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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy-Granite machine bases (was Polymer concrete frame?)
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  1. #1281
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    Glad to see the papers on ratios,mixes etc confirm my hands on experience.I have stated from the beginning 10% epoxy is impossible with our limited tools at home.I have stated in the past,which is better,10% dry epoxy mix or 20% with better wet out.The papers seemto say 20% is AOK.
    Cameron the carbon black ratio is way too high.Unscientific ratio:add to taste or its black enough.
    I was hoping for a Home Depot mix.Playsand,filter sand or aggregate,graded sandblast sand etc,for simple easy to obtain mixes.To dupe the big guys,impossible,at least on ratio.
    De-Gassing 7% German beers presently;conclusions,7% Alcohol is obtainable in beer mixes,not in epoxy.Outgassing is smelly,refrane from smoking or other sources of ignition.
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  2. #1282
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    I fine-tuned the ratios and did another run:


    Rock 1 __________ 12.5%
    Rock 2 __________ 17.5%
    Sand 1 __________ 15.0%
    Sand 2 __________ 15.0%
    Zeeospheres _____ 10.0%
    Fine quartz_______ 15.0%
    Carbon Black ______ 0.5%
    Epoxy ___________ 14.5%



    This time I had 30% of rocks, 55.5% of sand-fines-carbon black, and 14.5% epoxy. It was still black as hell.

    I was somehow able to "pour" it into the mold and my shaker did the rest- the mix started to liquify.

    We'll see what the strength test reveals.

  3. #1283
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    Carbon Black and other finely divided stuff

    Here is a quote from K. Gamski in the 1975 proceedings about the purpose of the regulator charge:

    <blockquote>For a chemically stable composite, chemically resistant charges must be used to regulate the reactivity of the binder and its viscosity and to reduce the hinderancy effect of inert charges on the evolution of shrinkage, regulation charges must be used. This type of charge is characterized by a high specific surface area of 3,000 to 5,000 cm^2/g (300-500 m^2/kg). In order to neutralize the hindering effect of inert charge on the evolution of binder shrinkage, a binder regulator charge ratio of at least 1:1.5 to 1:2 is recommended.</blockquote>

    The carbon black that we have actually has a much higher specific area than the stuff they specified. closer to 10,000 cm^2/g. The purpose of the carbon black is to prevent strains in the material caused by shrinkage and to provide some dispersion hardening as I and DAK3333 mentioned before. From Walter's results, it looks like the russian paper cited must have meant by volume. Either that or it's measured in terms of specific gravity of Peter the Great's urine or something. . .

    Gamski's data along with Gupta's and Walter's data show that by weight 9% epoxy is the minimum useful amount (less ruins strength) and that strength seems to go up until 12.5% and starts to go down above 14%. These were from specific mixes with fewer fines than the one I wrote up. Like I said before, the equation Gamski says should be used to predict the amount of epoxy combined with Gupta's optimal 33 micron thick epoxy layer result gets 35% epoxy by weight with the mix I put in the formula. This right amount of epoxy goes down with the larger rocks added by walter so I think he's got a reasonable mix.

    As for easier to obtain mixes, I still contend that Dupont Starblast Ultra Staurolite sand is near optimal for a no large rocks mix. Besides, it's heavy and one of the papers I read says that strength can be accurately predicted by a formula where weight per cubic foot is the only variable.

    Qualitatively, the homeshop folks will likely do a lot better with the larger aggregates as they are much less subject to the effects of poor deairing ruining the mix. Smaller aggregate mixtures appear to be stronger according to Gamski however.

    I think Walter ought to get some fairly decent results out of one of today's batches.

    I'll write up some more formulas as I get a chance. The formula in the Huntsman literature may be more appropriate for instance. I also owe calls to dow corning, agsco, and byk today.

    In summary, Rock on Walter. Thanks for the commentary on the carbon black, Larry.

  4. #1284
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    Quote Originally Posted by ckelloug View Post
    Secondly, and this is pragmatic to use fyffe555's euphemism for not thorough,
    Pragmatic; (ADJ) to deal with the facts, actual occurance in a practical manner....

  5. #1285
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    Quote Originally Posted by ckelloug View Post
    I'll write up some more formulas as I get a chance. The formula in the Huntsman literature may be more appropriate for instance.
    While I'm sure your efforts are appreciated, rather than speculative suggestions I'd think it would be more appropriate to publish your own results?

    Personally I'd be concerned if my personally untested 'predictions' were tested on someone elses dime.

    As Larry mentioned, there's already qualitive measures for epoxy ratios achievable in this thread.

    The papers cited are not consistant on ratios by volume weight or even aggregate shape with resultant variable wetted area to mass ratios. It's one thing to draw a conclusion but it's application or proving the conclusions meet expectation requires either more research or someone performing a lot of testing.

    At $30-$60 per gallon someone's paying a lot for the privilege of testing the theories.

    Andrew

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    Thanks Walter!,
    I'm not an engineer, I've just observed them in their natural habitat. They say that engineering is part using appropriate technology for a cost effective solution.

    It seems like in a nut shell the projected uses for E/G are Tables, (flatness and stability), Gantrys, (stiffness) and fillers, (vibration dampening). And always cost is always a consideration.

    There is a great way to make concrete strong enough in tension to span gantry distances: Add a bunch of after casting compression. (called for some reason "post tensioning"). The idea is that if you look at the beam sitting there it has weight pushing down, and strength (part tension). pushing up. If you add a lot of force squishing in, and the strength of the concrete pushing out, the resultant force pretty much cancels the up-down force and the whole thing gets more stiffer. http://en.wikipedia.org/wiki/Prestressed_concrete.

    The table's machining problems might be solved by casting inserts for say t-slots into the table. If a flat surface is real important, maybe a steel egg-crate grid could be cast in, sticking up an 1/8" above the EG, then machined back to flatter than flat. I think that the grid could be anchored within the E/G so that any tendancy to move with temperture would be restrained. Like wood veneer glued to plywood restrains the veneer.

    The filling - dampening application seems made to order, so long as the weight of the E-G doesn't cause things to sag.

  7. #1287
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    Spherical Aggregate?

    OK, so I'm not often watching this thread, but where did the obsession for sperical aggregate come from? I assume it's because there's some papers on spherical packing? Isn't that missing something? Anyone cite any concrete mix in a strength application that uses spherical aggregate?

    As suggested by others much earlier in the thread you will get better stength from non sperical irregular rounded, not sharp aggregates, ignore the 'perfection' of 'optimum' ratios, and concentrate on the methods and practicalities of actual production and material use.

    I assume the sperical packaging algorithim is proposed to get maximum aggregate ratio and greater strength? If so, why use sphere's as a starting point in the first place? Its the worst shape for maximum fill annd conferes no mecanical strength other than in compression. Spherical packing also only imparts strength when the pack is externally bound. That is, stack a load of cubes or other regular solids and it's stable without glue, now try that with marbles - exchange gravity for load - the pack will only be as strong as the sheer strength of the binder.

    Aggregate Ratio; In any regular right volume, say a cube, a sphere of the largest size will occupy 74%, the ratio of volume of sphere against cube of the same dimensions. Using perfect spheres actually leaves you with the MOST volume to make up over any other regular shape. Using cube material would allow perfect fill for example.

    Strength; Assume the strength of the composite epoxy aggregate material is a product of the mechanical strength of the epoxy, the sheer strength of the epoxy and the strength of the aggregate. The suggestion is the more aggregate elements in contact with the next the stronger it will be. Even in *perfect* spherical packing the maximum contact is four single point contacts. The interstitial fillers of smaller aggregate will not add contact strength unless they are also perfectly packed. Since its not reasonable to assure a high percentage first level (largest) perfect pack its not reasonable to assume the smaller aggregates will either. So you're left with epoxy as the load bearer with the smaller aggregates as mostly just fillers. A cube aggregate would make contact with flat planes and the strength be increased accordingly. A fibre composite aligns the fibres along the entire length.

    The strength of a composite is also a function of the sheer path. Glass fibre composite is strong because the fibres are good in sheer and even better in tension. If a material starts to fail, the sheer (cracking) either through exceeding the epoxy adhesion or epoxy strength will propagate through the plastic binder (epoxy) until it hits the strengthening element. If that element is a fibre the sheer will stop there. Until the element fails. With loads of elements there's loads of resistance to sheer. The fibres run a long way as a proportion of length over thickness through the composite so the material has no easy sheer plane.

    In EG with a perfect sperical aggregate with perfect packing the sheer plane is almost a perfect straight flat plane, with the varience only half the diameter of the largest aggregate. With epoxy granite as proposed the material will start to crack once the tension strength is exceeded and once it starts there's little to stop it. You do want the layup/filler/aggregate to be somewhat irregular and not present a simple sheer plane. Otherwise the aggregate adds little to the composite strength.

    Voids; Concrete stength is a function of the voids in the mix. E/G's the same, you do not want voids, even if that means you use a much higher ratio than the 'math' suggests simply because its better to have something in there other than air.

    Again, earlier in the thread someone suggested wetter mixes appeared stronger and someone proposed using excess epoxy and removing the excess with existing vaccum bagging methods. Both excellent observations.

    The 'perfect' spherical pack with optimum ratios not fully aligned in manufacture could be little stronger than the binder alone. A close ratio mix without voids will be stronger than one with voids. A mix with no regular sheer path will be stronger still.

    Andrew

  8. #1288
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    just in case;

    in case it's passed people in the excitement;

    Silanes are dangerous just reading the MDS. Commercial use is heavily controlled. nasty stuff you don't want in your house.

    Carbon Black is a carcinogen. Don't breath it in. There's a reason you don't get loose toner refills anymore.

    Several Epoxy wetting agents can affect the nervous system - permanently.


    Other than that its all easy! Well, other than epoxy being effectively a product of toxic substances and people can and do develop an intolerance to it it. Allergy like symptoms at best.

  9. #1289
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    Andrew,

    It is well known by walter at least, who's been the most interested in testing, that I am in the process of building my workshop area and will not be done for several more weeks. As a result, I cannot test my own formulas right now and have offered them here because there are others who want to try to make some progress with ideas besides randomly mixing epoxy and sand and hoping for the best. Walter and I have in fact had some discussions about sharing research costs off the thread. If walter would like to invoke that agreement then all he has to do is ask. Were I dishonest, Andrew, I would not have publicized the fact that the formulation I gave was untested.

    I will test and publish the results here, on my own dime, I might add, once I have somewhere to do testing which isn't my kitchen table which is already overburdened with jars of carbon black and pieces of workshop.

    As for pragmatic, I do know the definition and I felt that not-quite thorough was your implication by the use of the word in the context of your last message. I hadn't been thorough on the shear calculation and relied on accepted suggestions as to what was reasonable rather than my own experience with the problem at hand there.

    Finally, I do have the Proceedings of the First International Congress on Polymers in Concrete London, 1975 here which I bought for the purposes of furthering the understanding of the polymer concrete amongst myself and this group and thus the items I have been quoting are from legitimate researchers in the field.

    Virtually none of the ideas I've been publishing here are mine. I for the most part have published what I have been able to piece together and synthesize from research papers that were mainly posted here by others.

    As for your comments about my epoxy stuff being theories: They may be theories but they were theories cited by Gupta's paper posted by Brunog and published in the book of proceedings I have been working with.

    From Gamski's paper pg 225 in the London proceedings:

    Epoxy mass=(S1G1+S2G2+S3G3. . .)*gamma_b*t*eta*k. Where S1-Sn are specific surface ares of aggregate sieve n, G1-Gn are masses of that aggregate used, gamma_b is the specific mass of the epoxy and the carbon black,t is the thickness of the epoxy around each aggregate grain, eta is the ratio of the epoxy viscosity at mix temperature to its viscosity at 20C and k is the aggregate growth coefficient.

    K is taken by all papers I've found to be 1.05. The 33 micron thickness is taken from Gupta's paper.

    In short Andrew, you are obviously a sharp guy and one who I respect from my limited interaction with you so far. I appreciate your skeptical point of view and I want to be as transparent as possible here in the tradition of scientific research.

    If my technical perspective as someone trained as a systems engineer doesn't seem to fill the gaps in the knowledge on this thread; I am sure you have the capacity to pull the same or better references and post your own conclusions. I'd be happy to see you do that as the conclusions of 1 person are rarely as good as that of many.

    In short, Andrew, I don't have anything to hide and I welcome your criticism. I'd be even happier however if you would use your talent to provide another technical viewpoint on this thread.

    Best Wishes and Peace,

    Cameron

  10. #1290
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    Using E/G

    Again in all the excitement it seems from reading here the actual use of the material and design of machines using this stuff have dropped off the thread?

    The benefits of E/G where posted way back when by Walter and Larry, but it seem it's gone past that to now producing an entire machine from E/G? Is that the plan?

    While E/G has it's benefits; good compressive strength, Vibration damping, epoxy pourable to extreme levels of flatness, E/G cold castable to high degrees of accuracy and in irregular section, castable around fixtures and mounts and so on it also has it's drawbacks incomparison to usual material; heavy, weaker in compression, very weak in tension and not to mention epoxy is relatively expensive.

    It doesn't have to be applied to every part of a machine, further, I'd suggest E/G is not an appropriate material for the entire the machine structure, jus use it where it uses its benefits.

    For example, where anything moves weight is a consideration. More weight, more cost in the linear components. E/G is not a suitable material unaided for unsupported spans or load bearing spans until large cross sections are used - there is an unfortunate balancing act required since the low tensile strength and high weight mean the an unaided beam will deflect under its own weigth. This static deflection could eat up a significant proportion of the available tensile strength of the beam even before any load is applied.

    You need to find sizing and design that makes account of this. Looking at the commercial offerings EG is used extensively and massively in beds, uprights and tables. Gantries and cross members are usually steel reinforced with E/G, either with a steel tube E/G filled or with internal steel beam or steel tenson elements.

    Andrew

  11. #1291
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    Thanks Cameron, I appreciate the hard work you and others have contributed to the Formula.


    Fyffe555, Thanks for the thoughtful write-up. I think those issues will have to be addressed.

    Quote Originally Posted by ckelloug View Post
    I think Walter ought to get some fairly decent results out of one of today's batches.

    I'm hopeful but not necessarily optimistic.

    I'm coming to a conclusion that nothing really matters- aggregate, no aggregate- you could probably use puffed rice and get the same results. Matrix seems to be the tricky part and unless you can control it 100%, you wont get anywhere near commercial E/G.

    I think I have some major curing issues as I can't control every single Celsius degree.

    And, the problem is, I don't really want to control every single Celsius degree- that puts me beyond the hobby status...

    I wouldn't be doing this if I had to build the lab first.

    The original idea was to use a concrete like substance, with it's simplicity and ease of use. I may have to go back to that simplicity. I will get rid of most of the components, including carbon black, and go with the barebone system.

    The pursuit of commercial E/G should definitely continue, but for this machine, my mind is made up. Check out post 1181.
    :wave:

  12. #1292
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    Quote Originally Posted by ckelloug View Post
    I'd be even happier however if you would use your talent to provide another technical viewpoint on this thread.

    Best Wishes and Peace,

    Cameron
    Entirely reasonable, unless 'another technical viewpoint' is to agree with the entire pro super e/g solution.

    If you'd care to read the earlier in the thread again you'll see my viewpoint. If you want to take it to PM thats fine too.

    I posted some calc's for Larry about steel beam spans and how E/G filler effects strength a while back. You disagreed, that's fine. My point however wasn't that the numbers said it couldn't be done, but to show what the real effects where if you took one set of published E/G strength figures over another. In a context that the materials proposed hadn't yet demonstrably reached that of epoxy alone as yet, and that even the lower figures where going to be a challenge to reach currently.

    One set of numbers over the other produce entirely different engineering results.

    Your recent beam illustration material numbers have been consistantly on the very high end, basically that as produced in industry with all thier additives, autoclaves, vacuum processes and controls. That's politely optimistic at best. If you simply calculate the same with alternate published numbers, not even that probable from a home process and account for the beam weight as a uniform load as well as the proposed point load the result is not very good.

    Personally, and this is my 0.02 so take it for what it's worth, the beam sizes proposed don't work. For a non commercial build it's not worth the effort or financial risk trying to make it work when you have an easy, reliable, simple and probably cheaper solution in a rectangular steel tube. Fill it with a non load sensitive E/G mix to add the deadening properties.

    In brief I think you're trying to propose the equivalent of making a 10000psi pretensioned concrete span bridge with just 3500 psi concrete from Lowes with a few aggregate size changes and suggesting it can be done from home. I'm not suggesting it couldn't possibly be done, but is it reasonable to try? is it repeatable? can someone spending thousands on the machine be confident in the material? will it affect the machine in practicality?

    Probably not.

    That's not to say it isn't possible if you tried hard enough. More importantly it's not really necessary and the materials benefits and deficiencies in use and how it affects design and how design affects material selection have been forgotten.

    To engineer anything requires a compromise and the 'art' is to produce the most effective compromise as directed by the motivators. Material property and selection is just one component. The impression, deliberate or not from the last few weeks is that the ultimate E/G formulation will answer all things, is the only solution and entirely ignores the actual practical production and use.

    While I appreciate the effort in investigating and trying to engineer the material to this degree, at the end of the day it's just a material.

    You can build a concrete canoe, but other than the intellectual challenge why would you?

    Andrew

  13. #1293
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    Hi Walter - I think you are getting near optimum as well.

    A few more comments from the newbie here

    - Carbon Black - I tend to think of this stuff as a lubricant for rubber / tires, and a UV protector. I just cannot see how this would benefit your goals.

    - Surface finish - This might seem as a minor point, but as it turns out, a surprising amount of the strength of a structural beam are surface effects. Aerospace engineers really sweat over scratches in the surface of an airplance.

    Anything you can do to make the casting come out with a nice surface will help.

  14. #1294
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    Quote Originally Posted by harryn View Post
    - Surface finish - This might seem as a minor point, but as it turns out, a surprising amount of the strength of a structural beam are surface effects. Aerospace engineers really sweat over scratches in the surface of an airplance.
    This is an excellent point and reminds me of an idea, you might want to consider lining the mold with a layer of epoxy and structural ( E or S ) glass before a big e/g pour. Does nothing in compression but a lot in tension loads such as any component with a bending moment. It will reduce the vibration damping properties somewhat.

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    Response to Andrew

    <B>Toxicity of additives</B>

    I have looked over and attached the MSDS for Dow Corning Z6040. It doesn't look hazardous to me. If anybody has comments about why this particular compound is something we shouldn't consider for home shop use (not in kitchen anyway), please post.

    I've also looked over the MSDS for BYK525 available from http://www.byk.com/output/download/BYK-A_525_gb.pdf It is a bit more troublesome than Z6040 but it doesn't look prohibitively hazardous for shop (not in kitchen) use.

    <B>Spherical Aggregates</B>

    Most of the theoretical papers I have found do computations with spherical aggregates. They then correct with a shape factor for packing of non-spherical aggregates. The correction is rather small leading to the belief that spheres are a decent model.

    Papers which I've read (but can't find right now) on the aggregates indicate that heavily angular aggregates compromise strength on the basis of providing crack nucleation points in accordance with Griffith fracture theory.

    It's my understanding that as long as the epoxy layer is not too thick that the load even with large quantities of fines is adequately transferred to spherical aggregates. This is borne out by Gamski Formula 10 which has 23.2% 0.2-1.2mm, 28.35% .15 -> .3mm, 48.5% 0.05mm -> 0.2mm sand which got 20ksi in compression and 1.4 ksi in tension, and about 3.8 ksi in flexure.

    Finally, Spherical packing with one size of aggregates is a complete disaster as I think everyone here has acknowledged. It gives a shear plane as you said. For particulate reinforced composites with no fibers, it is essential to have multiple sizes of aggregates. The specific sizes appear not to be crucial to first order from everything that I have read as long as they are widely varied. Whether the aggregate are spherical or not, the general conclusion can be drawn that multiple sizes of aggregate are essential.

    I.E. Sand plus epoxy bad. Sand plus epoxy plus gravel plus stones much better.

    <B>Cross Section of Beams</B>

    From the work I did with bruno's 36 inch beam, a 4 inch wide x 12 inch high beam 36 inches long, it looks like the only way to make this remotely work is to make it hollow with 1.5 inch thick sides and IIRC 2 inch think top and bottom. My calculation (neglecting shear) assumed the weight of the beam plus 100 lbs load and got a deflection of around .0002 inches. It seemed like just about anything done in terms of changing the dimensions of the E/G beam made it heavier and have a higher static deflection. From an earlier post, it seems like it might be possible to make a gantry router beam 24 inches long of sufficient cross section with no reinforcement but beyond that it's pretty much not going to work.

    Either steel tension members or post tensioning are definitely needed for lengths beyond 36 inches and probably make things much easier beyond 24 inches. Several posters expressed a desire for making a machine without huge steel parts so I wanted to figure out if it was possible and my subjective answer is that it's probably not reasonable for anything beyond 24 inches long.

    <B>Conclusion</B>

    From the data sheets I've posted, I do not think either the BYK-A525 deairing agent or the Dow Corning Z6040 bonding agent are particularly hazardous. I agree with Andrew that a single size of spherical aggregate is bad however I see no problem with multiple sizes of spherical or any other aggregate. I agree with Andrew that making parts of an E/G machine beyond 36 inches in length with no reinforcement is unfeasible and that without heavily engineered designs that making parts beyond 24 inches without reinforcement will be impractical for the average home shop hobbiest.

    Using hollow steel channel reinforcement has the additional advantage of not requiring well engineered E/G and further, for the gantry router application, painted steel channel might very well be filled with Portland Cement as suggested by Bamberg avoiding E/G entirely.

    I will post some test results when I get my lab finished but I am now feeling a bit dubious that people are actually interested.
    Attached Files Attached Files

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    Why Are We So Concerned With Static Deflection?

    All the static deflection number tells us is that the beam will bend by a thousandth or two under no load. Why is that a big deal? We should be looking at the dynamic deflection under actual (varying) loads.

    If we use the beam as a support for a rail (or for a metal support for a rail), we can just machine out the static deflection. We would still be left with the dynamic deflection, though.

    So let's talk about the dynamic load and the deflection under that load. To do that, we need to know the mass of moving components and the forces (cutting and other) that act upon our beams.

    Ken
    Kenneth Lerman
    55 Main Street
    Newtown, CT 06470

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    Quote Originally Posted by lerman View Post
    All the static deflection number tells us is that the beam will bend by a thousandth or two under no load. Why is that a big deal? We should be looking at the dynamic deflection under actual (varying) loads.

    If we use the beam as a support for a rail (or for a metal support for a rail), we can just machine out the static deflection. We would still be left with the dynamic deflection, though.

    So let's talk about the dynamic load and the deflection under that load. To do that, we need to know the mass of moving components and the forces (cutting and other) that act upon our beams.

    Ken
    Entirely correct.

    However in materials which have a limited tensile strength, if the design for a beam produces static deflection sufficient to 'use up' the limited tensile strength available then the material is weaker than it might be expected to be. One of the proposed numbers on this thread have beams with static deflections in the 0.1 range with corresponding large stress before the dynamic load is applied. If the dynamic loads add to the tensile loads then the beam will fail in circumstances not expected.

    Even more relevant is your coment about the mass of the moving components and all the forces on them. Anyone priced the components needed to move a multi hundred pound weight gantry or table?

  18. #1298
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    CKelloug,
    The E/G may work well for you. I think as filler or as a table you are pretty much there. For a gantry, where stiffness is the premium quantity, there are fun things to mess with: http://stores.ebay.com/Honeycomb-and-More has aluminum honey comb for sale.

    I wonder what a multi layer sandwich of aluminum sheet, epoxy, honeycomb,epoxy,aluminum sheet, assembled on a flat plate, repeated to a beam 6x6 inches would do. All I know about this is what I read in Nat. Geographic about Burt Rutan and scaled composites, but it is available to the small shop through Ebay.
    Keep up the good work.
    roger

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    Flexural Modulus of Accures Material and Modulus Argument

    In keeping with my promise to Andrew to reread all of his postings, I am. My first comment is that I corresponded with the president of Accures castings today and confirmed that the correct elastic modulus for their material is 4.5*10^6 psi. The 4.5*10^5psi number on their website is in fact a typo that they are going to fix!

    As for my rough calculations on this thread , I have used a flexural modulus of 2.0*10^6 psi. If anybody thinks that this flexural modulus value is higher than we can achieve at home please post. This is towards the bottom of the range for either compressive or tensile modulus in the nist report originally posted by brunog: http://www.fire.nist.gov/bfrlpubs/bu...PDF/b99032.pdf

    --Cameron

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    groger,

    Thanks for the encouragement. For the record, I'm more interested in using the E/G for general machine design rather than a gantry router but the gantry router problem is interesting and the folks on this thread already had the best discussion on the internet long before I got here. I'm just trying to repay all of the stuff I've learned on this thread by giving back in research and engineering time.

    That honeycomb does look like good stuff. I suppose one would use it to separate the load carrying top and bottom of a beam to get a higher moment of inertia.

    --Cameron

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