Using the milling machine I began to finalise the tonearm, narrowing down the possible shapes that could support and hide the RFID reader, needle, wires but also still be aesthetically pleasing. Because the USB wire for the reader is relatively thick compared to the other single core wirings, it would be visible if the arm did not have a shell round the underside of it. This brought about the challenge of creating a long and light hollow arm that could house the wires but also not be bulky or heavy. Taking into account the dimensions of the reader, the cartridge and space for the head shell wires I decided to go with a rectangular end shape with a rectangular central hollow tube making up the arm body. After finishing the arm and settling on a final effective length of 220mm I could then begin working out the mounting distance, overhang and bearing position on the top piece.
Once the arm was made and the mechanism for its horizontal and vertical movements could be finalised. For the horizontal spin that would allow the arm to move along the grooves towards the centre of the record I decided to change from the point bearing that was on the Stanton Turntable. I sourced a couple of high quality Timken ball bearings from a shop called Brammer, with an inner diameter of 20mm, outer diameter of 47mm and a height of 12mm. This sizing although large was ideal for the cables to run through from the arm into the body and was large and heavy enough to wedge into the top piece, which took a lot of sanding and forcing in due to 47mm drill bits seeming to not exist. To attach the bearing to the rotating cylinder that the arm and vertical bearings rest on I managed to find some 20mm plastic plumbing tubing that wedged in perfectly to the inside of the bearing and use a joiner for these pipes on either end to secure, leaving plenty of space for the USB cable and arm wires to flow through without restricting the bearing movement.
Finally for the Vertical Movement of the arm allowing it to be lifted on and off of the grooves and its weight and balance to be control for groove tracking I experimented with variations of circular and linear blocks and assemblies for the most fluid movement to minimise friction and also which one was most aesthetically pleasing. For this movement originally I tried using similar bearings to the Timken for the top piece but smaller, taken from a skateboard but they were even too large and I found that the best way for fluid movement was to use tiny 2mm point pivot bearings that were embedded in both the arm and support.