© Graham Howe 2011
The following sections describe the various aspects and stages involved in making this Involute Gear Profiling Machine and hopefully you
will find it of interest.
An introduction about the original early Sunderland Gear Planing machine and how the model prototype
relates. This also includes a movie clip of the part finished machine during the early days of testing and cutting
a gear. Accompanied to the movie clip is a description of the machine operation, a parts diagram and a close
up of the gear.
Introduction to the Involute Gear Profiling Machine; Why? Machine Overview; Adaptation
Specifications and Scope; Updated information regarding the making of gears using the standard DP 20 gear
set which have a Different DP or MODule.
Initial design considerations; Quick operational overview
Gear Cutting using a Fly-Cutter or B&S Cutter
Basic spur gears can easily be cut using a fly-cutter which has the correct profile in the milling machine or lathe. Some sort of
accurate dividing head is required to ensure the gear teeth are spaced correctly. Another approach is to buy a Brown & Sharp
disc cutter which is effectively the same as the single fly-cutter but has many profiled teeth. The disc type cutter is however
very difficult to make in the home workshop and so most engineers buy ready made cutters.
Both types of cutters unfortunately can only cut the correct involute profile for a range of teeth in a gear and this usually
means that to have a complete set you need to either make or buy 8! Added to this the set is specific to the gear DP
(Diametral Pitch) and PA (Pressure Angle). As you can readily appreciate this becomes a very expensive method of making a
variety of gear types.
For one-off gears and assuming you make or buy a disc cutter then the results are very good a reasonable solution. The
problem only becomes apparent when you decide to make many gears having different numbers of teeth, DP and PA.
The following text and pages are extracts from the Designing book which is normally in PDF format and some 103 pages.
Designing and Building an Automatic Involute Gear Profiling machine
For me it was an interesting project as I had never actually ever seen a real Sunderland machine and my old text books provided little detail except a
brief description of the operating process. This meant that based on this description I could design a machine interpreting the operating process in a way
that would perform the task of profiling a gear and also cost little in terms of materials. In addition, it was essential that the design was relatively small to
fit on a bench and the parts could be made using equipment normally associated with the model engineer.
The end result is a machine which works and can accurately machine spur gear teeth to have a true involute profile. The design of the machine was
initially hampered because of the relatively small size of the machine to a lack of room to accommodate the appropriate mechanisms. A simple solution
thus had to be devised to ensure the correct rotation of the gear blank during the operating process. This was finally accomplished by effectively making
use of another gear of the same size and specification of the gear to be made and introduce another, non-cutting rack to mesh with this gear which
moved vertically in direct synchronisation with the cutter rack thus producing a simple and accurate method of rotation.
Eventually, this 'copy' approach was further exploited to enable the machine to make gears of a different size and or diametral pitch to the copy gear.
This also included gears which conformed to the metric Modulus notation instead of the Diametral Pitch. Whilst this greatly increased the scope of the
machine it was, by design limited to spur gears.
Introduction to Spur Gears
The incredible thing about gears is that they have changed very little over the years. The early engineers realised the need for gears and the
requirements for them to transmit power continually and evenly. On the face of it there seems little remarkable about gears as they basically have teeth
which mesh together and when rotated impart motion. To ensure that the motion from one gear to the next is continuous and even, demands that each
gear tooth, in mesh, must always remain in contact with its mating tooth. It is this simple requirement that forms the basis on which all gear teeth profiles
are designed and is not as simple as might be initially thought.
Introduction
I started this project to design and build a small involute gear profiling machine that could emulate the process used by the Sunderland Gear Planing
machine. The Sunderland process is unusual in that it exploits the fact that a rack will mesh to any gear having the same diametral pitch and pressure
angle. Unlike many of the modern gear making procedures which use specially formed cutters the making of a rack type cutter is very simple yet will, using
the Sunderland process produce gears with teeth accurately formed with an involute profile.
The use of a rack as a cutter means that like the Sunderland machine it has to be relatively short and thus requires additional mechanisms typical of a
Sunderland gear machine to have to continually re-set the rack cutter to a new starting position as it progresses in completing a gear. This problem of re-
setting the rack slows the machine down and for this reason is not favoured in modern production workshops however, although slow it can provide a very
cost effective method to manufacture gear specials where the standard tooling may not be available or very expensive.
