521,500 active members*
1,700 visitors online*
Register for free
Login
IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Filling steel tubes with epoxy granite- machine before or after?
Page 3 of 3 123
Results 51 to 55 of 55
  1. #51
    Registered
    Join Date
    Jan 2016
    Posts
    29

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

    Peteng, would MDF have similarly desirable properties like ply?

    I am considering a sandwich of 1/8”AL- ½” MDF - 1/8”AL for a router.


    Sent from my iPhone using Tapatalk

  2. #52
    Member
    Join Date
    Jul 2018
    Posts
    1374

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

    Morning Koenbro and others - See attached calcs and data.

    1) MDF has a modulus of ~3500MPa, cheap F8 plywood is about 9000MPa so is twice as stiff. MDF is about half the cost of plywood so its a cost benefit ratio
    2) for bending loads your proposed [1/8"Al / 1/2"wood / 1/8"Al] is equivalent to a 5/8" (17mm) piece of aluminium. Its 19mm thick so its very worthwhile for that purpose. MDF and Ply are about the same density so no benefit in weight
    3) In plane the stiffness of the sandwich is 6mm so you gain stability if the loads are inplane but you don't gain stiffness
    4) I'd take advantage of the sandwich effect and use thicker timber. Being a lightweight seeker I'd use lightweight ply (370kg/m3) but again dearer then MDF
    5) On a completely engineering note I'd use MDF as its cheaper and will do the job. 3mm is quite thick for this sandwich skin so I'd go thicker MDF
    6) Definitely edge seal with epoxy or suitable resin to prevent moisture ingress at edges

    The alloy and temper of the aluminium is not critical its its modulus (70GPa) that your using. But as you probably will bolt things through the sandwich use a hard temper to resist crushing. I use 2mm a bit as its lighter and by using a thicker core can get same stiffness. But then if its really overall thick this may impact your structure size.

    You can glue the sandwich with epoxy, urethane or contact cement. Do not use foaming urethanes I have found them to grow a little over time...

    Cheers Peter

    since this thread is about damping, the sandwich you describe will be very damp as well. Timber is extremely damp and in combo with the Al is a great solution I think. Start a design thread will follow with interest.

    If you live in an area of high moisture variation I'd go with the ply as it will be more stable over time. The cost of the timber in this project will be a small % of the total project whether ply or mdf. With any machine use the best materials you can afford for a project. If the machine has a long life the cost delta will be insignificant vs the machine reliability and performance in a couple of years time. Unless one of the design tenants is "lowest cost" of everything then mdf is the answer. I suppose you could use MR (moisture resistant) mdf in that case...

  3. #53
    Member
    Join Date
    Jul 2018
    Posts
    1374

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

    {Vibration Damping Analysis of Lightweight Structures in Machine Tools: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5503333/[/QUOTE]

    Hi Pippin and others - I've read this article a couple of times. Its interesting because they have gone to a lot of trouble evaluating various things. The author however has a bias towards aluminium foam AFS (or the work sponsor has probably) . Even though the aim is to reduce weight the AFS is the heaviest solution, he concludes that this can be fixed with a redesign. The CF however is lighter stiffer and damper yet its relegated to second choice. That's not really the point for me, the work shows that CF (and by extension) fibre reinforced laminates are stiffer stronger, damper then metals and much easier to make then foamed aluminium. Interesting also in the specific stiffness chart that steel does better then cast iron. I'm not sure why E to the third is used, E/density is good enough for this comparison. So I encourage people to get familiar with composites as that's the way these things have gone and will continue to go. Aircraft and planes have gone from steel to aluminium to composites in my working career so should we. I helped build a 20mx3mx3m 5 axis router some 25 years ago. It was 100% carbon fibre as the company made composite planes so said why not a composite machine? Other high level machine builders are already building CF parts so should we... Peter

  4. #54
    Member
    Join Date
    Jul 2018
    Posts
    1374

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

    Hey Pippin - I'm setting up some Tetrium and CF to be modulus and strength tested at a Uni so I'll have some good numbers very soon. Cheers Peter

  5. #55
    Member
    Join Date
    Jul 2018
    Posts
    1374

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

    Hi All you EG people out there - I have been thinking about how to evaluate the dampness of a material at home vs in a lab. Last night I thought about the concept of co-efficient of restitution. Many years ago I made scooter wheels for a company. My wheels had good "pop" apparently. This is because I used hot casting resins and post cure to create a very resilient resin. The company tested competitive wheels buy dropping them and noting their rebound height on the brick wall at their factory. I was going to make a fixture so it was a bit more formal but I could not make wheels at the price they wanted so that project stopped. But we can use the same approach for the materials. By dropping ball bearing onto the surface of a material we can either see its rebound or count its bounces. If you have dropped a steel ball onto a steel surface they bounce very well. If you dropped it into plasticene it would coalesce. So now we can compare the rebound of EG AL etc against steel to rank the materials. Now I have to find a good size ball bearing. I have the rest... Peter

Page 3 of 3 123

Similar Threads

  1. Replies: 7
    Last Post: 02-19-2017, 08:16 AM
  2. CNC lathe build, steel frame, HIWIN rails and epoxy granite headstock
    By Roadsidejobshop in forum Vertical Mill, Lathe Project Log
    Replies: 29
    Last Post: 01-12-2017, 04:02 AM
  3. Epoxy Granite Mill Head filling
    By d@niel in forum Epoxy Granite
    Replies: 12
    Last Post: 06-23-2015, 02:49 AM
  4. Router steel stucture....filling with Apoxy Granite
    By Marne in forum DIY CNC Router Table Machines
    Replies: 6
    Last Post: 07-30-2014, 08:50 PM
  5. Epoxy granite filled rails - how big to mill steel?
    By cnccnc222 in forum Epoxy Granite
    Replies: 1
    Last Post: 05-12-2014, 02:45 PM

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
  •