Hollow mill

Hollow mills are fairly inexpensive on ebay:

Best Regards Tom.

A Box tool is for this. It is a cutter (HSS or carbide) with two supports. Usually they are used on turret lathes, screw machines or chuckers.

Bob

Tim,

You could also consider upsetting extra-length 3/16 stock to form a 5/16 blank for the head. Make a one-up die with a 3/16+ hole and a 5/16 counterbore in a block of steel and a short length of 5/16 drill rod. Heat one end of 3/16 blank cut to length, drop in hole, insert drill rod, whack smartly, then push the blank out using the small-diameter hole thoughtfully provided in the bottom of the die.

The heat source could be a torch or something fancier. For 1000 it may or may not be worthwhile to build a heater from a length of 5/16 rod with a

Fred

I'm glad you suggested this. If you had not, I would. I've used them for taking 3/16" brass down to 0.100" diameter in a single pass for about 1-1/2" unsupported.

Think of it as a turning tool with a pair of follower support fingers mounted onto the same object. (The grinding of the tool bit is somewhat strange, as it cuts on the end, not on the side. If you are lucky, you will get one which uses carbide inserts, and not have to learn to grind the proper shape.

You can mount a box tool on a quick-change toolpost with a boring bar holder. Just be careful to get both the vertical and horizontal centering right, if you don't have a turret lathe of some form.

And -- they can be found on eBay, too.

Good Luck, DoN.

The trick is to take the 5/16" down to 3/16" in one pass with a sharp HSS bit with negative rake. I've made #2 screws that way from

I doubt that the 5/16" stock will flex unduly in 1.5 inches, but if it does then use larger stock that doesn't flex and still cut to final diameter or near final diameter first pass. High speed, slow feed, sharp tool negative rake. Turning a 1/16" workpiece 1.5" long out of 3/8" steel barstock is easy peasy if you do it in one pass with high speed, slow feed, sharp bit, with cutting fluid. .

Why negative rake? I've always read that negative rake involves more cutting pressure (and therefore more deflection) than positive rake.

Ted

Right you are, Ted. Brainfart, sorry. With brass I'd use about no rake, but with steel I rake the tool so the cutting angle forms an acute angle with relief on both front and top.

Apologies for delay in response -- been offline gone fishin' for a week.

Fishin' was excellent, by the way.