On Fri, 02 Nov 2007 21:03:59 GMT, Trevor Jones
wrote:


The gears for the myford and the hercus dont match at all, even in
similar diameters. this points to one set being 20 degree pitch
angle(PA) and one set being 14.5 degree PA.
does anyone know what PA the myford gears were? even after reading
Ivan Laws book on gears and gear cutting I still cant look at a gear
in my hand and work out just by looking at it what the pressure angle
would be. are the teeth of 14 and a half degree gears fatter or
thinner than similar gear diameter 20 degree pressure angle gears?



Pressure Angle

Diametrical Pitch.

pitch angle ...duh! I meant pressure angle.

Myford gears are 20 DP, 14.5 PA. You won't need a full set of cutters,
just most of the set of eight.
There are a couple sources of replacement gears for Myfords, other
than the factory, and if you have to buy the set of cutters retail, the
replacement gears are a pretty attractive proposition.

If Hercus followed South Bend's lead (it is a licenced clone of South
Bend) then the gears are IIRC 18 DP(or 16 DP) 14.5 PA. These are
not a "preferred" size, and thus limit the number of sources.

Myford gears will be iron. Any other materials will be from some other
source,except the first gears in the train from the spindle to the
leadscrew, which may be fibre, and are meant to provide a "fuse" in the
event of a crash.

there are two sets of gears involved here.
the gears from the tail end of the spindle to the leadscrew are all
cast iron.
the 65tooth bullwheel is cast iron.
the21/56tooth backgear is mazak and they carry the myford part number.
the gear which drives the pulley cluster is a remanufactured gear in
bronze


If you roll out a snake of plasticine and roll the gear over it, it
will leave a rack form impression. The number of degrees either side of
90, is equal to the PA of the gear.
Got a protractor?

I initially didnt understand what you wrote there that but the diagram
in Ivan Laws book put the finger on it. the angle of the face of the
tooth in the rack form equals the pressure angle. I must admit that I
never realised the significance of that piece of information,
presented as it is in a whole sea of dry theory.
gods it is easy! plasticene it out and measure directly.


The Super 7 bull gear is 60 teeth.. The most cost effective way to
change over is to rebuild the ML7, sell it, and buy a Super7. Decide if
you wish to rebuild the lathe, or build engines as a hobby.

The ML7 I had, had a 60 tooth worm grafted on to the spindle, to allow
the use of a dividing mechanism similar to a Radford dividing
attachment. I had the worm gear, but not the attachmentshrug. I have
some pictures around, somewhere, and will email them if you email a request.
To direct index, the cheapest method would be to mount a plate on the
back end of the spindle, with a index pin on an arm.

Cheers
Trevor Jones

Trevor thanks for the gear info. I could not find it anywhere.
I dont know whether you are being pessimistic about the ML7 or not.
I guess I'll find out.
In all I want to remake 12 gears in cast iron. how hard could it be?

the model diesel engines will come later.

TUMESFFF