RPM counter for Myford Super 7

Hello people, I've just converted my Myford Super 7 to 3 phase power via an inverter and so far I am more than impressed with the transformation. Now that I can change speed using the potentiometer on the inverter I would like to fit some form of RPM counter so that I can see what speed the spindle is doing, so my question is, has any one done this modification to there lathe? Thank you for taking the time to read this request,

Richard Elvin.

http://www.model-engineer.co.uk/forums/postings.asp?th=113949

Edited By John Stevenson on 09/08/2016 00:17:26

Hi Richard,
I think the simplest way is to use a hall effect gear tooth sensor mounted close to one of the back gear gears. There are pictures of how Roy Stark mounted one on his S7 if you look at "examples of sensor mounting" on my web page. You need a tachometer that will divide the displayed RPM value by the number of teeth on the gear wheel.

Les.

Richard, XV408? It was at Coningsby when I was there.

Martin

Conveniently the S7 bull wheel has 60 teeth!!

Hi KWILL,
That is very convenient so a frequency disply would display RPM directly.

Les

I have a Super 7 fitted with a very early inverter with no read out, I followed an article in MEW several years back, it works a treat. I can't remember the issue number but no doubt Neil will have it. Since then, the device to which John Stevenson refers to has come on the market so I think I buy one of those, but I get satisfaction on making small electronic gadgets. John.

An even cheaper method is to make a table or graph of Hz versus speed (just like a screw cutting chart?). You will soon find that belt pulley changes are rare and you will easily remember the usual speeds at different Hertz. Anyway, do we need to know the real actual exact precise spindle speed to the odd rev per minute or so?

I fitted a simple hall effect counter on my LJ, but rarely take any notice of it. Cutting depth and traverse rate, along with surface finish and how the lathe 'sounds' is far more important than setting it to an exact rotational speed.

Or you can buy one of those $10 digital tachometer guns off eBay. You attach a piece of reflective tape to the chuck and aim the gun at it to get a read out of the rpm. Then just mark the rpm on the existing dial of your VFD rig. Close enough for what we do, I reckon.

Have you tried the cheapo push bike computers ? attach a magnet to the mandrel and rig the sensor close to it, dead easy, shows rpm, and less than a tenner in cycle shops, less than £5 on eBay.

Thank you to all who took the time to reply to my question, I shall be looking at all the options you have given me and I will let you know how it all ends up,

Richard.

I don't have a fancy phone but there is bound to be an 'AP' that measures frequency. Just hold a bit of plastic against the wheel to make a click for it to count.

I bought a couple of Machtach kits which I built up myself, although you can buy them ready made IIRC. These not only tell you the RPM of the machine but can also indicate the surface speed if you tell it the diameter of the workpiece (or the cutter if you are milling), using imperial or metric units. After all, what really matters is the surface speed, not the RPM needed to achieve it.

You can set the number of teeth etc and it accepts a variety of sensors - IR, Hall, VR etc.

Some pics in my album showing one being built up.

Murray

There's also a 3D printable housing on Thingiverse, created with Fusion 360.

Edited By Muzzer on 10/08/2016 22:28:02