This project was undertaken in an attempt to transform the output of the award winning "Automated Keytag Machine" into a product with even greater appeal and utility.

The keytag rounder is a relatively simple machine that rotates a square keytag (1 1/2" x 1 1/4") through a rotating router bit. In doing so, the square corners are removed and replaced by lovely rounded ends. A 12 Volt DC motor is controlled by an Allen Bradley SLC 150 processor mounted to the side of the unit. This motor is clamped down onto the keytag, which is positioned and pinned in a holder that rotates in the base plate.

SLC 150 Process Controller

Five switches are used as inputs to the SLC 150 (3 limit switches and 2 pushbuttons):

• Door closed limit switch-door must be closed before process will begin.
• Part clamped limit switch-part must be clamped befor process will begin. Switch, mounted to top of unit, is actuated by arm connected to clamp.
• Run detect limit switch-mounted in the baseplate near part holder. Detects flat area milled into the rotating part holder.
• Start pushbutton-pressing this button at the appropriate time starts the cycle.
• Stop pushbutton-all processor outputs are turned off when this button is pressed.

There are 6 outputs from the SLC 150 controller (2 motors and 4 indicator lights):

• OK to cycle light-this output indicates that cycle is ready to begin.
• Run light-illuminated when process is underway.
• Cycle complete light-this light comes on when a cycle is successfully completed.
• Fault light-when part is not rotated to completion in a specified amount of time for any reason this indicator light comes on.
• Router motor-120 VAC motor controlled through "dry contacts" in the controller.
• Small part-rotating motor-12 Volt DC motor is most effectively run at 2-5 VDC for proper rotation speed.

The controller scans through the condition of the inputs and sets the outputs according to the ladder logic program stored in its memory.

Design Features

There was some concern on the part of the designers that positioning the motor inside a shaft that was under a 100 lb. axial load would significantly decrease the motor's performance. To minimize this axial load on the 12 volt motor shaft, a thin thrust bearing was strategically placed on the base of the shaft. Another identical bearing was positioned between the base plate and the part holder to minimize friction in that area.

The 12 volt motor was chosen for two reasons:

Torque-this small motor can produce a surprising amount of torque even at the slow speeds that were required.

Availability-they abound in numbers around here. (More than one motor was "used")

Alterations to Initial Design

In an attempt to simplify the design and minimize operator involvement, it was desireable to round both sides of the keytag in the same cycle. A simple way to perform the task was to rotate the part about its center, 360 degrees through a cutting device. It was thought at the outset of the project that the keytags would be 3" in length. With the 1.5" radius that resulted, however, the desired effect of smooth lines was unobtainable. At this length there was not enough rounding on the ends to eliminate the sharp corners.

It was discovered that, by reducing the length of the actual keytag by a factor of 2, the desired rounding was achievable. As a result of this decision, however, the positions of the sensors on the Keytag Machine required relocating.

Ladder Logic

Click here to view the ladder logic that controls the keytag rounder