Tachometers with hall proximity sensor question

[682bear]

I'm guessing, based on what I see in your pictures, that your mill does not have a back gear... you should be fine mounting the magnet directly to the spindle pulley.

It should be a pretty easy install.

-Bear

 

[BGHansen]

I'd stick the magnet on the step pulley (red) and make a bracket to mount the sensor (blue). You may want to mount the sensor to the side as it'll be out of the way when you're slipping the spindle belt when changing speeds.





The tach counts "blips" as the magnet passes the sensor, then does the math for "blips" per minute. Hman came up with an elegant solution to a tachometer problem I had on my DoAll ML 16" bandsaw. The speedometer was broken on my saw The bandsaw cares about surface feet per minute of the blade, not motor RPM's. The bandsaw wheel is 16" diameter or a circumference of 50.25".

Hman's idea was to mount 4 magnets on the wheel so instead of measuring wheel RPMs with one magnet (or number of times the 50.25"circumference wheel turns per minute), I'd be measuring 4 "events" per revolution which is 50.25" / 4 or a "blip" for every 12.6" of wheel movement. Ideally the math would work to 12" per "blip", but at 12.6" between counts there's less than a 5% error in the tach reading blade feet per second speed instead of RPMs. Here's the thread for my install.

Bruce

DoAll 16" ML band saw speed indicator install

This will take a couple of posts because as usual I'll go into nauseating detail. . . Back story is I bought a circa 1948 DoAll ML band saw between Christmas and New Years last year. Being 70+ years old, there were a few things that needed some repairs. DoAll saws are known for their rotating...

www.hobby-machinist.com

 

[Suzuki4evr]

I'd stick the magnet on the step pulley (red) and make a bracket to mount the sensor (blue).

Hallo Bruce.
Unfortunately I have a cover plate here and I dont realy want the sensor sitting exposed.

So I am thinking of putting it inbetween the idler and spindle pulleys using a bracket bolted to the base.


-Michael-

 

[BladesIIB]

Is there any room to come up from the bottom? Maybe mount the magnet on the bottom of the pulley and mount the sensor under it. That would keep it completely out of the way for any belt changes. Could even make a cover for the sensor. On my mill I would mount it where pointing in the pic.

 

[BGHansen]

BladesIIB has a great idea. Or can you mount the sensor at a 90? They have a pretty forgiving clearance spec between the magnet and sensor. I recall mine saying clearance of 1 - 10 or 12 mm.

Not the safest thing, but stick the magnet on the outside of a drill chuck on your mill. Power update the tach and carefully bring it up to the chuck at a 90 and see if it reads?

Bruce

 

[Firstram]

BladesIIB has a great idea. Or can you mount the sensor at a 90? They have a pretty forgiving clearance spec between the magnet and sensor. I recall mine saying clearance of 1 - 10 or 12 mm.

Not the safest thing, but stick the magnet on the outside of a drill chuck on your mill. Power update the tach and carefully bring it up to the chuck at a 90 and see if it reads?

Bruce

That's a good idea! Magnets with the poles oriented sideways are available

 

[Suzuki4evr]

Is there any room to come up from the bottom? Maybe mount the magnet on the bottom of the pulley and mount the sensor under it. That would keep it completely out of the way for any belt changes. Could even make a cover for the sensor. On my mill I would mount it where pointing in the pic.

Yes maybe that can work,then I can just tap the body,but I will have te relay the sensor wired around the back.

 

[Suzuki4evr]

BladesIIB has a great idea. Or can you mount the sensor at a 90? They have a pretty forgiving clearance spec between the magnet and sensor. I recall mine saying clearance of 1 - 10 or 12 mm.

Not the safest thing, but stick the magnet on the outside of a drill chuck on your mill. Power update the tach and carefully bring it up to the chuck at a 90 and see if it reads?

Bruce

Unfortunately that won't work here.

 

[Suzuki4evr]

Can I superglue the magnet to the pulley or make a divet first then glue.

 

[BladesIIB]

Can I superglue the magnet to the pulley or make a divet first then glue.

Looks like underneath will work for you. Either tap the cabinet or just double nut and pinch the sensor in place. I would make a divot to put the magnet in. Use an end mill and should be a pretty good fit and minimal impact on balance. I am sure super glue will work I tend to use epoxy for things like that myself.