I got me one of these! HASLER SPEED INDICATOR

[Finster]

RPM is RPM, no matter the diameter. You have agreement within 2%, which I would think is close enough for spindle speeds.

Why is that not sounding correct? I'm not arguing, just confused. I'll have to think about this for awhile. The strobe, by nature, is checking the mark on the outside of the bar. So, in essence it is actually checking surface speed, correct? The other is checking the center of the bar or "the shaft" of say a motor. Why do I think they should not be the same? By the way, I flunked algebra more than once.

 

[Tony Wells]

The timing mark is going to appear in the strobe just once per revolution, no matter what size the OD is. It doesn't take any longer to swing around the axis of rotation no matter what size it is. I think you are trying to integrate surface speed into this, but that is another thing altogether. That is diameter dependent. But put that out of your thinking on this one. 1 inch, 100 inches or 100 miles......how long it takes to complete a single rotation is the basis for how this works. The actual time it takes for that revolution does affect surface speed, but not RPM.

 

[Finster]

The timing mark is going to appear in the strobe just once per revolution, no matter what size the OD is. It doesn't take any longer to swing around the axis of rotation no matter what size it is. I think you are trying to integrate surface speed into this, but that is another thing altogether. That is diameter dependent. But put that out of your thinking on this one. 1 inch, 100 inches or 100 miles......how long it takes to complete a single rotation is the basis for how this works. The actual time it takes for that revolution does affect surface speed, but not RPM.

OK that helped and I agree. But now I have a different problem. (look at the picture of my first post) I use one of the little wheels and put it on the surface. My RPM is way off, not even close, off by more than a thousand. I put the pointed center in, take a reading in the center drill hole and it's dead nuts. Why is that?

 

[RandyWilson]

By using the rubber wheel against the surface, you are incorporating surface speed into the equation. The ratio would be your stock diameter divided by the wheel diameter. A 1/4" rubber wheel against a 3/4" piece of stock will give a reading three times faster than expected.

 

[Finster]

By using the rubber wheel against the surface, you are incorporating surface speed into the equation. The ratio would be your stock diameter divided by the wheel diameter. A 1/4" rubber wheel against a 3/4" piece of stock will give a reading three times faster than expected.

Humph. Learned something new. Retaining it will be the problem.

 

[Finster]

Thanks for the help and info everyone.

 

[Ken from ontario]

Thanks ! I uploaded the ebay site & ordered one immediately.

You won't regret buying that tach(the one in Bob's link), I have that model and it gives consistent readings , in my opinion this is one Chinese product that could easily cost more and people would still find it a good deal.

 

[Jericho]

I just use a strobe app on my smartphone.....it was free, but I'm cheap.

You got a smart phone for less than $10. Now THAT was a bargain.

 

[benmychree]

Interesting instrument. I would guess that it functions much like the old mechanical speedometers in cars. The spindle is attached to a rotating magnet and the magnet creates eddy currents which create a force that works against a clock spring. The faster the rotation the greater the force and the greater the deflection.

As I recall, the mechanical speedometers were notoriously inaccurate. Hopefully, the Hasler indicator doesn't suffer from the same problems.

Actually, this type of device operates by counting turns on the dial in a given period of time; I have a similar device and that is how it works. Read the instructions on the card on the back of the case, it spells out the operating mode. When you engage the button, you can hear the clock mechanism inside ticking; when it stops ticking, it disengages a clutch on the input shaft.

 

[ch2co]

My only problem with the el cheapo tach I got off of eBay is that it uses a 9 volt battery. I hate 9 volt batteries. My tach has a habit of not turning itself off
and 9 volt batteries are just too darn expensive to keep replacing every time I don't bother to turn it off. Otherwise that little guy is my goto tach.
The mechanical tach is beautiful to behold, but is difficult to use for determining the speed of your chuck for instance. I really like my Machtach
on my lathe. All three of my tachometers read within a couple of percent of each other.