Page 3 of 4 FirstFirst 1234 LastLast
  1. #21
    Sven's Avatar
    Lives in a, Netherlands. Last Activity: 3 Weeks Ago Has been a member for 3-4 years. Has a total post count of 45. Received thanks 4 times, giving thanks to others 0 times.
    Quote Originally Posted by D.C. View Post
    The sides of the bed are 3mmx80mm steel plate.
    The bottom is 3mm steel plate.
    The reinforcing is 20mm x 20mm hollow steel square.

    After much reading about the wondrous technology of constrained layer damping, it turns out that one of the very best 'viscoelastic damping materials' is butyl and it needs to 0.5mm to 1mm for the sort of things we do.

    Which is handy, because the super spiffy visc

    90 in steel
    10 in pond liner
    140 in epoxy
    20 in milled carbon
    25 in aggregate

    285 total

    I've been very generous with the epoxy as that is the scary expensive part, 140 assumes an 18% by volume mix but hopefully it will average out lower than that. I could still go to almost 25% epoxy and break even with the aluminium.

    Any thoughts or comments on this approach for a DIY bed?
    Forgot to reply to the general idea...

    Here are some thoughts

    - Epoxy adheres well to steel but may not stay bonded due to differences in thermal expansion. That would make the steel tub a bit overkill
    - If you use that much epoxy it is likely to form a layer on top of the casting.
    - Using milled carbon as well as steel tubing is a bit like suspenders and belt to keep your pants up. And still, 20.-- seems a small amount.
    - using tubing instead of bars lowers the mass/volume which I think is a good idea.
    - I would use round tubing though as I think it would leave for a stronger EG mass.
    - You can probably get away with using pvc piping instead of steel if the plate is thick enough
    Last edited by Sven; 29-07-2015 at 08:25 PM.

  2. The Following User Says Thank You to Sven For This Useful Post:


  3. #22
    D.C.'s Avatar
    Lives in Birmingham, United Kingdom. Last Activity: 05-01-2016 Has been a member for 4-5 years. Has a total post count of 326. Received thanks 30 times, giving thanks to others 24 times.
    Thanks Sven, after Robin's comment about having a big chunk of ALU that can be sold if things go horribly wrong I have to admit that I'm rethinking things a bit...

    I'm not too concerned about thermal expansion because I'm building a CNC machine in a garage that is attached to a house and the temperature doesn't won't really fluctuate more than 15C over the course of a year.
    I was banking on the epoxy getting vibrated to the top and selected the epoxy especially to do that as it will self level.
    The milled carbon amount is based on the best practice mix on the easycomposites website, 10% by weight compared to the epoxy. Obviously the quartz/granite/etc in the mix doesn't count, this results in a surprising small amount of milled carbon fibres that add greatly to stiffness and dimensional stability.
    I'm not sure exactly where the optimum lies between tube and square, I selected square so that I could weld it together easily, circular tube would be much more difficult to fabricate.

    I've been arguing the toss with a structural engineer and insurance company about the fact that my house has giant cracks in the extension so for the next couple of weeks/month I need to back burner the CNC which is very annoying, I am relying on it to do a lot house upgrades. :(

  4. #23
    Sven's Avatar
    Lives in a, Netherlands. Last Activity: 3 Weeks Ago Has been a member for 3-4 years. Has a total post count of 45. Received thanks 4 times, giving thanks to others 0 times.
    I' ve been reading up on EG as my own ideas are taking shape.
    As far as I' read, vibrating EG does not work unless you use a mix with too much epoxy for a small size casting. Too much meaning it will yield an end result that has some shrinkage and maybe some warp.

    The best seems to be a mix that is "very dry" compared to what most people on forums seem to be using: in the 4% area, or a bit wetter where it needs to adhere to another material.
    Also, best to use various grain sizes, the next size 1/5th of the previous.

    Put a measured amount in a jar, then add the smaller size and shake until the volume increases and you know the ratio.

    A dry mix like that will need stamping.

    And off course, make sure to do trials :)
    Last edited by Sven; 15-08-2015 at 06:59 AM.

  5. The Following User Says Thank You to Sven For This Useful Post:


  6. #24
    If all you want is to flow a flat surface, why not use Wood's Metal? That goes very runny and sets hard. You could even reflow it if you moved the machine.

  7. The Following User Says Thank You to Robin Hewitt For This Useful Post:


  8. #25
    D.C.'s Avatar
    Lives in Birmingham, United Kingdom. Last Activity: 05-01-2016 Has been a member for 4-5 years. Has a total post count of 326. Received thanks 30 times, giving thanks to others 24 times.
    Quote Originally Posted by Robin Hewitt View Post
    If all you want is to flow a flat surface, why not use Wood's Metal?
    Not a bad idea but Wood's Metal / Cerrobend etc looks to be about 40 per kg, so it would cost a lot more than epoxy levelling I think?
    Have you ever tried it if you have some lying around?

    Quote Originally Posted by Sven View Post
    I' ve been reading up on EG as my own ideas are taking shape.
    As far as I' read, vibrating EG does not work unless you use a mix with too much epoxy for a small size casting. Too much meaning it will yield an end result that has some shrinkage and maybe some warp.
    The best seems to be a mix that is "very dry" compared to what most people on forums seem to be using: in the 4% area, or a bit wetter where it needs to adhere to another material.
    Also, best to use various grain sizes, the next size 1/5th of the previous.
    Put a measured amount in a jar, then add the smaller size and shake until the volume increases and you know the ratio.
    A dry mix like that will need stamping.
    And off course, make sure to do trials :)
    For larger aggregate This place does washed, graded and dried quartz specifically for resin bonding:
    http://resinbondedaggregates.com/cat...ound-aggregate

    For the smaller sizes I think it would have to be blasting grits:
    http://www.stacey-processing.com/gla...ing-media.html

    Then Aluminium Oxide powder and milled CF.

  9. #26
    Linear or volumetric thermal expansion coefficient is irrelevant in constucting a CNC.

    First of all cement, steel and concrete have very similar thermal expansion. Even if the epoxy has higher thermal expansion its irrelevant at 1m and temperature changes. Plus the epoxy cement or epoxy granite will more similar expansion to the concrete




    EG is same like all, do it properly and it will work well.


    There are better options of course and not so expensive- purpose made epoxy concrete, especially made for the purpose. Problem is finding them close to you or in your country at all.

    But those who search will find :-).

    Key words:

    epoxy concrete cast machine bed, ultra-high performance concrete





    These guys http://durcrete.de/ can do machine bed design or cast inhouse for you or as far as i remember 1 ton of the stuff was like ~400euro

    Gues what i will be bringing home if i go to Germany :-)
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	thermal expansion.PNG 
Views:	222 
Size:	45.5 KB 
ID:	15884  
    project 1 , 2, Dust Shoe ...

  10. #27

  11. The Following User Says Thank You to Robin Hewitt For This Useful Post:


  12. #28
    Sven's Avatar
    Lives in a, Netherlands. Last Activity: 3 Weeks Ago Has been a member for 3-4 years. Has a total post count of 45. Received thanks 4 times, giving thanks to others 0 times.
    I may have had my expansion reasons mixed up...

    A guy I know built an epoxy-concrete machine with steel bars at the surface to connect the rails to.
    They were flat when casting started but the end result was not.

    If you cast EC in a steel tub, it may end up not being part of the construction but just a liner and not a reinforcement.

  13. #29
    There are many ways to not do it right. Apart from choosing the best epoxy for deep casting, is good idea to read the documents of the said epoxy and follow them instructions to the letter. best is to call the epoxy manufacturer and speak with them for the most suitable epoxy for the purpose.

    Cause at the end of the day they know their stuff and even can mix a custom epoxy for your purpose. I have talked with one company technician and he knew exactly about that situation and explained me the differences between the 3 suitable epoxies they had.
    project 1 , 2, Dust Shoe ...

  14. #30
    D.C.'s Avatar
    Lives in Birmingham, United Kingdom. Last Activity: 05-01-2016 Has been a member for 4-5 years. Has a total post count of 326. Received thanks 30 times, giving thanks to others 24 times.
    The http://durcrete.de is quite interesting.

    What I was aiming for was finding a sweet spot between price/performance and ease of construction given that I only have not very accurate tools to work with.



    The Durcrete site has some vibration damping data available and a demo:
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	daten-schwingungsdaempfung.jpg 
Views:	134 
Size:	46.8 KB 
ID:	15902  

Page 3 of 4 FirstFirst 1234 LastLast

Similar Threads

  1. Designing a Gantry type concert router
    By Jazmal in forum Gantry/Router Machines & Building
    Replies: 5
    Last Post: 09-01-2015, 05:52 PM
  2. Designing a Metal milling bushless Spindle
    By Kevman in forum Electronic Project Building
    Replies: 18
    Last Post: 14-04-2013, 06:43 PM
  3. A little help on designing in Solidworks
    By D-man in forum Computer Software
    Replies: 3
    Last Post: 04-11-2010, 10:49 PM
  4. Looking for some help designing my gantry please
    By psiron in forum Gantry/Router Machines & Building
    Replies: 13
    Last Post: 05-07-2010, 09:52 PM

Bookmarks

Posting Permissions

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