross slide, 

 - Nick


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## rodw (Apr 8, 2016)

Wizard69 said:


> Excellent thread for anybody making a ball turning tool.   My biggest concern is that there is no way to feed the tool in like you can with vertical turners.  The use of the Z to feed might not work too well on short shafted ball handles.
> 
> Otherwise the boring head based units in that thread are really slick, one of these days I may make one.



Not sure why you think you can't feed the tool in. You can either use the cross slide or centre the cutter and use the longnitudinal feed. Long feed works best.


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## Nick Hulme (Apr 8, 2016)

And don't forget that with a boring head you have micrometer adjustment of radius so instead of having to "feed in" you can start with a radius cut which just skims the corners of the stock and easily take measured cuts down to the desired radius. 
In machining terms that's less of a bodge than setting the final radius and gradually feeding it into the stock with the cross slide ;-) 

 - Nick


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## Wizard69 (Apr 8, 2016)

Nick Hulme said:


> And don't forget that with a boring head you have micrometer adjustment of radius so instead of having to "feed in" you can start with a radius cut which just skims the corners of the stock and easily take measured cuts down to the desired radius.
> 
> In machining terms that's less of a bodge than setting the final radius and gradually feeding it into the stock with the cross slide ;-)
> 
> ...




Thanks for pointing that out.   It should be obvious of course but I must have been drawing a blank then.


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## Wizard69 (Apr 8, 2016)

Nick Hulme said:


> How short?
> 
> That's an M5 thread on the bolt handle in my initial post, I wouldn't have been able to get close enough to the chuck to make it with the type that bolts down to the cross slide,
> 
> ...




I'm not sure I just had this image of the boring head and chuck jaws coming together in an undesired way.   Working close to the chuck jaws is always something a little fore thought should be put into.


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## rodw (Apr 10, 2016)

Wizard69 said:


> I'm not sure I just had this image of the boring head and chuck jaws coming together in an undesired way.   Working close to the chuck jaws is always something a little fore thought should be put into.



In practice, this is not an issue. You just need to have enough material sticking out to cut the diameter of the ball you want.


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