Tachometers with hall proximity sensor question

[pontiac428]

Just make sure you reverse the polarity of the magnet, because you are in the southern hemisphere.

 

[SLK001]

Just make sure that you place the magnet in an area where it cannot pick up steel or cast iron swarf.

 

[Suzuki4evr]

Just make sure that you place the magnet in an area where it cannot pick up steel or cast iron swarf.

Well it's enclosed, I don't think I can protect it more. But I got what you are trying to warn me against. Thank you.

 

[Suzuki4evr]

Use an end mill and should be a pretty good fit and minimal impact on balance

Now if only I had a milling machine to use an endmill on the milling machines pulley.
.......I'll make a plan.

 

[hman]

OK ... one more wild idea:
Use a lathe (I assume you have one) to turn a ring that will fit around the notched nut on top of your spindle pulley. You can use a setscrew to hold it in place. Mill a magnet sized pocket into the top surface of the ring. Press or glue the magnet there. Then mount the Hall effect sensor to the cover plate, pointing down toward the magnet. Given the wide distance range of sensitivity, there's no problem if the cover plate doesn't always close to exactly the same distance. Obviously, there's no way to read RPM with the cover plate open ... but you won't be running the mill uncovered, so no problem. You can make the ring as large as the topmost pulley flange and place the magnet near the periphery, so clearance between the hall sensor body and the upper parts of the spindle should not be an issue.

The only downside would be that you'd flex the sensor cable every time you opened the cover plate. A decent "service loop" in the cable should minimize strain. And you could always keep a spare sensor on hand, for quick replacement.

My major concern with mounting a magnet directly to one of the pulley flanges would be that, if you just glued it to the surface, it could be knocked off by the belt. And if you drilled into the pulley flange, you might weaken the pulley at that point (not to mention the difficulty of cutting the pocket (as you said, you can't use the mill to do this). Making a separate ring allows you to do what you need to do without disabling the mill.

 

[BladesIIB]

Now if only I had a milling machine to use an endmill on the milling machines pulley.
.......I'll make a plan.

Ha, fair point. For that small of an end mill you could likely get away with a drill press if you had one of those still assembled?

 

[Suzuki4evr]

You can make the ring as large as the topmost pulley flange and place the magnet near the periphery,

This is not a bad plan,I think Bruce gave about the same idea in post #32. But what I don't like about it is that the sensor would sit very exposed and very close to the drawbar. So with a slip of the spanner or,and I know I would probably get some flack and rightly so,lose concentration and LEAVE the spanner on,which happened once or twice, and bang there goes the sensor. As you can see in the pic below, it would sit pretty closo to the drawbar,otherwise I would have to make a very big ring to open the distance but then it would become difficult to slide the belt over should it be necessary to do so.

And if you drilled into the pulley flange, you might weaken the pulley at that point

Yoi do have a point about the pulley. It is very thin,the mag is 10mm×3mm. But so far I feel it is my best option coming from below.

 

[Suzuki4evr]

Hi guys.

So I have installed the tach and built a box and everything of which I will post after everything is sorted.

But now there is a problem and I don't know what. When I switch my vfd on which supplies 24V for the tach, the tachometer comes on and when I rotate the spindle by hand,there is a reading. BUT when I start the mill there only apears 4 dashes on the display..........WHAT did I do wrong? The VFD wiring used to supply power to the pot is shielded exept the last few inches offcorse. I even moved the tach wires totaly outsid the box but the last inches that needs to go in.

Is there something wrong with my wiring or the tachometer itself?


Thank you
Michael

 

[BladesIIB]

Michael, you may want to try dropping to 12v. The tach’s are rated for 12-24v if yours is like mine. When I installed mine it was recommended I buy a small transformer to drop to 12v. Was told the tachs liked that better. Not sure if this was the issue I avoided or not but I believe the little transformer was only about $10 on Amazon. mksj is who recommended that to me he likely has more detail as to the why?

 

[Suzuki4evr]

On the bacj it says 8-24v. I have three terminals available on my vfd 5v,10v and 24v. I was hoping that would work on the 24v