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What's a good vibration dampener?

CCWKen

Stainless
Joined
Mar 5, 2003
Location
Lytle, TX USA
I'm putting the final touches on a combination planishing hammer and english wheel frame. The frame is made from square and rectangular tubing. The problem is that it "rings like a bell".

Before I button up the frame, I want to fill it with something. Maybe sand? Lead shot is out. That's toooooooo heavy. The space to be filled will be about .6 cubic feet (1024 cubic inches).

I need something that won't explode or burn when I weld up the caps.
 
Thanks Tom but I've tried that before on another project and it didn't help. Too much air I guess. It would have to be really dense foam to deaden sound (I found out).

Besides that, it won't take the heat.
 
You might fill it with concrete. If you use the masonry patching type that expands on curing rather than shrinking it will be tight inside the weldment. ITW makes the epoxy granite material that is routinely put inside welded steel cans to make precision machine tool and CMM bases. That is more expensive and I am not sure it is a lot better than concrete. Sand would damp it some but the concrete will add some stiffness to the structure as well as some damping. I think that will stop the ringing.
 
In the 80's there was a company that made high end industrial wood whacking equipment, and filled the welded frames with concrete for vibration damping. Hardinge, of course, pours their lathe beds out of concrete now, instead of CI. Supposedly same reason (vibration damping) Couldn't be for lower cost, of course.

(Unmodified) standard concrete weighs about 150 lbs/ft^3. Your call wether to go with the nylon strands mix. Or an epoxy modifier. Think I'd keep it cheap, use the straight mix pretty dry, and vibrate the heck out of it to settle/pack it in tight Weld the "bottom" end caps on before starting. You won't need caps on the "top" if the concrete is smoothed off nice.

smt
 
You might also try drilling and tapping some holes at irregular intervals around the frame. Put some nuts jammed together on the end of a threaded rod. Insert the threaded rod in the holes, torque down, tack weld, and cut off the rod. It shouldn't take much to alter the frequency response of the frame so it doesn't resonate.

The tapped holes would only be on one side of the frame so the end of the rod would press against the opposite side.

Roger

[This message has been edited by winchman (edited 05-05-2004).]
 
Non shrink grout works as well and is potentially better than concrete. Concrete shrinks just a little and pulls away from the metal frame. I used 5 Star brand because it was available. Check with a local masonry supply for what ever is locally available.
 
Hardinge lathe beds are concrete??? (!) Do you mean the machine base or the bed itself? Stan.
 
Use gravel, old chain, or junk nuts and bolts but don't fill the spaces up. Dense random sized stuff is better. The media has to have freedom to jostle and rattle. Several trays of loose stuff in a single layer is far more effective than a loose but deep pack.

You only need damping at the ends of an "C" shaped structure. This catches the first and third order resonances and the feet in contact with the floor will deal with the second and fourth. Generally there's so much intrinic damping there's little problem with third and higher orders unless there's direct excitement.

Don't use oil or grease thinking the viscous damping will help. It's effect is mostly as a coupling medium unless fluid shear han be evoked somehow. There's also too much chance for a leak unless the sturcture is seal welded.
 
Deere used some type of clay for noise and vibration to isolate cabs. I don't remember what was special about it and I'm sure they wouldn't tell.
 
Dang Forrest, you've hit upon my idea EXACTLY but put me off it. But I don't understand your answer!

In order to add density and vibration damping to my knee-mill I was thinking of filling it with sand AND soaking the mixture with oil, sort of a slurry. No good reason for this, it just seems like an approach that might work to me. The sand provides the weight, the oil-slurry effect adding to the vibration dampening.

Forrest, you sound like you've come across such a nutty thing. Can you tell me why it won't work well, and whether capping the bottom of the column and filling up with plain ol' sand will help keep down chatter? I'd like to maximize the ability of this mill and don't mind making a few modifications. Seems simply adding mass to the column might be a step forward.

By the way, I've stumbled across a source of anti-vibration mounting pads on eBay. They're made by Paulstra, the Stabiflex model 530622, hardness of 45.60.75. (Took a while to figure this out.) If you go to the Paulstra website and navigate through the 'flexible mountings' catalog you'll come across the Stabiflex mounts on page 40. Or, on the odd chance this link will work, you might go straight to it here:
http://www.paulstra-vibrachoc.com/Stabiflex_GB.pdf

The eBay link to these mounts is right here:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3812310776

The seller has more of these.

This French company lists the nominal static load of the mount as 95-380 dekaNewtons. A whuuut? I tried to find a conversion table on the 'net and the best shot I've got is a conversion of 2.25 pounds per dekaNewton. If this is right, then each mount is suited to support ~200 to ~850 pounds. The mount is shown in the catalog as suitable for machine tool usage and the load range looks good. Somebody here might need a few of these, and at $10 for a set of 8 how can you go wrong?
 
Elliot. What kind of knee mill? What conditions produce chatter of a severity to require damping of large elements of the machine's structure?

Yours sounds like a heroic effort to cure a problem that may have origins elsewhere.

If yours is a theoretical concern let me set your mind at ease. All chatter (cut geometery induced, mass/elasticity propagated cintinuous vibration) is either work or cutter originated. Any chatter in a knee mill may be cured by adjusting the cutting variables, using stiffer spindle tooling, or in the event you're trying to run a 5" shell mill in and R-8 spindle or soemthing sibilarly futile re-think the job.
 
I was going to suggest dry sand, since it is looser, and damps vibrations very well. Just go ahead and fill the frame.

The sand will fill up spaces that concrete misses. If it settles, just add more.

You probably have two types of ringing. One will be the whole frame vibrating, but that will be a lower frequency "boing".

Another higher frequency noise is diaphragmatic (bell) resonances of the tubing itself.

Sand will damp both.
 
Mr. Addy,

I really don't have a chatter problem - yet. What I've been doing for the last 2 years is slowly assembling my modest suite of manual equipment while slowly finishing my building. I'm about done and ready to find final spots for the machines and put them into action. If I'm going to fiddle with it, now is a good time.

What I have is a standard import knee mill based on the ol' Bridgeport column. A nicer one, brand new from a guy in Florida who has a line on only the bases, somehow. Not a cheap Chinese piece of crap but identical to the column Jet carries on their $5-$7K mills. I like it, and seeing as how I have a li'l time to spare, I'm of a mind to tart it up, if possible. Or maybe I've just got a bad habit of trying to 'fix' things that aren't broken....

Basically, all I'm thinking with the sand-filling idea is trying to add weight to the machine in whole. A column filled with sand ought to add over 500 pounds and surely this will help reduce general vibrations a tad, wouldn't it? Plus, it seems to me sand is a natural viration dampener as well. Could it hurt to try?

Does anybody ever do this, or am I just crazy?
 
"A column filled with sand ought to add over 500 pounds..."

Yikes! How big is that column? Play sand weighs about 100lbs. per cubic foot. Wet sand about 130lbs. (1728 cubic inches per cubic foot.)

I set up some tests using some cutoffs I have. I filled one with concrete and that should be set up by tomorrow. I'm using 2x3/16 x 15" pieces of pipe for the test. I drilled a through-hole at the top of each so I can hang them in free air for the ring test. I'll do the tests tomorrow but here's what I'll be using--Mostly because this is what I have on hand. I don't have any test equipment so I'll be playing this one by ear.
biggrin.gif


1. Dry Play Sand
2. Dry Gravel (pea size)
3. A mix of 1/4, 5/16 and 3/8" x 1" nuts and bolts
4. Concrete

I'll take the best one of these four and compare it to an oil-wet play sand trial (I only have four tubes to test with). I should have the results by this time tomorrow.
 
Bulk silicon sealer (blue goo) poured in and cured. Used a lot in motorcycle handlebars to dampen vibration.
 








 
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