Filling steel tubes with epoxy granite- machine before or after?


Page 1 of 3 123 LastLast
Results 1 to 20 of 55

Thread: Filling steel tubes with epoxy granite- machine before or after?

  1. #1
    Member catahoula's Avatar
    Join Date
    Mar 2020
    Posts
    179
    Downloads
    0
    Uploads
    0

    Default Filling steel tubes with epoxy granite- machine before or after?

    Q: If I want to fill a steel gantry tube with epoxy granite to add mass and damping, should I do it before or after face milling the tube square and parallel?

    I realize this isn't specifically related to machines built on epoxy granite bases, but figured the know-how would be here.

    Thanks and cheers,

    Brian

    Similar Threads:


  2. #2
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hello Brian - There's a lot of discussion about EG filling of members for damping and stiffening. 1) the stiffening component from engineering calculations is inefficient. If you need more stiffness and you are designing the machine then use bigger, thicker tubes. EG filling will help thin tubes in torsion but if this is the case then the tube is too thin for the application anyway 2) vibration, there are many steel tubed machines out there that are not filled and they work fine. Vibration is a subtle area and its better to fix a vibration then try to guess at it in the first instance 3) Mass - EG is an expensive way to add mass. Adding mass is the easiest way to damp a structure. If this is the strategy then use thicker tube, you will win in stiffness and weight as steel is 7800kg/m3 and EG is about 2200kg/m3. Adding mass is a poor strategy if you want to move your machine fast as it has more inertia 4) vibration - if this is an actual problem then fill with foaming urethane, much cheaper then epoxy and it will work as well and is light.

    Square or rectangular steel or aluminium tubes do not vibrate much in a global sense in machines. The free edges can, so support free edges , don't have little cantilevers of metal like flanges and sheet metal. Construction extrusions have heaps of free edges at their ends and along them so have various vibration modes. Cheers Peter



  3. #3
    Member routalot's Avatar
    Join Date
    Dec 2003
    Posts
    1206
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    I agree with what peteeng said and the economics don't stack up in favour of epoxy anyway.I can buy steel for a great deal less that epoxy and I expect you could too.I also know a couple of people with epoxy sensitisation and would only use the material with a job that really leaves me with no alternative.



  4. #4
    Member catahoula's Avatar
    Join Date
    Mar 2020
    Posts
    179
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi guys, thanks, that seems totally reasonable. Initially I got onto the idea because I was looking at t-slot machines and it seemed like a good way to add mass the machine (definitely an inefficient way to go after stiffness), but after looking more at extrusion tolerances have decided against that style. So I guess I was in the "may as well" mindset with the steel tube. I'm also super comfortable with epoxy as it's the main thing I use in my workshop, both for end products and tooling. It'd take $100 USD of epoxy to fill the steel gantry in question with 20/80 epoxy/granite, which isn't a huge expense but definitely more expensive than just going with a larger or thicker tube. And I think the gantry tube in question is plenty big enough anyway at 8"x6"x3/8" for a 26-30" length.

    Cheers



  5. #5
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1523
    Downloads
    2
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    As Peter has pointed out, the first thing is to make the gantry / machine as stiff as possible.

    Go big on the gantry tube. Increasing the section size is much more effective than increasing wall thickness. Look up a table for steel RHS moment of inertia.

    However, I don't think EG fill is a waste of time for a metal machine at least. Chatter and cutting induced vibration are major limiters of performance, both in part quality and tool life. The purpose of EG fill in this case is vibration damping not structural. Steel is vastly stronger and stiffer than EG.

    There is research data to show that filling steel with epoxy granite results in improved vibration damping.

    I am planning a steel weldment with epoxy granite fill for a metal mill. However, the epoxy granite may end up a bit different. There are some interesting papers on using crumb rubber (rubber granules) in the mix to improve damping. If the EG is not structural (e.g. in a weldment) then the composition can be tailored optimally for vibration damping.

    The greatest gain will be from the EG in contact with the steel tube.

    An easy way to achieve this is to use a foam core, or a light tube in the middle. For example, a 200x200mm steel SHS tube, with a 100mm PVC pipe in the centre. You can then fill with EG between the steel and PVC.

    Generally, material close to the neutral axis (i.e. the middle) is of very little benefit in engineering.


    8x8" would be a better choice than 8x6". Gravity is not the only or most important force. Cutting is and there is usually more cutting force in X and Y and in torsion.



  6. #6
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1523
    Downloads
    2
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Peter, do you have any references to the use of foam fill for vibration damping in machine tools?

    I have seen it discussed in multiple forums with frequent concern that the foam tends to deteriorate over time when subjected to repeated vibration. It is commonly used to reduce ringing noise in metal furniture, which is due to local vibration rather than structural resonance.



  7. #7
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi Pippin - I agree with the research but the research did not compare various methods to determine a comparison. Much easier/cheaper to fill with a medium density PU result will be the same. But if the wall is thick and stiff then its debatable if this is helping or not. I forget the correct term for transfer of energy from the tube say to the fill. I think its radiation. But if the wall is supported on one side and unsupported on the other its asymmetric so damps easily especially with a damp elastic foundation such as any foam provides. So are we talking about global vibration of the gantry or local vibration of the sides of the gantry? Peter I'll build a quick model...



  8. #8
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi Pippin - Structural resonance I'd call global vibration and ringing is a local vibration. If a good quality medium density foam is used I doubt it will decouple over time. You could use an epoxy foam or a PVC foam if this is really an issue. So I made a steel tube 8"x6"x30" as cata suggested. I supported it lightly at the ends sort of how it would be in practice.

    235htz it lozenges
    632htz it hammocks up and down (if square it would be much better)
    788htz the top and bottom flats pant as they are wide

    So if there is a mechanical excitation at these frequencies the gantry will get excited and move like shown. The issue then becomes is it a damped vibration or a self exciting one that leads to a ringing and a problem? I'll now fill it with 80kg PU foam to see what happens. I can also find out its damping ratio but I need to know the materials damping ratios to model this as a transient dynamic model.

    Now we know that the first mode is lozenging we can put webs on the end to stop this by the way...Peter

    Attached Thumbnails Attached Thumbnails Filling steel tubes with epoxy granite- machine before or after?-235htz-jpg   Filling steel tubes with epoxy granite- machine before or after?-632htz-hammock-jpg   Filling steel tubes with epoxy granite- machine before or after?-788htz-jpg  


  9. #9
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    outcome - the lozenging changed from 235htz to 577htz, the next is a lozenge with a twist at 564htz and the panting is about the same at 850htz. This is 80kg PU if you used 190kg then it would be heavier and stiffer so would move these up further.

    https://dalchem.com.au/product/polyu...dfoam-190.html

    Being stuck on one side this will damp very well as well. Adding a heavy material like EG will move it even further I expect. But it didn't..

    So I filled it with EG and its first significant vib was at 401htz was a torsional vib. There were two lesser vibs at 330 and 350htz and these were the EG free ends bulging out of the tube ends, very interesting. Beware free edges and surfaces! Would be good to be able to put up MP4 vids...

    So conclusion. Nearly anything you can couple to one side of a piece of metal will damp its motion (if it vibrates) mass helps but is counter to inertial requirements. I'm sure filling a tube with sand is more economical then filling it with EG and it will give a good result. If you make it watertight and fill it 90% with water you will create viscous damping and it will be better as well. But if you size your tube right in the first place then these things may not happen... Peter

    Attached Thumbnails Attached Thumbnails Filling steel tubes with epoxy granite- machine before or after?-564htz-jpg   Filling steel tubes with epoxy granite- machine before or after?-577htz-jpg   Filling steel tubes with epoxy granite- machine before or after?-850htz-jpg   Filling steel tubes with epoxy granite- machine before or after?-eg-401htz-jpg  



  10. #10
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    something that may help - peter

    Attached Files Attached Files


  11. #11
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi All - Vibration analysis is very specific thats one reason this is a difficult discussion point. So I remodelled the steel beam as a 1/2" thick version.

    3/8" thick weighs 3.76kg and we have the initial modes for that 235 and 632htz
    if we fill with EG then its weight leaps to 8.69kg yet its vib modes don't change dramatically. Thats because the steel part is still dominant in stiffness. But its damper due to the weight gain and the constraint it places on the sidewalls
    Then we look at the 1/2" thick section. It weighs 4.90kg yet its first vib mode is 664htz this is a leap up in freq. Its the twisting lozenge. Then 675htz is the lozenge.

    These numbers do not address damping only the excitation mode. Excitation comes from the step motion input of the motors and the cutter teeth impacts. Motors can be isolated from the frame using damp materials, the cutter vibs need to be addressed as the structure around these has to be very stiff.

    So I think tubes have to be very heavy wall and large... Peter



  12. #12
    Member catahoula's Avatar
    Join Date
    Mar 2020
    Posts
    179
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Interesting analysis and discussion. Thank you. Sounds like practical considerations mean creating less symmetry in the tube structure and dealing with the free edges. It would be easy to do that with welding but I'm trying to minimize that, as post-weld stress relieving the large gantry tube would be a bit difficult for me. I'll talk to my local metal supplier to see if 1/2" walls are an option.



  13. #13
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1523
    Downloads
    2
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    You can epoxy in bracing / bulkheads. Ideally a tight dry fit and then epoxy to hold in place.



  14. #14
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi Pippin - I don't think its coupled well enough together using epoxy. So I made a model of the 150x150x6mm SQ tube and epoxied a 6mm steel end cap into it with a 1mm bondline. The open ended gantry vibrates at 125htz (lozenge mode) the capped at 135htz not much of a diff. If I change the 1mm thick epoxy to steel then the lozenge disappears and its first mode is a banana mode at 250htz.

    So unless analysis is done I think you have to be careful with doing stuff... Current best advice - go thick to stiffen the corners... Peter

    Attached Thumbnails Attached Thumbnails Filling steel tubes with epoxy granite- machine before or after?-125htz-jpg   Filling steel tubes with epoxy granite- machine before or after?-135htz-jpg   Filling steel tubes with epoxy granite- machine before or after?-steel-cap-250htz-jpg  


  15. #15
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1523
    Downloads
    2
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    I was proposing a tight fit, i.e steel on steel. Have to tap / press the plug in.

    Of course not as good as a solid steel joint, but if welding is not desired...

    I would weld and stress relieve, or repeated machining for the weld distortion.

    Last edited by pippin88; 04-02-2020 at 10:49 PM.


  16. #16
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi Pippin - I still don't think a "tight" fit is coupled enough. Peter



  17. #17
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi Pippin - I tried to run the modal analysis with a friction fit but the solver won't do it so just have to guess. But soft solder would be an answer for minimal heat effect. Or bolted brackets....Peter



  18. #18
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1523
    Downloads
    2
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Peter, an interesting paper is below:
    Experimental Investigations of Steel Welded Machine Tool Bodies Filled with Composite Material
    Authors: Pawe? Dunaj(&), Tomasz Okulik, Bartosz Powa?ka,Stefan Berczy?ski, and Marcin Chod?ko

    If you don't have access to get the paper, send me a PM or have a look at sci-hub.tw

    In short:

    EG material:
    Resin 26.1%
    Ash 1.7%
    Small fraction (0,25–0,2) 15.7%
    Medium fraction (2–10 mm) 13%
    Coarse fraction (8–16 mm) 30.5%
    Steel fiber 13%

    Structure:
    steel welded body with no filling, weight: 21,33 kg (figure 2a)
    steel welded body partially filled with composite material, weight: 31,85 kg (figure 2b)
    steel welded body fully filled with composite material, weight: 37,76 kg (figure 2c)
    Filling steel tubes with epoxy granite- machine before or after?-figure-2-png

    Filling steel tubes with epoxy granite- machine before or after?-table-2-png

    Filling steel tubes with epoxy granite- machine before or after?-fig-9-png

    The question is for moving structures where inertia is an issue.

    I can't find much for polyurethane foams. I have found papers on aluminium foams which look very good, but not something you can easily DIY.



  19. #19
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Hi Pippin et al - My "feelings" on this sort of thing are as follows:

    1) Keep within one material space if possible eg steel, aluminium, composite, cast iron, chewing gun etc Once you try mixed media you are up against all sorts of unknowns and complications. With metals use very thick walls or solid castings to minimise the issue of local vibrations. Try to make structures that have no parallel or square or rectangular surfaces. Remove free edges and any unnecessary cantilevers. Use automotive anticanning materials on surfaces if they do vibrate
    2) Keep away from welding unless you can do a stress relief. This is for steel and aluminum. Metals can be brazed (red 600deg C) even soft soldered (no colour change 200deg C) to minimise heat change affects. The connection strength requirements are generally very low and soft solder will do the job. We are also getting to the point where adhesives are up to the task.They are strong enough but you need a big surface area for the stiffness
    3) if you have the resources do modal analysis and eliminate modes near the operating speeds and cutting speeds of the machine
    4) Material dampness alone is not enough for precision machines. They rely on mass and in some cases viscous damping of some kind. Shear mechanisms in viscous materials and tuned damping
    5) I'm now heading for full composite construction due to limitations of metal pressing. Composites are considerably damper then metals so at least that's a step fwd.

    Unfortunately there is not enough info for DIYers to take advantage of various materials. A DIY shotgun approach works generally because of the mass gain vs the apparent material dampness. One aluminium foam article I found measured the difference of a un-coupled foam fill that had interface friction and a coupled foam. The uncoupled foam was much better as the friction was the significant damper. So any sort of epoxy filling that couples to the structure maybe the wrong way to go. Plus every case is specific so its hard to say this way always works.

    So perhaps a bolted plate along a gantry with snug bolts is as good as it gets (adds mass, allowing the interface to slide and use the friction for damping) or interfacing with a rubber strip (visco-elastic damping). Many people also interpret acoustic noises as machine vibration. The air in hollow sections resonates as well but this does not affect the machine. So plug up hollows with rags, foam or plastic caps etc

    The vibration journey is a big one and I'm only a small way into it myself

    I look at the "machine element" in the article and its totally amateuristic. Thin steel, square shapes, welded, open ends, small cantilever sections . What are they thinking!! But for the exercise I suppose its OK...

    So pick your poison and keep Making. Peter


    I have played around with azodicarbonamide foaming agent and its interesting stuff.

    Last edited by peteeng; 04-04-2020 at 04:16 AM.


  20. #20
    Member
    Join Date
    Jan 2008
    Location
    Australia
    Posts
    1523
    Downloads
    2
    Uploads
    0

    Default Re: Filling steel tubes with epoxy granite- machine before or after?

    Peter, definitely a deep and winding rabbit hole.

    I've read a lot of paper on this topic now and most leave a lot of unanswered questions.

    Constrained layer damping with a viscoelastic materal looks interesting, however not easy for the hobbyist to find and implement.

    For a wood router all of this is not necessary. I have a router with a 200x200x6mm gantry, 1400mm long. It plows through wood with excellent surface finish at good feeds and depths of cut. It does howl due to the steel ringing (which I will do some work on for the placating the neighbours). However for a metal mill it is a different kettle of fish. Chatter becomes a major issue.

    I am working on a large (for hobby) metal mill design. I have gone back and forth between steel rhs tube weldment, laser cut steel weldment, epoxy granite alone and various combinations. At present I'm strongly leaning towards a laser cut steel weldment with EG fill. Stiffness from the steel, damping from the EG.



Page 1 of 3 123 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Filling steel tubes with epoxy granite- machine before or after?

Filling steel tubes with epoxy granite- machine before or after?