Foundation for Cylindrical Grinder 1

[pioneer09]

We are currently working on the foundation design for cylindrical grinders that are in an industrial type building, total weight of unit and work piece would be approx 130kip. The owner/client is specifying an 8' depth of footing for a 6'x70' footprint. This would match an existing unit they already have in there facility. Through discussion in our office, we believe the only reason a footing of this depth would be required is for damping of dynamic forces. Looking at how these machines run, it seems there would not be that much vibration/dynamic forces to require this.

The machines they plan on putting in are used equipment, and no manufacturer information with regards to the foundation requirements can be obtained. Wondering if anyone else has designed for cylindrical grinder foundations and if this thickness of slab seems reasonable, we feel this is overkill for the foundations.

 

[EngineeringEric]

8 Feet or 8 inches? 3360 cu ft of concrete?

 

[pioneer09]

8 Feet. That is correct, 3360 cu ft of concrete for one of the machines. Seems very overdesigned in our opinion.

 

[EngineeringEric]

I cannot rationalize why it should be that deep, i would think you would have problems placing that much concrete at once. I would think a thick slab with deep & stiff turn downs would be more than sufficient. Unless that grinder is something crazy, I'd call the manuf and ask what sort of vibration one would expect.

I have not designed one that big, but i will not say it is overdesigned.

 

[JedClampett]

There's some old "rules of thumb" guidance, that the foundation needs to be 3 times the weight of the equipment or 10 times the rotating pieces.
Look at it this way, if you don't provide the 3 times the equipement weight in the foundation and there's a vibration issue, they'll find some crusty old engineer to regurgitate that rule of thumb. Concrete foundations are cheap. I might reproportion the depth, but I would end up with close to the same quantity.

 

[EngineeringEric]

That makes the mass ratio 3.7.
Jed may be onto something! Damn those old crusty engineers and their rules!

 

[pioneer09]

I had never heard this before. It does give some practical insight into an approximate depth check. Thanks

 

[hokie66]

Agree with Jed. If the client has specified it, just do it. Vibration in industrial facilities is not to be taken lightly.

 

[SlideRuleEra]

There is a 1973 magazine article on my web site that essentially backs up Jed's excellent advice and adds some detail:

http://www.slideruleera.net/MachineryFoundations.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[racookpe1978]

Machining foundations and grinding specifications need to be "funny" some times to get what the machinists actually need.

I was helping at a high school band competition a few years back. The machine shop across the street from the high school had to stop work that day because the base drums and drum lines in the high school warm-up practice area (the parking lot near the school) were creating ground vibrations that marred the finish on the parts they were trying to grind.