Re: [CAD_CAM_EDM_DRO] Re: Adding inertia to an axis

Peter wrote:

> In the recent thread about X-Axis won't do as it's told - there was a
> suggestion from Hoyt to try adding inertia to the axis. As it turned
> out that wasn't the problem in Richard's case - but it may be the
> problem for one of my machine axes. But I'm curious as to how much
> extra inertia to try adding... I'd like to start in the right ballpark.
>
> I have a NEMA42 motor so I will probably try turning a solid steel disc
> around 3" dia and say 1" long as a starting point, recognizing that the
> disc's OD is most significant in moment of inertia calculations. Would
> appreciate any suggestions other than my wild guess as a starting point.

Adding true inertia only moves the resonance to a lower speed. that may
not help at all, as it may intensify the resonance by adding more mass to
vibrate. The professional approach is a viscous damper. Early ones
were made by attaching a disc to the shaft, and clamping a heavy metal
disc to that one with a rubber sheet between. With the rubber sheet loosely
clamped, the attached disc would rub against the dead weight and absorb
the vibrational energy. getting the clamping pressure right, and keeping it
right was not easy. The current approach is to mount a hollow round
cavity to the shaft, and have a heavy metal disc free floating in the cavity.
The cavity is partially or completely filled with a viscous oil to give the
desired vibration absorption. I would think it wouldn't be too hard a
lathe project to make one of these out of aluminum, with a steel disc
inside, and a cover plate with a gasket. SAE 90 gear oil should provide
good damping.

Jon