John

McDonald's

Project

Cornucopia


Making a Sine Bar

March 12, 2024

Calculation Tools

While waiting for the hot plate for transferring numbers onto the D&D dice, a machining diversion was found, a sine bar, whose manufacture was described in Machinist's Workshop, Vol. 32, No. 1, 2019.

A scrap of 1/2" thick aluminum about 3 1/2" long was located in the scrap box. It was marked out for hole locations using the Starrett height gauge. With the aluminum block held in the vise on the mill, set perpendicular to the table with dial gauge, the first hole was located and drilled 3/16" (probably should have reamed to 3/16"). The table was moved 3.000" and the second hole was drilled. About half of the block was sawn off with the hacksaw as shown in the photo below.

Rough cutting the aluminum to sine bar size

The majority of the inside waste was removed with a 1/2" end mill lowered vertically through the part as seen in the following photos. Due to the supports the last 1/32" of material was not removed initially, but only after changing the setup to parallels at the ends, not quite as sturdy, but sufficient for the small amount removed.

The setup for removing the wasted between the ends. Most of the waste removed in half a dozen passes of the end mill A finish pass after removing the waste Removing the last of the waste in a new setup.

The rotary table was set on the milling table and centered with the dial gauge. A bronze spud was made to sit on a screw with a 1/4" round extension in the lathe to fit the 3/16" holes. The part was held in place with a step clamp using a brass block and paper packing underneath. The round end was then milled to most of a circle and the final handwheel setting was noted. The other end of the part was set up similarly and also milled to the noted handwheel setting. Neither end was milled all the way to the inside as too much material had to be removed and this setup was not conducive to removing that much aluminum. The first photo below shows the beginning of milling one end round. The second shows the sine bar at this stage of construction.

Milling the end round on the rotary table. The ends partly rounded.

The nascent sine bar was clamped to an angle plate with a machinist's clamp. The inside area next to the round ends was milled out with a 5/16" end mill. The part was returned to the rotary table and the inside parts of the ends were rounded.

Cleaning up the waste near the ends.

The part was held with the inside up in the vise. The inside was milled flat along its length as seen in the first photo below. The part was flipped over and the ends were set on parallels before clamping the bar in the vise. The top side was milled with the two insert end mill until a nice finish was achieved as seen in the second photo below.

The inside of the sine bar was milled. Milling the topside of the sine bar.

Burrs were removed and the sides sanded completing the sine bar. It is seen below set on a 1-2-3 block. The angle is determined as follows:

1" = sine θ X 3"

θ = sin-1 1/3

θ = 19.47°

The completed sine bar set for a 19.5 degree angle.

I don't possess a sufficiently accurate level to check the sine bar. The phone when set on the bar above indicated the angle was 19° or 20° varying from measurement to measurement.