Lathe tachometer

[Michael Cox 1Participant @michaelcox1]

Posted by Graeme W on 11/02/2015 11:50:57:

Murray, Richard,

I added a tacho to my Warco GH1330 when I upgraded to a VFD controlled motor, bought from that well known auction site, like this. Just need to add a 12v supply, and a small magnet, works very well.

Graeme

Hi Graeme,

I have just purchased a similar tachometer. However, connections on the 5 pin socket on the display are in Chinese. Did you get any information in English? How did you wire it?

Mike

[John CParticipant @johnc47954]

Mike – this should help – I have wired up mine using this diagram.

Rgds,

John

[John CParticipant @johnc47954]

Which translates to:

Wire 1 : +ve supply and brown wire from sensor.

Wire 2 -ve supply

Wire 3 Blue wire from sensor

Wire 4 Nothing

Wire 5 Black line from sensor.

I used an 18 v printer power supply for mine.

Rgds,

John

[Michael Cox 1Participant @michaelcox1]

Thanks John. That is just what I needed.

Mike

[john carruthersParticipant @johncarruthers46255]

I use a Wilko bike computer, £5 or less, comes with the magnet as well

[Michael Cox 1Participant @michaelcox1]

Posted by john carruthers on 09/12/2015 17:08:37:

I use a Wilko bike computer, £5 or less, comes with the magnet as well

So do I on my mill but it does not respond at the highest speed. I am planning to upgrade my mill soon and I am going to fit a better tachometer. The new tachometer is no more expensive than the old Wilko bike computer and will provide a much easier to read display.

Mike

[john fletcher 1Participant @johnfletcher1]

There was good article in MEW a couple of years back. One version was to fit a ABS brake sensor adjacent to the Myford super 7 bull wheel it having 60 teeth, feeding its output to a LED display. I did this to my lathe and it works very well. The other method was to make a disc with 60 slots and use an optical slot coupler again to counter slots. I did the this to my mill using a piece of printed circuit board as the base for the 60 slots. Also I've seen on the ebay a unit for doing much as what I have just mentioned for about £6.John

[duncan webster 1Participant @duncanwebster1]

Lots of good advice in earlier replies, I made mine for the lathe many years ago using a refective opto sensor and a PIC, just painted half the pulley black and half white. It's not that easy! Found that black gloss paint reflects just as well as white, so had to use blackboard paint, then found if it gets a film of oil that reflects as well, so every now and again I have to give it a wipe. I know, not hard, but on the mill I used a magnetic sensor. Just to make life interesting the pulley on the mill doesn't go at the same speed as the spindle, so I used an Arduino and LED display, more interesting than just buying it anyway.

[ANDY CAWLEYParticipant @andycawley24921]

I calibrated the numbered dial on my speed control by measuring the rpm by using a longish piece of all thread, a loose nut and a stop watch.

Measure and mark a suitable length on the all thread using a marker pen then time the nut running between the marks. The all thread is gripped in the chuck and for safeties sake the opposite end is in the tail stock barrel The lathe is run with the pointer on the various marks and the nut held by hand to run it down the thread whils timing. A chart can then be made.

Simples, may not be super accurate but good enough for setting a lathe speed.

[Peter Wood 5Participant @peterwood5]

As with several of the previous posts I have fitted an inverter to my Myford S7 but wanted a read out of RPM. So I purchased the cheap tachometer off eBay used by others.

The Hall sensor provided is far too big to fit anywhere in the belt drive housing so I replaced it with an A3144 chip housed in a short strip of carbon tube.

I noticed that the large belt pulley had a small hole drilled opposite the oiling nipple so I used this to hold a small magnet (about 8mm diam). The thin carbon tube holding the sensor is fixed to the housing adjacent to the pulley with a small clamp. All works fine.

But I am having second thoughts!!

How critical is that small hole to the balance of the spindle assembly? Am I likely to put undue stresses on the rear bearings?

Any views?

Peter

[KWILParticipant @kwil]

Why bother with a tacho?

You know the speed range of any pulley (or gear) setting, use a 10 turn knob on the speed pot and you have a 1/100 scale available. A lot of lathe users manage quite well with the fixed speed steps available without VFD.

p.s. I have a VFD on all my machines just to save some replies/comments.

[Ian PParticipant @ianp]

As Kwil and others have said, why bother with a tacho.

My (geared head, nine speed) lathe has a VFD and I spent a couple of hours fitting one of the eBay type digital tachometers.

After fitting it about one year ago, I checked that it worked and can honestly say that since then have never even glanced at it!

I run the lathe in the one gear ratio that it is quietest at and use the unmarked pot knob to set the speed so that it feels right for the job. The only time I change ratio is for very large diameter work or screwcutting purposes.

Ian P

[Bob StevensonParticipant @bobstevenson13909]

As mentioned a lathe tacho is not that useful in my view, however, this video shows a simple and inexpensive installation which a friend has used for his new mill;

[Peter Wood 5Participant @peterwood5]

Why bother with a tacho?

A number of reasons, and respecting contrary opinions, they come down to personal preferences.

I use the tacho on my mill all the time. I have developed a mental picture of what speed to start with for any particular combination of tool, metal or task. I felt I was lacking that info on the lathe.

However, and primarily, I fancied the project.

But back to my main question – how critical is the balance hole on the large pulley.

Peter

[Mike PooleParticipant @mikepoole82104]

As it costs less than a tenner to fit a tacho it is not the end of the world if it is not as useful as you first anticipated. It seems that the speed is of interest as people have other strategies to determine the speed. With the wide speed range possible with a flux vector VFD you are going to check somehow what your speed is. Just going by feel requires some experience or you could be well away from optimum or safe RPM to not compromise tool life. I still check which pulleys I am using before setting my speed as I feel that adequate power is required as well as the right speed and if you reduce speed using the VFD then you also reduce the available power.

Mike

[Neil WyattModerator @neilwyatt]

My new SC4 has a tacho built in. I fitted one to my mini lathe.

In practice listen and feel how the cut is going and look at the surface finish, and adjust the speed to get best results.

There are so many variables (tool style, tool material, tool wear, tool height, tool angle, lathe rigidity, type of bearings, adjustment of bearings, toolpost style, workpiece size, shape, overhang, diameter, material, use or not of coolant, cutting fluid, depth of cut, feedrate, your own style of working, even whether the lathe is cool or has been run for and hour and warmed up) there is no magic number for any job unless you have a controlled production environment where you control as many of these variables as possible. In a home shop, all a tacho can do is get you in the right ballpark, or repeat a setting you found worked earlier.

In the past, most people only had six speeds to choose from and got on fine, having minute control over our lathe speeds convinces us that getting the speed right to within a few rpm is essential, just because we can.

Neil

[Martin King 2Participant @martinking2]

Posted by Gordon W on 11/02/2015 17:03:22:

I was just looking for a tachometer ,for a different application, and found a lot of cheap, hand held, infra-red jobs. Ideal for my use. Would these not do the job ? Only about £10.

Got one of these and it works well, not that I use it much…….

Martin

[KWILParticipant @kwil]

Neil,

"Just because we can". How very true of so many "new" and seemingly unnecessary products. eg *phone 9-10—X–Y and many other things.

[Peter Wood 5Participant @peterwood5]

I am sorry – I really did not intend to re-ignite the whole pro-con tacho debate again.

I just wanted to know whether the weight of the sensor magnet on the large belt pulley would seriously upset the balance.

Anyway I have done some calculations and reckon that the centrifugal force of a 1g magnet, 50 mm from the centre revolving at 600 rpm is 0.02 kg.f.

I am going to stop worrying.

Peter

[John HaineParticipant @johnhaine32865]

Peter, on my S7 that hole is used for the spindle locking pin! Does yours not have one?

[Peter Wood 5Participant @peterwood5]

Oh ******** !!

I thought it was to balance the oil nipple cut out opposite. Learn something every day.

Anyway no great problem as I don't think I have ever used the locking pin.

Thanks John for solving my problem.

Peter

[not done it yetParticipant @notdoneityet]

Why bother with a tacho

It just happens that some lathes have a mechanical variable speed drive, so the motor speed is constant, so not proportional to the speed.

That small hole is close to the axis, so will unlikely to affect the balance of the whole assembly to any discernible degree. Think of how the length of the grub screw would be considered at installation. Interrupted cutting, offset turning, or out of balance parts would have a much greater effect.  Lathe bearing sizes should be designed to be sufficiently robust.  To what degree are most (cheap chinese) chucks dynamically balanced?

However, I would like to be sure the magnet is: a) readily removable and b) unlikely to ever fly off (unlikely but…).

Edited By not done it yet on 08/01/2018 16:08:59

[SillyOldDufferModerator @sillyoldduffer]

Posted by Peter Wood 5 on 08/01/2018 15:33:34:

…

I just wanted to know whether the weight of the sensor magnet on the large belt pulley would seriously upset the balance.

…

I am going to stop worrying.

I'm not familiar with the lathe or the pulley Peter but I wonder if the hole is for balance; maybe it's a manufacturing artefact? I wouldn't expect a small hole or 1g magnet to make any difference at 600rpm.

Never mind accidentally re-igniting the great tacho controversy, it's all part of the entertainment!

Personally I find tachos moderately useful and am pleased to have them fitted on both lathe and mill. Although they can be used to pre-select theoretical cutting speeds, that's rarely what mine are used for. Now I have some experience I tend to settle on cutting speeds by informed experiment. The tacho's role is to tell me exactly what that speed is. Makes it very easy to go back to the same rpm, perhaps days after a job was interrupted.

Dave

[Colin LLoydParticipant @colinlloyd53450]

Tachometers are quite useful if you happen to be a novice. They provide you with a visual guide to spindle speed and a link to the recommended operatingspeed based on material, object diameter and all the other factors that experienced machinists know off by heart. Eventually I won't need to use the tachometer – but at present, I find they provide me with a safety starting point on the lathe and milling machine. Rally drivers never look at their speedometers but novice drivers would be well advised to just glance at their speedometer before taking that sharp bend.

[Neil WyattModerator @neilwyatt]

My mini lathe has operated for 10+ years at up to 2000 rpm with a small neodym magnet on the locking nut, held in place by nothing more than its magnetism.

[Author]

Posts