Explain to me about dividing heads vs rotary tables please

[Brian Rupnow]

When I first started machining 6 or 7 years ago, I bought a rotary table which came with a set of divider plates. I mounted a 3 jaw chuck on it, and have since built numerous spur gears and used it for putting a radius on the corner of plates, connecting rods, etcetera. It is a good rotary table, in the sense that it has two machined mounting faces, so it can be mounted with the center of the 3 jaw chuck mounted either vertically or horizontally. Now I am seeing posts on this forum which talk about dividing heads. I don't know much about dividing heads, and I would like to know where they would be used and what makes them in any way "better" or "worse" than the set-up that I have. Can someone enlighten me please.---Brian

 

[Mechanicboy]

The dividing head is adjustable in all degree from 0 to 90 degree in angle while the rotary table can be mounted in 2 positions horizontal or vertical.

 

[ddmckee54]

I always thought that a dividing head was used to divide a 360° circle into a fixed number of positions, where a rotary table can be turned to an infinite number of positions.

They can both do almost the same thing, but each has it's advantages. If you need accurate positioning to a fixed number of positions and you had the correct dividing plate, if you were cutting a gear for instance, it would be easiest to use the dividing head. If you needed to mill an arc of 42° then you would use the rotary table.

If you have a rotary table with dividing plates then you can use the table to divide 360° into a fixed number of positions, otherwise the dividing is only a accurate as the Mk. I eyeball.

Clear as mud?
Don

 

[Brian Rupnow]

I THINK that probably the dividing head that can be tilted is how you would grind a relief onto a milling cutter or a tool like the George Britnell valve seat cutter. I'm not sure of that, I have a hard time getting my head around it, but I have never figured out a way to do it with my rotary table.

 

[goldstar31]

Actually, you are sort of right because my Quorn's rotary table tilts. Again, my Clarkson has a rotary table as an accessory but it is limited to about 7 degrees tilt. So if you have a rotary table you can add a tool or workholder which tilts. My Vertex BSO dividing head tilts progressively to become a dividing head.

It get's even more confused when one can utilise a faceplate and fasten a vertical slide on it with gears and then attach a chuck driven b y a catchplate striker. That isn't anything new, it was written about by Charles Holzapffel in the days of Maudsley.

Sadly, it is yet another solution which has become virtually forgotten

 

[Brian Rupnow]

This is one of the amazing valve seat cutting tools, originally designed by George Britnell, for cutting the valve seats in model engines. I have made two or three of these, in varying sizes, to suit the engines I have built. there is supposed to be a back relief on the four cutting edges. I have stoned a relief on the cutters I make, because as far as I am able to tell, there is no way to machine that relief in with my conventional rotary table. I THINK that with a pivoting dividing head you can do this, but the geometry involved makes my head hurt. this is one of those situations where I think I'm right, but I just can't visualize it.

 

[bazmak]

If you cut the 4 teeth with an end mill then can you not rotate the workpiece
so that that the meat is cut out at the back of each tooth.If you do it by eye
until you have a land of say 1mm the this land is easier to stone for clearance
I have often run the end mill by eye to produce the secondary unimportant clearance and to leave a small land to stone for the more important edge clearance