email: tony@lathes.co.uk
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MYFORD Screwcutting Gearboxes
- early and kit-built types -
Myford Home Page   Myford ML7  Myford ML7 Tri-Leva  Myford ML7 Photographic Essay
ML7 Rebuild   Myford Super 7 and ML7R  Myford ML8 Wood lathe 
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  Myford Mini-Kop  Myford Special & Production Capstan Lathes  Myford 280   
Accessories   Myford Replicas and Clones  Serial Numbers
   Early and third-party screwcutting gearboxes  Rodney Milling Attachment
Amolco Milling Attachment  Staines milling and "Big Swing" attachments   
Super 7B power cross feed--photographs
Myford Super 7 "new in the box"   First Myford ML7 Catalogues

Comprehensive Data Packs with Operation Manuals, Parts Lists
and Catalogues, etc., are available for most Myford lathes


Gearboxes and Screwcutting:
In standard form both lathes used changewheels for screwcutting and could generate (with the standard changewheel set) pitches from 6 to 112 t.p.i. (or 0.25 to 4 mm). However, both could be ordered (or retrofitted) with a screwcutting gearbox thus becoming, with the addition of a suffix to their model numbers, the ML7B and Super 7B. The gearbox generated 48 threads from 8 to 56 t.p.i. and the same number of feeds (by the simple expedition of pulling out a double gear mounted on the banjo) of  0.139" to 0.002" per revolution of the spindle. Only an Imperial box was ever offered, metric pitches being obtained by sets of  conversion changewheels. However, on  lathes sent to America the gear cluster inside the box was modified, 23T gear replacing the 19T gear normally used - the result being that the box could generate North American pipe-thread pitches.
Although in the late 1940s a kit-form gearbox had been designed and marketed by L.H.Sparey (author of
The Amateur's Lathe) it was not until 1953 that Myford's first effort appeared. Lubricated by an oil-bath it was designed along long-established "Norton Quick-change" lines with a single-tumbler and a reversible gear on its left-hand face that allowed a change to be made between fine feeds and threads. Early boxes were fitted with unhardened gears and (hidden under a rounded, aluminium cover) a pair of external gears on the right-hand face (from which the leadscrew drive was taken) but in 1956, from box QC 2495 onwards, important alterations were made - with a change to hardened gears and a leadscrew that was much better supported by being allowed to pass all the way through the box with the drive taken from its left-hand end - so allowing the external gears to be dispensed with. It is worth noting that the Metric Conversion Set for the early box is different - the four gears needed being: 2 x 60t, 1 x 44t and 1 x 52t. Later boxes required five gears: 2 x 60t, 1 x 50t, 1 x 45t and 1 x 63t. The standard Metric Conversion Set was replaced during the 1990s by a different design of slotted quadrant arm on which could be mounted a greater variety of changewheels - and so enabled the generation an almost unlimited number of English, Metric and odd threads and feeds. The Myford gearbox was a beautifully made and very tough unit and, with a supply of lubricant in its base (not something that every maker of small lathes considered important) very reliable. The only signs of wear one should encounter are in the shaft bushes; if the gears show signs of damage then the box must have been mishandled or denied lubrication, in normal use it is simply impossible to wear them out.
Supplied as standard with an ML7 or Super 7  the changewheel set comprised: 2 x 20, 25, 30, 35, 38, 40, 45, 50, 55, 60, 65, 70 and 75t. To cut a wide range of metric threads requires, in addition, just two 21t wheels. Myford Series 7 10 changewheels of all years are 20 D.P. with a 14.5-degree pressure angle, 3/8" thick with a 5/8" bore and 1/8" keyway.
A reproduction of the gearbox mounting template can be found below..

Although a kit-form gearbox had been designed and marketed in kit form during the late 1940s by L. H. Sparey (author of "The Amateur's lathe"), it was not until 1953 that Myford's first effort appeared. Lubricated by an oil-bath it was designed along long-established "Norton Quick-change" lines with a single-tumbler and a reversible gear on its left-hand face that allowed a rapid change between fine feeds and threads. The early boxes (as shown here) were fitted with unhardened gears and (hidden under a rounded, aluminium cover) a pair of external gears on the right-hand face (from which the leadscrew drive was taken) (later boxes had all the gears inside)
A data pack that includes the manuals for both gearboxes is available


If an owner bought a gearbox kit for an early lathe a template was provided (Part No. 232) to help mark out the position of the holes that had to be drilled and tapped - on later beds these were already provided. The plate was secured to the tapped holes that held the screws used to push the headstock back against its alignment flange and holes drilled through the two centre holes such that they could be tapped 1/4" BSF. The maximum holes depth was 0.625" (though the right-hand hole may break through at that setting), the tapped length 0.500" and drill specified a 0.0204" (i.e. a No.6)

A gearbox drilling template in place

Designed in the late 1940s by L.H.Sparey, author of the indispensable book "The Amateur's Lathe" and a prolific writer on model engineering and model aero engines this screwcutting and feeds gearbox was produced in advance of Myford's own in 1953 - with a surprisingly large number appearing to have been constructed by enthusiastic owners. The box economised by using standard Myford changewheels.

Featured on the BBC "Inventor's Club" programme during 1949. Sparey, right, demonstrates to  Geoffrey Baumfrey one of the modifications to his ML7 lathe

The WMED screwcutting gearbox - of which nothing is known. Can any reader help?


email: tony@lathes.co.uk
Home   Machine Tool Archive   Machine-tools Sale & Wanted
Machine Tool Manuals   Catalogues   Belts   Books  Accessories

MYFORD Screwcutting Gearboxes
-
early and kit-built types -
Myford Home Page 

Myford ML7  Myford ML7 Tri-Leva  Myford ML7 Photographic Essay
ML7 Rebuild   Myford Super 7 and ML7R  Myford ML8 Wood lathe 
Myford ML10: (Modern 31/4" Lathe)  Myford 254 and 254 Plus 
Myford/Drummond M Type  Myford ML1, ML2, ML3 & ML4   4-inch Precision
  Myford Mini-Kop  Myford Special & Production Capstan Lathes  Myford 280   
Accessories   Myford Replicas and Clones  Serial Numbers
   Early and third-party screwcutting gearboxes  Rodney Milling Attachment
Amolco Milling Attachment  Staines milling and "Big Swing" attachments   
Super 7B power cross feed--photographs
Myford Super 7 "new in the box"   First Myford ML7 Catalogues


Comprehensive Data Packs with Operation Manuals, Parts Lists
and Catalogues, etc., are available for most Myford lathes