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  1. #21
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    Default Re: Epoxy granite in metal frame.

    I wonder about urethane-foam filled carbon-fiber frames. Dealing with mass is a major hassle for hobbyists - you can ship carbon fiber parts cheaply and handle them easily. You'd need to pay a little attention to chemical incompatibilities (no acetone), but carbon fiber is both rigid and stable. Some multi-axis machines are using spindles on carbon fiber arms now...



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    Default Re: Epoxy granite in metal frame.

    It seems to me there is a bit of a mix-up in theories here.

    - You can add EG to a steel frame. That will increase stiffness and it will reduce the amplitude of vibrations. It will probably also dampen vibrations a little because of its amorphous structure.
    - If you add just sand, that will dampen also, but it will not add much stiffness.
    - Filling with oil or water is totally pointless. Al lot of hassle for just about no benefit.
    - If you want to use steel,and EG filling, forget about the filling, just get thicker steel.
    - Stress relieving steel is only needed if the mounting surfaces for the rails will be milled.
    - Using carbon fiber for a gantry is pointless for a hobby machine, especially small ones. A buildlog somewhere else is by a guy who works with the stuff daily, then it makes sense. Otherwise, go with steel
    - I would not recommend using polyurethane foam in a composite frame. It still expands a bit after initial cure, that adds tension inside the cavity which takes away any precision you may have been able to realise. Use epoxy foam instead, that has way less expansion power.

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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    Default Re: Epoxy granite in metal frame.

    Quote Originally Posted by genixia View Post
    I wonder about urethane-foam filled carbon-fiber frames. Dealing with mass is a major hassle for hobbyists - you can ship carbon fiber parts cheaply and handle them easily. You'd need to pay a little attention to chemical incompatibilities (no acetone), but carbon fiber is both rigid and stable. Some multi-axis machines are using spindles on carbon fiber arms now...
    Being able to move it is important. Speaking as someone who just went through the hassle of moving a large epoxy granite part and injuring the ligaments in my arm in the process - it weighs a ton. You have to buy a shop crane or some other type of lifting device just to move it onto your frame. Not great for a one off hobby project....

    If you have a moving gantry, you might need a motor upgrade too. I don't really know the limits of a Gecko driven 381oz 3a motor but my guess is that you'd want more to move a 900lb gantry with any speed.

    For reasons I'll never fully understand, a lot of people like to offer advice on the use of carbon fiber (or urethane foam) for CNC parts even though they have never tried it and don't know much about it. It has many advantages for machine building and is superior to steel and aluminum in many ways. It's not for anyone else to say what matters for your project. Welding steel is harder than using aluminum t-slot extrusions but many hobby users see a point in using the stronger material.

    Making carbon fiber parts is a lot of hassle. There is no doubt on that and paying someone else to make them is too expensive for a hobby project. IMO, it only makes sense for someone who already has experience of making cf parts, or.... someone who is interested in learning how to make them as part of the project. People learn how to weld steel for their CNC projects so learning how to use composites is not that far fetched. It's a useful skill for many future projects and a lot of fun.

    Making larger shapes without small details or complex curves is not super difficult with carbon fiber. A basic gantry beam or gantry risers are fairly simple projects. People struggle with making the fabric conform to tight curves but they aren't needed for this. Used vacuum pumps and other gear are cheap, as are the raw materials.

    If you look at the desirable properties everyone here talks about for CNC machine parts, cf is a very good fit. pound for pound, it is stronger and stiffer than steel, iron or aluminum and has superior damping. It's easier to fabricate than steel too . If there is a point in welding steel, there is a point in using cf. Obviously if you don't care about strength or precision, you may as well use the cheapest easiest material possible. Plywood is fine in that case.

    Urethane foam is an excellent filler for cf parts (and many other things including steel). It cures incredibly fast. It starts to solidify (from it's liquid starting state) in just 45 seconds and it's all done in 5 minutes. Even if you over fill a part cavity, the pressure or force from expanding foam is not sufficient to effect the integrity of a well made cf part, or an aluminum or steel tube. I use it regularly for rifle stock fillings where any change to the outer shape would cause the action to not fit properly. Excess foam is more likely to ooze out of the end of the tube or the hole you poured it into.

    Urethane foam is an excellent material to have on the shelf for any cf or fiberglass parts maker. I highly recommend buying some to experiment with as it's so useful. It is very easy to carve and yet very stiff so I use it to carve new patterns to make molds from. It can be easily injected into any part cavity to fill a void and it adds a lot of strength and stiffness so you can use less cf. Higher density closed cell foams can even be CNC'd into low volume molds. Or, it can be coved with a gel coat for higher volume work.

    Basically, anyone who makes parts from a mold, should own some urethane foam.



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    Default Re: Epoxy granite in metal frame.

    Quote Originally Posted by genixia View Post
    Somewhere on YouTube is a series where someone built a gantry router doing exactly that with sand, asked it appeared to have worked very well. Sand is a cost-effective improvement to a hollow frame. Just make sure it's totally dry!

    Sent from my SAMSUNG-SM-G900A using Tapatalk
    What sort of improvement did he (or she) see and how was it measured? It's an easy, cheap and reversible mod to try but I haven't seen anyone describe a method of measuring success.

    Maybe it was a simple test of harmonics or noise - I.e. Maybe the machine was less noisy after it was filled?



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    Default Re: Epoxy granite in metal frame.

    Quote Originally Posted by Goemon View Post
    What sort of improvement did he (or she) see and how was it measured? It's an easy, cheap and reversible mod to try but I haven't seen anyone describe a method of measuring success.

    Maybe it was a simple test of harmonics or noise - I.e. Maybe the machine was less noisy after it was filled?
    It's been a long time since I watched those videos. I can't remember whether he took measurements or not. They're linked above...

    Sent from my SAMSUNG-SM-G900A using Tapatalk



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    Default Re: Epoxy granite in metal frame.

    Quote Originally Posted by genixia View Post
    It's been a long time since I watched those videos. I can't remember whether he took measurements or not. They're linked above...

    Sent from my SAMSUNG-SM-G900A using Tapatalk

    I think this topic topic is a lot more complicated than it looks (and it didn't look that simple). I was watching the Haas video on vibration where they show the cool ping pong ball trick with the tuning forks to demonstrate how the natural frequencies of cutting tools and the parts being cut can play a role in vibration control / improving cut quality. The way they describe the problem, it doesn't sound like it could be solved fully on the machine design side.

    You don't need any special equiptment to see that filling the void in a steel or aluminum tube with something will change the frequency. You can hear it when you tap the surface with a screw driver or other metal tools. Maybe it is as simple as that if the natural frequencies of part and tool don't match. After all, in applications where vibration is desirable (e.g. a musical instrument) that large void is necessary. It's logical that removing the void is the way to go where vibration is not desirable.

    If you filled the void in a guitar with anything, you wouldn't be able to hear it anymore.



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    Default Re: Epoxy granite in metal frame.

    In epoxy granite you use sand and gravel (Isn't it beacause different sizes pick up different frequenses). Would that be any idea if you are filling your metall tubes.?


    If you mixe it before you pour it in it will probably end up with the gravel in the bottom and the sand on the top after a while.
    But if you first fill it with gravel to the top and then, with help of some vibrator pour in the sand



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    Default Re: Epoxy granite in metal frame.

    Quote Originally Posted by JoFlo View Post
    In epoxy granite you use sand and gravel (Isn't it beacause different sizes pick up different frequenses). Would that be any idea if you are filling your metall tubes.?


    If you mixe it before you pour it in it will probably end up with the gravel in the bottom and the sand on the top after a while.
    But if you first fill it with gravel to the top and then, with help of some vibrator pour in the sand
    Other way around - larger particles float up over time. I don't that matters though - if you don't prevent migration with a binder you might as well stick to one size particle.

    Sent from my SAMSUNG-SM-G900A using Tapatalk



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    Default Re: Epoxy granite in metal frame.

    But if you fill the tubes full with up to the top with the bigger particle (and vibrate) I asume they can't/wan't move anymore and then fill up the gaps with sand (and vibrate). If the already are all up to the top they can't go any higher up (or lower down) . Maybe you then only should have one or not so many sizes of the bigger particles

    (And by the way, doesn't the larger parts end up on the bottom - lager density)



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    Default Re: Epoxy granite in metal frame.

    not many have actually measured the vibration dampening coefficient of their epoxy granite mixes.. to know if simply sawing up some slabs of granite and gluing them together would be better, and cheaper.



    I have about 5 different samples of polyester resin, synthetic granite counter top remnants and none of them are particularly good at vibration dampening. i mention this because many people here have considered using them. the real slabs of granite i have.. in the same size and shape as the synthetic stone, similar frequencies.. you have to hit them hard enough to break them before you can hear their natural resonant tone (in the case of a 1.125" thick bar 4 feet long, its fairly low and hard to hear anyways. but the synthetic stone rings for a long time, the granite rings for such a short time that you have to strike it very hard with a rubber mallet to hear the tone.. which is only there for less than a second.

    so, as i've explained elsewhere..

    The dampening coefficient that you get will be a result of the sum of the components, according to their share of the total stiffness, and energy stored in said stiffness.

    For example: an 8 inch diameter pipe, 3/4th inch thick side wall has 226 inches^4
    a solid 8 inch rod is 402inches^4

    The stiffness of epoxy granite being on the order of 1/8th (maximum) that of steel, means that if you fill the .75" thick sidewall, 8 inch outside diameter steel pipe, you've only added 1/8th of the difference (402-226)/8 is 22in^4 equivalent. this means the epoxy granite will take 22/(226+22) parts of the strain, or about 9%

    Assuming the steel has a dampening coefficient of .001, and the epoxy granite a dampening coefficient of .05, this means you now have a final result of (.91*.001)+(.09*.05) which is .00541.

    .0054 is a lot better than .001, (and this is enough to make people think its no longer resonant) but the weight was nearly doubled by adding the epoxy granite, thus the resonance frequency dropped by the square root of 2 if i recall correctly, and the final dampening coefficient still worse than cast iron.


    often times very high dampening coefficient, but low stiffness materials such as sand, rubber, silicone, polyurethane (density can vary by two orders of magnitude for polyurethane) are added between tuning forks made of very stiff materials. they call this "constrained layer dampening" and the purpose of it is to cancel out specific frequencies.

    for general machine tool purposes, the best material remains cast iron because you can machine it cheaply and it is stable after heat treatment.

    if you want the highest dampening coefficient for the highest stiffness, solid granite may be the best option, basically epoxy slabs of cheaply available granite counter top together (ideally, get all the pieces cut from the same sheet) and bolt or epoxy on certified flat granite straight edges (or cut up a surface plate) with inserts drilled and tapped for the linear rails.


    there are very few other materials besides granite and cast iron that have any use in machine tool bases, you may be able to get higher dampening coefficients from epoxy granite as opposed to solid granite, but such results depend entirely on how well you fitted the mass fraction of all the separate ingredients of the epoxy granite. (too much epoxy will drastically reduce the stiffness)

    so just to make it more obvious: in the case of a .75" thick side wall 8 inch steel pipe (which is a similar ratio as a .2" thick side wall 2" square steel.. filling it with epoxy granite halved the resonant frequency and only increased its stiffness a maximum of 10%.. and that's if your epoxy granite is 1/8th as stiff as steel. which it most likely won't be,



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    Default Re: Epoxy granite in metal frame.

    find an old granite surface plate. epoxy in anchors and build from there. theres a 48x96x12 table local to me for $500 that i plan on doing this with, but leaving 2ft of the end of the table bare to use as a surface plate



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    Default Re: Epoxy granite in metal frame.

    Interesting, don't forget to tell us about the result



  13. #33

    Default Re: Epoxy granite in metal frame.

    This is an idea I have been thinking about lately. I've only ever run a small router table and am currently building a plasma table so bear in mind im no expert.

    My 2c

    Grind your linear rail mount bars flat first
    Have tapped holes on the underside for bolts/anchors to be attached
    Grind a thick (25mm) plate flat for mounting of the head/ non moving gantry whatever its called, again with tapped bolt/anchor point on the underside
    Make a welded together frame that the ground mounting surfaces can bolt to, all flat steel, no hollow sections
    Align everything while bolted together, with anchors in place
    Fill er up with epoxy granite
    Do the same with the mounts for the Z axis
    Profit

    Does this seem plausible or am I tripping?



  14. #34

    Default Re: Epoxy granite in metal frame.

    The way I see it goes as follows - please correct me if I am wrong- :
    -each mounting surface of rails is essentially a plane, therefore the first step is to find a way to have all points of the surface in the same plane (milling, grinding,scraping)
    - two mounting surfaces for rails should be in the same plane, therefore the second step is to find a way to have both planes co-planar (milling, grinding, scraping)
    -having accomplished that, the third step is to keep the 2 planes co-planar at all times. Here comes the stiffness issue. Before anything else, just moving the finished machine from one place to the other (eventually loading it/unloading it) is a matter of screwing up with the alignment, no matter how it was achieved. To me, the calculus for obtaining the desired stiffness when the machine is working statically is of little consequence - if any- compared to what it takes to have no misalignment at all after the machine has been moved around, because the machine is facing its own weight - depending on the moving procedures-to its own disadvantage. Therefore the chassis of the machine should be as sturdy as hell, much sturdier that it needs to be when the machine is resting in its final position. The other side of the story is a very light weight machine - possibly aluminium made- which is so springy that , after it has been moved around, it reverses to its original state when resting in its final position. Vibration is just a matter of accumulated dynamic energy in the 'wrong' place. To dissipate it, sand is hardly a solution, because it does not act as a whole. I believe the chassis of the machine should be designed out of steel as if nothing else would be poured into it, and then UHPC poured into it to complement steel (not doing its part) . UHPC would ''back up'' steel in those situations where cutting forces and torsion moments would tend to ''beat'' steel. Vibration wise, nothing beats UHPC/EG.



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    Default Re: Epoxy granite in metal frame.

    You're almost correct. All machines bend and settle, it's just a matter of how much. An important consideration of machines is designing their foundations, including feet that can be adjusted to level machines so that they settle and bend consistently.

    Think of a granite surface plate. It is usually supported by three feet, carefully placed at the Airy points, which are mathematically known to minimise bending across the plane. That doesn't eliminate bending though - the plate will be highest at those the points, concave within those three points, and will fall away outside them. The thicker the plate, the less bending will occur. If the plate is leveled, whilst sitting on those three points, and then the top surface lapped flat, then you know that if the plate is moved and exactly re-leveled on those points that the same flatness will be achieved. If the level is off, then the flatness will be diminished. The same principles are used in machine design - adjustments are made with the machine bed leveled, and after the machine is moved and re-leveled similar results should be obtained.

    Sent from my SAMSUNG-SM-G900A using Tapatalk



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    Default Re: Epoxy granite in metal frame.

    This is one of the paradoxical problems with machine building. On the one hand, you want more weight from thicker materials to create a stiffer base with better vibration damping. On the other hand, more weight can also increase bending. A long steel plate can easily bend just under it's own weight.

    This is one one of the reasons why I used carbon fiber in my gantry design. My gantry is fairly long and I found that the mix of carbon fiber and epoxy granite over a steel frame to produce the best overall results. The mix of materials solves many of the problems found when using these materials on their own.

    Creating flat and level mounting surfaces is relatively easy with epoxy (with proper technique and quality resin). Squaring the gantry mounting surface with the table is a different matter. I am still working on this challenge.... I made sure to allow for some fine adjustments by mounting detachable actuators to my one-piece cf / epoxy granite / steel gantry and epoxy granite base. I think I'll need some shims...



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    Default Re: Epoxy granite in metal frame.

    So I have been away from the forums for a while. The initial plan has changed and we moved away from the idea of using granite at all.
    We have build a iron tube frame. It was welded with tig weld and then sent to be faced and also have the guides for the X linear guid rails machined.

    Here is the model for the frame
    Epoxy granite in metal frame.-frame-model-jpg

    And here is how it is after the machinning process.
    Epoxy granite in metal frame.-0-02-03-8f74b7c86f557803d20b2c9bb27bf3953b755ada29825f500d139f5c0f1756b0_4b1a7d62-jpg
    Epoxy granite in metal frame.-0-02-03-09ce098039f6fa7629ecc82d2f7c21c0b852e4d1c4c9823c44e597a9cb92359e_60dcaee8_1535527340-jpg
    Epoxy granite in metal frame.-0-02-03-28e32994aa85d40ae3d325e5852ec91ef7039f3f73b2a445399babe2b03e94c0_41a40ac4-jpg

    This frame is being built in order to replace a less rigid and lighter frame our machine already has. Also there will be some changes on the rest of the assembly as well. I try to get video footage from the process and create a nice video in the end.
    The tubes are 60*60mm and 5mm thick. The weight of the frame alone is around 300kg.

    Attached Thumbnails Attached Thumbnails Epoxy granite in metal frame.-frame-model-jpg   Epoxy granite in metal frame.-0-02-03-8f74b7c86f557803d20b2c9bb27bf3953b755ada29825f500d139f5c0f1756b0_4b1a7d62-jpg   Epoxy granite in metal frame.-0-02-03-28e32994aa85d40ae3d325e5852ec91ef7039f3f73b2a445399babe2b03e94c0_41a40ac4-jpg   Epoxy granite in metal frame.-0-02-03-09ce098039f6fa7629ecc82d2f7c21c0b852e4d1c4c9823c44e597a9cb92359e_60dcaee8_1535527340-jpg  



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    Default

    hi,

    Good day!
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    James

    E:service@cncmachiningchina.org



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    Default Re: Epoxy granite in metal frame.

    In my building router machine, 100x100x4mm steel tubes are used for the frame. I still don't know how weird it will be after the arc welding that I will do. Firstly, I am a poor welder. Another things are the said deformation and the stress inside after the process. I want to change my mind to use as least welding as possible and use screw bolting method. Firstly, the ends of tubes will be welded with a small square plate said 92x92mm "Inside" (I don't know if it is easy to do). Then it can be bolted to the sides of the left and right tubes with 4 screws (of course 4 additional holes needed to be drilled on opposite wall for inserting the hex key for fixing the nut on, even then, the holes needed to be larger for facilitating to put the nut through it if there is no other way to do). ...Of course, the rigidity of the whole assembly is less for this method than that of directly welding method among the tubes, but the pay-for is a better precision and also I haven't get resources to do the stress relief and face milling process in my living city. Is it okay and any advices?



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    Default Re: Epoxy granite in metal frame.

    Can you switch to having the end plates be outside ( > 100x100mm) caps rather than plugs? Much easier to get a strong weld.



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