I'm Baaaaaack

Not that anyone is reading, but oh well.
Anyway, the day job is sending me away all of the time and I don't always have time to update. I have a rather involved project at the moment that I will add here soon. Tonight we're just going to talk about my new dividing head for the mill.

New dividing head. An infinitely useful fixture in a machine shop. Used for cutting gears, flutes, flats, hole patterns, and a host of other features.

It is pretty common to mount a chuck onto a dividing head. This is a 5" lathe chuck.

The chuck must be mounted onto a backing plate. There are a few reasons for this. One is that there are a few different mounting methods. For instance, this is a threaded backing plate (of which there are different sizes). Another is that there are different styles, such as cam actuated. It is by far easier to make chucks generic and make a variety of backing plates. The trade off is that the backing plate needs to be machined in place.

A couple of the other parts that come with the dividing head. A tail stock, dividing disks, handles, etc. The disks are used to generate different numbers of divisions of a circle. More importantly, they help you repeat those divisions perfectly. Since we're on that topic, this is where the dividing head gets its name...because it divides a circle.

Mocking up the chuck in the vertical position shows that this is going to be tight. One of the draw backs of using small machinery.

Onto business! First step is to remove the backing plate and set the head square to the spindle of the mill.

Now to find the center of the bore.

Part of this process is machining a step into the plate that matches the chuck. The manufacturer of the chuck will supply the necessary measurements to cut the lip. They will also provide the measurements for the bolt pattern for the mounting screws.

Once the step is cut (and I think the actual height is arbitrary), it's time for a...

...test fit. I walked up to the measurement and took a couple of light cuts so that I didn't over cut the shoulder. The purpose of the shoulder is to locate the chuck and keep it concentric to the spindle of the head. You want a good fit there.

Once the fit was right, it's time for bolt holes. The chuck has three holes spaced 120 degrees apart. I elected to shoot six holes at 60 degrees. This gives me the option to rotate the chuck for alignment purposes if I ever need to. The mounting screws are 6mm. That happens to be just a hair under 5/16". I used a 5/16" hole to maintain a tight clearance (about .003"). This is much tighter than a normal clearance hole, but if you make it work, it just keeps everything that much tighter.

All fit up!

The chuck is back onto the head.

This will have to wait til morning. This is a part for a project I'm building. We'll catch up on that soon.