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I bought a $20 photo tachometer on eBay. Just search for photo tach*.
It has a visible red laser beam, that you aim at a piece of reflective tape (about 24 inches supplied, I used just 3/8 long piece) you attach to the side of the rotating item and it counts the reflections as it passes by.
I checked the accuracy by pointing it at a flourescent light which lights twice per power cycle or 120 times per second. It readily read the output of the light as a reflection at 7203 RPM. 120 times per second is 7200 RPM so it was .04%; high, not bad I guess but I would have expected a better crystal oscillator time standard than 416 ppm. Usually the power frequency is very, very accurate, but maybe it was off. Anyway plenty good enough for WW machinery.
I checked using the reflector tape on my drill press with pulley sets at several rates and found them to be about for example 1180 RPM for the 1100 RPM setting which is to be expected with no load and an induction motor.
The Bosch 1617EVS has an electronic speed control supposedly with constant speed so that the speed does not vary with load. The speed is set with an orange dial marked 1 to 6. Its more or less continuously variable but has very slight "detents". Felt like four detents per number which I suppose is to keep the dial from vibrating to another value, but it made it easy to set the number closely instead of guessing.
I set up the router with the tape reflector on a flat of the collet nut. No bit, no load. Router on its side.
As you can see from the attached plot, the Bosch numbers don't quite match. They're as much as 5000 RPM off in the middle or at #4. They do match at the endpoints, but the bosch suggeted values are all high in between. Actually I find my curves more believable as they are at least in a smooth line. I have no reason to think my numbers are anything but correct to better than .1%, for my router at no load.
Some possible explanations for the differences:
No load vs. load for Bosch's figures (well, its supposed to be constant speed feedback, so I doubt it)
Router position (turns easier when up and down as opposed to horizontal? Doubt it)
Different router, electronic component differences (maybe... but probably not; if so, why the 2nd order wobble in their plot?)
Bosch numbers Just Plain Off (most likely).
It is not convenient for me to load the router and measure the speed without some help, furthermore, it's hard to control the load at anything but no load. So I'm not going to do that .
Anyway, what it is, is what it is.
You might want to print it off and keep with your router or router accessories.
It has a visible red laser beam, that you aim at a piece of reflective tape (about 24 inches supplied, I used just 3/8 long piece) you attach to the side of the rotating item and it counts the reflections as it passes by.
I checked the accuracy by pointing it at a flourescent light which lights twice per power cycle or 120 times per second. It readily read the output of the light as a reflection at 7203 RPM. 120 times per second is 7200 RPM so it was .04%; high, not bad I guess but I would have expected a better crystal oscillator time standard than 416 ppm. Usually the power frequency is very, very accurate, but maybe it was off. Anyway plenty good enough for WW machinery.
I checked using the reflector tape on my drill press with pulley sets at several rates and found them to be about for example 1180 RPM for the 1100 RPM setting which is to be expected with no load and an induction motor.
The Bosch 1617EVS has an electronic speed control supposedly with constant speed so that the speed does not vary with load. The speed is set with an orange dial marked 1 to 6. Its more or less continuously variable but has very slight "detents". Felt like four detents per number which I suppose is to keep the dial from vibrating to another value, but it made it easy to set the number closely instead of guessing.
I set up the router with the tape reflector on a flat of the collet nut. No bit, no load. Router on its side.
As you can see from the attached plot, the Bosch numbers don't quite match. They're as much as 5000 RPM off in the middle or at #4. They do match at the endpoints, but the bosch suggeted values are all high in between. Actually I find my curves more believable as they are at least in a smooth line. I have no reason to think my numbers are anything but correct to better than .1%, for my router at no load.
Some possible explanations for the differences:
No load vs. load for Bosch's figures (well, its supposed to be constant speed feedback, so I doubt it)
Router position (turns easier when up and down as opposed to horizontal? Doubt it)
Different router, electronic component differences (maybe... but probably not; if so, why the 2nd order wobble in their plot?)
Bosch numbers Just Plain Off (most likely).
It is not convenient for me to load the router and measure the speed without some help, furthermore, it's hard to control the load at anything but no load. So I'm not going to do that .
Anyway, what it is, is what it is.
You might want to print it off and keep with your router or router accessories.
Attached Files
Loring in Katy, TX USA
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