Berger Sphere Caliper

[killerbeast]

i remeber seeing som online video on how this thin works but i cant seem to find the any where ??????

http://www.highlandwoodworking.com/i...OD&ProdID=9896

[joe greiner]

A preferred method for turning a sphere is to first turn a cylinder of a length/"height" equal to the diameter, with tenons at both ends. Then, turn chamfers to create an octagonal shape, and continue lopping off corners until a spherical shape is achieved. This can be accomplished with cardboard templates, but you need a set of templates for each sphere size.

As I understand it, Berger eliminates the need for templates with his caliper. Google [berger sphere caliper] provides several hits. The pdf file from opcaaw has a description, as well as a url for a video by yoyospin. That may be the one you seek. The url doesn't function as a link from my version of Acrobat, but you can type it into the address field of your browser. As luck would have it, my compu-duh-r and my browsers have been mis-behaving lately, so I can't verify any of this.

I'll try to restrain myself to a short rant, but it seems to me that just because a video CAN be made, doesn't demand that a video SHOULD be made, as a substitute for a written explanation with pictures. Some videos are made simply because they can be made.

Rant off.

Joe

[killerbeast]

thanks ... it was the yoyospin video i was looking for ) but i like the idea of this tool ... anybody outthere own or have operatede one ??

[Skew ChiDAMN!!]

OK, so I've rad the PDF,as well as the original by Al Hockenberry, DL'd & watched the video and... well... I'm underwhelmed.

There are easier ways to turn a sphere, that are just as accurate. As a matter of fact, Al used one of these techniques when removing the tenons. (The good ol' "turn a cylinder to diameter, rotate it 90° and remount between cup centres, then turn to the shadow line" trick. )

I appreciate the ingenuity behind it, but even with the calipers in lieu of measuring it strikes me as a damned fiddly method.

[killerbeast]

well let´s hear some of the ways ) i have just gotten an order for some 12cm i diameter Oak fence post tops. i need to either have a tennon to mount into the top of the post or a hole for mounting ... but the job at hand is to get the buggars turned.... so all good tips and trix are more than welcome

[Skew ChiDAMN!!]

The simplest is the one I mentioned;

You turn a cube of timber into a cylinder with the same diameter as the desired sphere - or just a couple of mm larger if you want to allow for sanding - and then mark the centre-line with a pencil. Much the same as the first mark for using berger's calipers.

Rotate the axis of the cylinder 90° (turn it sideways so the ends are cartwheeling) and mount it between... well... I called them cup chucks, but they're actually just blocks of wood which are contoured to hold the sides of the cylinder. Ensure the pencilled line is centred on the turning axis so the piece is evenly balanced.

For larger cylinders (spheres) it is an idea to use double-sided tape between the cups & cylinder, just for a bit of safety.

When the lathe is switched on, you can see the shape of the future sphere inside the "shadow line" formed by the whirling ends. This shadow line can be made more visible by placing dark or light cards behind the piece and arranging good lighting on the front of the blank.

Then it's just a case of turning away the material forming the shadow line until only the solid-seeming sphere stays behind. (Be very, very careful your fingers don't get bitten by the shadows! )

If you have a circular template about 1/3 to 1/2 the sphere diameter, you can lay it on the sphere, where it should sit flat. This is a quick way to check for high spots.

Or you can simply remount the whole sphere in cup chucks a few times, changing the axis the ball's spinning each time, and look closely for small shadow lines to turn away.

It sounds complicated, but is actually fairly simple & straightforward when put into practice. As with any form of "winged" turning, it needs sharp tools and good control.

[Skew ChiDAMN!!]

I guess I should also point out that the above method won't leave a tenon... and Al's method would probably be better if you want the tenon and don't mind if the very top is a bit off spherical.

My criticism was made solely on the basis of turning a "perfect sphere."

BTW, a commercial sphere jig will make a perfect sphere with a tenon even more quickly & easily, but is $$$...

[Texian]

It's a neat tool (the Berger caliper), but easy enough to do the very same thing with regular dial calipers, which are also useful for many other things. Can use a cheapie calculator to calculate the required dimensions. A good thing for tool junkies. Was going to add, for professional sphere turners, but they can do it by eyeball.

[Skew ChiDAMN!!]

A good thing for tool junkies. Was going to add, for professional sphere turners, but they can do it by eyeball.

Sounds painful! I'm pretty sure that chisels would be a LOT more effective?

[killerbeast]

thanks skew that exp. i did understand ) i think i will try it ... i might get away with drilling and mounting a tap later for mounting... will try to get pics before i send the stuff out..