Myford big bore back gear

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).

Hi John,

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

Frank

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

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

Frank

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

... Very curious situation

Here's a 60 tooth one:

**LINK**

MichaelG.

Gents,

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

MichaelG.

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.

.

John ... ^^^ ...

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

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

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

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.

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 '

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.

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.

.

John,

If what you have read, and tested, is correct

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

MichaelG.

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.

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.