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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

Why do antique auto tachs do this?



 
 
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  #1  
Old January 31st 17, 12:05 AM posted to rec.crafts.metalworking
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Posts: 1,554
Default Why do antique auto tachs do this?

I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric
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  #2  
Old January 31st 17, 12:12 AM posted to rec.crafts.metalworking
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Posts: 199
Default Why do antique auto tachs do this?

On Monday, January 30, 2017 at 6:00:50 PM UTC-5, wrote:
I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric


I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.

I started sports car racing in 1966, and my first tach was a Sun Tach that was all-electronic and very smooth -- aftermarket, on my John Fitch Corvair.

--
Ed Huntress
  #3  
Old January 31st 17, 12:48 AM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 1,554
Default Why do antique auto tachs do this?

On Mon, 30 Jan 2017 15:12:29 -0800 (PST), wrote:

On Monday, January 30, 2017 at 6:00:50 PM UTC-5, wrote:
I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric


I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.

I started sports car racing in 1966, and my first tach was a Sun Tach that was all-electronic and very smooth -- aftermarket, on my John Fitch Corvair.

Maybe that's why the motion isn't smooth, there is some stiction maybe
going on.
Thanks,
Eric
  #4  
Old January 31st 17, 02:45 AM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 463
Default Why do antique auto tachs do this?

On Mon, 30 Jan 2017 15:05:47 -0800, wrote:

I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric


I believe that you are talking about a Cronometric tachometer. Smith's
cronometric speedometers and tachometers were common on both
automobiles and motorcycles at one time.
See
http://tinyurl.com/h6n8m47 for some details.
--
Cheers,

John B.

  #5  
Old January 31st 17, 07:08 AM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 2,326
Default Why do antique auto tachs do this?

On 1/30/2017 6:12 PM, wrote:
I don't really know about what you're talking about, but really old tachometers had centrifugal weights and displaced according to the force on the weights.
...


3:16 here
https://www.youtube.com/watch?v=VMP7fW7tj3w

  #8  
Old January 31st 17, 07:37 PM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 1,554
Default Why do antique auto tachs do this?

On Tue, 31 Jan 2017 08:45:10 +0700, John B.
wrote:

On Mon, 30 Jan 2017 15:05:47 -0800, wrote:

I have looked at a bunch of websites with no luck. But someone here is
sure to know. All the mechanical tachs I am familiar with work the
same, with an eddy current disc and a spinning magnet. I figured this
out when I fixed a speedometer in a VW Bug way back in 1980. But I
have seen several antique race cars with tachs that don't seem to work
this way because the needle moves in a jerky fashion. It will swing
fast to a position and then stop. The rpm will then audibly change and
there will be a time lag before the needle quickly swings to another
position and stops dead. It's as if the needle can only move in
discrete steps. I can't figure out why this is, if it's done on
purpose, or if it's desirable. I have seen this type of action on
several different makes of race cars. So, who here knows about this?
If you want to see this in action search Youtube for the TV show
"Victory By Design". If you like cars at all, and race cars in
particular, and have never seen any of these shows then by all means
look it up. A retired race car driver, Alain de Cadenet, does a
wonderful job driving and showing off the cars. His obvious joy
driving the cars and his obvious skill driving the cars makes for a
really enternaining show. He talks about brakes, engines, suspensions,
frames, superchargers, carbs, etc. But he never says anything about
the tachs.
Eric


I believe that you are talking about a Cronometric tachometer. Smith's
cronometric speedometers and tachometers were common on both
automobiles and motorcycles at one time.
See
http://tinyurl.com/h6n8m47 for some details.

Greetings John,
That's it! Thanks! I went to that site already but only saw the eddy
current type. It has bugged me for a long time why the jerky motion
tachs were used and no I know. Cool.
Thanks again,
Eric
 




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