Rotary table digital readout

[petetwissellParticipant @petetwissell]

I have one of the 6″ rotary tables of generic design which can be mounted on edge as a dividing head.
For various reasons, it would be advantageous for me to have a digital readout for the table angle.
I had expected to find suitable kits readily available, as they are for linear readouts – but nothing came up in my searches.
I found a rotary encoder with remote display available, but the encoder is a 37mm high box which would require lifting the rotary table high off the mill bed and reducing available part and tool height capacity.

So – I had a look around to see what I could adapt. What I found was an inexpensive “digital level / angle finder”, the small box type, with a tilting display – various brands available…

This was actually something I had for several years, but it never worked correctly after I dropped it. With nothing to lose, I set about dismantling it.
Inside, the ‘heart’ of the device consists of a pendulum and an inductive encoder mounted on a pair of PCBs.
The front half of the box houses the two AA batteries and the display, which is connected to the main PCB by a short ribbon cable. In the photo I cave cut the ribbon cable and battery wires to seperate the encoder board out.

The pendulum is attached to the encoder rotor with an M3 nut (on the back side) and is easily removed.

Mechanical installation to the rotary table requires a simple aluminium ‘slug’ to press into the bottom end of the table’s hollow spindle, with an M3 hole tapped centrally.
To mount the PCB I cut a disc from some 2mm rigid plastic sheet (I happened to have some clear sheet, which is exceedingly brittle!). The disc is cut out to clear the smaller of the sandwiched pair of PCBs and holes drilled to mount the larger PCB with M2 screws and nuts.

The resulting assembly protrudes around 4mm from the underside of the rotary table, so I am making a simple rectangular aluminium sub-plate, recessed where required to clear the encoder PCB and to create a channel for the ribbon cable connecting to the display. The display will also be mounted on the sub-plate.

The origianl ribbon cable has 8 conductors connecting the encoder PCB to the display. I replaced this with a 10 way ribbon cable, which also carries the connections from the batteries in the display box to the encoder PCB.

The on/off switch is mounted on the encoder PCB. I attempted to create a remote switch, but without success. I suspect the switch on the PCB in not simply a normally open ‘push to make’ type.
I have decided to go for a slightly Heath-Robinson solution, with a pushrod in a groove in the sub-plate to operate the switch.

I’ll post more photos soon. I just need to machine the sub-plate.

[Russell EberhardtParticipant @russelleberhardt48058]

Interesting project Pete.  The 0.1 degree resolution might be a bit limiting though depending on your requirements.  The calibration on the handwheel is at least an order of magnitude better although what the absolute accuracy is I don’t know.

Russell

[Author]

Posts