Shop-made carbide tools

I have been experimenting with the use of carbide tools for some time now.
As a traditional turner, I use conventional bowl gouges for most everything I turn. 
I don't do much spindle work so the bowl gouge is my go-to tool.
That said, I have a set of carbide tools that I keep trying in different situations. 
Last time I tried my carbide set while on my small Jet lathe I realized that the tools were just too big!
So I decided to fabricate smaller versions of the carbide tools that I use on my stubby.

Short tool

Materials

1x 1/2 square stock: McMaster https://www.mcmaster.com/9143K17/

1x 1" round alum tube with 1/2" ID: https://www.mcmaster.com/9056K28/

4x 1/4-20 set screws

Carbide cutters*: https://amzn.to/3pzTKiD

* Caution: I have ordered these cutters twice and have gotten two different sizes of cutters and screws. Check your cutter order before you start this build.

Design

The tool consists of a 1/2 x 1/2 bar with a cutter recess and a milled tang which is fit into a handle insert. The 3.5-inch handle insert is epoxied into a turned wood handle.

Cutter mounting 

A cutter recess is milled into the cutting end of the bar stock. The recess is made slightly longer than the cutter that will be mounted. The recess depth is less than the thickness of the cutter. The cutter will be mounted touching the edge of the recess but the recess must not be so deep that the cutters cutting edge touch the bar. Meaning, when mounted the cutters cutting edge must be proud of the bar's top surface.

For square cutters, the recess is milled perpendicular to the bar

For round cutters, the mounting recess is milled from the tip of the bar toward the tool's tang leaving a half-round surface for the cutter to index against. The end mill's diameter should match the diameter of the cutter. 

The cutter is then positioned in the recess and the mounting hole is marked and subsequently drilled and tapped to match the size of the mounting screws. Mine was a 4mm-.7 screw.

The tool that mounts the round cutter is subsequently modified to mount the pointed V cutter. This is done by milling down the center of the tool so the back of the V cutter is relieved. The end mills diameter depends on the size of your V cutter. I lay the cutter on the tool and mark where the Vcutter intersects with the 1/2 moon recess. Then using that size end mill cut a recess along the tool's length and through the 1/2 moon long enough for the V cutter to mount flat on the tool.

The cutter, slightly proud of the bar top surface

Modified bar to fit point carbide

Shaping the bevel

The face of the tool is then ground to a shape to match the cutter's bevel angle and shape.

Handle Insert

The handle insert is made from the 1" aluminum stock. A 3-inch piece is mounted in the lathe and the center hole is drilled out to 1/2inch. The raw tube stock had a slightly undersized 1/2 inch ID.

A 1 1/2 inch long tang which is 3/4 inch in diameter is turned on one end.

The part is then turned around and the front of the handle insert is finish turned to create a smooth surface.

Four holes for the set screws are drilled and tapped to 1/4-20. The holes are positioned 1/2inch back from both ends of the main body of the insert.

Tool

The toolbar is made from a 1/2inch x 1/2inch steel bar. The cutter recess is at one end and a tang is milled in the other. The tang on the tool is milled to a square such that it fits into the 1/2" hole in the insert.

The tang is milled to the largest square that is inscribed in the inserts 1/2 inch hole.

Calculate the Tang Size:

The problem is to calculate the size square that will fit snuggly into the 1/2 hole in the handles insert. We will mill a tang on the 1/2 x 1/2 inch toolbar the size of this inscribed square. The tang is inserted into the handle insert and set screw'd in place.

What we know:

Tool bar crossection = .5 x .5

Insert hole r = .5 / 2 = .25 = hypotnuse

angle theta = 45 degrees

Calculate the size of the inscribed square

We need to find the side opposite the angle theta (see sketch above) . 

Once found 2x that value is the length of one side of the inscribed square.

Using this trig function: sin theta = Opposite/Hypotnuse

Then transposing to find the Opposite: Opposite = sin Theta x Hypotenuse

Since: 

sin 45 = .707 and Hypotnuse = .25

    Opposite = .707 x .25

    Opposite = .1768

Therefore:

    One side of the inscribed square = 2x opposite = (.1768 x 2) = .3535

    The inscribed square i.e. the tang needs to be milled to .355 square.

How much must be milled off each side of the toolbar to create the insert tang?

Bar = .5" square

Tang = .3535" square

Mill off each side = .5 - (.3535/2) = .07"

Mill .070 off each side of the toolbar to make a tang that fits the 1/2 inch hole in the handle insert.

Handle

The handle is turned from the appropriate wood blank in the shape and length that matches your turning style. I used maple and since this was for my small lathe the handle was turned just long enough to fit my hand.

A 3/4 x 1 1/2 hole is first drilled into the blank with one end in a chuck and Jacob's chuck in the other. The blank is then held between centers with a cone in the tailstock live center. This cone is inserted into the drilled end of the stock for turning.

The handle is then turned to shape making sure that the insert end of the handle is the same diameter as the insert's tang.

The adapter is then epoxied into the handle.

Long tools

A long set of tool bars was made for another turner at the same time. I did not make handles for those tools.

Bar Length: 12 inches (includes the tang)

Short tool

Bar Length: 7 inches (includes the tang)

_______________

Enjoy and please comment

Don