[ad_bfl]

One thing not discussed in this thread is mixed material designs, meaning a welded/normalized steel frame with usage of EG for vibration damping, either contained inside some of the steel structural members or surrounding them, similar to the work done in the "Rapid Machine" thesis.

I am game for investigating that area. Any suggestions as to how?

Lets say I take a 4x4x1/4" wall A36 steel tube 16" long, and fill it with EG (Mix tbd).

Now how would I test the vibration damping characteristics without a room full of expensive stuff and get some quantitative results that we can use?

ideas anyone?

[romihs]

ad_bfl,

A quick, and pretty simple, method would be to use a microphone (and perhaps an amp) hooked up to an oscilloscope; place the microphone close to the beam under test and hit the beam with a hammer.

You could measure the resonant frequency and duration of the oscillation of the beam empty and then when filled with EQ, and compare the two.

Just me 10c worth...

Regards

Sandi

[lgalla]

Alan there has been discussions on filling weldments with E/G for dampening in the thread at the beginning.The posts of late have concentrated on fine tuning for E/G in a stand alone configuration.
I you took that 4X4 and filled with E/G there would be an improvement in damping.To confirm an improvement without a room full of test gear,use a hammer instead.Hit the tube with a hammer and it will ring.Fill with E/G and you will get a low dud showing improved vibration damping.My only concern has been to damp existing structures and don't know or care how much an improvement as long as I know I have better performance over a hollow structure.Needing specific #'s only slows the progress kinda like [being stuck in the mud].
Larry

[roach]

been making "GRANITAN" for 24 years
be glad to help

24 years you name it ive made it
ask and ill tell you

[ckelloug]

ad_bfl,

Really accurate measurements are hard to get. I've been taking at face value the 7x damping of cast iron numbers from an old article in Machine Design magazine. Calculating he exact properties of the damped tube is probably a fun masters thesis.

On a similar note, take a look at this paper. You can likely get the modulus using a microphone, a hammer and a PC sound card.
http://www.ncdot.org/doh/preconstruc...06proposal.pdf

Also see www.grindosonic.com. I have some better references but they aren't in the thread index and I'm in windows where my E/G work isn't. There is a NASA paper at grindosonic's website that explains the formulas etc to extract the tensile and shear moduli from microphone and hammer type tests.

Qualitatively speaking, by my understanding, the difference in density between the E/G and the steel tube will form the vibrational equivalent of a fiberoptic cable channeling the vibration through the E/G preferentially where it will be turned into heat due to the very high damping factor. Wave Physics also suggests the maximal effect will be had if you can make E/G with a continuous density gradient. I haven't even though of practically handling this. I believe the difficulty of modeling the situation is why whack and check style methods of testing are popular.

Regards all,

Cameron

[ckelloug]

Hey roach,

Welcome to the controlled chaos! Don't forget to check the thread index page which is a sticky in the forum that this post is in.

So tell us, what do you make?

Regards all,

Cameron

[roach]

ill tell you

optical grinders,lathebeds,surface measurement columns bases,grinding beds heads,castings for centrafuges,lasers,high frequency test beds,milling beds columns heads laser engravers lots fabricated infills

[romihs]

Hi Roach,

Welcome to the thread.

You do know that you are going to be 'pestered' with loads of questions... I'll be one of the first...

You mentioned lathe beds, well, I intend to use this material for a lathe bed.
I am in the process of designing the lathe; I would like to build it so that I don't have a steel insert the length of the rails, I would like to have inserts present only for the mounting screws.

My question is this: Is it simpler to construct a precise mold so that the linear rail beds are ready to receive the rails right away when the lathe bed is de-molded, or is it simpler to just post grind the E/Q (polymer concrete) before mounting the rails?

Thanks and best regards

sandi

[lerman]

If we use an electrical analogy, the damping will determine the width of the peaks when we measure the resonant frequency of a component. It will also determine the rate of decay when we ring a bell.

We could put a piezo tranducer at one each of a rod of our material. Put a signal in one end and display the signal at the other. Then sweep the frequency from low to high. Plot the signal amplitude as a function of frequency. The peaks we see will be the resonant frequencies of the assembly. Materials with low damping will have narrow peaks. Materials with high damping will have wide peaks.

Instead of applying a sine wave at the input, apply an impulse. The output signal will be a pulse if the material is well damped. If the assembly is under damped, there will be a decaying sine wave.

The various resonant frequencies will depend on the dimensions of the sample, the speed of sound in the sample, and probably lots of other things that I am ignorant of.

If all you want is comparative information, that should be pretty easy to get with simple apparatus. Quantitative info is harder to get without calibrated transducers.

[This stuff is off the top of my head. It might be partial or total BS. Feel free to tell me so. In fact, I insist.]

Ken

[greybeard]

Cameron -if I spin test samples, they will have directional in their properties, stronger in one direction.

If I do this and send them over, can you produce info that might be useful in comparison to static cast blocks ?

John

Point of interest - what about the aggregate size being restricted to 1/5 minimum dimension ?
This would mean the test samples at 3/8" thick would only have 2mm max particle size ?

Not a problem for me, but what of others ?

Further question to the above - which way up do you test the specimens, with the x-section portrait or landscape ? My specimens will have different values in each direction, I'd guess.

Regards
John

[ad_bfl]

Great suggestions

I may actually try to build one into my machine frame to measure dynamically the resonance as the machine is traversing, cutting etc..

I will be trying this over the next few weeks, as I get results in, will post them. My first attempts will be on my upper axis (design heavily based on Rapid Machine design Principals).

Thanks Guy
Al

If we use an electrical analogy, the damping will determine the width of the peaks when we measure the resonant frequency of a component. It will also determine the rate of decay when we ring a bell.

We could put a piezo tranducer at one each of a rod of our material. Put a signal in one end and display the signal at the other. Then sweep the frequency from low to high. Plot the signal amplitude as a function of frequency. The peaks we see will be the resonant frequencies of the assembly. Materials with low damping will have narrow peaks. Materials with high damping will have wide peaks.

Instead of applying a sine wave at the input, apply an impulse. The output signal will be a pulse if the material is well damped. If the assembly is under damped, there will be a decaying sine wave.

The various resonant frequencies will depend on the dimensions of the sample, the speed of sound in the sample, and probably lots of other things that I am ignorant of.

If all you want is comparative information, that should be pretty easy to get with simple apparatus. Quantitative info is harder to get without calibrated transducers.

[This stuff is off the top of my head. It might be partial or total BS. Feel free to tell me so. In fact, I insist.]

Ken

[jhudler]

Now how would I test the vibration damping characteristics without a room full of expensive stuff and get some quantitative results that we can use?

ideas anyone?

Sound card is great for this.

You can test a piece of steel and strike it with a known force, then test an equivlent on EG.

No fancy software, you can just record it and view waveform in a WAV editor program.

[ckelloug]

John and Gizmot,

Your comments about the sample dimension needing to be 5 times the largest aggregate vs. the 1/2 x 3/8 x 7 1/2 are spot on. This sample size limitation is due to the fact that I have the wrong test fixture in my machine for bigger samples. I expect to be able to test 1x1x 19 1/2 samples eventually but until I get my bridgeport fixed to build the larger test fixture, we're stuck with these small samples and the lower density which will be caused by the disturbed region around the edges of the samples.

John,

The 3/8 dimension is the depth., The 1/2 inch is the width.

Ken,

I think that your electrical analogy for vibration looks good to me. I studied general engineering myself so I am by no means an expert on what should happen here. It's all the same second order differential equation however.


Regards all,
Cameron

P.S.

I know I still owe some answers on simulation benchmarks etc.

[roach]

sandi
depends on how many castings your going to produce
1-5 off id go for grinding the casting then bolt your rails on
is it slant bed or center bed ie chuck on end tailstock the other
alot ot castings the a better mould
the granite will reproduce the tolerance the mould been machined to
if your going to have slideways you can cast those of of a composite aswel

[lerman]

Cameron,

Why don't you draw up the plans for the test fixture you need and post them here?

I wouldn't be surprised if someone here would just make one for you. (I'm out of commission for a while due to recent surgery, or I'd do it myself.)

Ken

[jhudler]

Cameron,

Why don't you draw up the plans for the test fixture you need and post them here?

Great idea! Those little sticks are a bugger to make!

[romihs]

Roach,

Thanks for the reply and info.

I just want to ask you for more clarification on the last thing you said; "if your going to have slideways you can cast those of of a composite aswel". Are you referring to the 'classical' lathe slide ways?
I will be using linear bearings.

To answer your question about the configuration, I think I will be going for the slant bed because it is the best configuration to use with this material (in my opinion, it handles compressive forces best).
But I am still in the very early stages of the design.
I will start a separate thread about it soon, and post it here to let you guys know. That way I will stop posting off topic replies and questions on this thread.

Regards

Sandi

[ckelloug]

Hi all,

If there are any lurkers or regular contributors who want an excuse to read the last thousand or so posts and update the thread index, please send me a PM.

The index is generated manually with the help of special software I wrote that can convert post numbers to links. (When folks ask questions here and I respond with a reference, It's not that I have the posts memorized, I look in the thread index.)

The job entails reading posts and writing index entries in a simple notation I developed. My index parser then downloads the thread contents and writes HTML that can be posted to the index thread. I then post the new index and have a moderator delete the previous index post since occasionally vbulletin renumbers posts internally and breaks the links.

Regards all,

Cameron

[roach]

create two lands where your rails go then it will ne easier to grind sandi
r you dowelling your rails or setting them upif dowell the in you can put a ground plate into your mould which is ground with dow holes in
hope it helps

[lgalla]

Sandi,I don't think discussing your machine designs is off topic.The beginning of the thread had many ideas for E/G use.An actual build deserves a separate thread.Here ideas are welcomed.Walter's original posts were to design machines requiring little or no welding.
Sorry to say I was going to use a welded base for a 6'X12' table with 14"X14" 1/4"tubing like some pro routers.See attachment.
The base would weigh 3600lbs and probably cost $4,000.
If I used E/G as legs for a self supporting table top it would be cost effective and easyer to implement.
Say the legs were 12"X12"X24".This would be 2 cu ft of E/G at240lbs and about $300per leg.Using 6 legs the cost is $1800,much less than steel and possibly better.The idea is only one hour old,so not much detail.Any comments?