CNC: Turning – Part bending and L/D ratio
Part bending increases very rapidly with increase in L/D ratio.
For a given radial cutting force, the part bending increases as the square of the L/D. Compared to a part with L/D of 1, a part with L/D of 2 bends 4 times as much, one with L/D of 4 bends 16 times as much, etc. The orange line in the graph below shows the ratio of deflection for various L/D ratios compared to L/D ratio of 1.
The L/D ratio makes a big difference to the quality of the turned part, so ensure that your work holding is good, by using thumb rules like in this earlier post on thumb rules for work holding on CNC lathes. If you have a long or a thin walled part, ensure that you reduce cutting the depth of cut and feed rate as the L/D increases.
The data for this post is the result of work done by a couple of Mechanical Engineering students interning in Cadem during their holidays after the 6th semester – Srinivasulu Reddy and Damodar R, and from SVCET, Chittoor.
Pics. and text source: CADEM NCyclopedia multimedia CNC training software.
