email: tony@lathes.co.uk
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Atlas 10-inch Lathe Gearbox 1947
and "Pick-o-Matic" Screwcutting
A dedicated manual was issued for the gearbox unit - copies are available - together
with a complete data pack for the Atlas 10-inch and other Lathes


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Screwcutting Gearbox and Pick-O-Matic Threading   Atlas Factory   
Catalogue Covers   Accessories   Countershafts   Atlas Miller   Atlas Shaper



It took a little over 10 years for a screwcutting and feeds' gearbox to become available as an option for the Atlas lathe but, when it was introduced, in 1947, it was also offered as complete conversion kit to for retro fitting to earlier lathe - both those with 3/4" and 5/8" diameter leadscrews. An unusual Pick-o-Matic semi-gearbox was also available, where gears, clustered into sets , were supplied pre-assembled to speed up the thread-cutting process. Just before the introduction of the official gearbox another was offered by the Western Aircraft Tool Co. and described by them as the "New-All" unit.
Issued with the Atlas gearbox was a special handbook, though in its first edition this omitted several key factors in its explanation of how to generate metric pitches--a mistake not corrected until 1959 when an updated version was published for the same gearbox when fitted to the later and heavily revised 12-inch Atlas and Craftsman lathes.
However, there is a simple way (cleverly worked out by Atlas-owner Carvel Webb) to generate a limited range of the more common metric pitches. Because the 30 t.p.i.,  24 t.p.i and 20 t.p.i positions represented the same ratio intervals as 1 mm, 1.25 mm and 1.5 mm pitch if one could convert the 30 t.p.i. position to 1 mm pitch, then the 24 t.p.i and 20 t.p.i positions would correspond to 1.25m and 1.5 mm. Now, 30 t.p.i = 25.4/30 = 0.8467 mm. Close, but not close enough, so how to get this closer to 1 mm ? Using 52 and 44-tooth gears gives 0.8467 x 52/44 = 1.0006 mm - which is almost spot-on. The tumbler gears in the Atlas set include a 32/16 shielded gear driving a 40 tooth sliding gear which in turn drives the box through a back-to-back pair of 48-tooth idlers. Because the 52/44 combination fits neatly in place of the 48/48 idler the job can be done. With the 40-tooth sliding gear engaging the 52-tooth gear to the box, the 52-tooth gear is acting as an idler (with the 44-tooth gear as its spacer) and the gearbox operates in its normal `Imperial Mode' - but with the exception of the coarsest (seldom-used) range. However, with the 40-tooth sliding gear in the other position, it engages the 44-tooth gear of the 52/44 combination and introduces the 52/44 ratio into the train. The 30, 24 and 20 positions, or 60, 48  and 40 positions, become the desired 1 mm, 1.25 mm and 1.5 mm pitches, depending upon whether the 52-tooth gear of the 52/44 pair has been placed closest to, or away from, the headstock. However, placing it away from the headstock maintains the bulk of the t.p.i. and feed settings (as per the chart on the gearbox). It also means that it's not necessary to remember to double everything - as would be the case if the sliding gear was driving off the 32-tooth part of the shielded tumbler gear. All that is now required to switch between the normal "Imperial Mode" and the "Basic Metric Mode" is the few seconds it takes to loosen the yoke and to move the sliding gear into or out of mesh.
One problem with box (and this applies to many other less-expensive lathes) was the lack of any shear pins or safety slipping clutch in the drive. The result of ham-fisted operation was for the cast-in key on the ZAMAK changewheel that engaged with the leadscrew to shear off. The fault was corrected on the post 1958 box (fitted to the 12-inch lathe) by the inclusion of a safety slipping clutch within the box..

Screwcutting gearbox kit for the earlier Atlas 10" lathe. The assembly was complete in every detail and included the complete tumble-reverse quadrant plate and arm - the original bed-mounted, leadscrew-reversing gearbox being made redundant when the installation was fitted. A cast-iron cover was also supplied together with a comprehensive instruction and screwcutting-chart book.

Gearbox-mounted Screwcutting Chart from the first gearbox equipped model - 1947



Designed in 1944, the unfortunately-named "Pick-O-Matic" screwcutting set was conceived as a half-way house to a full screwcutting gearbox. The mechanism used changewheels grouped into "Gearsettes" of which six were available: three were used for threading (to give a range of pitches from 5 to 64 t.p.i.) and three for fine carriage feeds (along the bed) from 0.0024" to 0064" per revolution of the spindle. For each setting of the changewheels 6 different feeds or threads could be selected; three were obtained from the "translation" gearbox fitted to the end of the leadscrew, whilst moving a two-position sliding gear arrangement fitted to a stud on the quadrant arm - a mechanism reminiscent of that used on a traditional Norton-type screwcutting gearbox - put them into high or low ratio. The gears were arranged into sized pairs and, consequently, could be attached to their mounting studs without the need to adjust the latter's spacing; a slotted steel yoke held the gears in place. 
The normal "leadscrew-reversing gearbox" was removed and replaced by the tumble-reverse mechanism used on the re-badged lathes that Atlas supplied to the Sears, Roebuck Company for sale under the Craftsman label. The Pick-O-Matic was normally a factory-installed unit but could also be retrofitted on any F or D series lathe. However, the device did not last long and had disappeared from the catalogs during 1947; however, even today, there are still examples in use, several owners having been in touch to say that their particular lathe is equipped in this way - with even a long-bed version turning up in England. A special screwcutting manual (copies available) was issued with every Pick-O-Matic and listed the thousands of odd threads and feeds (including metric pitches) that could be obtained by juggling combinations of standard and special gear sets..

Pick-O-Matic Gear-selection Chart

Pick-O-Matic gear retaining arm



A dedicated manual was issued for the gearbox unit - copies are available - together with ac omplete data pack for the Atlas 10-inch and other Lathes

Atlas 10-inch Lathe Gearbox 1947
A dedicated manual was issued for the gearbox unit - Copies are available
Atlas 6"    Atlas 9"   late-model Atlas 12-inch   
Atlas Utility Lathes  Restored 10-D & 10F
Acorn, Halifax & Sphere Copies   Early Metalcraft Lathes 
Atlas Screw-Machine (capstan)
Screwcutting Gearbox and Pick-O-Matic Threading   
Atlas Factory   Catalogue Covers
Atlas Home Page   Accessories   Countershafts   
Atlas Miller   Atlas Shaper


email: tony@lathes.co.uk
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