Form Gear Cutting Processes

Form Gear Cutting Processes

Form Gear Cutting Processes - The majority of gears, and particularly those for transmitting appreciable amounts of power and those having high accuracy ate made by machining, and form cutting is one of the machining processes.

Form cutting makes use of a gear cutter that has the same form or shape as the space between two adjacent teeth. Cutting tools commonly used for this purpose are form disc and end mill gear milling cutters. The process is accomplished on milling machines with the application of index heads. 

From cutting of Gears on Milling Machine

Multiple Tool Form Cutting	Template Method of Cutting Gears
A - Form Tools	A - Formed Milling Cutter
B - Gear Blank

(a), the cutter is fed radially toward the centre of the gear blank, to obtain the desired tooth depth; it then is moved across the tooth face to obtain the required tooth width. When one tooth has been completed, the tool is withdrawn, the gear blank is indexed, and the cutting of the next tooth space is started.

To obtain the theoretically exact tooth profile, a special milling cutter should be used for machining each gear with a definite module and number of teeth. As this calls for a large number of cutting tools, sets of eight disc type gear milling cutters are used for each gear module, and for more accurate machining, sets of 15 or 26 cutters.

Gears machined by disc and end mill cutters are not adequately accurate and, in addition, this method does not provide for sufficiently productive output because of the time consuming process of indexing. Accordingly, this gear cutting method is used on relatively rare, occasions, mainly in repair shops and for roughing operations.

A method to cut all the tooth spaces simultaneously by using a number of cutting tools equal to the number of teeth in the gear is the solution to speed up gear cutting process using form cutters. The gear shaping cutter head used in this method has a series of form tools each form tool having the shape of a tooth space.

The high productivity is due to the fact that all the tools operate on the gear blank, 2, at the same time and thus all the teeth are cut simultaneously. b, form tools 1, are arranged radially around the outside of the gear blank, 2. Cutting is affected by the vertical reciprocating motion of the blank. All the toots are fed radially inward simultaneously when the blank is at the lower end of its stroke and out of contact with the tools.