Myford big bore back gear

[John HaineParticipant @johnhaine32865]

Can anyone confirm how many teeth the bull wheel on the big bore Myford S7 has please? The original S7 (and ML7?) had 60 (convenient for dividing), the bigger spindle has (I thought) 65 but I just counted 66! I'm wondering about fitting a hall effect tooth sensor to drive LinuxCNC for threading (using the existing optical index sensor just for indexing).

[John HaineParticipant @johnhaine32865]

[brickyParticipant @bricky]

Hi John,

I have just counted mine and get 67 I checked twice .

Frank

[speelwerkParticipant @speelwerk]

This **LINK** is the backgear on the official site, indexed for easy counting, perhaps there are different versions. Niko.

[brickyParticipant @bricky]

Mine is an early one 2001 so perhaps they changed them as time went on.

Frank

[John HaineParticipant @johnhaine32865]

Yup, I get 67 too on re-counting twice.

[Michael GilliganParticipant @michaelgilligan61133]

… Very curious situation

Here's a 60 tooth one:

**LINK**

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Gents,

Have a look at the [concluding] post by Andrew Moyes, on this thread.

MichaelG.

[John HaineParticipant @johnhaine32865]

It is curious, but I have always known that the big bore lathe has more teeth on the bullwheel. I think what it says about 60t in that advert is wrong, in making a larger spindle bore I think they had to make the gear bigger too. It means that the big bore S7 can't do h/s dividing very well as it's a prime number! Anyway, who cares, as long as Linux CNC can work with 67 teeth it's fine.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 10/04/2016 22:17:54:

Gents,

Have a look at the [concluding] post by Andrew Moyes, on this thread.

MichaelG.

.

John … ^^^ …

[Andrew Moyes 1Participant @andrewmoyes1]

When introduced, the big bore Super 7 had a 67 tooth bull wheel. This number seems to have been chosen to allow Myford to use the same DP as the standard Super 7 but with different gear centres resulting from the bigger spindle. As 67 is a prime number and useless for dividing, by popular demand Myford changed in 2006 to a 60 tooth bull wheel. These are the tooth counts…

Bull wheel Cluster Pulley

Small bore 60 17/53 24

Early big bore 67 16/53 30

Later big bore 60 16/53 30

On the later big bore machines, the 60 tooth and mating 16 tooth gears have a larger tooth form with a non-standard DP. The 53 and 30 tooth gears remained unchanged with the standard DP. The early and later big bore machines therefore have different gear ratios.

All Connoisseurs were produced with the later 60 tooth bull wheel.

All this resulted in a confusion of speed plates. Some early big bore lathes were produced with the speed plate of the small bore Super 7, which was never correct. Later ones had a speed plate which was correct for the 67 tooth bull wheel. This plate seems to have continued in use when the bull wheel was changed to 60 teeth and was therefore incorrect again. I haven't seen any speed plates with the correct ratios for the 60 tooth big bore Super 7 Plus and I suspect it was never corrected but I'd be happy to be proved wrong. The backgear ratio is 6.625:1. The Connoisseur has a different plate as it has poly-vee belts and variable speed drive and is, I believe, correct.

My ex-demo Super 7 Plus lathe was one of the first to be made in 2001. When I bought it from Myford in 2011, it had been converted to the later 60 tooth bull wheel but had (and still has) the incorrect 67 tooth speed plate.

Andrew M

[John Stevenson 1Participant @johnstevenson1]

According to the cutter that came from Myford's the DP was changed to 18.31DP

[Andrew Moyes 1Participant @andrewmoyes1]

PS – The 60T bull wheel and 16/53 backgear cluster are available from Myford/RDG as spares for the Connoisseur. I am pretty certain these would fit the big bore Super 7 Plus if John wants to upgrade from 67 to 60 teeth.

John S – does that mean you are custodian of the special 18.31DP cutter? Keep it safe, please!

Andrew M

[John HaineParticipant @johnhaine32865]

Well, what a kettle of fish! Thanks for all the help, I got my lathe probably a year or so before they changed back to 60 teeth. From my point of view, going back to 60 would be a downgrade as more teeth give better resolution for linuxcnc, so I won't be trying to dismantle the headstock.

[John Stevenson 1Participant @johnstevenson1]

I bought all the gear cutters and all the leadscrew taps prior to the sale.

When I say prior this was whilst they announced they were 'restructuring '

[John HaineParticipant @johnhaine32865]

Just a follow up question if I may. Does anyone know what the DP of the 67 tooth wheel would be please? I guess it might be (60/67)x18.31?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 15/04/2016 09:25:46:

Just a follow up question if I may. Does anyone know what the DP of the 67 tooth wheel would be please? I guess it might be (60/67)x18.31?

.

John,

I had always assumed it to be 20 DP … which is roughly (67/60)x18.31

… But I seem to remember reading somewhere that even the original S7 back-gears are not standard profile.

[Hopefully, J.S. will leap-in to advise.]

MichaelG.

[John HaineParticipant @johnhaine32865]

Mystery solved I think, doing a quick search I found a thread in RGgroups. That directed me to the Geo Thomas Workshop Techniques book where he gives a design for a headstock dividing attachment based on the VDH, and specifies a worm cut for 16 DP. This gives a gear PCD of 67/16 = 4.1875 inches =106.36 mm. Checking on the lathe a 20 dp changewheel doesn't engage. On the basis that Myford used the same DP for the 67 tooth wheel as originally the 60 t bullwheel, and this checks with my approximate measurement, I'll go with this. The reason for asking is that I want to shape a "polepiece" as part of a Hall effect sensor that conforms to the outer curve.

Thanks for the help.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 17/04/2016 08:58:15:

Mystery solved I think < etc. >

.

John,

If what you have read, and tested, is correct

Apologies; I must have completely 'lost the plot'.

MichaelG.

[John HaineParticipant @johnhaine32865]

No problem Michael! I measured almost exactly (exact by eye) 5mm pitch per tooth on the periphery, x67 gives 335mm circumference, divide by pi gives 106.63 dia, = 4.2 inch. 67 teeth divide by 16 dp = 4.1875 inch. Good enough I think.

[Björn BursellParticipant @bjornbursell]

Some info in this thread, I upgraded my early (2001) S7 plus to connoisseur spec a while ago. Also cut a worm for my GhT dividing attachment.

[Björn BursellParticipant @bjornbursell]

Hello, Some info can be found here, I upgraded my early S7 plus to connoisseur specs a while ago. Also made a worm for my GhT headstock dividing attachment.

Regards, Björn

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