Sunderland Gear Cutter
Note that the Involute Gear Profiling machine adheres fundamentally to the same involute generation concept as that used by the Sunderland Machine,
however, the mechanisms actually used to accomplish this are totally different. In the Involute Gear Profiling machine a copy-gear and copy-rack is used to
ensure the relative motion conforms precisely to a rack and gear in mesh and also, the arbor holding the blank gear is able to move in and out of engagement.
It appears with the Sunderland Machine above, there is no copy-gear or copy-rack and this is substituted by internal worm and gear mechanisms plus the arbor
appears fixed with no movement and instead the main machine 'head' mechanism moves.
As might be expected, the Sunderland Machine is designed and built to provide total flexibility for gears which can be manufactured and appears not restricted
to only spur type gears. It is unclear exactly how some parts of the mechanism work from the picture but one has to take into consideration the size and weight
of the machine.
Model Prototype based on the SUNDERLAND
The foregoing basic introduction to making spur gears shows how the use of geometric
curves, such as the involute curve, enables gears to transmit power evenly and with a
minimum of noise and friction. The introduction of the involute curve in the tooth profile
allowed teeth in mesh to 'roll' together as if they were rolling on their respective pitch circles.
It can be seen that the shape of the involute curve is not easy to manufacture and in fact
varies according to the size of the gear being made. Brown and Sharp commercially made
disc-type cutters are readily available, but for any particular pressure angle and diametral
pitch, the user would need a set of eight cutters to cover the complete range of gear sizes.
Commercially available hobbing cutters provide the most accurate and fastest method of
making spur gears however these cutters are very expensive and require a specialised
hobbing machine to work.
The simplest and most intriguing method of making spur gears is to use a standard short
rack which is easily and cheaply made using basic workshop equipment. Such a rack does
however need to work in a specialist machine similar to and operating using the Sunderland
Gear Planing machine principle.
Because the short rack is so easy to make it was a good choice so long as a small machine
could be designed and made to emulate the Sunderland operating principle. Such a
machine would enable a large variety of gear teeth to be made by generating an accurate
involute profile. The actual machine prototype, being relatively small, can cope with many
different gear teeth sizes (DP) however, in the case of those gears with larger teeth it is first
necessary to remove the bulk of the material off machine and then use the prototype
machine to generate the required involute shape of the teeth.
The model prototype involute gear profiling machine works using the Sunderland principle but varies in the detail design and operation as compared with the
full size Sunderland planer. The machine is automatic and the head, comprising the vertical slide which contains the reciprocating rack-cutter, remains
stationery at all times in the horizontal plane. The gear blank is held in a support unit which can move in and out of engagement with the rack-cutter. The
rotation of the gear blank is done by using a second copy-rack which engages with a copy-gear. This approach whilst requiring a copy-gear does provide a
simple and accurate translation of the relative vertical movement of the cutter-rack to the rotation of the gear blank. The Sunderland full size machine does this
using a set of change gears and worm drives but this method is totally impracticable in the case of the model prototype due to limited space. Finally, the model
prototype machine is designed to be 'true' to the spirit of the Sunderland Gear Planing machine and relies totally on mechanical devices to perform its
emulation of the generation process.
© Graham Howe 2011
operational
guide
Picture (right) was seen
recently on Ebay for sale.
Clearly this is a modern
version of the Sunderland
and is a very big and
heavy machine.
close up
view
Before a concept becomes viable it has to be designed in more detail and constructed to demonstrate it has the capability to make gears. The only problem
with this thought was that demonstrating capability meant almost all of the machine would have to be made first and only then would it be categorised as a
dream to far or a working model. Since the material costs were negligible I decided to give it a go. During the construction phase many changes have been
made to the drawings as unseen problems surfaced but one-by-one, so far a solution has been found.
To accompany the development of this machine will be three guides - Designing, Building and Operating.
movie clip 1
simple copy
method
movie clip 2
Different DP
method
method outline
description
close up of
finished gear
close up of gear
involute curve
