|Design of Parts for Turning|
The following are general guidelines for design of turned parts:
- Where possible, turned parts should be designed so that a tail stock is not required. This is done by designing the part to be stubby rather than long with a high aspect ratio. The figure below shows the difference.
- Chuck-clamped cylindrical surfaces should not contain parting lines so that flash does not introduce errors.
- For cast parts with surfaces to be faced, cast-in relief allows for tool clearance, as shown below.
- On cast parts that are subsequently turned down, burrs can be avoided by avoiding surfaces perpendicular to the turned-down surface, as shown below.
- Be as specific as possible when referring to removal of burrs. Blanket specifications such as "break all corners" are not recommended since removing all burrs is expensive. Only certain burrs are gross enough and compromise safety and functionality enough to warrant removal.
- Keyways should be able to be milled with the endmill traversing the part axially. Radii at the ends of the keyway are those of the endmill.
- Avoid turning in the areas of weldments, parting lines, and flash. This will tend to extend cutter life.
- Minimize the number of set ups required. Milling should be grouped into sets of parallel planes.
- Design for the largest diameter cutters possible. Larger cutters are less prone to breakage and require lower speeds when compared to smaller cutters. Larger cutters also can accomodate carbide cutting inserts.
- Carbide cutting surfaces require fewer tool changes and have higher cutting performance.
- Blending of radii into existing surfaces should be avoided, even with a ball end mill. Cosmetic-quality blending is expensive to achieve.
- If a surface is to be faced, it preferably should be angled in order to provide tool clearance.
- Sharp inside corners need to conform to the cutter radius that is used in that vicinity. If possible, inside corner radii should be left to the discretion of the fabricator.
- For the cutter perpendicular to the turning axis, rules of thumb for angles on the part are shown below:
- For the cutter at fifty-five degrees to the turning axis, rules of thumb for angles on the part are shown below:
- Boring is more expensive than drilling, so drilling should be used if possible.
- Deep holes with aspect ratios greater than 3:1 should be avoided since accuracy and cutting time will suffer.
- Use through holes instead of blind holes where possible.
- As with all machining operations, the part must be as rigid as possible while being machined. With boring, this applies to the boring bar itself as well as to the part.
- As shown below, relief for the bottoms of blind holes should be provided.