Re: [CAD_CAM_EDM_DRO] Cheap tach - was r.p.m. kit??? / 4 digit under $20

Yes it's a simple idea.... but nothing like looking at some digits and not having
to bother with coupling to a moving parts and the danger associated with it.
Fingers and eyes can be difficult to replace.... ! Now if you make it a permanent fixture
sure it's great...
I'd say the idea has been around about 100+ years ! :-)
The eddy current driven version has been around almost as long, in most cars it known as the speedometer !
If you goto a car junk yard you may even be able to find one of the older eddy current version speedo's and
adapt it directly to the mill.... just a thought... give me LED's and LCD's any day... ! :-)

Best Regards
Hans W



"deanc500 " wrote:

> Hi, I just tried one of the suggestions on another group regarding
> this subject. I was intrigued by the simplicity of the idea and the
> fellow mentioned that this is an old trick thats been around a while.
> You just need any small DC motor, a potentiometer, and a volt meter.
> The first potentiometer that I found in the junk drawer was a 50K
> although other values will work. I hooked it up as in this picture.
>
> http://www.members.shaw.ca/axxus4/cheaptach.jpg
>
> The motor is connected across the pot and the meter is connected from
> the center of the pot to one side. To calibrate, spin the motor in the
> chuck, and adjust the pot to read your known rpm (in mV or whatever).
> I was spinning it at 1460rpm in my mill drill. I adjusted the pot to
> read about 1.460V on the 20V scale. I walked over to the drill press,
> and spun the motor. I read 0.354V. I was amazed to see that the drill
> press was set to 360rpm. Very neat trick. I will use this method to
> measure servo and stepper rpm.
>
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