Stroboscopic tachometer app for iPhones - great for finding RPM’s of your spindle

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Jennifer Edwards

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There is a nice free tachometer application available at the iPhone “AppStore” that uses the camera flash on your phone as the strobe.

It is accurate to within .001 percent. To find it just search the AppStore for "tachometer". There are two applications returned from the search, choose the one labeled: "Strobe Tachometer (RPM Meter)"

it is pretty slick, just dial in the RPM you want, push the button, and your camera flash LED will flash at that exact rythm.
Point the strobe at the tool in your mill, or at the chuck in your lathe, and simply adjust the speed of your machine until the object freeses. At that point you have matched that RPM exactly.

I do not have s built in tachometer in either my lathe or mill. This app is s lifesaver for calculating Surface Speeds of your tooling in the case of a mill or material speed in Meters per second on your lathe.

If you use it with the link below you are almost guaranteed the best finish possible for any material.

Meters per second to RPM calculations:
https://www.peter.com.au/metalwork/turning-finish.html

The strobe app is free with some occasional annoying adverts, but for a couple quid you can purchase the full app.

Have fun!
Jenny
 
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Pauldg

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Thanks Jennifer, is there an equivalent Android version that you're aware off?
 

Jennifer Edwards

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Paul,

None that I am aware of, but it would stand to reason, that the Android O/S being in use by ten times more users than apple there would be. I believe there is some parody of Apple's "App Store" available to Android users, I would search there.

sorry I cannot be of more help
Jenny
 

Pauldg

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Thanks Jenny, I'll do some research and post it here for others to use. I think it's a great tool to have if you're starting with CNC.
 

XD351

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I downloaded two of them and both work really well , the one Jennifer recommended has a few more bells and whistles like the ability to use an external torch a camera and a few other things .
Thanks Jennifer ! I would have never even thought about using my phone as a tacho if you didn’t bring it to our attention ! There is even an app to turn your phone into a dro using Bluetooth measuring devices . I am now interested in testing the accuracy against my laser tacho and hall efect tacho .you could make a nifty looking tacho with an old iPhone and a xenon strobe .
 

Jennifer Edwards

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What I did with the strobe was started at 100 rpm, and made a mark on the speed control dial on my machines every 100 rpm up to their max of 2500. This way I only had to use the strobe one time for each machine.

Since I posted this thread I have been working on an Arduino application that plugs into the RPM ports on my Axminster SC2 and SX2 lathe and millimg machine.

I have the code complete, and have tested the hardware interface. I am awaiting delivery of the housings for the LCD displays. When they get here i will post a new thread showing how to make one and the code that goes with it.

All said the Arduino board, LCD, jumpers, conector, arduino housings, and LCD housings i came to less than £22 for each one. A heck of a lot better than the £150 that Axmister wants for the same thing. You just plug it into the port marked RPM and thats that. The RPM port on the machines provide the signal from the logic section of the speed controller as well as the 5v DC power for the Arduino board.so no external power source is needed.

It should work with any Sieg SC2 lathe and SX2 milling machines.
 

goldstar31

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Hopefully, I shall take delivery of my repaired SiegC4 milling attachment today.
On the delivery note from Axminster it suggests that a new motor from a X1 mill is the driving force.
I had so little use with it earlier to realise that there was no tach on the mill part.

I now have got interested . I presume 'What FitzWilliam, FitzHerbert!' so Thank you.

Norm
 

XD351

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Sounds like it is using the frequency of the driver for the motor to give an an approximate of the rpm , better to use a stand alone unit with a hall effect sensor and an arduino / lcd combo as this will give a real time readout - i usually use one of the cheap units i purchased off ebay as the tachoand led display are conveniently packaged as one unit and they come with a nice sensor . I used an arduino and rotary encoder to make a power feed display for the z axis on my mill ( stefan gotteswinter on youtube inspired this ) and it works nicely .
 

Jennifer Edwards

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Sounds like it is using the frequency of the driver for the motor to give an an approximate of the rpm , better to use a stand alone unit with a hall effect sensor and an arduino / lcd combo as this will give a real time readout - i usually use one of the cheap units i purchased off ebay as the tachoand led display are conveniently packaged as one unit and they come with a nice sensor . I used an arduino and rotary encoder to make a power feed display for the z axis on my mill ( stefan gotteswinter on youtube inspired this ) and it works nicely .
That’s a possibility. I’m really not sure what the origin of the binary signal that the controller is sending is.

It is sending a 39 bit header and simple binary numbers for the thousands, hundreds, and tens.

The ones column is always zero, so it cannot be more accurate than +- 10 hz. I will test it against the strobe which has an accuracy of .001% and let you know.
 

Jennifer Edwards

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Hi Again XD351,

OK i just played around with my Arduino app Vs. the strobe of known accuracy, here is what I found.

It is suprisingly accurate. I tested on my SX2 Mill, which has the identical mtor and controller as the SC2 lathe. It took a litte fiddling with the speed control knob to get small incerments in rpm's i needed but after a while minutes I was able to determine this:

It is suprisingly accurate, at exactly 500 rpm (as measured by strobe of known accuracy) the displayed speed was spot on. the display is indeed rounding the ones column at 496 - 505 rpm it displayed 500, from 506 to 514 rpm it rounded to 510 & etc... So the maximum error in the Arduino app's dispayed RPM is +/- 5

So I must assume that the speed controller board has a somwhat accurate clock for a timebase and may be getting feedback from the motor of some type to be as accurate as it is.

I tried to test under load, but found I would need an extra couple of hands to operate the mill and the strobe at the same time. My attempt was actualy quite entertaining,

As a hobby model engineer, using the relatively small diameters that I do, an RPM variance of +/- 5 rpm is plenty accurate for me. I could understand the large diameter pieces and cutters used in industry requiring greater accuracy, for exmple: a five foot diameter bearing race being turned would have quite a large circumfrence, a one rpm difference would mean 15.7 surface feet per minute difference. At the small diameters we typically work a five rpm difference in surface FPM is neglidgible.
 
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XD351

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Hi Jennifer ,
I tested the strobe on my engraver spindle and had no problem setting the rpm to what i wanted , i settled on 3600 rpm because that was what the strobe was set for at the time and found that with a little patience i could get very close with the speed pot then adjust the strobe to get it spot on so it is also capable at higher rpm and would be ideal for setting the idle speed on a model engine .
If you set the speed on your mill using the onboard tacho does the readout change when you take a cut ? If it does track the actual engine rpm it must be sensing either the output of an encoder or back emf pulses, maybe these pulses are being used to tune the internal clock or something .
 

goldstar31

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The Mill attachment has been delivered and bolted down and the wheels actually turn now.
Thanks to Jennifer, I'm ready to see if my IPhone will work on it.

I also have a RPM counter for diesel engines but it really is too bulky in such a small footprint and have put it back on my mill drill

Thanks

Norm
 

Jennifer Edwards

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What happens when I pace aload on the spimdle of the mill or lathe, is there is a momentary small dip in rpm's, then the controller increases torque to compensate, in about one second even less it is up to speed again. The Sieg people use a pretty smart controller.

There is also a ton of other data being sent out of the boards interface, but I have not yet tried to pick it apart. I have a datascope and a logic analyzer, if I ever get the time or inclination i may try to understand what that other thirty some bits contain.

I think it actually works the other way: the clock is constant, and if the spinde speed varies from where it is "set" by the speed pot it increases or decreases the currents freq until the spindle speed once again is where it "should" be against the constant of its clocking chip.

I bet something like a simple 555 chip is what they use as a clock, it is certainly cheap enough, you can get a dozen on amazon for like two quid.

I am glad someone made use of my post. have a good time with the strobe, they are all kinds of fun.
 
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GregNixon

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That's very useful information. I have never known the speed of the C1 minilathe or the X2 mill. Now I will be able to "calibrate the knob". Many thanks
 

Jennifer Edwards

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That's very useful information. I have never known the speed of the C1 minilathe or the X2 mill. Now I will be able to "calibrate the knob". Many thanks
I am glad I can help. It makes a difference when you know the surface speed of the material you are cutting.

You would be really surprised at how many people run their machines far too fast for the material they are working.
 

gunner312

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There is a nice free tachometer application available at the iPhone “AppStore” that uses the camera flash on your phone as the strobe.

It is accurate to within .001 percent. To find it just search the AppStore for "tachometer". There are two applications returned from the search, choose the one labeled: "Strobe Tachometer (RPM Meter)"

it is pretty slick, just dial in the RPM you want, push the button, and your camera flash LED will flash at that exact rythm.
Point the strobe at the tool in your mill, or at the chuck in your lathe, and simply adjust the speed of your machine until the object freeses. At that point you have matched that RPM exactly.

I do not have s built in tachometer in either my lathe or mill. This app is s lifesaver for calculating Surface Speeds of your tooling in the case of a mill or material speed in Meters per second on your lathe.

If you use it with the link below you are almost guaranteed the best finish possible for any material.

Meters per second to RPM calculations:
https://www.peter.com.au/metalwork/turning-finish.html

The strobe app is free with some occasional annoying adverts, but for a couple quid you can purchase the full app.

Have fun!
Jenny
Just found one on my phone for Android, cost 3.50 but works well.
 

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