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Optimark
7th May 2018, 05:26 PM
Today a friend came over with his new toy, we had a bit of a play; his toy is a portable digital tachometer.

We attached a small piece of the reflective material onto the hand wheel of my Nova 16-24-44 8 speed lathe, then fired it up. The lathe belt was on the 300 rpm pulley, the digital readout was substantially higher, hovering around 344 rpm.

This lathe has two speed ranges dependent upon whether you are running 50Hz or 60Hz. As Australia is 50 Hz we are on the lower speed and the selected belt should give close to 300 rpm. If in the USA at 60Hz then according to the chart on the Nova it would be running at 360 rpm.

If the error is in the pulley ratios, then in the USA this machine would be running at 412 rpm, instead of 360 rpm, which for the second of eight speeds, is getting up there for off balance heavy stuff.

As the lathe had a big blank on, I wasn't about to change speeds to see how different from stated speeds the other 7 pulley set-ups were.

I am not worried about this, just thought it was interesting.

Mick.


434961

China
7th May 2018, 05:53 PM
!00 rpm would make little difference

Pat
7th May 2018, 06:12 PM
I have one of them, not the most accurate toy, but gives you a ball park figure, especially with a variable speed lathe.

You would have to spend more than $20 on ebay to get an accurate version :;

Gabriel
7th May 2018, 06:13 PM
I've been wanting to set up something to get a readout on my lathe. At the moment on evs I have a dial which has numbers 1 - 10 which don't equate to anything.....
I turn pens at 4, apply CA at 1 and have turned some really out of balance burl at 2......
Buggered if I actually know what speed I'm doing it all at.... Maybe I'll just get a little banger like this and make some notes (to put beside my sanding colour charts and micromesh chart....another chart)

Thanks Mick...may be the inspiration I need

BobL
7th May 2018, 07:18 PM
I have one of them, not the most accurate toy, but gives you a ball park figure, especially with a variable speed lathe.
You would have to spend more than $20 on ebay to get an accurate version :;


When I tested mine against an accurate frequency source from work I found it was surprisingly accurate.
If the measurement was based purely on counting the number of pulses, with a measurement time of 1 second on 360 rpm it would only count 6 +/-1 light pulses so it would have no more than +/-16% reproducibility .
However they usually measure time with a 6MHz clock and measure time using the steepest slopes as triggers in a signal output pulses so they end up having an accuracy of about +/- 1 RPM at 600 RPM and this is what I saw when comparing it to a accurate frequency source.

The most surprising thing about mine has been that I have only gone through 2 sets of batteries in the 10+ years I have owned mine and I use it a lot.