rpm measurement?

[Slow6]

Gday folks

I have a few machines waiting for motors, an old cast iron table saw thanks to rowie that wants a single phase 3hp motor, My old woodfast lathe is begging to be an outboard only bowl lathe and wants a variable speed jobby and I've slowly scrounged a few old cast iron bench grinder spindles and plan on putting together a table for them with a 2 speed pulley get up. all easy enough.. but to my eye speeds come in at fast or faster, I can't look at a spinning saw blade and tell you even remotely how fast its going.

long story short... I remembered the little computer that I had as a youngster that would sit on the handlebars of my bike and tell me how fast I was going and (if I remember rightly) ppm's "peddles per minutes"
I doubt they would handle 3000 plus rpm's and I'd reckon it'd fly apart anyhow.. but it got me thinkin there must be something like this that one can retro fit to the final pulley or spindle of a machine and get an rpm readout.

or fit beside the pulley and have it read off a mark would make more sense.

am I dreaming?

or should I have knicked by the patents office before posting here

[watson]

The latest and the previous SILICON CHIP magazine have a project on a Tachometer that you might find fille your need.
www.siliconchip.com.au

Regards,
Noel

[bsrlee]

I'm pretty certain there are a few ready-built units around also - I'd say check at your local rev-head shop in the engine & tacho section.

Basically a strobe with a known frequency, when a mark on the rotating thingy stands still, you are at what-ever rpm.

[tashammer]

i seem to recall a little device that had a dial on it that was connected to a small shaft that terminated in a cone-shaped rubber bit. i was told that what one did was to hold the rubber piece against a shaft which would spin and the speed would be shown on the dial.

The device was purely mechanical, no electronics at all. Now it has been some years since i had the thing and i do not know if they are still made.

The device was old when i acquired it about 40 years ago off an old bloke who said you can have that if you want it. Me, being a typical bower bird, said yes, thanks very much.

To picture it, think of the letter q, with the rubber bit being at the end of the tail of the q.

[SawDustSniffer]

JayCar sell a hall effect sensor ZD-1902 for $4.95 http://www.jaycar.com.au/products_uploaded/ZD1902.pdf
in that pdf it will show you how to rig up a "notch sensor" then all you need is a good hz counter , cheap multimeters have them now
Qm-1535 for $29.95 from jaycar has a 0-20mhz with +- 0.05%
the hall effect sensor will only go to 23,000 Hz before it turns into a randem number generator ( not that bad )

needs a voltage regulator LM7805 with a few capacitors all under $5
http://jaycar.com.au/products_uploaded/LM7512C.pdf


so an old moble 6v powersuply ,a 7805 (+5v regulator ) , a hall effect sensor , some plugs so you can plug in your new multimeter and still use it as a mulitmeter for other things and you have your hz (not RPM , just devide by 60 )read out for $50 and a lot of stuffing around

hope i helped , if you dont have a soldering iron , i didn't

[Slow6]

The latest and the previous SILICON CHIP magazine have a project on a Tachometer that you might find fille your need.
www.siliconchip.com.au

Regards,
Noel

looked good, started reading an article about modifying a car tacho.. but had to subscribe to contine I reckon I've got the jist tho.. I'll see what I have left in the old holden pile. thanks Noel

I'm pretty certain there are a few ready-built units around also - I'd say check at your local rev-head shop in the engine & tacho section.

Basically a strobe with a known frequency, when a mark on the rotating thingy stands still, you are at what-ever rpm.

sounds like just the thing.. I'll pick the autopro blokes brains on monday. cheers bsr

i seem to recall a little device that had a dial on it that was connected to a small shaft that terminated in a cone-shaped rubber bit. i was told that what one did was to hold the rubber piece against a shaft which would spin and the speed would be shown on the dial.

The device was purely mechanical, no electronics at all. Now it has been some years since i had the thing and i do not know if they are still made.

The device was old when i acquired it about 40 years ago off an old bloke who said you can have that if you want it. Me, being a typical bower bird, said yes, thanks very much.

To picture it, think of the letter q, with the rubber bit being at the end of the tail of the q.

this is by far my favorite... I'm now destined to spend sunday trawling the bendigo swap meet asking people if the've seen a q with a rubber bit

[Slow6]

JayCar sell a hall effect sensor ZD-1902 for $4.95 http://www.jaycar.com.au/products_uploaded/ZD1902.pdf
in that pdf it will show you how to rig up a "notch sensor" then all you need is a good hz counter , cheap multimeters have them now
Qm-1535 for $29.95 from jaycar has a 0-20mhz with +- 0.05%
the hall effect sensor will only go to 23,000 RPM before it turns into a randem number generator ( not that bad )

needs a voltage regulator LM7805 with a few capacitors all under $5
http://jaycar.com.au/products_uploaded/LM7512C.pdf


so an old moble 6v powersuply ,a 7805 (+5v regulator ) , a hall effect sensor , some plugs so you can plug in your new multimeter and still use it as a mulitmeter for other things and you have your RPM read out for $50 and a lot of stuffing around

hope i helped , if you dont have a soldering iron , i didn't

good reading.. I do have a soldering iron... buuuuuuuuuut, I'm dangerouse with it. I reckon this would be a good one to take from machine to machine.
cheers sniffer

[Skew ChiDAMN!!]

Open the chuck jaws right up, then rest a chisel on top while the lathe's running. Divide the no. of clicks you hear per minute by four.

Actually, somewhere around here I've got some old ETI magazines with easy to make tacho's in 'em. From memory, one uses a magnet on the shaft, which actuates a reed-switch... well... that one's probably not a good idea for a lathe, but t'other counts light reflected from a white dot. Just a dab of paint on the shaft and aim the tacho like a timing gun.

I really should see if I can find 'em and do something similar for myself...

[SawDustSniffer]

hz is RPSeconds not RPMin sorry about that and you will also need a bridge rectifer , holds his head in shame

[SawDustSniffer]

set up a set of points with a load resistor the same as a coil and use a tacko , might stop at 10,000 rpm , well the neadlel would hit the post
and have to find one for a 2 stroke moter bike ,
sends him back out to his holden stock pile

[Slow6]

I really should see if I can find 'em and do something similar for myself...

if you do... would you be so kind as to throw a copy my way?

[joe greiner]

On my list of things to do is a tachometer based on a bicycle speedometer. Not even on paper yet, so YMMV.

Even bicycle speedometers are now computerized. Sensor detects a metal bit; mine would be a nail or such in a wooden wheel, such as a wooden handwheel on my lathe, or the workpiece itself. With some arithmetical legerdemain, I lie to the computer about tire/tyre diameter and radius to the metal bit, so that it reports rpm directly.

I also have the q-thingy. But it doesn't report rpm, just counts revolutions. The rubber tip is placed in the lathe center/centre (little V-shaped hole) of the shaft. Hold in contact for 6 seconds and remove. Multiply displayed number by 10 to get rpm. Hold in contact again, as long as needed, to wind it further for reset to zero. (Winding back by hand is a PITA.)

Joe

[tashammer]

...

I also have the q-thingy. But it doesn't report rpm, just counts revolutions. The rubber tip is placed in the lathe center/centre (little V-shaped hole) of the shaft. Hold in contact for 6 seconds and remove. Multiply displayed number by 10 to get rpm. Hold in contact again, as long as needed, to wind it further for reset to zero. (Winding back by hand is a PITA.)

Joe

Joe, is there a maker's name on the q-thingy? I wonder what it's real name is?

Tom

[marker]

Jaycar list a optical digital tacho for $69.95 that reads from 2.5 to 99,999 RPM.That should cover most speeds.
Mark

http://www.jaycar.com.au/productView...Max=&SUBCATID=

[Cliff Rogers]

G'day Slow.

I dicked around with this a while back, bought & built a car tacho kit, set up a wheel with 4 holes (4 cylinder car setting) & a light source & sensor, got it all working after a couple of weekends of dicking around, played with it for a while & found that I totally ignored it anyway.
My big variable speed Vicmarc lathe has a digital readout on it & I never look at it either.

Interesting aside to the hobby but of very little use in my opinion.