[graham_f]

Using water weight as a vibration damper... is it a bad idea? I have a machine that I have been working on for a little while and now that its cutting (aluminum mostly) i have a bit of resonance that I'd like to remove.

I'll be filling hollow tube sections with an epoxy sand/gravel mixture, but more is better right... so i was thinking of putting the coolant tank (green box in the picture) under the table attached to the frame for some extra mass. In solidworks it says I'd be gaining about 300lbs.

Think it's worth my time? or would it have any negative effect?
I'm open to ideas.

Thanks

[Hezz]

Sand would probably work much better but it would weight more and not give you your integrated coolant reservoir. Is this a moving gantry machine or something else. For pure vibration control sand is excellent but it will not add any stiffness. If the water is in a section that moves it will cause problems. If it is stationary it might work to some degree but the water transfers resonance rather well. So it won't damp too much I don't think.

[peteeng]

Hi Graham - Firstly you need to identify what the resonance is before you can figure out a solution. It maybe simple as tightening the bearing cars that have come loose. Water dampers work if they are tuned. The water column has to be tuned to a particular frequency so the moving water gets out of phase with the structures mass so slows its action. First thing to do is to check everything mechanical is correctly functioning and is tight. Then you can move on. You will need someway of measuring the vibration so you can determine its frequency then that will give you a clue to what is the cause. If you have FE in solidworks you can do a modal analysis to determine the probable structural vib modes and that will give you more information. If the measured vib is not one of the modes then adding mass, epoxy etc will not change the condition. You will need to figure out how the motors (this will be at a particular speed or maybe two speeds) or the tool is exciting the structure.

Use a bigger stiffer tool, reduce the shank length to a minimum and check out your chip loads (chip thickness) to ensure the tool is operating where it should be. For instance if the chip load is too small then the tool is rubbing a lot which is pushing the tool sideways which is exciting the machine vs cutting... Use a 3 or 1 flute tool to change the cutting freq to see if this changes the resonance. Change your feed rates to change the driving freq but keep the chip load the same... Is the "resonance" showing up in the part finish? or is this just some acoustic vibration the machine is making that does not affect the job? many things to work thru before you do any mitigating activity otherwise you waste a lot of $$$ and time.

https://en.wikipedia.org/wiki/Tuned_mass_damper

Good luck these things are one of the most interesting issues to fix on a machine. Often it turns out to be something really simple... Peter

[pippin88]

Just adding mass is not a good solution for vibration / resonance.

Sand / particles can diminish vibration by converting the vibration energy into heat essentially as the particles have friction as they bounce around.
(Best data for sand is to place it on top of a vibrating tube, not within)

[servtech]

Using water weight as a vibration damper... is it a bad idea? I have a machine that I have been working on for a little while and now that its cutting (aluminum mostly) i have a bit of resonance that I'd like to remove.

I'll be filling hollow tube sections with an epoxy sand/gravel mixture, but more is better right... so i was thinking of putting the coolant tank (green box in the picture) under the table attached to the frame for some extra mass. In solidworks it says I'd be gaining about 300lbs.

Think it's worth my time? or would it have any negative effect?
I'm open to ideas.

Thanks

Definitely check for wear in the axis and spindle bearings, backlash can cause resonance during cutting and even standstill. If no wear can be found in the system the solution on machines I have worked with was to tune the drives. Adding weight might dampen things but may do nothing.

[ardenum2]

Since you're just changing where the coolant tank is, I'd say go for it and then share the results with us.