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GJLawlor
02-01-2003, 10:08 AM
Any one out there know if tachometer kits are available from a supplier in Canada? Thanks


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George L

wierdscience
02-01-2003, 11:48 AM
Don;t know about Canada but have you checked out usdigital.com?

Thrud
02-01-2003, 08:01 PM
George

You talking about your VFD? Does it have a tach input? I can program mine to display proper rpm based on the VFD output.

You can build one yourself - just need an DAC and phototransistor input. Check your local Active components store - they may have kits for a tach, or you can buy cheap ones at Canadian tire and just roll your own.

GJLawlor
02-02-2003, 09:04 AM
<font face="Verdana, Arial" size="2">Originally posted by Thrud:
George

You talking about your VFD? Does it have a tach input? I can program mine to display proper rpm based on the VFD output.

You can build one yourself - just need an DAC and phototransistor input. Check your local Active components store - they may have kits for a tach, or you can buy cheap ones at Canadian tire and just roll your own.</font>

Hi Thrud: I looked at the CTC and Princess Auto tachometers and I may end up with one of those. I really want a digital one though. Next chance I get to visit the local Radio Shack store I'll look there too. Thanks

PS Yes the VFD is programmed to read rpm for the lathe but, since I will be running either the lathe or the mill I will need a tachometer for one of them or I shall have to re-enter the parameter each time I change machines.

[This message has been edited by GJLawlor (edited 02-02-2003).]

[This message has been edited by GJLawlor (edited 02-02-2003).]

[This message has been edited by GJLawlor (edited 02-02-2003).]

Herb Helbig
02-02-2003, 02:05 PM
Don't know how many would want to go to this much trouble, but here's what I did to measure the rpm of my mill/drill spindle. Put a T-shaped piece like a lathe chuck wrench in the mill collet. Put a small magnet on one end of the T. Place a coil of fine magnet wire near the end of the T so the magnet passes it at each revolution. Attach the ends of the magnet wire to the mike input of the computer sound card. Use the sound recorder software under utilities/multimedia in the programs directory to record the resulting signal. Use the AudioView software to display the waveform and count how many peaks occur per second. For more accuracy, run the digitized wave data through a fast Fourier transform (Excel has one). I found all this software (except Excel) on my computer as it was delivered. The Sound Blaster audio card that came with the computer has an analog to digital (A/D) converter (at the end of the mic input) that handles up to 40 KhZ (and down to DC). The signal from the magnet/coil detector is not likely to overload the A/D, but start with the volume controls turned way down.

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GJLawlor
02-02-2003, 03:22 PM
Herb that is absolutely ingenious. What a marvelously inventive approach. I have all the stuff to do this with but I will still try for an inexpensive digital tachometer. Thanks

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George L

docsteve66
02-03-2003, 02:04 PM
Please, why is a digital tach needed? How accuartely do you need to know RPM or what ever with a VFD?
Steve

GJLawlor
02-03-2003, 04:12 PM
<font face="Verdana, Arial" size="2">Originally posted by docsteve66:
Please, why is a digital tach needed? How accuartely do you need to know RPM or what ever with a VFD?
Steve</font>


Good Question Steve. I wish to know the spindle RPM to be able to calculate the cutting rate in Feet Per Minute based on the size of the work piece or the cutting tool. Good CNC machines and software use RPM data accurate to 1 or 2 RPM to control feed and / or RPM to give good tool life and fast performance and a good finish.

George

Al Messer
02-03-2003, 05:20 PM
Glad my machines are obselete like me---all I gotta do is check the belt positions on the pulleys and I can quickly look at the chart and tell what rpm I'm turning.

Tadd
02-03-2003, 07:47 PM
Hi, Just read the above and the timing was perfect. I just installed an older AB (Bulletin 1333) VFD on my lathe and am now thinking about adding some of the bells and whistles it came with. The manual says I can add a 0 to 1ma "frequency meter" to the drive to read speed. What is this meter and where might I find one? Are they talking about an analog meter like in a older voltage meter? Can the signal be used to drive a digital meter? Not being an old timer at this, I turn to the experiance on the board for help and I am never disapointed.

darryl
02-04-2003, 03:12 AM
Tadd, a 0 to 1 ma meter is just a device that reads current, in this case, l ma, or .001 ampere. It's being called a frequency meter in your case because your vfd has an output to the meter that corresponds frequency (rpm) to a level of current, 1 ma, at full needle deflection, where I assume is at maximum rpm. Any analog meter will work for this if it has a range where 1 ma can be read on one of it's scales. It doesn't matter if the scale is, say, 10 ma, just assume full rpm is read at the 1 ma mark on the scale. A digital meter may or may not give a proper reading because it doesn't necessarily interpret the input signal from the vfd properly. Get a cheap analog meter with a 1 or a 2 ma range, it will do the job fine.

Thrud
02-04-2003, 03:38 AM
George

Once you get use to using it, you will not need the readout (unless curious). I adjust purely by cutting performance pushing the tools as far as I can without ruining the carbide.

Tadd
02-04-2003, 09:22 AM
Thanks, Thats kind of what I thought the manual was talking about. Get the meter out of a $10.00 Radio Shaft meter and use it for freq/speed meter. Your right Thrud, so often I install the bells and whistles and end up not using them because the "feel" method seems to work better.

[This message has been edited by Tadd (edited 02-04-2003).]

GJLawlor
02-04-2003, 10:21 AM
<font face="Verdana, Arial" size="2">Originally posted by Thrud:
George

Once you get use to using it, you will not need the readout (unless curious). I adjust purely by cutting performance pushing the tools as far as I can without ruining the carbide.</font>

Thrud I don't have the touch that some of you guys who wave been machining for , shall we say extended periods of time, do. Ever watch a TIG artist at work laying down a beautiful almost flat bead that fills the weldment gap? I can TIG weld but it sure don't look like that. And you are quite right about feed rates that may be pushed to escessive limits. Some of the books say, and my experience confirms this, that the single biggest mistake beginners make is that they are too timid about feed rates and cutting speeds. Since I'v made some improvements to my Grizzly it seems that the finish of the cut is definitely better at higher speeds and feed rates. So with th Tachometer I guess I am trying to assist my lack of experiende and ability with better data.

George

GJLawlor
02-04-2003, 10:36 AM
<font face="Verdana, Arial" size="2">Originally posted by darryl:
Tadd, a 0 to 1 ma meter is just a device that reads current, in this case, l ma, or .001 ampere. It's being called a frequency meter in your case because your vfd has an output to the meter that corresponds frequency (rpm) to a level of current, 1 ma, at full needle deflection, where I assume is at maximum rpm. Any analog meter will work for this if it has a range where 1 ma can be read on one of it's scales. It doesn't matter if the scale is, say, 10 ma, just assume full rpm is read at the 1 ma mark on the scale. A digital meter may or may not give a proper reading because it doesn't necessarily interpret the input signal from the vfd properly. Get a cheap analog meter with a 1 or a 2 ma range, it will do the job fine.</font>


Darryl's right on the money. On the face of the meter there will be some fine printing saying something like 'x number of ohms per volt' or 'x number of volts per milliamp' or something that tells one what is required to give a full scale deflection on the meter. You want to know that so as to avoid overloadng the meter. Use a digital volt meter and check (between VFD ground and the output)what that special output on your VFD does as you vary the speed. If the readings look strange put a 10,000 ohm (10 k ohm) accross the output and ground and then put the meter across the resister. Of course if you have an oscilloscope use it. (boy I sure could use a spell checker here) Good luck, let us know how you make out.
George.

mbensema
02-04-2003, 03:28 PM
Any testing you do with a voltmeter needs to be done relative to the control common, not the VFD ground. Look in the control diagram and see what terminals are used for the meter, that is where you would check your output. If your meter cannot read milliamps, you can add the resistor as George mentioned and calculate the current.

Many VFDs have an adjustable output, so you can change the scale to suit your meter. You can also select what you want the output to be, frequency, current, etc. Not all of the smaller drives have this option, but some do.

Mike

docsteve66
02-04-2003, 07:21 PM
REason I asked about how accurate you need the RPM: Take most any dc motor (with PM) and couple it to your shaft and put that 1Ma dc meter with and appropriate resiistor (or varible resistor) in series and you have apretty accurate RPM meter. At zero rpm it wil read 0 volts. at say 3600 rpm (an unloaded induction motor) or 1800 rpm (an unloaded 1725 induction motor) gives you two point on a straight line. The rest is easy
Steve'

GJLawlor
02-04-2003, 08:05 PM
Hi Steve: So we use the permanent magnet DC motor as a generator of RPM data to drive an analogue meter. It should be revatively easy to calibrate and be pretty reliable. I have to try this, it should work well to drive a digital display too. Thanks for the great idea steve.

darryl
02-06-2003, 04:48 AM
The dc motor idea is reasonable. It could be almost any small motor, a kid's toy motor would be good, or a cd player motor. The brushes wouldn't be carrying any current to speak of, so they will last a long time, and if they start to go bad, you'll see a rapid fluctuation in the rpm reading, which you know isn't happening by the sound of your machine running. Replace the little motor at this point. The challenge for some of you will be working with something that small. Anything bigger, like a windshield wiper motor, will be major overkill to drive a meter movement, but will work fine also. Set your voltmeter to any dc voltage range that puts your rpm readings somewhere near half deflection, and it'll be easy to read. Any of those little motors will be happy to spin at whatever speed your lathe or mill can do. Range switching on the voltmeter will allow you to read from very low speeds to router speeds. Just don't use a larger motor for the sensor if your speeds are more than, say, 5000 rpm. Cheap cd player motors will handle 20-30,000 rpm, and put out 30 or so volts doing that. ( I had one running on 80 volts, and it just screamed, it was literally doing 100,000 rpm, but then it blew. I guess that was a bit much.) At very low speeds, you'll have some needle fluctuation, but the average position of the needle will be accurate. You'll have to find some means to calibrate the setup.

asallwey
02-06-2003, 09:00 AM
[B]Any one out there know if tachometer kits are available from a supplier in Canada?

George, if you are still interested in the original topic, check out this site: http://www.seanet.com/~dmauch/ His tach kits are from $35-$47, easy to put together, work, and don't cost an aim & a leg. Not quite Canada, but from my Virginia perspective, Washington is close (hee hee).
I have one and am finally mounting it now.

Alex

SGW
12-23-2003, 05:39 PM
Tony Jeffree at http://www.jeffree.co.uk/Pages/speedmeasurement.html has a whole bunch of ideas for measuring rpm.

I just tried his strobe disk approach to calibrate the rpm readout on my VFD. The spindle rpm isn't *exactly* linear with Hz -- probably motor slip, or belt slip -- but it's pretty close. 400 rpm (measured by strobe disk) reads out as 403, while 1200 rpm (measured by strobe disk) reads out as 1195.
Close enough.

BillH
12-23-2003, 05:54 PM
www.littlemachineshop.com (http://www.littlemachineshop.com)

I think they sell a Tachometer kit, like the one used on my 7x14 lathe. Truth is that I dont need it, I adjust speed based on how it sounds and if it chatters or not. Seams more like a gimmick than an essential tool.
Anyhow, it works by sensing a magnet on the spindle somewhere, counts revs.

IOWOLF
12-23-2003, 06:15 PM
I have a tach . from my r/c aircraft days, It is a digitach has a switch to go from 2 to 3 blade prop. works great with a 3 jaw chuck in 3 blade pos. and for a 4 jaw divide X 2, simple yet efective. as i recall it was $20 or so at hobby lobby.