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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Filling tubular steel with EG. Pros and Cons?
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  1. #1
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    Filling tubular steel with EG. Pros and Cons?

    I'm gathering info for my new mid size machine build.

    As te title says what are the pros and cons filling a tubular steel frame with EG?

    Thanks in advance.

  2. #2
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    Re: Filling tubular steel with EG. Pros and Cons?

    Personally I haven’t read in builds that have used it that it does offer a clear improvement.Perhaps someone who has used it will offer before and after experience.

    Cons,
    Does it actually significantly improve machining performance?Could be expensive for large quantities.Will make structure much heavier.Cant be removed.


    Vibration reduction (or improved damping) can be achieved in a number of ways.Improve stiffness and/or increase mass.Or use a material with better intrinsic damping properties.

    Steel is probably bottom of the ladder(EG,cast iron,aluminium,steel)in intrinsic damping but its stiffness/$ can overturn this disadvantage.

    Best of those choices IMO is probably to increase the amount of steel used.This will add stiffness and mass ,efficiently reducing vibration.Closing the ends of tubes will add around 30% stiffness.Chosing a stiffer closed loop structure like a portal before an open loop like c-frame or moving gantry is best.

    My choice of fill would actually be to half fill tubes with either river sand(cleaned) or steel (or lead shot) and oil.The advantage is its removable.

    I would expect that the material carrying most of the machines loads will dominate vibration properties.Steel in this case.
    I recall reading a report where a major manufacturer back filled a large cast iron slant bed lathe with EG.They saw a 30% improvement in damping,from memory.

  3. #3
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    Quote Originally Posted by shedbob View Post
    Personally I haven’t read in builds that have used it that it does offer a clear improvement.Perhaps someone who has used it will offer before and after experience.

    Cons,
    Does it actually significantly improve machining performance?Could be expensive for large quantities.Will make structure much heavier.Cant be removed.


    Vibration reduction (or improved damping) can be achieved in a number of ways.Improve stiffness and/or increase mass.Or use a material with better intrinsic damping properties.

    Steel is probably bottom of the ladder(EG,cast iron,aluminium,steel)in intrinsic damping but its stiffness/$ can overturn this disadvantage.

    Best of those choices IMO is probably to increase the amount of steel used.This will add stiffness and mass ,efficiently reducing vibration.Closing the ends of tubes will add around 30% stiffness.Chosing a stiffer closed loop structure like a portal before an open loop like c-frame or moving gantry is best.

    My choice of fill would actually be to half fill tubes with either river sand(cleaned) or steel (or lead shot) and oil.The advantage is its removable.

    I would expect that the material carrying most of the machines loads will dominate vibration properties.Steel in this case.
    I recall reading a report where a major manufacturer back filled a large cast iron slant bed lathe with EG.They saw a 30% improvement in damping,from memory.
    Plus 1 for sand oil mix. Dampens the most but adds zero to rigidity or strength. But much cheaper and can be removed if needed.

  4. #4
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    Re: Filling tubular steel with EG. Pros and Cons?

    Unless you are a very experienced machine builder I would not fill steel tubes with EC, I would spend the same money on buying thicker wall steel tubes.

    The rigidity for the amount of money spent is much higher with steel than with EC.
    And also, the stiffness for the amount spent is higher for steel than it is for EC.
    Finally, the weight for the amount spent is higher for steel than EC.

    That means that steel wins over EC. Except....

    If I had not been offered help in building my next cnc, I would have gone with EC, as I am a poor steelworker and I love working with molds.
    Sven
    http://www.puresven.com/?q=building-cnc-router

  5. #5
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    Re: Filling tubular steel with EG. Pros and Cons?

    Thank you all for your responses.

    As all of you recommended I'll use thick wall tubes and in the end of the project I will probably fill the tubes with sand-oil mix. That wont hurt.

  6. #6
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    Re: Filling tubular steel with EG. Pros and Cons?

    You should use the thickest steel you can get, and also fill atleast part of the tube. The tubes are just like bells, so they will resonnate a lot.
    Click image for larger version. 

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  7. #7
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    Re: Filling tubular steel with EG. Pros and Cons?

    Quote Originally Posted by shedbob View Post
    I would expect that the material carrying most of the machines loads will dominate vibration properties.Steel in this case.
    I recall reading a report where a major manufacturer back filled a large cast iron slant bed lathe with EG.They saw a 30% improvement in damping,from memory.

    yes, that is a topic i have been intending to write an essay on for over a year now.

    basically the dampening and stiffness of a blob of metal and xyz is a simple multiplication and addition problem.

    30% stress retained by 0.1% dampening
    30% stress retained by 1% dampening..
    40% stress retained by .2% dampening..

    equals a dampening coefficient of .41% if i'm not retarded.


    the modulus of elasticity of epoxy granite which is on the order of 40 GPA, is far less than 130 for cast iron or 200 for steel. but it has a far higher dampening coefficient, on the order of 100 times that of steel and 10 times that of cast iron. its also about one third the density.


    of course, using oil and sand as a dampening medium offers no rigidity, other papers i've read have talked about it being non linear and hard to predict.

    two component silicone and sand might be a good fit.

  8. #8

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    Quote Originally Posted by Azalin View Post
    Thank you all for your responses.

    As all of you recommended I'll use thick wall tubes and in the end of the project I will probably fill the tubes with sand-oil mix. That wont hurt.
    Sounds like a great approach!

    One caution when doing further welding on something that's had oil in it. Gasoline and air make an explosively flammable mix because the gas evaporates, mixes with air and will burn very rapidly. Oil heated by welding will also vaporize, mix with air and burn very rapidly.

    YouTube video about a worker killed by welding on a drum with about a tablespoon of acetone inside a 44 gallon drum.
    https://youtu.be/9DP5l9yYt-g

    There's a dry ice trick (CO2) or open both ends and have a fan blowing through, or whatever it takes to prevent an explosive vapor mix.

  9. #9
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    Re: Filling tubular steel with EG. Pros and Cons?

    Hi Azalin - Captain V is perfectly correct. Better off paying for steel and making it locally much stiffer. Most builds are too thin and can vibrate. There are lots of steel tube builds with no filling and they are fine. Epoxy is very expensive and does not contribute to stiffness. If you are building a 100% EG machine then that's different. Also just because people hit tubes with hammers and they ring does not mean they will ring when built into a machine. Plus if they did ring this may not affect the machine performance anyway. What does affect performance is poor Z axis stiffness and gantry stiffness which can be cured by bigger, thicker steel tubes. Can't be too stiff. cheers and get some CAD candy up for us to look at...

    welding is probably your biggest enemy here as well. Distortion, full energy transmission and people build square structures which globally vibrate easily. Use lots of triangles, stiffer and harder to get vibrating... use tabs and bolted joints much damper. More damp than cast iron in fact... The CI vs steel damping argument is tough because depending on how you test for damping depends on the result you get. Most steels and cast irons have a similar damping co-efficient. But there are alloys of both with excellent factors. Cast iron used in machines are damp because they are cast thick, they have rounded edges and draft ie few parallel sides and definitely no thin sections. dampness is a secondary property for machine parts, its castability is its primary property. Peter

    https://stacks.cdc.gov/view/cdc/10399/cdc_10399_DS1.pdf

  10. #10

    Re: Filling tubular steel with EG. Pros and Cons?

    Hey. Let me give you my opinion. I have a lot of experience with epoxy granite in machine tool construction. Your idea is down the drain. It is useless to fill a steel pipe with this material. You will not get any benefit.
    The stiffness of steel is much higher. The vibration damping properties of epoxy granite material will not be useful to you, since the steel frame will be rigidly fastened, right?
    Epoxy granite is very attractive when used as a material for molding an embedded frame.

  11. #11
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    Re: Filling tubular steel with EG. Pros and Cons?

    Filling a steel tube does have benefits.

    There are a number of research papers as well as:
    https://durcrete.de/technical-data-nanodur/?lang=en
    https://www.youtube.com/watch?v=pCU7...ature=emb_logo


    For most of a machine base it may be better just to use very large bits of epoxy granite or UHPC, however for moving elements, such as the saddle, the high stiffness of steel may be needed - filling with epoxy granite or UHPC can improve the damping.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  12. #12
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    Re: Filling tubular steel with EG. Pros and Cons?

    Every one have opinions , there are tests made with measurements , and the damping properties on frequencies vibration with eg are true , they are more signifiant when u use a steel construction , vs a iron cast one .

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