# Radius ball turner



## SubtleHustle (Jan 27, 2019)

Not sure I posted this correctly...


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## Rootpass (Jan 27, 2019)

Looks great! I’m wanting to make one too.


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## 682bear (Jan 28, 2019)

I just finished one, also...




I sort of copied Jim Dawson's design, except I used my existing boring bar holder for the block...

It works pretty well, using a modified end mill as a temporary cutter until I get motivated to grind a dedicated tool.




-Bear


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## jwmelvin (Jan 28, 2019)

Would someone be kind enough to explain what drives the choice of axis orientation for a ball turner? The two in this thread are not the same, highlighting the issue for me.


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## 682bear (Jan 28, 2019)

jwmelvin said:


> Would someone be kind enough to explain what drives the choice of axis orientation for a ball turner? The two in this thread are not the same, highlighting the issue for me.



It is mostly a matter of personal choice, I think... the one that I used in tech school 20-something years ago was more similar to SubtleHustles design. I chose to build mine more like Jim's design because I had an extra boring head, so it was a matter of 'quick and easy' for me.

Either design is very effective, both have their own pros and cons...

-Bear


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## C-Bag (Jan 28, 2019)

The major drawback for use of the boring head design is while it can do ball/convex shapes it can't do the opposite concave radii. The first design depending on where the cutter is positioned can do concave or convex. In my instance I need to do concave and convex so I'm gathering my resources to make one similar to the first design.


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## SubtleHustle (Feb 1, 2019)

Well, got the insert attached, with the help of a small tap wrench I made.





After that, it was time to try my first shot at turning a ball...


Worked out really nicely! Thanks again for looking.


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## Rootpass (Feb 1, 2019)

Cool!


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## WesPete66 (Feb 6, 2019)

Very nice.  A question though, when using one of these it seems the centerline of the pivot should be exactly on (and perpendicular to) the centerline of the spindle. How does one measure this to know when it is on center?


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## SubtleHustle (Feb 6, 2019)

So the cutter is on the center height. You start taking cuts closest to yourself, not on center, and you move your crossfeed in slowly, between each subsequent cut. You will know when you've reached center, when your ball is completely formed. It's much like knowing when you've reached center during facing operations.


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## Latinrascalrg1 (Feb 6, 2019)

C-Bag said:


> The major drawback for use of the boring head design is while it can do ball/convex shapes it can't do the opposite concave radii. The first design depending on where the cutter is positioned can do concave or convex. In my instance I need to do concave and convex so I'm gathering my resources to make one similar to the first design.



A Ball Turner made from a boaring bar holder head can cut both concave and convex parts depending on which side of the pivot you have the cutting tool mounted.


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## SubtleHustle (Feb 6, 2019)

Latinrascalrg1 said:


> A Ball Turner made from a boaring bar holder head can cut both concave and convex parts depending on which side of the pivot you have the cutting tool mounted.


Very true, you just spin the boring bar 180, in the holder.


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## C-Bag (Feb 7, 2019)

Latinrascalrg1 said:


> A Ball Turner made from a boaring bar holder head can cut both concave and convex parts depending on which side of the pivot you have the cutting tool mounted.


??????. That is true with the first type , but I've never seen concave cuts done with boring head type. Got pics?


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## Latinrascalrg1 (Feb 7, 2019)

C-Bag said:


> ??????. That is true with the first type , but I've never seen concave cuts done with boring head type. Got pics?


No I dont have any pictures but ive seen it done first hand on a HF 7x12 lathe if that makes a difference!
If you sit and think about the mechanics in making a ball on a lathe you will see that your tool needs to smoothly rotate around a "Pivot Point" (cutting edge facing inward towards the pivot point) in order to cut said ball. How far away from that pivot point you set the cutting tool will determine how large of an arc your tool can make which determines how big or small your "Ball" will be, correct?   Now if you move only the cutting tool to the opposite side of the pivot point and then rotate just the tool 180° from how you had it setup for making the ball ( cutting edge facing outward away from the pivot point) you will see that the cutting edge will now face the work correctly and will rotate around the pivot making concave cuts in your work piece.

I hope that helps clear things up a bit without adding further confusion.


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## C-Bag (Feb 7, 2019)

Sorry, this is just more confusion because you are describing how THIS WORKS:



where I was talking about the boring head like THIS works:


this is a boring head.


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## Latinrascalrg1 (Feb 7, 2019)

C-Bag said:


> Sorry, this is just more confusion because you are describing how THIS WORKS:
> View attachment 287078
> 
> 
> ...


Which is Exactly what i am speaking about!  Looking at the bottom  picture of the boaring head with end mill....you see the cutting tool is to the right of the central pivot which creates the ball or Convex shape.  Now imagine the endmill to the left of the central pivot and you will see the tool will cut in a concave arch.  I dont know a better way to explain it other then both style tools work the exact same way however they look different because their pivot rotation "SEEM TO BE" on 2 different plains which is where I believe your confusion is coming from however you could mount your tooling anywhere along the 360° rotation of the chuck and it would work just the same because both ball turners are actually mounted at different degrees around the Same Rotational plain of the chuck.


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## C-Bag (Feb 7, 2019)

Sorry, I'm not the one who's confused. I give up.


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## Latinrascalrg1 (Feb 7, 2019)

C-Bag said:


> Sorry, I'm not the one who's confused. I give up.


Lol ok so Im the one who is confused?  Maybe you actually Should give up!


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## Rootpass (Feb 7, 2019)

I picture the pivot point being at the end of the boring-heads centerline along its  length and then if the tool is to the right of that center line and rotated up and to the left (towards the headstock) it makes a ball. Like the above picture. 
If the tool is located to the left of the boringheads centerline and rotated up and towards the tail stick you get concave features.


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## 682bear (Feb 7, 2019)

Latinrascal is correct... the boring head design will cut a convex radius also...

-Bear


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## 682bear (Feb 8, 2019)

682bear said:


> Latinrascal is correct... the boring head design will cut a convex radius also...
> 
> -Bear



I meant concave radiuses... it will do both concave and convex...

Now I'm the one getting confused... lol

-Bear


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## 682bear (Feb 8, 2019)

Ask and ye shall receive...




-Bear


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## Jimsehr (Feb 25, 2019)

I think the guestion is can it cut a concave radius in the end of a bar ?
Not on the OD of a bar.


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## Jimsehr (Feb 25, 2019)

If you want to see a hemispherical radius cut into the end piece of stock to make  radius to make a mold for a cannon ball google     Hemispherical radius cutter I made jimsehr


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## Latinrascalrg1 (Feb 25, 2019)

Jimsehr said:


> I think the guestion is can it cut a concave radius in the end of a bar ?
> Not on the OD of a bar.


The answer is still Yes.  You just need to have the cutter facing  the correct direction on the correct side of the boaring head holder closest to the work stock so that the cutting edge swings in the concave arch you are trying to cut!


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## Aukai (Feb 25, 2019)

Reverse the cutter position to the outside of the ball turner, so the point is facing away, flip the bar(180) back to the work, so the cutter is closest the the work, and it will do concave.


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## Jimsehr (Feb 25, 2019)

I still don’t think you can cut a half of a full radius with any tool shown in this thread. In order to make a mold to make cannon balls you have cut at least half the full radius.  The hemispherical radius cutter I made will go a little deeper then half way .
I know you can cut a  true radius part way into the the end of the material but not enough to get half the depth of the radius.  








						New item by Jim Sehr
					






					photos.app.goo.gl


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## 682bear (Feb 26, 2019)

Theoretically, you can... if you can make a cutting tool that can articulate around the end of the material. It would have to have some sort of 'dogleg' incorporated into it...

-Bear


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## 682bear (Feb 26, 2019)

I am mistaken... after drawing it out, i think you are correct... the tool would contact the end of the workpiece before a full radius is achieved...




I'll have to study on that one a bit...

-Bear


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## 682bear (Feb 26, 2019)

Jimsehr said:


> I still don’t think you can cut a half of a full radius with any tool shown in this thread. In order to make a mold to make cannon balls you have cut at least half the full radius.  The hemispherical radius cutter I made will go a little deeper then half way .
> I know you can cut a  true radius part way into the the end of the material but not enough to get half the depth of the radius.
> 
> 
> ...



After thinking about this for a few minutes, I have concluded that we have started comparing apples to oranges...

The original topic was about ball turning tools... but I can't seem to picture in my head how your tool could turn a ball... so would it actually be a radius ball turner?

Or maybe I'm just missing something?

I'm not trying to be argumentative... just trying to connect the dots...

-Bear


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## Latinrascalrg1 (Feb 26, 2019)

With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?


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## Jimsehr (Jan 10, 2021)

Latinrascalrg1 said:


> No I dont have any pictures but ive seen it done first hand on a HF 7x12 lathe if that makes a difference!
> If you sit and think about the mechanics in making a ball on a lathe you will see that your tool needs to smoothly rotate around a "Pivot Point" (cutting edge facing inward towards the pivot point) in order to cut said ball. How far away from that pivot point you set the cutting tool will determine how large of an arc your tool can make which determines how big or small your "Ball" will be, correct?   Now if you move only the cutting tool to the opposite side of the pivot point and then rotate just the tool 180° from how you had it setup for making the ball ( cutting edge facing outward away from the pivot point) you will see that the cutting edge will now face the work correctly and will rotate around the pivot making concave cuts in your work piece.
> 
> I hope that helps clear things up a bit without adding further confusion.





Latinrascalrg1 said:


> With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?
> View attachment 288906


You can cut part of a radius until you get to the axis of the swing part. The only way to cut a full radius deeper than half the radius is to swing radius from inside the radius. Look at post #30 Posted by Bear.
Jimsehr


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## Dan Krager (Jan 21, 2022)

Imma gonna jump in here since I am a curious newbie looking to obtain (make?) a combination convex/concave turning tool. At first I couldn't conceive how a boring bar tool could do concave, but it all depends on where the pivot point is.  And Latinrascalrg1 and 682bear confirm it.
In the case of convex (ball) the boring head cutter pivot axis passes through the work piece axis at the ball center and perpendicular it.  If the workpiece is not a ball but a circulare plate with rounded edge, the pivot axis of the cutter is elevated (in the case of the boring bar holder) above the axis of the workpiece so that the apex of the cutter pivoting circumference coincides with the circumference of the workpiece. If the cutter pivot axis is moved further up so that the boring bar cutter is cutting in the bottom semicircle of it's arc, the apogee, and the cutter axis is tangent to the circumference of the circular plate, one gets a semi-circular groove in the edge of the plate.  

So that geometry works for a wide range of stuff.  Now my question is, most bending dies are fairly large diameters.  How does one hold the boring bar axis high and rigid enough to cut a 4" or bigger tube bending die?  And be infinitely adjustable from min to max height?

Ultimately, I don't want an array of tools, but one tool that can cut convex up to about 2 1/2" diameter and concave up to 2 1/2" diameter on the periphery of a circular disk up to maybe 8".  It's a wide range, but hey. There's enough expertise here to make rocket ships and nuclear subs isn't there? Am I expecting too much? I don't want to reinvent the wheel if it isn't necessary.

DanK


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## Dan Krager (Jan 21, 2022)

Oh, re: cutting a hemispherical cavity in the end of a workpiece, I think it is possible with simple tooling. I've tried to illustrate this with a simplistic sketch showing a cross section looking downward on the action. The cutting point (short segments illustrating a 135° orientation between cutter and holder) sweeps only 1/4 of the hemisphere diameter.  That means that the tool holder (longer segments) sweeps only 1/4 of it's sector also. It's easy with line segments, but I think doable with appropriately narrow tools with the appropriate overhangs to clear the edges of the cavity.  A cutter held in a post won't work in any circumstance.  A boring head or a swivel plate on cross feed would have to hold a cutter with offset overhang long enough to reach the cut. Think allen wrench at 135° instead of 90°. That might get sketchy if the cut is large or material difficult. 

Woodworkers do this all the time with hand held tools turning the inside of a bowl. 

DanK


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## Jimsehr (Jan 21, 2022)

Dan Krager said:


> Oh, re: cutting a hemispherical cavity in the end of a workpiece, I think it is possible with simple tooling. I've tried to illustrate this with a simplistic sketch showing a cross section looking downward on the action. The cutting point (short segments illustrating a 135° orientation between cutter and holder) sweeps only 1/4 of the hemisphere diameter.  That means that the tool holder (longer segments) sweeps only 1/4 of it's sector also. It's easy with line segments, but I think doable with appropriately narrow tools with the appropriate overhangs to clear the edges of the cavity.  A cutter held in a post won't work in any circumstance.  A boring head or a swivel plate on cross feed would have to hold a cutter with offset overhang long enough to reach the cut. Think allen wrench at 135° instead of 90°. That might get sketchy if the cut is large or material difficult.
> 
> Woodworkers do this all the time with hand held tools turning the inside of a bowl.
> 
> DanK


Jimsehr’s super simple ball turner.


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## Jimsehr (Jan 21, 2022)

Jimsehr said:


> Jimsehr’s super simple ball turner.





Dan Krager said:


> Oh, re: cutting a hemispherical cavity in the end of a workpiece, I think it is possible with simple tooling. I've tried to illustrate this with a simplistic sketch showing a cross section looking downward on the action. The cutting point (short segments illustrating a 135° orientation between cutter and holder) sweeps only 1/4 of the hemisphere diameter.  That means that the tool holder (longer segments) sweeps only 1/4 of it's sector also. It's easy with line segments, but I think doable with appropriately narrow tools with the appropriate overhangs to clear the edges of the cavity.  A cutter held in a post won't work in any circumstance.  A boring head or a swivel plate on cross feed would have to hold a cutter with offset overhang long enough to reach the cut. Think allen wrench at 135° instead of 90°. That might get sketchy if the cut is large or material difficult.
> 
> Woodworkers do this all the time with hand held tools turning the inside of a bowl.
> 
> DanK


Simple tool to cut radius in od of bar.


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## Jimsehr (Jan 21, 2022)

Latinrascalrg1 said:


> With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?
> View attachment 288906


That type would cut into the od of a bar. But not into the face of a bar. You could cut part depth of radius into face but only till you hit shank dia of axis of cutting tool.


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## Jimsehr (Jan 21, 2022)

Jimsehr said:


> That type would cut into the od of a bar. But not into the face of a bar. You could cut part depth of radius into face but only till you hit shank dia of axis of cutting tool.


Hemispherical radius cutter to cut radius in face of part.


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## Jimsehr (Jan 22, 2022)

Jimsehr said:


> Hemispherical radius cutter to cut radius in face of part.
> 
> View attachment 393247


If your cutter is held in tool holder with 3/4 dia shank you can only plunge into face till shank hits end face of part. You would be 3/8 shy of full


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## Rootpass (Jan 22, 2022)

Jimsehr said:


> Simple tool to cut radius in od of bar.
> 
> View attachment 393236


Can you post a link to this post on Practical Machinist?


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## jwmelvin (Jan 22, 2022)

Rootpass said:


> Can you post a link to this post on Practical Machinist?



Google: 

“simple to make tool” siteracticalmachinist.com


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## Dan Krager (Jan 22, 2022)

The illustration Jimsehr shows is a "post" cutter holder which obviously doesn't allow a full hemispherical sweep in the face.  If the cutter holder is U shaped this allows clearance when the pivot point is directly under or slightly past the face plane. 
DanK


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## Rootpass (Jan 22, 2022)

Have you tried that? About 2,000 results. Thanks


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## Jimsehr (Jan 22, 2022)

682bear said:


> After thinking about this for a few minutes, I have concluded that we have started comparing apples to oranges...
> 
> The original topic was about ball turning tools... but I can't seem to picture in my head how your tool could turn a ball... so would it actually be a radius ball turner?
> 
> ...


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## Jimsehr (Jan 22, 2022)

The pics in post #36,#37,and #38 show actual cutters and parts made with them.
Tool in pic #36 will cut a ball or a radius into od of a bar. Tool is made to cut 1 inch dia ball. Or you could use outer swing of tool And cut 1 1/2 radius into od of bar dia .

Bear
look back at post # 30.  

To look back at early posts you can search forum for topics like BALL TURNER and posted by Jimsehr


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## jwmelvin (Jan 22, 2022)

Rootpass said:


> Have you tried that? About 2,000 results. Thanks



The first result is the pictured thread.


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## Jimsehr (Jan 22, 2022)

Dan Krager said:


> The illustration Jimsehr shows is a "post" cutter holder which obviously doesn't allow a full hemispherical sweep in the face.  If the cutter holder is U shaped this allows clearance when the pivot point is directly under or slightly past the face plane.
> DanK





WesPete66 said:


> Very nice.  A question though, when using one of these it seems the centerline of the pivot should be exactly on (and perpendicular to) the centerline of the spindle. How does one measure this to know when it is on center?




This is one way to find lathe center. If 1 inch dia bar extending from spindle depth mic down to tool tip 1/2 bar dia and you have center.


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## Jimsehr (Jan 22, 2022)

Dan Krager said:


> Imma gonna jump in here since I am a curious newbie looking to obtain (make?) a combination convex/concave turning tool. At first I couldn't conceive how a boring bar tool could do concave, but it all depends on where the pivot point is.  And Latinrascalrg1 and 682bear confirm it.
> In the case of convex (ball) the boring head cutter pivot axis passes through the work piece axis at the ball center and perpendicular it.  If the workpiece is not a ball but a circulare plate with rounded edge, the pivot axis of the cutter is elevated (in the case of the boring bar holder) above the axis of the workpiece so that the apex of the cutter pivoting circumference coincides with the circumference of the workpiece. If the cutter pivot axis is moved further up so that the boring bar cutter is cutting in the bottom semicircle of it's arc, the apogee, and the cutter axis is tangent to the circumference of the circular plate, one gets a semi-circular groove in the edge of the plate.
> 
> So that geometry works for a wide range of stuff.  Now my question is, most bending dies are fairly large diameters.  How does one hold the boring bar axis high and rigid enough to cut a 4" or bigger tube bending die?  And be infinitely adjustable from min to max height?
> ...


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## Jimsehr (Jan 22, 2022)

I have made a number of radius turners and I make them so I can adjust the radius I want. One thing I don’t think a ball bearing is needed. I don’t think a HOME shop is going to make more than 100 balls. If more than that are needed I would go to a shop with CNC machines. If anyone wants to build a radius turner
email me and I will try to help .        Jimatcf@hotmail.com


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## Lewie (Jan 26, 2022)

Here are few I made with a Holdridge and an offset tool holder I made to reduce the width of the "groove" behind the ball.  Oh and I have done full hemispheres in the end of a  bar with an angled cutter in the same tool .


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## Jimsehr (Jan 26, 2022)

Nice work ! I like it.


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## Jimsehr (Jan 26, 2022)

Latinrascalrg1 said:


> With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?
> View attachment 288906


Pic shows bor


Latinrascalrg1 said:


> With the boaring bar holder mounted the same way Jimsehrs tool is mounted or how the OP has his tool mounted for that matter since they are pretty much the same (here I substituted a screw driver to play the part of cutting tool and handle which can be mounted in a few different ways,) How is this ANY Different?
> View attachment 288906


Pic shows end of boring head with screwdriver to show how radius could form radius in end of bar. Bit if you look at other end of boring bar you will see cutter will only go deep enough to to hit shank of boring Boring head. So you can cut radius depth till you hit half of boring head shank dia. You can’t make a mold for a ball.


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## Jimsehr (Jan 26, 2022)

Dan Krager said:


> Oh, re: cutting a hemispherical cavity in the end of a workpiece, I think it is possible with simple tooling. I've tried to illustrate this with a simplistic sketch showing a cross section looking downward on the action. The cutting point (short segments illustrating a 135° orientation between cutter and holder) sweeps only 1/4 of the hemisphere diameter.  That means that the tool holder (longer segments) sweeps only 1/4 of it's sector also. It's easy with line segments, but I think doable with appropriately narrow tools with the appropriate overhangs to clear the edges of the cavity.  A cutter held in a post won't work in any circumstance.  A boring head or a swivel plate on cross feed would have to hold a cutter with offset overhang long enough to reach the cut. Think allen wrench at 135° instead of 90°. That might get sketchy if the cut is large or material difficult.
> 
> Woodworkers do this all the time with hand held tools turning the inside of a bowl.
> 
> DanK


Looking down on a boring bar trying to cut a hemispherical radius in the end of a bar the cutter has to be inside the sphere or the shank holding the cutter hits the outer edge of the bar. You can only cut deep enough to hit the shank of the boring bar. If shank is .750 dia your radius will be .375 shy of full radius.


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