RPM counter for Myford Super 7

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RPM counter for Myford Super 7

This topic has 13 replies, 11 voices, and was last updated 10 August 2016 at 22:01 by Muzzer.

Viewing 14 posts - 1 through 14 (of 14 total)

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8 August 2016 at 23:58 #249960
Richard Elvin
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@richardelvin67896
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.
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8 August 2016 at 23:58 #32758
Richard Elvin
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@richardelvin67896
9 August 2016 at 00:16 #249962
John Stevenson 1
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@johnstevenson1
http://www.model-engineer.co.uk/forums/postings.asp?th=113949

Edited By John Stevenson on 09/08/2016 00:17:26
9 August 2016 at 08:38 #249976
Les Jones 1
Participant
@lesjones1
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.
9 August 2016 at 09:13 #249979
Martin Connelly
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@martinconnelly55370
Richard, XV408? It was at Coningsby when I was there.

Martin
9 August 2016 at 09:13 #249981
KWIL
Participant
@kwil
Conveniently the S7 bull wheel has 60 teeth!!
9 August 2016 at 09:27 #249984
Les Jones 1
Participant
@lesjones1
Hi KWILL,
That is very convenient so a frequency disply would display RPM directly.

Les
9 August 2016 at 09:40 #249986
john fletcher 1
Participant
@johnfletcher1
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.
9 August 2016 at 09:51 #249987
not done it yet
Participant
@notdoneityet
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.
9 August 2016 at 11:10 #250009
Hopper
Participant
@hopper
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.
10 August 2016 at 08:28 #250091
john carruthers
Participant
@johncarruthers46255
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.
10 August 2016 at 21:37 #250220
Richard Elvin
Participant
@richardelvin67896
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.
10 August 2016 at 21:48 #250224
Bazyle
Participant
@bazyle
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.
10 August 2016 at 22:01 #250225
Muzzer
Participant
@muzzer
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
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