Tacho on a Hercus

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 20x20mm x 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, on which the Al tube is mounted 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 square 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.

Attachment 380257

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
Attachment 380258

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.
Attachment 380259

Nice work, Bob. Is that VFD display/tacho really mounted inside an old blow-moulded screwdriver/socket set case?

If so...outstanding! :2tsup:



Moz

Quote:

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Originally Posted by MosquitoGarage

Nice work, Bob. Is that VFD display/tacho really mounted inside an old blow-moulded screwdriver/socket set case?
If so...outstanding! :2tsup:
Moz

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An early 1990's B&D ROS case. The sander fell apart about 10 years ago - so glad I kept the box - Although it sis starting to fall apart.
Here's the inside with the PowTran PI160 VFD.
the twin pots are for fine and coarse speed control
Attachment 380275

Here's another good use for an old power tool cases.
Attachment 380274

I absolutely love it. Little touches like this are practical but really bring a sense of fun to the shed.

Legendary.

Hmmm....I have a couple Bosch and Metabo blow-moulded tool cases stored away out in the shed, and the VFD wired to my Hercus 260 is yet to be given a permanent home. Thanks for the inspiration!


Moz

Quote:

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Originally Posted by MosquitoGarage

I absolutely love it. Little touches like this are practical but really bring a sense of fun to the shed.

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I'm really into repurposing stuff.
Here are two SS clothes dryer drums turned into a camping Bbq/Oven.
It call comes apart for easy transport.
Pizza, Bread, roasts, etc - the other folks in the campground walks past drooling . . . .
Attachment 380276

Quote:

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Hmmm....I have a couple Bosch and Metabo blow-moulded tool cases stored away out in the shed, and the VFD wired to my Hercus 260 is yet to be given a permanent home. Thanks for the inspiration!

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Unfortunately I've found most Power tool cases to be too shallow for VFDs otherwise I would have more of them inside these cases.

Here are the results of the vibration testing on the 9" plain bearing Hercus "with" and "without" the Tacho Magnet.

The units of vibration are milli, "g's" and are the vector sum of the vibe in the X-Y-Z directions.
Z is vertical and X and Y are along and across the bed.
In all classes the X-Y was <10 mg's and the vibe was dominated by the Z or vertical vibe.

Given the tolerance of the measurements is of the order of +/- 10% the first thing that stands out is that whether the magnet is attached on not makes little difference so this means what vibe being detected is inherent to the machine itself.
There are a couple of higher than vibes measured at 150 and 500 rpm, but these could be resonant points in the system


Attachment 381151

Quote:

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Originally Posted by BobL

Here are the results of the vibration testing on the 9" plain bearing Hercus "with" and "without" the Tacho Magnet.

The units of vibration are milli, "g's" and are the vector sum of the vibe in the X-Y-Z directions.
Z is vertical and X and Y are along and across the bed.
In all classes the X-Y was <10 mg's and the vibe was dominated by the Z or vertical vibe.

Given the tolerance of the measurements is of the order of +/- 10% the first thing that stands out is that whether the magnet is attached on not makes little difference so this means what vibe being detected is inherent to the machine itself.
There are a couple of higher than vibes measured at 150 and 500 rpm, but these could be resonant points in the system



Attachment 380279

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Bob,

What equipment are you using to measure the accelerations? Something you put together yourself or something commercial?

Eric

Quote:

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Originally Posted by lamestllama

Bob,
What equipment are you using to measure the accelerations? Something you put together yourself or something commercial?
Eric

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I spent a lot of time researching and starting to cobble something together until I discovered a mobile/tablet App called Vibration, by Diffraction LTD Design LLC in the US.
Vibration Version 2 and later
I'm pretty sure it's an Apple only product but there must be something similar out there for other platforms.

From the website

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Vibration is a true vibration spectrum analyzer using the built in accelerometers and gyroscope inside the iPhone, iPod Touch, and iPad. It acquires and displays time series data, optionally removes DC bias, applies a Hamming window and performs an FFT on each channel to produce frequency spectra. The 3-channel accelerometer has a sensitivity of approximately 0.02g and a range of ±2g making the iPhone and iPod Touch sensitive enough to analyze the vibration of most vibrating machinery. The internal gyroscope is sensitive to about 0.5 deg/sec and can also be used to analyze vibrating machinery.

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It costs $5 for a basic version and $15 for the pro version the basic difference being the pro has data logging and transfer capability. I've got version 3 as this allows for the use of the internal microphone as a vibe sensor so higher frequencies can be used than the internal phones accelerometers are capable of.

I use it quite a bit by just laying my iPad or iPhone on a clean piece of MDF on machinery - I usually use the iPad because it can be removed from it's case more easily than my iPhone. Ideally the iPad or iPhone should be clamped to the machine but provided the vibe is small it seems to make no discernible difference. I think the iPad is perhaps bit better probably because it is heavier than the phone so makes better contact. Anyway I'm using it always as a relative measuring tool so I'm not worried about absolute values and just looking for improvements.

Last year I used it to assess the vibe on my modified wood working dust extractor impeller motor and found it quite useful for that.
https://metalworkforums.com/f65/t201...-2#post1934828
Heres the typical output, it provides the Min, Max and RMS for vibes in each of the X/Y/Z directions and total Average RMS Vibe.
You can change the sample time/frequency and bunch of other parameters etc.
Attachment 380314

Having the tacho working so well on the lathe I decided to put one on my mill.

This time I was feeling lazy and instead of powering from the VFD I just used a Mains to 12V DC adapter.
Bit of a pain as it's just one more thing to turn off.

Blue LED RPM display
Attachment 381146

Sensor location using a SS bracket mounted on the drawbar collar at back of mill
Attachment 381147

Magnet is just self attracted onto the collar.
It looks way out of alignment but it's not as bad as it looks and the magnet only has to get close enough.
Attachment 381148

Bob -

Talk about a deep dive! I'm just about to try fitting a cheapo ebay tacho onto my Hercus 260. My Huanyang has a 12V output, so I'm hoping I can make it work. Thanks for the inspiration!



Moz

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Originally Posted by MosquitoGarage

Bob -
Talk about a deep dive! I'm just about to try fitting a cheapo ebay tacho onto my Hercus 260. My Huanyang has a 12V output, so I'm hoping I can make it work. Thanks for the inspiration!
Moz

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Most of those cheap tacho's say they will work at DC voltages anywhere between 8 and 24V DC . I tested one on a DC power supply I found it would even run at 6V, but that might not be good for it in the long run.