506,330 active members
2,501 visitors online
Register for free
Login
Page 1 of 3 123
Results 1 to 12 of 27
  1. #1
    Member
    Join Date
    Dec 2010
    Posts
    12

    Smile CNC machines from plywood

    Recently, on the forums and YouTube, I started to get materials on the construction of CNC machines from plywood. The topic intrigued me. The fact is that such a machine can be assembled by virtually anyone, if there is a project and the possibility of cutting plywood on a large CNC machine. The assembly does not require the help of expensive specialists - a lathe, a welder, a milling cutter. You don't need to have any special tools. Pretty much the minimum that is available to every master.
    And since I have access to a large, good CNC machine, I decided to try to implement such a project.
    First, I project a stand in SolidWorks.
    The machine has not yet fully finished. A little later, I will show the continuation of the series ...

    Attachment 424716
    Attachment 424714
    https://youtu.be/XaBFQXRELe0

  2. #2
    Registered
    Join Date
    Jan 2008
    Posts
    1006

    Re: CNC machines from plywood

    It is quite possible to build a good plywood CNC.

    Unfortunately your design has many weaknesses.

    It seems the people inevitably start - designing a CNC that looks like they think a CNC router should look like. Many of the early DIY CNC router designs are very poor but are still around and influencing current designs.

    I recommend you do some reading on stiffness and the engineering principles behind a stiff machine.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  3. #3
    Member
    Join Date
    Jul 2018
    Posts
    748

    Re: CNC machines from plywood

    Hello Yuri - Its good to work in plywood. You will need to make it quite a bit stiffer. Use Boxes for the gantry and the columns. Single plane pieces of PW are not stiff enough in transverse bending. Boxes can be stiffer than metal if big enough. There are many very good timber machines in this forum. Look for videos and info on the Mosquito airplane it was made from plywood and was an advanced machine at the time. I'm designing a mast for a large catamaran and it will be plywood and it will be lighter than the carbon fibre version so go for it.. Peter

  4. #4
    Member
    Join Date
    Dec 2010
    Posts
    12

    Re: CNC machines from plywood

    Thank. I will definitely consider your comments.

  5. #5
    Member
    Join Date
    Apr 2016
    Posts
    780

    Re: CNC machines from plywood

    Quote Originally Posted by peteeng View Post
    Hello Yuri - Its good to work in plywood. You will need to make it quite a bit stiffer. Use Boxes for the gantry and the columns. Single plane pieces of PW are not stiff enough in transverse bending. Boxes can be stiffer than metal if big enough. There are many very good timber machines in this forum. Look for videos and info on the Mosquito airplane it was made from plywood and was an advanced machine at the time. I'm designing a mast for a large catamaran and it will be plywood and it will be lighter than the carbon fibre version so go for it.. Peter

    Peter, when you say "boxes" do you mean "torsion boxes?" Given that Yuri is from Ukraine and English probably isn't his first language, he may not understand the term "boxes" to mean "torsion boxes."

    IMO, torsion boxes are the best option for a build in plywood, assuming the boxes are built correctly. The inner grid members must be cut precisely, and the boxes need to be assembled on a perfectly flat reference surface. Any irregularity will be reflected in the finished product. It's very easy to induce twist, high stops and/or low spots, if one is not very careful. I'm a big fan of torsion boxes. Lot's of strength and rigidity.. However, very fussy to build correctly.

    Yuri, If you are not familiar with torsion boxes, you should know that the greater the distance between the two outer skins, the stiffer your torsion box will be. So, a torsion box with an internal webbing that is 100mm in height will be considerable stiffer than one with 25mm webbing. I've read that if you double the thickness, you increase strength by 8 times. A dramatic increase.

    Here's a link to ger21's wooden CNC build thread. Gerry has been working on his build for more than 10 years, so his threads are pretty long to wade through. Still, they contain useful information on torsion boxes. https://www.cnczone.com/forums/cnc-w...0-autocad.html The Internet also contains a much information on torsion boxes. Here is a thread showing an 8 foot (2438mm) long torsion box made exclusively of 3/16" (4.76mm) hardboard. https://www.popularwoodworking.com/p...a-torsion-box/ Loaded with 300 pounds (136 kilos) of bricks in the center, the deflection was only 1/2 inch (12.7 mm). Had the box made made of 18mm baltic birch plywood, I'd guess the deflection would have been measured in the hundreds of a mm or less. If thick enough, there may have been no deflection.

    Here's another link to get you started on research: https://www.google.com/search?sa=N&r...w=1093&bih=530 The link is to a number of photos which are linked to threads, blogs or articles on actual builds.

    To add some perspective, aircraft wings are built on the torsion box principle. If you think in terms of the gigantic military transport aircraft, you get an appreciation of just how strong they can be.

    Hope this helps.

    Gary

  6. #6
    Member
    Join Date
    Jul 2018
    Posts
    748

    Re: CNC machines from plywood

    Hi Gary and Yuri - Torsion boxes are specific designs to take torsion. The general term is box beam as far as I know. Lets just call them tubes. Square tubes in torsion require internal ribs to maintain the tubular shape. Otherwise the sides can cup (if they are thin) and become inefficient. A circular section is the only shape that does not change shape under torsion, that's why shafts are round. Many of the timber "torsion box" designs use more internal ribs then needed but these are seat of the pants engineering solutions. If people have engineering backgrounds the required ribs can be calculated easily. In Yuris machine it is not big enough to warrant internal ribs in my view. A simple box or tube will be good enough for the gantry. See the attached article I have written.

    Now I have kept this simple as once you get into secondary structures such as internal ribbing and thin structures you need to investigate these with FEA methods and be familiar with advanced analysis as thin structures buckle and warp. These are not considered in simple linear analysis which is on a lot of CAD systems these days, so you can analyse a thin structure such as a piece of paper and a linear solver will say its quite strong. But in fact it will buckle under a puff of wind. But this is in plywoods advantage because its thick and does not locally buckle. Its main issue is change of shape due to moisture, so sealing with paint or resin is a good idea.

    I have been involved with timber boats and civil structures for over 30 years there is no doubt that timber is strong and stiff when used in the correct manner. Peter

    Edit - A modern approach would be to use foam in the middle vs the ribs. As long as the foam is flat (and surfaces are parallel) then this could solve the accuracy issue. The foam transfers the shear loads from side to side (like a web in an I beam) and it holds the faces (flanges) together everywhere vs in zones that ribs would. This is called a sandwich construction. One way fwd that I like is to use aluminium skins on lightweight plywood. See article for more info.

    As structures get more complex the issue is making them flat and true. The more bits you have the more construction error you have. The trick is to make it as simple as possible yet achieve the desired result. Most times easier said than done. Occam and Einstein said everything should be as simple as possible but not any simpler....Peter

    Gary sorry to be a wet blanket but aircraft wings are poor torsional structures due to their very large aspect ratio. So they have an inner spar that is circular or near circular to take the torsion loads of the wing. The wing skins take the bending loads like an I beam and the spar takes the torsion. A gantry would be great if round but hard to mount things to. Every design aspect is a compromise...

    Gary FYI - the stiffness of an element is related to its geometric inertia which is its depth to the 4th power. So if the element is made 1.2x deeper it doubles in stiffness (1.2^4=2.07 eg 100mm change to 120mm deep) . If you make it twice as deep its 16x stiffer and stronger

  7. #7
    Member
    Join Date
    Dec 2010
    Posts
    12

    Re: CNC machines from plywood

    Hello, friends. I am very pleased that such experienced, competent colleagues became interested in my modest work. Thank.
    I really am not friends with the English language, I use Google translator. But unfortunately, I see that Google also does not know English well.
    But we will overcome everything. In general, I understand your criticism.
    The weakest point in my CNC machine is the side walls of the portal. I think to strengthen it - make the walls of the portal 15 mm 2 times thicker - 30 mm. I think that should be enough.

  8. #8
    Registered
    Join Date
    Dec 2003
    Posts
    388

    Re: CNC machines from plywood

    You have done a good thing by making the walls thicker.A box,as the earlier posters have described,would just have meant including some spacers between the original panel and the second panel you have added and the increased distance between the panels would give greater stiffness.The same principle would apply if you need to add stiffness to the gantry beam at some point.It can make things a bit awkward if you need to get inside the box to bolt tracks in place.

  9. #9
    Member
    Join Date
    Dec 2010
    Posts
    12

    Re: CNC machines from plywood

    I understood your point.
    But this can affect the design of the machine - its appearance will become very cumbersome. I want to make it elegant, pleasing to the eye. Therefore, I want to test first. The machine is not being built for metal processing, but for working with wood, MDF, plywood. And I do not set a goal to achieve high performance. This is a machine for a hobby, not for professional work ... Therefore, the technical requirements for it are low.
    When there is free time, I’ll finish assembling the machine, shoot a video and we will try it. Good?

  10. #10
    Registered
    Join Date
    Dec 2003
    Posts
    388

    Re: CNC machines from plywood

    I expect we are all looking forward to seeing the parts you will be producing on your machine and learning about the build process.

  11. #11
    Member
    Join Date
    Dec 2010
    Posts
    12

    Re: CNC machines from plywood

    Continuing my saga:
    https://youtu.be/1UM4MxeJ5Ww

  12. #12
    Registered
    Join Date
    Dec 2003
    Posts
    388

    Re: CNC machines from plywood

    Good progress.I see you changed the coupling to an Oldham type and that should be a better solution.Will you be using a clear finish on the wood or will it be painted?I find either helps with preventing the wood becoming dirty.

Page 1 of 3 123

Similar Threads

  1. First MDF/plywood CNC
    By Kazik_Wichura in forum DIY CNC Router Table Machines
    Replies: 0
    Last Post: 06-11-2012, 10:29 AM
  2. MDF vs Plywood
    By RockBoy in forum DIY CNC Router Table Machines
    Replies: 17
    Last Post: 01-17-2011, 05:24 PM
  3. best plywood
    By beamer in forum General Laser Engraving / Cutting Machine Discussion
    Replies: 6
    Last Post: 08-06-2007, 11:27 PM
  4. Sizing of CNC Machines For plywood cutting
    By dswink in forum DIY CNC Router Table Machines
    Replies: 5
    Last Post: 05-17-2007, 08:50 AM

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
  •