Not much about tachometers in the Hercus forum, the last reference being in 2014, one in 2010 and one in 2008 so I thought I would post my efforts on this topic.

I've had a couple of tachos f for about a year or so but was put off installing them on machinery by the fact that I would need to power the tacho with 8-24V DC. The other day I was reading a VFD manual and it stated that the 24V output on the terminal block of the VFD can deliver up to 100 mA so I mocked up the tacho and sensor and powered it from a bench top PS and found it only drew around 22mA.

Then finding a location on the lathe itself was not that easy.
A small magnet needs to be attached to an exposed part of the spindle and enough space is required to mount a sensor just above the rotating magnet
There's not much exposed spindle to work with on a Hercus so I part milled and part sanded a 60 mm length of 1.5mm square Al tubing and mounted it a shown below.
The small (button size) REE magnet that rotates past the sensor is currently just self attached to the bit of smooth exposed pulley edge and it seems to stay there even running it up to 1250 rpm (its only a plain bearing Hercus) but I will glue it down at some stage.
The reason I went for a square tube like this is because the gear cover is an awkward shape (it's curved in two directions) to attach to a piece of flat bar to, whereas the two edges of the tube only needs to cope with the curves across the cover.

The hall effect sensor is the thing with the red LED on it held in place and adjusted for height above the magnet place by a couple of nuts. The LED flickers slightly brighter when the distance is between the magnet and sensor is OK.

Tachosensor.JPG

Because the readout is powered by the the VFD I located the readout on the VFD enclosure like this.
The 24V comes from the VFD and this also powers the sensor via the black cable
HercusTacho1.JPG

The (black) Sensor cable is a tad "in the way" and has been zip tied in a few places so it won't get caught up in any belts and gears. Eventually I will lengthen that cable so it can be moved further out of the way.

I did a similar thing the other day on my DP.
The Sensor (S) pokes thru the belt pulley cover and the magnet sits on top of the spindle pulley just underneath.
Interestingly the magnet on the DP is located about the same rotational radius as the magnet on the Hercus but introduces a fair bit of vibe to the DP so I had to place an equivalent mass of metal on the opposite side of the pulley to balance the magnet mass out.
Full details of the install and vibe analysis here Tacho install on DP
Tomorrow I will explore any vibe out on the Hercus.
DPTacho1.JPG
Attached Images




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