Radii, Radius, Ball Turning Attachment - What works Best?

dalmatiangirl61 · Jun 29, 2021

A radius/ball turning attachment has been on my wish list for many years, but since I've never used one I honestly do not know what works best. There is the classic Holdridge set, a few other mfrs pop up from time to time, some yt vids of people using boring heads (not sure if that works for concave), and of course shop made versions.

What do you guys recommend?

Cyclotronguy · Jun 29, 2021

I grew up with a Holdridge, so am familiar with. It was a family run operation in So Cal, nice people!
I have a #4S on the home shop 10ee (replaces the compound) and I use it when the work is too much for a form tool or I'm feeling nostalgic.

They do work, albeit slowly. But on the plus side, consumables (drill blanks) are cheap and easy.

Normally I step the radii out to within a bit of being finished with conventional tooling (on a manual machine) before installing the Holdridge attachment

The Holdridge is only good for light cuts, but by the time you're roughed out, light cuts are good enough. That said don't try and make a living with one.

And BTW they are not self contained, you need depth mics or similar to set them.

Clive603 · Jun 29, 2021

CNC is the best way!

Realistically not something to arrange unless you either need it or desire home shop folk level tool bragging rights.

I did the up'n over, boring head based, version when a job surfaced that needed one. Even went to the effort of keeping the R8 taper mount. Which shows how often I expected to use it. Three times in 15 years and two of those were same job twice. Worked well enough but setting the tool just so and getting the shape right if going past about 1/3 rd of a circle is a faff. Objectively lost money on the job but kept the customer.

20-20 hindsight says coming up with something to follow a simple vertical cylinder or part cylinder former would have been quicker and easier to tooling. I mean how hard is a simple cylinder to make. But at the time I could find no sensible former following design to steal, was too lazy to roll my own and had a decent write up of the up and over hanging about.

For small radii using one edge of a concave radius milling cutter is the easy way. Especially for just one.

Easiest one to make is a basic horizontal swing type running around a vertical pivot. Can generally use a triangular insert too which simplifies tooling. Hafta at least pull the tool post or, more likely, the top slide. For simple ones accept that its going to be scraping around on the slide top surface as it rotates and tool setting will be more error than trial. If you do it right with its own sliding surfaces and a calibrated tool setting device the thing starts getting complicated and build time long.

Proper commercial engineering standard devices seem to be rather thin on the ground. Prices seem to be held up by the tool bragging folk with more money and cupboard space than sense.

Clive

EmGo · Jun 29, 2021

A tracer might be just as cheap. It'll definitely do a better job, and be capable of a lot of other things, too.

jims · Jun 29, 2021

Ball turner

EmanuelGoldstein said:
A tracer might be just as cheap. It'll definitely do a better job, and be capable of a lot of other things, too.

Simple turner I made .

iCloud

Clive603 · Jun 30, 2021

Jims

I like that.

I guess the tool tip shape is basically a triangle.

Impressively simple and effective. Drilling the tool carrier hole in the right place for the job in question is a great idea for saving all the faff of setting up.

Like all great ideas its obvious when pointed out. But seeing it in the first place is hard as we are so wedded to the idea that machine needs to be adjusted to an "infinite" number of different sizes.

Objectively a lifetime supply of carrier plates adds up to far less work and material than making a proper tool. Still feels wrong tho'.

I think I shall bin my up'n over and just copy yours if there is ever a next radius turning job!

Clive

Peter from Holland · Jun 30, 2021

For a bigger radius I have seen a rod with 2 pivots One pivot connected to the crossslide on the side and the other pivotpoint connected to a clamp on the bedways
The lenght of the rod is the radius then
For concave it is mounted on the right side of the crossslide
For convex the space is limited on the left side

Peter

jim rozen · Jun 30, 2021

I've always used a simple over-the-top ball turner from a small boring head:

Lewie · Jun 30, 2021

The Holdridge that I used (and probably several hundred kids) at the high school for 20 years worked fine. I came up with a tool holder that allowed the ball to be nearly complete without a large area of reduced diameter behind it. It can also do internal radii of full hemispheres, or even a little over with another modified tool holder. Pictures if anyone is interested.
...lewie...

DDoug · Jun 30, 2021

Lewie said:
The Holdridge that I used (and probably several hundred kids) at the high school for 20 years worked fine. I came up with a tool holder that allowed the ball to be nearly complete without a large area of reduced diameter behind it. It can also do internal radii of full hemispheres, or even a little over with another modified tool holder. Pictures if anyone is interested.
...lewie...

Post those pix right here, so as to keep all the info in one place.

jims · Jun 30, 2021

Simple ball turner

jims said:
Simple turner I made .

iCloud

If you watch the video of the ball turner that I made the 1/4 round cutting tool that I used has NO CLEARANCE.It is straight up . So it will not face a part but it cuts the ball with no problems. Because it is straight up you can drill your swing point then move over half the radius plus half cutter dia and drill and ream to locate where to tool is located. The top of tool should be on dead centerline of lathe. I was told it would not cut but video shows it does.
Jim Sehr

MilGunsmith · Jun 30, 2021

jim rozen said:
I've always used a simple over-the-top ball turner from a small boring head:

I am in the process of making a similar one now. What are you using for a cutter?

jim rozen · Jun 30, 2021

It's the same one I made years ago, from a bokum boring bar. I just profiled the edge a bit so the geometry was good.
A few more photos although not really any good shot of the actual cutting tool:

This does a pretty good job (first one is a better pic of the tool):

This was a handle repair for an old pratt whitney horizontal mill.

dalmatiangirl61 · Jun 30, 2021

Thanks guys, you gave me a little to think about. How often I need one vs the cost of a nice one is the reason I don't have one. I've gotten pretty good at the 2 handed see & see method, but can only approximate half a ball, all attempts at finishing a ball have been failures.

The swivel plate and boring head methods appear to do well on convex forms, correct me if I'm wrong, but they won't do concave?

Lewie
Yes, post some pics, show me what the Holdridge can do that the others can't.

EG and Clive
This dog is probably too old to learn new trix, so CNC is out, and I do not have room for more machines. Since I can't buy more machines, its time to buy/make more attachments to expand what my machines will do.

fciron · Jun 30, 2021

Swivel plate should do concave just fine if the cutter is on the opposite side from the handle.

Clive603 · Jun 30, 2021

Tool rigidity and clearance angles are always an issue with ball turners of the size being considered when dealing with concave radii. Tool has to project at least a little further than the radius and needs enough clearance angle to ensure the heel doesn't ruin what you have just cut.

Things tend to end up unreasonably slender in smaller sizes.

The pivot bar type mentioned by Peter from Holland generally has the best chance at tool rigidity followed by the swivel plate type. But you need to think through the geometry very carefully as its easy to get a different radius than you expect if proper account is not taken of the tool tip offset relative to the pivot.

The Holdrige layout supports the tool pivot from both ends which helps but the body casting is also deceptively sturdy. Most of the pictures on the internet give a false impression of this.

Something to be said for moving over to the Bridgeport and using the head tilt method for generating concave radii.

My up'n over tool is similar to that shown by Jim Rozen with a few refinements of possibly dubious necessity.

Examples of how the professionals did it from the Holbrook Model D accessories list :-

Convex

, Concave

, Face profiler for following a template

All very heavy (it is Holbrook after all), rigid and accurate. The spherical turning attachment bolts direct to the upper cross-slide (Holbrooks have a second cross-slide below the usual one for taper turning purposes)and face profiler goes between the top and cross-slides. Might be interesting to copy the face profiler system, certainly a rigid way of going about things.

Capacity may be surprisingly limited.

The spherical turner for the D13 (13" swing) and D 15 (15" swing) can handle diameters up to 3" and that for the D18 (18" swing) up to 4 1/2".
The D13 profiler can do depths of 1 1/2", the D15 and D18 versions 2".

When fitted to the high speed plain bearing diamond turning equipped Holbrook C such attachments are were said to be capable of generating surfaces of optical quality in both form and finish. Knowing the plain turning capabilities of diamond turning Holbrooks I'm inclined to believe it.

Clive

jims · Jul 1, 2021

Concave cutting a ball shape

Clive603 said:
Tool rigidity and clearance angles are always an issue with ball turners of the size being considered when dealing with concave radii. Tool has to project at least a little further than the radius and needs enough clearance angle to ensure the heel doesn't ruin what you have just cut.

Things tend to end up unreasonably slender in smaller sizes.

The pivot bar type mentioned by Peter from Holland generally has the best chance at tool rigidity followed by the swivel plate type. But you need to think through the geometry very carefully as its easy to get a different radius than you expect if proper account is not taken of the tool tip offset relative to the pivot.

The Holdrige layout supports the tool pivot from both ends which helps but the body casting is also deceptively sturdy. Most of the pictures on the internet give a false impression of this.

Something to be said for moving over to the Bridgeport and using the head tilt method for generating concave radii.

My up'n over tool is similar to that shown by Jim Rozen with a few refinements of possibly dubious necessity.

Examples of how the professionals did it from the Holbrook Model D accessories list :-

Convex View attachment 323789, Concave View attachment 323790, Face profiler for following a templateView attachment 323791

All very heavy (it is Holbrook after all), rigid and accurate. The spherical turning attachment bolts direct to the upper cross-slide (Holbrooks have a second cross-slide below the usual one for taper turning purposes)and face profiler goes between the top and cross-slides. Might be interesting to copy the face profiler system, certainly a rigid way of going about things.

Capacity may be surprisingly limited.

The spherical turner for the D13 (13" swing) and D 15 (15" swing) can handle diameters up to 3" and that for the D18 (18" swing) up to 4 1/2".
The D13 profiler can do depths of 1 1/2", the D15 and D18 versions 2".

When fitted to the high speed plain bearing diamond turning equipped Holbrook C such attachments are were said to be capable of generating surfaces of optical quality in both form and finish. Knowing the plain turning capabilities of diamond turning Holbrooks I'm inclined to believe it.

Clive

When cutting a concave shape into the od of a shaft you can use a swing tool like swinging a compass. And you could cut all the way thru shaft. But if cutting a concave shape into the face of a part you can not go deep enough to make half a ball shape unless your radius tool is inside the ball shape.
I made a tool to cut a hemispherical radius into the end of a bar to make a mold for a 2 1/2 ball . I cut the radius with no chatter problems on my 11 inch Logan. I made it out of alum but I could have done it out of steel.
Jim Sehr

Look closely at the radius on the parts inside my Avatar and you can see I like to cut balls.

dalmatiangirl61 · Jul 1, 2021

jims said:
When cutting a concave shape into the od of a shaft you can use a swing tool like swinging a compass. And you could cut all the way thru shaft. But if cutting a concave shape into the face of a part you can not go deep enough to make half a ball shape unless your radius tool is inside the ball shape.
I made a tool to cut a hemispherical radius into the end of a bar to make a mold for a 2 1/2 ball . I cut the radius with no chatter problems on my 11 inch Logan. I made it out of alum but I could have done it out of steel.
Jim Sehr

Look closely at the radius on the parts inside my Avatar and you can see I like to cut balls.

Care to show that tool, or is it just a modified version of the one shown above? I've got you on the big screen, but cannot see any detail in your avatar, can we get a full size pic?

dalmatiangirl61 · Jul 1, 2021

Clive603 said:
Something to be said for moving over to the Bridgeport and using the head tilt method for generating concave radii.

I have not seen, heard, or read of this method, thinking about it I'm not getting how this is done. Do you have more info how, or a vid, I learn fastest by seeing.

jims · Jul 1, 2021

Concave radius

dalmatiangirl61 said:
Care to show that tool, or is it just a modified version of the one shown above? I've got you on the big screen, but cannot see any detail in your avatar, can we get a full size pic?

To see cutter for hemispherical radius.
Google Hemispherical radius cutter I made Jimsehr

To see balls in balls

Google Jim Sehr’s
Metal sculpture balls in a ball

Jim

Radii, Radius, Ball Turning Attachment - What works Best?

Diamond

Stainless

Titanium

Diamond

Hot Rolled

Titanium

Diamond

Diamond

Cast Iron

Diamond

Hot Rolled

Stainless

Diamond

Diamond

Stainless

Titanium

Hot Rolled

Diamond

Diamond

Hot Rolled

Similar threads