Anti Vibration Goo?

[Forrest Addy]

OK you want inert? Uncured rubber blots up an amazing amount of energy. I kinda prefer rubber crumbs from the tire prep area of a tire recapper. Spring suspend a mass in contact with a fixed tray of these crumbs and most vibration is swallowed up.

First of all in machine tools it's wise to eliminate vibration instead of mitigating it. If your small lathe vibrates track down the source and eliminate it. It's that simple. Adding hardware fixes is only make-up on the corpse; it may look better but it's still dead.

None of my machine tools have any vibration mitigations gimmicks nor do they need them. The factory motor balance is already pretty good. All motors are three phase the run from VFD so very smoothe there. All my lathe chucks run in good balance when gripping round stuff dialed in to 0.001".

Some machine tools driven by single phase motors are plaqued by a mysterious vibration problem that clears up as soon as the machine is re-motor to DC or three phase. You can argue the cause or the reason but the fact remains that single phase motors often introduce vibration in machine tools. "Often" is to me about 1/3 of the statistical universe of all single phase powered machine tools. Ranking descriptors: "sometimes" means less than "often." "Frequently means more.

The ranking of frequency of incidence I've adopted is: Never, Rarely, Seldom, Occasionally, Sometimes, Often, Frequently, Nearly always, Continually, Always. Dispute this rough ordewring at your own risk. To do so revealed you as anal compulsive and control obsesed. Yes it is a test and I bet Sami and Bodger bites.

[dian]

cast the whole riser from epoxy granite. do it on the machine and top it off with pure epoxy. it will selflevel. you can incorporate any fixing features and even t-slots, if neccessary.

[firemandiver]

Thanks for the lesson on eleminating vibration. That's really a little deeper than I needed. Good reading all the same...you never know when that info may come in handy.

Let me be clear...I may have put the cart before the horse. I just got this machine and am new to machining. I have only done one little thing with the mill, so I honestly can't attest as to whether the machine has much vibration at all. I've used the lathe more than the mill, but still not much. I didn't notice anything that seemed abnormal to me. Unless it's some behemouth machine that by sheer size absorbs it all...... most benchtop machines are gonna have some rattle and hum. I'm not trying to eliminate a problem, just put a little extra thought into the design/build process.

I'm gonna make a fixture, and if there is any merit with trying to build in any inherit damping, of course it's better to do when it's made rather than trying to retro fit it later.

Never heard of the epoxy granite thing. Where can I find it?

Thanks, FD

[dian]

you have to make it. get some epoxy, i use sikka 156 (is used for floors and has low viscosity), get some gravel used for concrete, dry the gravel thouroughly and try mixing 1:7 epoxy/gravel by volume. play around with it a bit to get a feeling for it. forget about degasing or vibrating. make a mould and line it with ordinary polyethylene foil (0.2 mm works well). put in the mixture and enjoy your riser the next day (@ 20°c).

[tdmidget]

The epoxy granite ( or is it granite epoxy is not a bad idea. The worlds foremost grinding machines, Kellenberger and Studer are made this way. The metal ways and other parts that need to be metal are cast in and machined in place. They say that it damps vibration better than cast iron and as previously noted, it is easier to work.

[Thruthefence]

Just for fun, I once cut open an aircraft engine mount from a Lycoming recip, and inside of it was a sort of highly viscous rubbery material, that if rolled into a ball & left alone, would "flow" out to a puddle after a few hours. Sort of an aerospace "silly putty", I suppose.

hope it doesn't cause cancer.

one of a few experts in the field:

http://www.lord.com/products-and-solutions/vibration-and-motion-control.xml

[darryl]

I would go epoxy/granite as well. There have been suggestions to look for aquarium gravel, as it's already clean and of a good size to maximize the gravel to epoxy ratio. For the amount you need it should be easy to find and fairly cheap- same for the epoxy. I'm not sure what the gravel mixture would be, but I don't think it's all that important for a simple filler like you're looking for.

I might be inclined to get a plastic container of about the same volume that you're wanting to fill, and put some gravel in it to a measurable height. A kitchen measuring cup would be fine for this. Then add water until it just covers the gravel. Pour the water out and measure the quantity. Now you know fairly closely how much epoxy it will take to fill the gravel. Once you get going, a procedure might be to pour most of the epoxy into the cavity, then add gravel, shaking and tamping it down as you go, then add more epoxy and gravel to bring the level close to the top, then kind of tuck the gravel into the sides with a stick, then fill the remaining cavity with gravel, then top with epoxy. Seems like a procedure to me that will get the air out easily, and get the high ratio of gravel to epoxy that these E/G guys are going for. I would roll the structure around a bit so that any air bubble trapped at the top of the fill could escape through the fill hole- then give the final compaction and complete the fill.

By the way, don't use the wet gravel that you measured with for the fill. You could dry it first, then use it, but you'll likely already have bought enough to experiment with, then set that aside and use the dry for the fill. You could still use that wet stuff later, since it will have had lots of time to completely dry before use at that later date.

[CCWKen]

I experimented with this years ago while building my planishing hammer. I tried a number of medium and for sure, you don't want anything solid or semi-solid. The filling actually needs to be able to move some to reduce transmission of vibrations. I ended up filling the frame with oil-dampened sand. Just below that in my tests was gravel, if I remember correctly. Worst was concrete. I tested water, foam rubber, steel shot and some I can't think of just now. I think I posted the test here some years ago.

[firemandiver]

I kinda thought about the solidness issue...if it is a little loose it should help to dampen vibratons. Kinda like a deadblow hammer. I think I've decided what I'll do: I have several dive beanbag weights with little holes that I've saved with the intent of sewing up one day, but just got new ones.

I think I'll dump the lead shot in my fixture. They're about the size of BB's. Can't hurt....and I'm out nothing if it's a bust.

Thanks for all the insight.

FD