traditional-tools
Diamond
- Joined
- Aug 10, 2007
- Location
- West Coast
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.
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.
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". 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.
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.
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.
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.
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.
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.
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". 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.
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.
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.
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.
Last edited: