Bench Top Mills - Filling Base with Aggregate/Epoxy Mix

Thomas, a bit hard on the back to anchor benchtop machines to the floor :). I checked out the link, and one thing that I noted is that he kept referring to increasing the stiffness of the machine base. Vibration dampening and stiffness are loosely connected, but I doubt adding the epoxy granite helped his stiffness much, as it will have a very low modulus of elasticity, compared to the cast iron. More stiffness means less deflection, but it also tends to increase the natural frequency of a structure. If that natural frequency is high enough to be out of the range of frequencies created by the machine, then it will help reduce unwanted vibration. Vibration dampening tends to absorb the vibration and dissipate it, like a shock absorber on a car. Part of the vibration dampening comes from just adding mass, I believe the lower modulus of the infill will probably help (if there are any MechEs in the house that specialize in vibration, here is where you can chime in). There has been quite a lot of talk on other forums specifically about using material such as that to make parts for home brew CNC machines. While I think it would be great for some parts, actual testing of the stiffness of the mix you planned to use would be needed in order to determine proper sizing or applicability for some parts to reduce deflection to acceptable limits for making heavy cuts. Some machine tool manufacturers are using it, but I expect extensive testing was done in the design phase to ensure that the machine would meet their specifications with its use. I also suspect that machine tool manufacturers went that way as much to get away from having to deal with outside foundries as they did for improving machine performance.
 
There is a ongoing debate about bolting/not bolting lathes on PM.com, probably still going on now...
P&W suggests to not bolt their machines down, to prevent twist, which makes sense. L&S flip flop between bolting and not bolting. I think my clausing manual suggests bolting it down. I am of the opinion that it can be a good thing, just to prevent tipping, especially for 9-12" swing lathes. However, on bigger lathes, i dont see as much of a benefit. different horses for courses
 
If you could bolt it down with a 3 point mount, with one end free to swivel, it would eliminate that problem. I'm thinking of doing that on my Craftsman. Bolt the headstock end down to the table, then bolt the tailstock end to a mount that is hinged in the center and then that is bolted to the table. Kind of getting off topic for this thread, though.
 
cjtoombs said:
Thomas, a bit hard on the back to anchor benchtop machines to the floor :). I checked out the link, and one thing that I noted is that he kept referring to increasing the stiffness of the machine base. Vibration dampening and stiffness are loosely connected, but I doubt adding the epoxy granite helped his stiffness much, as it will have a very low modulus of elasticity, compared to the cast iron. More stiffness means less deflection, but it also tends to increase the natural frequency of a structure. If that natural frequency is high enough to be out of the range of frequencies created by the machine, then it will help reduce unwanted vibration. Vibration dampening tends to absorb the vibration and dissipate it, like a shock absorber on a car. Part of the vibration dampening comes from just adding mass, I believe the lower modulus of the infill will probably help (if there are any MechEs in the house that specialize in vibration, here is where you can chime in). There has been quite a lot of talk on other forums specifically about using material such as that to make parts for home brew CNC machines. While I think it would be great for some parts, actual testing of the stiffness of the mix you planned to use would be needed in order to determine proper sizing or applicability for some parts to reduce deflection to acceptable limits for making heavy cuts. Some machine tool manufacturers are using it, but I expect extensive testing was done in the design phase to ensure that the machine would meet their specifications with its use. I also suspect that machine tool manufacturers went that way as much to get away from having to deal with outside foundries as they did for improving machine performance.
Click to expand...

The inhomogeneity of concrete should help considerably with vibration damping. Might be a reason to include larger aggregate than you might otherwise choose. Need to know the wavelengths in concrete of the most troublesome frequencies.
 
I would think varying the density of the aggregate would help more than the difference in size. I think some. of the difference in size is to help fill interstitial volume.between the larger pieces.
 
toag said:
I would think varying the density of the aggregate would help more than the difference in size. I think some. of the difference in size is to help fill interstitial volume.between the larger pieces.
Click to expand...

After a bit more thought I realize that the wavelengths (in concrete) of interest are much larger than the aggregate size anyway. Some relevant papers: http://www.sciencedirect.com/science/article/pii/S0008884699002252 http://wings.buffalo.edu/eng/mae/cm...einforcement and steel surface treatments.pdf
 
Why not just pour a nice concrete bench top with 4 studs in it and bolt your mill down with the studs?
Michael
 
There is a desire in the epoxy based concrete to get the aggregate fill percentage as high as possible, as that gives you the essentially the compressive strength of the aggregate. Using low fill percentages and you get more epoxy between the gains and that gives you the compressive strength of the epoxy, much lower than the aggregate. I think for filling a machine simply for vibration dampening it makes no difference. I think the relatively low modulus of elasticity of the epoxy coupled with the aggregate winds up acting as a spring mass damping system, with the concrete being the mass and the epoxy being both the spring and the damper, soaking up all that high frequency vibration coming from the tool face hitting the work piece.
 
Hi Frank,

I have read a lot about filling the base of a Drill Mill with Epoxy Granite to increase the mass and dampen vibrations. I know that this thread is old, but just in case some of you have been also reading up on this, I thought that I would let you know that I have just completed filling my ZX45 with Epoxy Granite. Came out really good and it is now heavy as.

Have not run it yet to check out the actual benefits as I am installing the "one shot" lube system.

I will post photos if there is an interest.


Cheers,

Rangikea.
 
Our new $1.5 million new Mazak horizontal mill does not have grout, it sits on a concrete pad that is poured into the floor to stabilize it. Not many people use grouts our epoxy anymore because you have to jack hammer it out when your survivors take it out of your garage or basement after the estate sale.....
 
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