DP which stands for Diametrical pitch is the number of teeth per inch measured on the pitch diameter. #Gear cutting process with form tool mod#O/D x Mod / DPĪ quick note here on the difference between DP CP and module. PCD Number of teeth x Mod No of teeth / DP So if we take two disks of known radius and present them to the tooth so that they fit snug all we need to know is the distance apart and the distance fed in to duplicate the tooth. Looking at one tooth on a gear it is obvious that it has the same radius both sides to form the tooth. The main principle behind the form tool is to adapt the radius of the involute to the form tool. Number 5 cutter 21 to 25 teeth is only accurate for 21 teeth. These are listed in Table 1.īecause of the differences in shape the lower number in the range is correct for that gear, the other numbers are a compromise i.e. #Gear cutting process with form tool series#As this is undesirable a standard was introduced using a series of eight cutters to cover the range. To cut gears with different number of teeth a different cutter is required for each gear. If one looks at a gear with 12 teeth and two others with say 25 and 60 teeth it will be obvious that the shape of the involute changes from a small radius on smaller gears up to straight sides on a rack. Most of the early work on form tools was done by Brown and Sharp where a lot of this information has come from. The geometrical build up of the involute is quite complex but for our use it can be simplified into a single radius. The shape of the tooth form can be best described as the path taken by a point on a piece of string, as it is unwound of the circumference of a circle. The involute form is now the presently accepted form of gear tooth is general use. Enough drivel, now to work!Ī lot of books have been written on gears and gear cutting and it will serve the reader good to read up on the overall principles before getting stuck in to practical work. Some of this work is what I would state was mine but when like minds ponder on a problem there is often duplication of ideas, all that matters is the information is readily available to others. I make no claim that all of this is my own work only that I have pieced together the relevant details from many sources. As I lot of this material has been collected over the years from a lot of sources I am bound to be repeating pieces that have been published before. Secondly a note on the contents of these articles. As I realise that not everybody has a well-equipped workshop so these notes will be written with a lathe and milling machine in mind, however a miller is not completely necessary and with a little forethought all the work can be done on a lathe with a vertical slide fitted. Firstly a few notes about tools required. I am proposing to write two articles about gear cutting, this the first will be about making and using form tools and the second will be about making and using hobs.
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