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Understanding the Rivett 1020/1030 Tachometer

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Aug 10, 2007
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I don't think this is specific to the F model, although the S models are slightly less RPM on the top end, someone with an S might be able to chime in and say if they have the same generator or not. I suspect the generator is the same.

The drive shaft of the Rivett has a Servo-Tek DC voltage generator, it generates 7 volts DC for every 1000 RPM.

A pin resides in the center of the drive shaft which couples to the pin of the DC generator, and the original design is to use a plastic/rubber tube to couple the drive shaft and generator. As it turns out, the Servo-Tek DC generator was commonly used and you can get them NOS on ebay, here's a pic of one that is for sale for $99.99.

ebay-servo-tek.jpg

Now to understand why my tachometer doesn't work. I was pointed to a video on YouTube that James Kilroy had done when he fixed his Rivett tachometer, and this put me on the right path to understanding why mine didn't work, which was different than James' machine.

First a picture of the generator in the adapter that secures at the end of the drive shaft. Next to it you can see the pin with the tube attached, and the other end of the tube goes to the generator pin. The large diameter secures to the drive shaft with 3 allen head screws.

rivett-servo-tek-generator-plastic-coupling-pin.jpg

The pin is supposed to be in the center of the drive shaft, but when I took mine off, this is what I saw...someone had tried to use epoxy to secure the broken pin to the drive shaft. I'm giving them some credit, it actually looks like brown woodworking glue, but I'm no expert on glues, so I'm going to say it's "epoxy". :rolleyes5: You can see the 3 holes which the adapter secures to, and you can barely see the 3 belts on the drive shaft, this is at the bottom of the lathe inside the left opening.

rivett-drive-shaft-previous-fix.jpg

I knocked that goober off there with a cold chisel, it took enough force that a 3 year old could have hit it off there. As you can see there's a castle/slotted nut that is turned backwards, with some type of slotted plate that keeps it from spinning off. They didn't seem to use a cotter pin, which is how a castle/slotted nut would be secure today. I thought of thinning out or using a fabricated nut that has a flat surface on the outside with a pin in the center. But first I want to see if I can use a left handed bit and try to get the center of the drive shaft clear. If so, I can just fabricate a pin and get it in there. I will create a metal coupling with set screws similar to how James Kilroy did for his lathe, his was merely breaking the tube, and he mentioned it was the 3 time trying to fix it. However I do this, I need to get the pin on the end of the drive shaft and be secure to provide an accurate reading.

rivett-drive-shaft-without-fix.jpg

Now, I wanted to wrap this up and explain how this work, because they make these Servo-Tek DC generators in various voltages per 1000 revolution. There's one that is 2.65, and if you multiply by 4, a 0-10 volt milliampere/voltmeter would provide the appropriate voltage on the drive shaft. In the case of the Rivett OEM 7 volts per 1000 revolutions, they used a 0-28 volt gauge to handle 4000 rpm on the face plate, but using a 0-30 will only be off by one line on the scale, and it should be able to adjust that out with the adjustment screw on the front.

My gauge was completely broken and now I'm sure that is because someone thought the problem was in the tach, as I had once thought, and trying to fix it probably broke it. I was never able to get the needle to move at all. John Wolfe also gave up trying to fix it, and he specializes in vintage gauges.

This is the meter I just bought, it actually has a 4-1/4" round back that fits in the same tach hole on the Rivett. I will use my original face plate and front bezel. with this gauge. Understanding how the system work helps a great deal, it's merely a DC milliampere/voltage gauge. :)

westinghouse-milliampere-gauge.jpg

Now, let's say you replaced your Servo-Tek with a 2.65v per 1000 RPMs, in that case a 0-10 would work. They also make a 20.8 per 1000 RPMs, and for that a 0-80 volt DC milliampere/voltmeter would work with it. If you look on ebay, there are many of them. This is a pretty common part, and although the company exist, it's not clear if they make them still. There are many on ebay.

The common failure is the coupling tube getting brittle, cracking and breaking off off. A metal coupling bushing with set screws will take care of that.
 
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although the company exist, it's not clear if they make them still.

The new ones are similar - some may need an SKU cross-reference lookup and/or go to a smaller physical size is all. Their data sheets help explain that.

Several types of couplings are in the Servo-Tek catalogs and brochures as well - also new, not used.
 
Thanks for this, I have an F model and just assumed the Generator was a small synchronous motor.


quasi,

Have you seen this video that Robin Renzetti on his solid toolpost ? I've been pondering making one for the Rivett. I remember that you don't have the original compound, but this could really make sense on the Rivett.

 
Now, I wanted to wrap this up and explain how this work, because they make these Servo-Tek DC generators in various voltages per 1000 revolution. There's one that is 2.65, and if you multiply by 4, a 0-10 volt milliampere/voltmeter would provide the appropriate voltage on the drive shaft. In the case of the Rivett OEM 7 volts per 1000 revolutions, they used a 0-28 volt gauge to handle 4000 rpm on the face plate, but using a 0-30 will only be off by one line on the scale, and it should be able to adjust that out with the adjustment screw on the front.

My gauge was completely broken and now I'm sure that is because someone thought the problem was in the tach, as I had once thought, and trying to fix it probably broke it. I was never able to get the needle to move at all. John Wolfe also gave up trying to fix it, and he specializes in vintage gauges.

This is the meter I just bought, it actually has a 4-1/4" round back that fits in the same tach hole on the Rivett. I will use my original face plate and front bezel. with this gauge. Understanding how the system work helps a great deal, it's merely a DC milliampere/voltage gauge. :)

View attachment 200829

Now, let's say you replaced your Servo-Tek with a 2.65v per 1000 RPMs, in that case a 0-10 would work. They also make a 20.8 per 1000 RPMs, and for that a 0-80 volt DC milliampere/voltmeter would work with it. If you look on ebay, there are many of them. This is a pretty common part, and although the company exist, it's not clear if they make them still. There are many on ebay.

The common failure is the coupling tube getting brittle, cracking and breaking off off. A metal coupling bushing with set screws will take care of that.

Just to pick a nit, the picture of the meter is labeled "Westinghouse". That looks like a Simpson meter. It is made to use with a shunt and the meter actually measures a much smaller current. Chances are that it will be only a few milliamperes. You can add a resistor to make it read any voltage. For a 1 milliampere full scale meter, use 1000 ohms for each volt. For a 2 milliampere meter, use 500 ohms/volt, etc. There will also be an internal resistor used to calibrate the meter to 50 or 100 mullivolts full scale. Shunts in that era were usually trimmed to 50 millivolts voltage drop at the rated current

Bill
 
Just to pick a nit, the picture of the meter is labeled "Westinghouse". That looks like a Simpson meter. It is made to use with a shunt and the meter actually measures a much smaller current. Chances are that it will be only a few milliamperes. You can add a resistor to make it read any voltage. For a 1 milliampere full scale meter, use 1000 ohms for each volt. For a 2 milliampere meter, use 500 ohms/volt, etc. There will also be an internal resistor used to calibrate the meter to 50 or 100 mullivolts full scale. Shunts in that era were usually trimmed to 50 millivolts voltage drop at the rated current

Bill,

I believe the gauge is a Westinghouse. My original is also. I do have the resistor from the original I could use if I need, but I will first measure the DC voltage I get after I repair the drive shaft pin, and see if the gauge matches up.

Isn't a milliampere always 1 volt ? 50 milliamperes is 1/20th of a volt. I could live with that...

I've seen some gauges that had multiple scales on them, but in most cases the lower voltage was recognized. As an example, 0-6 volts and 0-30 volts on the same gauge...maybe what you say would be correct for that type of gauge ? I have another smaller Westinghouse gauge that looks exactly like mine, with the exception that it is a 3.5" gauge rather than 4.25". I could adapt it to my lathe I believe, if needed. The one above should fit into the original case and use the original face plate.

This gauge above is in shipping, I'll know better when I get it. I should be able to connect a DC battery and read the voltage.

Cheers,
Alan
 
The meter is almost certainly 50 mv full scale. Even a AA cell will slam it. You need to establish the full scale current required, then pick a resistor to pass that current at the max voltage. Good old Ohm's law, voltage/current=resistance. Normally a meter will have something like 50 mv fs on the dial at the bottom. Looking at the picture again, I see Westinghouse at the top of the scale. There may be a resistor or shunt inside, but not likely a 30 amp shunt. You won't know until you get it.

Bill
 
The meter is almost certainly 50 mv full scale. Even a AA cell will slam it. You need to establish the full scale current required, then pick a resistor to pass that current at the max voltage. Good old Ohm's law, voltage/current=resistance. Normally a meter will have something like 50 mv fs on the dial at the bottom. Looking at the picture again, I see Westinghouse at the top of the scale. There may be a resistor or shunt inside, but not likely a 30 amp shunt. You won't know until you get it.

Bill, the one that is on it now which is temporary is FS = 10 volt, so a 2.65 / 1000 generator would work with it. That is not my original meter. But it is accurate for volts. The original says 0 - 28 volts on the face plate. The one above is 0 - 30 volts.

As I said, I'll see when it gets here. If I connect a battery and it does as you suggest, I 'spose you're right. I need to see that to believe it however. A volt is a volt, no matter how you slice and dice it. If the meter can't measure volts, I'd say it's no good for a voltmeter.

This was common for airplanes it seems that a DC generator was used on the prop or engine to measure RPMs. In fact, they used similar Servo-Tek DC generators, AFAICT.

EDIT: I just took 2 x 1.5v "new" Duracell AA batteries. I have 2 meters. One meter is 0-2v DC and the other is 0-30v DC, both are Westinghouse 3.5" front diameter, 2.750 rear diameter.

Using 1 battery connected to my Fluke 175 meter, I get 1.609 vdc, and I show that on the 0-2 meter. I also show the same on the 0-30 meter. Coincidently, if I connect 2 of the AA batteries in series, I get 3.218 vdc. I did this on the 0-30 meter. Strangely, I measured 1.611 on the second battery. Hard to hold them in series with the voltmeter and fluke, the .002 of a volt on the fluke is because I'm draining some on the battery. :rolleyes5:

I admit, I'm pretty bad with electronics, but this seems correct on measuring DC volts.

As they say, a picture is worth a thousand words...(dropping below 1.6vdc...)

200971d1497326771-understanding-rivett-1020-1030-tachometer-volmeter-measuring-battery.jpg
 

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The meter you have coming reads amperes, not volts. The meter movement is almost certainly not a 30 amp one. As I keep repeating, it actually likely reads millivolts. Think of a pressure gauge set up to read water flow. It will not read flow directly but if you connect it to read the pressure drop across a restriction in the pipe, you can calibrate it to show flow. A meter shunt is a very low resistor that is inserted in the line and the meter reads the voltage drop across it. That meter may have an internal shunt, but more likely it is intended to be used with an external one. 30 amps is about the crossover point where a meter may be a standalone or may need an external shunt. Much below 30 amps, say 5 amps, the meter will be all internal. Above, maybe 100 amps, the heat from the shunt would be too great and it would not fit well in the space, so it would be external.

You do not seem to have a clear picture of volts and amps. Volts are like pressure. You can have a high voltage (pressure) with little flow or a high flow with little pressure, or any combination. The meter measures flow with a very small voltage drop. It is designed to keep the drop low because it is subtracted from the voltage in the line, wasting power.

Bill
 
The meter you have coming reads amperes, not volts. The meter movement is almost certainly not a 30 amp one.

As I said, that's a 0-2 vdc gauge. There's a 0-30 vdc gauge in the lower left of that picture, it reads correctly for 1.5v and 3v.

You do not seem to have a clear picture of volts and amps

That's certainly true, I consider myself to be electronically challenged! (probably good I didn't get a square dial Monarch :)). The gauge reads for me what I expect. That goes for both the 0-2 vdc and 0-30 vdc. I realize amps and volts are different, but these gauges say VOLTS on the face plates. However the one above says Amperes, so maybe you're right about the above gauge and my bad in thinking it was a voltmeter. I could use this 0-30 vdc gauge I have here, if that is so. I was under the impression that the one I listed above measures DC voltage, in how the numbers are laid out on the gauge. Will find out soon enough. The question as I see it is what resistance is in the gauge, as that will determine how it is converted to volts. I think that is what you're saying with the shunt. Isn't that the barrel type component that is hooked to one of the poles ?

Originally when I got the 3.5" 0-30vdc gauge, my plan was to take it out of the case and put it in my case...but I saw that wouldn't be so easy. One way I could do it is to mount the small back on the bigger back, the holes are the same spacing for the threaded bolts (poles) on the back.

Right now my bigger concern is getting the pin in the drive shaft repaired. not sure if I can drill the old one out and loctite another in it's place or not. This 0-30vdc gauge I have already will work for certain, just need to figure out how to mount it.

EDIT: I think this might be part of my confusion. This calculator says that there are 1000 milliamps in 1 volt. If the first gauge I listed reads 30,000 amperes, isn't that 30 volts ? If I punch in 30000 for amperes, the calculator converts it to 30 volts. Maybe my calculation is off by 1000 ? In regard to comparing millamperes to amperes. Isn't 1 ampere equal to 1 volt ? (I'm proving I'm electronically challenged :) )

http://www.convertunits.com/from/mA/to/volt/ohm

Here's one last question for you Bill. If I have a 0-10 voltmeter, if I make the resistance 1/3rd, will I then have a 0-30 voltmeter ?

Cause that's another option for me. I have a voltmeter that is 0-10. Or I can get a 2.65 / 1000 Servo-Tek to use with the 0-10 voltmeter.
 
Now I see where your confusion comes from. The converter does not convert volts to milliamperes. It converts volts divided by ohms to milliamperes. Converting volts to milliamperes is like asking how many hours in a mile. That question makes no sense. You need to think in miles per hour, not just miles.

If you apply 1 volt to a 1 ohm resistor, 1 ampere will flow.

If the resistance is 2 ohms, the current will be 1/2 ampere.

If you have 2 volts on 1 ohm, the current will be 2 amperes.

If you know any two of the quantities, it is easy to calculate the third.

The meters in question are probably D'Arsonval movements that respond to current, usually between 1 and 10 milliamperes. The voltage is just however much is required to push the current through. By changing the resistance in series with the meter you can configure the meter to read whatever voltage you want. Changing a 10 volt meter to 30 volts requires 3 times the resistance, not 1/3.
 
Now I see where your confusion comes from. The converter does not convert volts to milliamperes. It converts volts divided by ohms to milliamperes. Converting volts to milliamperes is like asking how many hours in a mile. That question makes no sense. You need to think in miles per hour, not just miles.

Yes, that's the part I didn't understand completely. As I said, I'm electronically challenged! :o


By changing the resistance in series with the meter you can configure the meter to read whatever voltage you want. Changing a 10 volt meter to 30 volts requires 3 times the resistance, not 1/3.

Ok, so I should be able to convert the 0-10 voltmeter to 0-30 by changing the resistor.

The barrel looking component on the pole I mentioned, is that the resistor ? Also, is that what you call the shunt ?
 
Yes, that's the part I didn't understand completely. As I said, I'm electronically challenged! :o




Ok, so I should be able to convert the 0-10 voltmeter to 0-30 by changing the resistor.
Yep or adding to it.

The barrel looking component on the pole I mentioned, is that the resistor ?
Yep, a picture would help
Also, is that what you call the shunt ?
A voltmeter will not have a shunt only a current meter will have a shunt.The meter that you are getting may or not have a shunt if it does you will need to remove it so you can use it as a voltmeter by adding a resistor.
 
Yep, a picture would help

I'll post a pic of one later after I get home.

A voltmeter will not have a shunt only a current meter will have a shunt.The meter that you are getting may or not have a shunt if it does you will need to remove it so you can use it as a voltmeter by adding a resistor.

Ah, so you can go both ways and the meter must be the same. If I can swap out the shunt with a resistor and do the same, I might have the resistor I need from the old meter. Maybe the resistor is color coded ? I'll look to see if it is marked tonight.

Thanks,
Alan
 
I'll post a pic of one later after I get home.



Ah, so you can go both ways and the meter must be the same. If I can swap out the shunt with a resistor and do the same, I might have the resistor I need from the old meter. Maybe the resistor is color coded ? I'll look to see if it is marked tonight.

Thanks,
Alan
The shunt is connected in parallel with the meter the resistor is in series with the meter. Be warned that some high current meters do not have a proper movement for voltmeter just a magnet close to the shunt.
 
The shunt is connected in parallel with the meter the resistor is in series with the meter. Be warned that some high current meters do not have a proper movement for voltmeter just a magnet close to the shunt.

I'll open it up when it gets here and compare it against one of the voltmeters to make sure it's similar before doing anything. Thanks for the help! :)

EDIT: adding pics.

Here's a pic of the resistor, not sure if these numbers mean anything. These pics are parts from the original tachometer gauge.

201072d1497418447-understanding-rivett-1020-1030-tachometer-rivett-tach-resistor.jpg


Now, this next pic I *think* is the common ground. I've seen this on other gauges, it is basically a screw with wires connected to it and has some type of black coating over the entire thing. Is this a common ground ?

201073d1497418447-understanding-rivett-1020-1030-tachometer-rivett-tach-ground.jpg
 

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The meter is almost certainly 50 mv full scale. Even a AA cell will slam it. You need to establish the full scale current required, then pick a resistor to pass that current at the max voltage. Good old Ohm's law, voltage/current=resistance. Normally a meter will have something like 50 mv fs on the dial at the bottom. Looking at the picture again, I see Westinghouse at the top of the scale. There may be a resistor or shunt inside, but not likely a 30 amp shunt. You won't know until you get it.

Bill

Bill, (or labeeman if you're still following)

Here's what I have inside. Is this flimsy wire coiled up the shunt you speak of ?

201236d1497584799-understanding-rivett-1020-1030-tachometer-westinhouse-amperes-gauge.jpg


The results I get are approx 2x the amount showing on the gauge. IOW, I see approx 3 - 3.5 volts DC with a 1.5 volt battery and a little over 6 volts when I put 2 batteries in series.

Could this be as simple as taking my resistor from the original gauge and replacing this flimsy coil ?

On the original it had a black screw that I see now basically connects both poles and the needle. I do have continuity between the poles on the new one, although it is done slightly different.

I also see what you meant about this gauge looking like a Simpson. I agree, the front of it does in fact look like a Simpson.

Strange enough, this does fit in my original case front, although it uses 4 screws rather than 3 to attach it to the back...the holes are drilled and tapped for the 4 screw spacing...how convenient is that ? :cheers:

Would be nice if this gauge would work. I need to figure out how the other end of that flimsy coil is soldered. I can solder, and have a small tip iron, that much I can do... :rolleyes5: But with that said, I am electronically challenged... :o
 

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In the first picture that is a wire wound resistor one % or better.
In the second picture that looks to be a rectifier. It is used so the meter will read positive when the tach is turning in the reverse direction.
In the third picture that flimsy coil is a resistor that connects the meter movement to the shunt, the shunt looks to be that brass that is connected from each terminal.
 
In the first picture that is a wire wound resistor one % or better.
In the second picture that looks to be a rectifier. It is used so the meter will read positive when the tach is turning in the reverse direction.
In the third picture that flimsy coil is a resistor that connects the meter movement to the shunt, the shunt looks to be that brass that is connected from each terminal.

I agree.

This meter is an ammeter with an internal shunt that will need to be disconnected for this service. There is no practical way to make it work with the shunt in the circuit. One end can be connected as long as one is disconnected or cut. The coiled resistor is a low value used to trim the reading, sort of the electrical equivalent of a shim. It can stay there.

Once again, the meter does not read volts. It reads amperes. If this had been an external shunt meter, connecting it to a battery like that would have damaged it. Don't do it again. The meter was reading the current produced by the battery voltage divided by the internal resistance of the battery, which has nothing to do with this project.

The meter will need to have the shunt disabled and a resistor added to match the generator. I don't know any way to have you do that. If you send me the generator and meter, I can calibrate it. I rebuilt countless GE tach generators back in the day and still have the setup. The generators had been run into scrap with bearings that were mostly dust. I asked where they were getting such heavy use and was told that they came from the printing presses of a large pornography printer. Business must have been good. If you send it, include the rectifier and I may be able to make it work both ways.

Re mounting screws, typically round meters had three screws and square ones four.

Bill
 
I agree.

This meter is an ammeter with an internal shunt that will need to be disconnected for this service. There is no practical way to make it work with the shunt in the circuit. One end can be connected as long as one is disconnected or cut. The coiled resistor is a low value used to trim the reading, sort of the electrical equivalent of a shim. It can stay there.

Once again, the meter does not read volts. It reads amperes. If this had been an external shunt meter, connecting it to a battery like that would have damaged it. Don't do it again. The meter was reading the current produced by the battery voltage divided by the internal resistance of the battery, which has nothing to do with this project.

The meter will need to have the shunt disabled and a resistor added to match the generator. I don't know any way to have you do that. If you send me the generator and meter, I can calibrate it. I rebuilt countless GE tach generators back in the day and still have the setup. The generators had been run into scrap with bearings that were mostly dust. I asked where they were getting such heavy use and was told that they came from the printing presses of a large pornography printer. Business must have been good. If you send it, include the rectifier and I may be able to make it work both ways.

Re mounting screws, typically round meters had three screws and square ones four.

Bill

Bill,

Would be willing to send it to you, and would be willing to pay you for your time.

I'll PM you.

Cheers,
Alan
 








 
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