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View Full Version : Digital photo tachometer info wanted.



Your Old Dog
01-27-2008, 11:59 AM
I'd like to have a tachometer in the shop. Anyone know if this thing looks promissing as a simple means of confirming speed of lathe, mill, dp and belt grinders?

John Stevenson
01-27-2008, 12:09 PM
Don't look promising to me.

.

Lew Hartswick
01-27-2008, 12:14 PM
I don't see what you are referring to?
For many years I used a "Strobatack" (sp?) to measure rotation
speeds. They take a little care in using but are good. Don't know if
they even still exist but bear consideration.
...lew...

Deja Vu
01-27-2008, 01:36 PM
I'd like to have a tachometer in the shop. Anyone know if this thing looks promissing as a simple means of confirming speed of lathe, mill, dp and belt grinders?
I don't know about your thing, but I got one of these off ebay ($20 to $30) plus shipping..... I'm happy with it.

The small picture is the one I got...sturdy case for long-term nonuse :)
http://www.freewebs.com/jmnotions2/FWThumbnails/Tachometer-thumb.png

http://www.freewebs.com/jmnotions2/prm2.jpg

tony ennis
01-27-2008, 01:44 PM
I'm making one for my lathe. I'm using a vintage analog amp-meter so it fits in with my vintage lathe :cool:

jcarter
01-27-2008, 01:46 PM
I picked up two from Princess Auto. I think they were around $60 each. I don't use them very often but they sure are handy for verifying RPM. I have used them on the lathe and mill but I got them primarily for checking rpm on diesel engines. Kinda hard to use an inductive type tach on a diesel.

SGW
01-27-2008, 02:15 PM
If you're in a do-it-yourself mood, this page http://www.jeffree.co.uk/pages/speedmeasurement.html has some good ideas for home-brew tachometers.

dp
01-27-2008, 02:15 PM
http://bbs.homeshopmachinist.net/showthread.php?p=292238

He's selling on Ebay and has actually referenced this thread. I'm still very happy with the meter and have no qualms recommending him.

Evan
01-27-2008, 02:28 PM
Here is a sneak preview;

This is how I measured the rpm of my new high speed spindle. I'll be posting more in a new thread later.

First is a simple IR phototransistor mounted next to the spindle with a regular incandescent bulb shining on the reflective metal. Half the spindle diameter is covered with black electrical tape.

http://vts.bc.ca/pics3/hsstest1.jpg

That's the cheap part. :)

The other part is a frequency counter.

http://vts.bc.ca/pics3/hsstest2.jpg

That is the reading in revolutions per SECOND. :D

dp
01-27-2008, 02:56 PM
I did the exact same except used a rare earth magnet and a bobbin of wire I wound. My freq meter is lab quality and was picking up 60hz from the bobbin, of course as there's so much of it around the shop, so I clamped the coil with back to back diodes and removed most of the windings. The resulting near square wave worked out fine and it was quite accurate. What it lacked was portability. The intention at the time was to build it into the system permanently, and I bought a small 4-digit tach just for the purpose, but the portable has proved so handy that I dropped the home brew project.

tony ennis
01-27-2008, 04:56 PM
I'm going to use a Hall effect sensor, a rare-earth magnet, and add a thin ferrous toothed gear to the spindle. The gear doesn't engage anything - its purpose is to focus the magnet's field on its points so the Hall sensor can pick it up easier. The more revolutions, the more current measured by the sensor. This is then fed to the amp-meter (ammeter?)

The devil is in the details of course.

halac
01-27-2008, 06:18 PM
Here's a couple I've had the opportunity to calibrate.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41727

http://www.extech.com/instrument/products/451_499/461895.html

http://www.extech.com/instrument/products/451_499/461825.html

For inexpensive units, they should be able to give you a better than 0.5% accuracy.

Doc Nickel
01-27-2008, 08:18 PM
I've got this unit I picked up out of a junque shoppe for $8:

http://www.docsmachine.com/nonPB/tach1.jpg

Press the button and one "barrel" lights up like a flashlight, the other holds a photodetector. You need a reflector, and the unit was originally sold with a packet of stick-on dots, but naturally they weren't included- this thing's gotta be 30 to 40 years old. It uses a 3" long 6v battery for pete's sake.

Anyway, that parts easy- $1.95 for a reflective stick-on house or mailbox letter at Home Depot and a plain stationery type hole punch, and you have all the stick-on dots you need.

http://www.docsmachine.com/nonPB/tach4.jpg

You calibrate it by pointing it at a fluorescent light and adjusting the needle to 7200. After that, it's seemed dead on. Works fine, and it's already proven very handy- instead of making a bunch of calculations between the motor and two jackshafts for a bandsaw, I just read the saw tire wheel speed directly, and worked out the SFM from there.

Doc.

Your Old Dog
01-27-2008, 09:29 PM
I don't know about your thing, but I got one of these off ebay ($20 to $30) plus shipping..... I'm happy with it.

The small picture is the one I got...sturdy case for long-term nonuse :)
http://www.freewebs.com/jmnotions2/FWThumbnails/Tachometer-thumb.png

http://www.freewebs.com/jmnotions2/prm2.jpg

Thanks Deja Vue, that's the one I meant to post but didn't. Sorry I didn't get back sooner.

Deja Vu
01-28-2008, 08:37 AM
You're welcome...
I'd like to have one that has the "contact" feature incorporated as you often can measure without the little reflective tapes to attach.

As it is now, after running around and finding all the turning objects on the premises to stick and measure:) , I've settled to checking the lathe chuck and the variable speed makita router on my homemade table machine. I've got a QC tool holder that protrudes farther than desired and too high a speed introduces vibrations or can loosen the tool from centrifugal forces on the retaining spring:eek: .

John Meissner

Evan
01-28-2008, 09:13 AM
Here is another I use from time to time. It's quite accurate and is somewhat unusual as it goes to 12,000 rpm.

http://vts.bc.ca/pics/tach1.jpg


This is another. The unit is my design built with TTL logic originally used for an anemometer I made. It's adjustable enough to use on just about anything that makes pulses and should be able to count up to a few million rpm. :D

It's shown connected to an encoder on the end of the motor I use on the mill. The RPM reading is X 10.

http://vts.bc.ca/pics/rpm2.jpg

aboard_epsilon
01-28-2008, 10:42 AM
here's my old mechanical one
bought off ebay about 2 years ago ..
think it was about 15

http://img.photobucket.com/albums/v190/aboard_epsilon/rev1.jpg

http://img.photobucket.com/albums/v190/aboard_epsilon/rev2.jpg

all the best.markj

Your Old Dog
01-28-2008, 10:54 AM
Evan, as we're reading 'revolutions per MINUTE", does this device require using a watch also or does it use a magnet inside and then calibrate the rms value to the speed?
http://vts.bc.ca/pics/tach1.jpg

Evan
01-28-2008, 11:03 AM
??

I'm not quite following you. The frequency counter readout is simply RPS. So, multiply times 60 and you get 26,280 rpm. No watch required.

The Jones-Motrola mechanical tach has three scales. you engage them by sliding the input shaft to one of three positions and lock it there with the small knob on the side of the shaft. Inside is a geared down three arm flyweight device that is spring loaded. It drives the indicator. It's generally accurate to within a few percent. You apply the end of the shaft with a suitable adapter attached to directly read the rpm. The wheel has a circumference of exactly one foot so if held against something rotating it reads in surface feet per minute directly.

Your Old Dog
01-29-2008, 07:33 AM
UPDATE: I'm now the owner, proud or otherwise, of a Shimpo DT-107. Looks like it reads it all without calculations being necessary. Won't get here till a few days.

Evan, thanks for the explanation. I knew the frequency counter is a clock but it was the mechanical one I couldn't figure out. I thought it relied on the rotating movement of a magnet moving through a coil and displayed with analog type meter. I didn't realize they three fixed geared systems in one device.