Fitted a tachometer to my lathe

[skotl]

Following this thread, I ordered two of these and have fitted the first to my lathe (bringing a 1944 Denham into the 21st century ) - the second will go on the vertical mill.

Works pretty well! I suspect it will be more useful on the mill - hopefully get that done tomorrow

 

[rockweasel]

I reckon a Flux Capacitor would be an interesting addition

 

[roofman]

I want,i want,i want
UPDATE.....ive just orded 2 of them myself...great find Scott

 

[Maker]

Am I right in thinking it's not reading the spindle but a shaft below the spindle? Are you sure they're geared 1:1? It also looks like the sensor will block a long piece from passing through the head.

 

[armalites]

What happens if you want to put a long piece in the head stock? Surely the wire is in the way?

 

[dobbslc]

First thing I saw

 

[slim_boy_fat]

You look to have extra components behind the tacho readout panel than those shown in the listing photos, what are they and what function do they perform?

Also, do you just stick a magnet to the spindle for the head to pick up?

 

[skotl]

Am I right in thinking it's not reading the spindle but a shaft below the spindle? Are you sure they're geared 1:1? It also looks like the sensor will block a long piece from passing through the head.

Re the 1:1 yes - exactly. You can just about see a white piece of tape on the chuck and I measured the speed with a lasert tacho to verify.

Re the long piece - yes, oops didn't think of that! Oh well - it's relatively easy to unbolt the sensor if I ever need to do that!

 

[skotl]

You look to have extra components behind the tacho readout panel than those shown in the listing photos, what are they and what function do they perform?

It's just a piece of vero board, bolted to a plastic riser, to take all the connections. I soldered the incoming power, 3 leads for the tacho and 3 leads for the sensor with a 2.7K resistor between +ve and the sensor.
I'll get a pic of that tomorrow - I'll probably fit a plastic cover / box to the back to protect it from crud.

Also, do you just stick a magnet to the spindle for the head to pick up?

Yep - just a neotheodyninnynanayaboosucksnaniyium magnet

 

[skotl]

@roofman asked for some info on wiring up the tachos so here's the details on how I wired mine.

As luck would have it, the two I ordered had completely different wiring at the back so hopefully this will help you out if you have either of these displays

First - a schematic layout, for those of an electronic bent;

Note that the wire colours on the sensor were the same for both of mine, however both did have a tiny sticky label on them so double check what is written there to confirm the wiring;

The (bad) instructions suggested a 22k pull up resistor between the signal and the +ve supply. A little research suggests that the LED displays already have a pull-up resistor so, if you have one to hand, I would wire it in. If not then it certainly worked fine for me without them on the bench.
I wired them in, anyway, as I had some handy.

This is the first type of display, which has a 4 pin header at the back;

The board is clearly marked that the left most (red) is +ve, the next (black) is -ve and the right most (yellow) is the incoming signal.

The other board had five pins and was more of a challenge as it was marked in Chinese!

Here, +ve is the left most, -ve is the next one and signal is the far right. In fact, the wiring is effectively the same as the other unit.

Finally, here's some larger pics of the two LED modules;

 

[skotl]

You can use a pushbike speedo as a tacho, 1mph = 1rpm....
It won't have light up LED segments though, and the display will be invariably smaller than that in the op...

Edit: wheel circumference set to 268mm to display in rpm=mph, or 167mm to display in rpm=kph.

You see where you're going wrong, then

 

[RichardM]

are you going to convert it back to ft/s for the cutting speed?

 

[Pete.]

Yeah the SFM changes with diameter. Some lathes have constant SFM as a feature, they change the speed according to the tool position but you couldn't incorporate that into something as basic as this. A chart on the wall will have to do.

 

[skotl]

DRO encoder reporting tool position linked to a VFD running a 3~ motor using the tacho for feedback.

'Tis but the work of a moment

Think the tacho in the OP cost me £9 - plenty value for money in that without any of your fancy schmancy three-letter acronyms and three-phase supplies

 

[Pete.]

DRO encoder reporting tool position linked to a VFD running a 3~ motor using the tacho for feedback.

'Tis but the work of a moment

Yeah right

 

[roofman]

Big Thanks to skotl for taking the time to write and update this thread in such a detailed way

 

[skotl]

Big Thanks to skotl for taking the time to write and update this thread in such a detailed way

No worries - look forward to seeing what you do with them

 

[dobbslc]

I've just ordered on of those tachometers for my lathe as I think the belts are slipping and it's running slow.
I went into Maplins to see if they had one I could pick up and when the gormless spotty youth typed it in the search bar he put in "tacos" !

 

[slim_boy_fat]

and when the gormless spotty youth typed it in the search bar he put in "tacos" !

 

[roofman]

No worries - look forward to seeing what you do with them

Pretty much what you did mate