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Tachometers sensor magnet

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Ian Parkin15/09/2020 18:22:14
972 forum posts
231 photos

I need to fit a tachometer on a machine in the morning

how do i fit the small button magnet to a shaft?

if i glue it to a mild steel shaft does the steel sap the magnetism ?

JasonB15/09/2020 18:26:01
21307 forum posts
2419 photos
1 articles

Araldite worked OK on mine

Steviegtr15/09/2020 22:41:16
2225 forum posts
311 photos
Posted by Ian Parkin on 15/09/2020 18:22:14:

I need to fit a tachometer on a machine in the morning

how do i fit the small button magnet to a shaft?

if i glue it to a mild steel shaft does the steel sap the magnetism ?

No it will be fine.


Brian Sweeting16/09/2020 00:10:24
453 forum posts
1 photos

Make sure that you stick the magnet the right way around, you just know that it will happen.

Neil Wyatt16/09/2020 15:57:27
18727 forum posts
729 photos
80 articles

I found the small neodymium magnets are so strong that popping one in a keyway or spanner notch has always worked for me without adhesive.


Enough!17/09/2020 01:29:22
1719 forum posts
1 photos

... which probably makes Brian's admonition even more important cheeky

Ron Laden17/09/2020 06:59:34
2236 forum posts
443 photos

I have fitted one to my mill and one to the lathe ( dry with no adhesive) and neither have budged yet.

Edited By Ron Laden on 17/09/2020 07:07:17

SillyOldDuffer17/09/2020 10:22:15
7476 forum posts
1648 photos

My lathe's magnet sits in a slight recess, which I guess gives it more grip on a machined flat surface and stops it sliding on a smooth round shaft.

Sliding may be a problem - although I can't imagine a strong magnet coming off, it might move sideways. Sideways movement may not show up in practice. Provided the magnet's close enough right-left to activate the hall sensor, rpm will still be measured. Even if a magnet gradually walks around the circumference, the effect on rpm readings will be small.

A spot of glue would also stop sideways movement and be less trouble to apply at home Another guess; it's cheaper for the manufacturer to machine a flat recess on a lathe spindle than it is to clean it carefully and apply a glue resistant to oil and heat. Also easier to fix an unglued magnet if untrained labour puts it on upside down.


Ian Parkin17/09/2020 16:30:57
972 forum posts
231 photos

I did the job today just ground a flat on a 20mm silver steel shaft and placed the magnet and it stays there even at 1000rpm

its been running an hour or so now

I had it in my head that a magnet would have need putting in a non ferrous collar to work adequately

thanks for all the help with this

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