# Radius turner from boring bar



## Tio Loco (Mar 30, 2020)

I'd been wanting to do this for a while, finally got a 




(sorry, a little quarantine humor)

Pretty much copied the design in this video by Ade Swash:  




Parts almost complete, waiting on the M2.5x.45 insert screws (finally found them at Shars).




Is it incestuous to use a new tool to make the last part for the tool?




All done.




See her chooch...


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## WesPete66 (Mar 30, 2020)

Wow, loving it!  I snagged a boring bar out of the scrap bin at work a while back, and have been trying to find a use for it on my lathe. I think I just found it.  Thanks!
What is the tool/insert that you are using?


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## benmychree (Mar 30, 2020)

A good holder for that style of ball turner is the Aloris boring bar holder with the hole through it, the hole is quite accurate and provides a good bearing surface for the rotating shaft.


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## Tio Loco (Mar 30, 2020)

@WesPete66  The cutter is RCMT-0602   https://www.ebay.com/itm/RCMT-0602-C-6-TiN-COATED-CARBIDE-INSERT-6034-3062/232563558261

Screws:  https://www.shars.com/mts-255-m2-5-x-45-insert-screw  They take a T7 driver if memory serves.

@benmychree The problem, at least with my PM1022, and I suspect all small lathes is that the Aloris (and the like) tool holder pushes the boring head too close to the centerline of the lathe, even withe the cross slide full retracted, leaving zero clearance between the boring head and the work. That's the reason for the offset rectangular mount for the body of this design.

Also, notice the cutter holder in first picture of the assembly, compared to the last photos. I had to neck it down to prevent it from rubbing the 1" brass. It's a downside of the small cutter...


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## aliva (Mar 30, 2020)

The price on Ebay is pretty reasonable, but the shipping is ridiculous. That's why they can sell the insert so cheap.
It wouldn't cost 21$ ship an envelope


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## Tio Loco (Mar 30, 2020)

It's a Canada thing... US shipping is $8.90...


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## ttabbal (Mar 30, 2020)

aliva said:


> The price on Ebay is pretty reasonable, but the shipping is ridiculous. That's why they can sell the insert so cheap.
> It wouldn't cost 21$ ship an envelope




It's $8.90 here to the US. Still overpriced, but not quite so much. Those round inserts are available all over the place though. I'm sure you can find some that are more reasonable on shipping.


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## benmychree (Mar 30, 2020)

Tio Loco said:


> @WesPete66  The cutter is RCMT-0602   https://www.ebay.com/itm/RCMT-0602-C-6-TiN-COATED-CARBIDE-INSERT-6034-3062/232563558261
> 
> Screws:  https://www.shars.com/mts-255-m2-5-x-45-insert-screw  They take a T7 driver if memory serves.
> 
> ...


The boring bar holder that I have been using has about the same offset as the one that you made; the one that I and a friend made uses a purpose built adjustable head to hold the cutting tool, also made special out of HSS.


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## brino (Mar 30, 2020)

@Tio Loco ,

I have been wanting to build one like this for years.......but I cannot find any of those round tuit's.
Someone must be hoarding them all!

Anyway, yours is a great execution!
Thanks for showing it.

-brino


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## mattthemuppet2 (Mar 30, 2020)

very neat, way fancier than mine, though the principle is the same. Means I can use the boring head in the mill too.

If you need to get into a corner, a CCGT/DCGT insert face mounted like your round insert works well.


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## Aukai (Mar 30, 2020)

What tap was used for the insert screw?


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## Tio Loco (Mar 30, 2020)

@Aukai it's M2.5x.45 

Picked up an inexpensive set on Amazon:  amazon.com/gp/product/B07DPRVSCR


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## Aukai (Mar 31, 2020)

Thank you I'm not up on metrics, just checking.


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## Tio Loco (Mar 31, 2020)

One other change that I forgot to mention. Not sure why they are designed this way, but the adjustment screw for the boring head only has a hex on one end, which in this application means that it's on either the bottom or on the chuck side as you use it. 

This is fine as long as you're just rounding off the end of a rod. You can just set the cutter to the top of the rod, then work your way in making passes along the z-axis. But if you're trying for a ball, you need to change the diameter of the cutting arc as you work.

The solution is to remove the adjustment screw from the boring head, drill and tap the blind end, and loctite a grub screw into it so you can adjust the head from either side.


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## ErichKeane (Mar 31, 2020)

Could you have removed the bottom piece and just reversed it?  It seems you could just disassemble it and turn it around, right?


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## r3292c (Apr 6, 2020)

The same idea, but much easier to build
https://www.hobby-machinist.com/threads/simple-raduis-ball-turner-using-qctp-and-boring-head.77383/


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## Tio Loco (Apr 6, 2020)

@r3292c as mentioned above, in a smaller lathe a standard boring bar holder forces the boring head too close to the centerline of the lathe, even withe the cross slide full retracted, leaving zero clearance between the boring head and the work. That's the reason for the offset rectangular mount for the body of this design.


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