# Lathe Tach



## Kernbigo (Mar 7, 2016)

4 Digital Red LED Tachometer RPM Speed Meter + Hall Proximity Switch Sensor NPN
( 301805369305 )
szy6815077*Feedback percentage of*99.7%
Has anyone installed one of these, could use some advice, one thing where to mount the magnet, not much clearance on the needle bearing take up nut. I have a south bend 9" wide bed( Thanks)


----------



## mattthemuppet2 (Mar 7, 2016)

i have one of those on my Atlas 618 and it works a treat. magnet is on the bearing collar between the bearing and the spindle gear and i glued a magnet onto the pick up to stick it to the head stock. it does get knocked occasionally but it's easy to move back. i like it allot - looking forward to putting one on my drill press


----------



## TOOLMASTER (Mar 7, 2016)

how did you power yours?


----------



## mattthemuppet2 (Mar 8, 2016)

some random 12V wall wart from my "might be useful one day" stash. It only needs 20mA or so and from 9-15V, so most likely you'll have something lying around or Goodwill will have one for $1 or so. I stripped mine of its casing so I could wire it direct to the on-off switch of my treadmill board.


----------



## Kernbigo (Mar 9, 2016)

anyone have pictures of there mounting?


----------



## mattthemuppet2 (Mar 9, 2016)

here's mine, Greatwhite has one on his Atlas (bigger) from memory too



you can just see the 12V wall wart in the bottom right of the picture



shonky mounting. I'll get round to a better mount at some point, but this works fine for now and I have plenty of other projects to do first


----------



## T Bredehoft (Mar 9, 2016)

Do these RMP Hall units come with a magnet, or if not how much magnet is needed?  I have access to some 1/4 dia, .100 thick, rare earth magnets,  would these work?


----------



## mattthemuppet2 (Mar 9, 2016)

I'm pretty sure both mine did, although the 2nd one is still in its packet and I haven't looked at it for a while. Any rare earth magnet should work just fine.


----------



## T Bredehoft (Mar 9, 2016)

mattthemuppet said:


> I'm pretty sure both mine did, although the 2nd one is still in its packet and I haven't looked at it for a while. Any rare earth magnet should work just fine.



Thanks, Matt.  My mill lost it's RPM capability, power surge, I think. It reads 0 at any speed. I'm going to order a whole unit then try to wire the reader into the old unit.


----------



## mattthemuppet2 (Mar 9, 2016)

you're welcome and that sucks  Is it one of these units that blew or one integrated into your mill (like one of the small PM25 style mills?). Mine reads 0 whenever the pickup gets knocked out of position, so it may just need a new pickup if it's an integrated one. They're really cheap, so that might be worth checking out before buying a whole new one.


----------



## T Bredehoft (Mar 9, 2016)

It's the rpm readout on my PM25, a few weeks ago, we had a power outage. When the power came back on, my modem was fried as was the rpm.  Still lights up, but no numbers. I have no idea where the reader is. I expect it's inside the head. I can put a magnet inside the spindle pulley on top with the reader right there.


----------



## mattthemuppet2 (Mar 9, 2016)

that's a bugger. It'd be worth talking to matt to see if he knows where the reader is, might be a simple and cheap replacement job. There's nothing wrong with these standalone units, but if it were mine I'd rather try and fix it, just to keep it simple and looking good if nothing else.


----------



## Kernbigo (Mar 10, 2016)

got the tack the other day thought i would wire it up and try it today. Got power to the prox switch but nothing to the readout, any ideas. Put 9 volts to it with a battery and later on also tried a power supply 9 volts


----------



## mattthemuppet2 (Mar 10, 2016)

You should just be able to wire up the wall wart or power supply to the box and get it to light up. Pay attention to polarity of course, but there's nothing else to it. I don't think you even need the pickup plugged in, although it wouldn't hurt if you did - it'd just read 0.


----------



## Kernbigo (Mar 11, 2016)

nothing lights up accept the pickup led light, i used the wiring on inkfrog.com nothing came with the unit, checked the polarity first


----------



## mattthemuppet2 (Mar 11, 2016)

sorry man, sounds like a duff unit - there must be power getting to the board otherwise the pickup LED light wouldn't come on. Only thing I can think of is to power it up and then wave the magnet close to it, just in case the display is activated by the pickup receiving a signal. Seems unlikely and you may have already tried it, but worth a shot if you haven't. If that's a no go then file a  complaint with the seller, most likely they'll send you another FOC.


----------



## Kernbigo (Mar 13, 2016)

bought it on ebay and the seller is going to send me another one


----------



## mattthemuppet2 (Mar 13, 2016)

neat, fingers crossed that one will work OK


----------



## Kernbigo (Apr 14, 2016)

got another tack today, the seller did not replace it had to go to pay pal for a refund. This on i ordered out of L.A., did not have to wait for China's mail. This one works great


----------



## Bill Gruby (Apr 15, 2016)

T Bredehoft said:


> Do these RMP Hall units come with a magnet, or if not how much magnet is needed?  I have access to some 1/4 dia, .100 thick, rare earth magnets,  would these work?



 Yes, they come with the magnet.

 "Billy G"


----------



## Bill Gruby (Apr 15, 2016)

Matt;

 How about posting a wiring diagram. I have a  a 618 and this looks like a neat upgrade. I have 4 of those units on hand. They were given to me some time ago.


"Billy G"


----------



## T Bredehoft (Apr 15, 2016)

Bill Gruby said:


> Yes, they come with the magnet.



Between the ask and the answer my unit came, no magnet in sight.  I had some 3mm by 2mm magnets, buried two in the pulley of my spindle (together), buried the sensor in "akupucky" and we're good to go. I intend to mfg a permanent mount, but at least now I can use my slitting saw knowing it's not going too fast. 

The magnets do need to be aligned with a specific end toward the sensor. I cannot tell one end from the other, just changed them until it worked.


----------



## brav65 (Apr 15, 2016)

mattthemuppet said:


> that's a bugger. It'd be worth talking to matt to see if he knows where the reader is, might be a simple and cheap replacement job. There's nothing wrong with these standalone units, but if it were mine I'd rather try and fix it, just to keep it simple and looking good if nothing else.




I had the same issue on my PM-25


----------



## T Bredehoft (Apr 15, 2016)

brav65 said:


> I had the same issue on my PM-25



What was your solution?

just want to know I did it right.


----------



## brav65 (Apr 15, 2016)

T Bredehoft said:


> What was your solution?
> 
> just want to know I did it right.




I replaced the sensor, and there was no change, Matt sent me a new screen which I have not installed yet. I have been super busy at work and have not been in the shop for a long time.


----------



## T Bredehoft (Apr 15, 2016)

brav65 said:


> Matt sent me a new screen which I have not installed yet.



I'm sure between you it will be fine eventually. I hadn't realized how much I depended on that little meter.


----------



## brav65 (Apr 15, 2016)

T Bredehoft said:


> I'm sure between you it will be fine eventually. I hadn't realized how much I depended on that little meter.


 I'm not too worried about it, I just need the time to run through the problem, but that pesky work gets in the way.  I really need to stop doing that whole work thing!


----------



## CraigB1960 (Apr 16, 2016)

I just purchased two of these off of eBay.  Hard to beat the price.  http://www.ebay.com/itm/391309753179

The wiring for this model is as follows:
Sensor: 
brown wire +12vdc 
blue wire -12vdc 
black wire signal

Display:
red.wire +12vdc 
black wire -12vdc 
yellow wire signal


----------



## whitmore (Mar 6, 2017)

T Bredehoft said:


> Between the ask and the answer my unit came, no magnet in sight. ...
> The magnets do need to be aligned with a specific end toward the sensor. I cannot tell one end from the other, just changed them until it worked.



The sensor head (if it's like the crankshaft sensor on my car) is a coil of wire, a soft iron core, and a magnet. 
If yours sticks to a nail, it has a magnet inside, all it needs to sense is a tooth (or gap) in soft iron.  Yes,
a magnet (if it's aligned with the one inside the sensor) will work, but really all it needs is to see
a bit of iron pass next to the tip (which causes an electrical upward blip) or a gap/hole in the
rotating iron next to the tip (which causes an electrical downward blip).

Sense heads are available separately, of course <http://www.banggood.com/DC-6V36V-In...h-p-925067.html?rmmds=detail-left-hotproducts>   in case one wishes
to experiment.   These are, as I understand it, passive sensors (don't need power supply), but you'd never
know that from the descriptions....  Beware, there are Hall effect variants, the 'inductive' type 
is what I'm describing (Hall effect needs power, probably 3-wire connection, inductive type is  usually two-wire connection).

This kind of sensor is disturbed by nearby iron; it might sense moving iron bits other than
at the 'tip' region, and could become less sensitive if surrounded by steel.


----------

