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  1. #1
    Hi I'm a newbie here and to CNC.

    I've read up on design principles and think I have a fair understanding of the moments these machines go through.

    I basically need some help with design, I want to build a machine with a cutting size of around 900 x 400 to build guitars on. It'll be cutting hard wood and doing a good few hours a week hopefully.

    I've seen a few build in MDF and thought could I build in maybe ply (I'm not a fan of MDF) or would it really need to be welded steel for hard wood like maple and ash?

    I have a basic idea of my design but I could do with knowing if the idea of a ply build is just silly before I start drawing.

    Cheers Kenny

  2. #2
    My advice would be use metal for the build, wood of any sort would be a waste of time and money. You need more accuracy and maybe more important, repeatability, and I do not think you will achieve that with a ply or MDF built machine. Think of the accuracy required for a neck pocket as example or maybe you want to cut an accurate rebate for binding.
    Last edited by EddyCurrent; 13-11-2014 at 11:16 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  3. #3
    Hi,

    Quote Originally Posted by Hopey View Post
    I've seen a few build in MDF and thought could I build in maybe ply (I'm not a fan of MDF) or would it really need to be welded steel for hard wood like maple and ash?
    Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.
    Steel is not necessary for hard wood but I'd at least use aluminum extrusion.

    Christian
    2D / 3D CAM Software and CNC controller: http://www.estlcam.com

  4. #4
    Quote Originally Posted by Christian Knuell View Post
    Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.
    I'm not sure I agree with you regarding plywood being worse, good birch plywood I mean, but I do know that among other things moisture makes MDF swell. Also if there's that much moisture in the air then the hardwood being cut will also be useless, especially for guitars.

    Quote Originally Posted by Christian Knuell View Post
    Steel is not necessary for hard wood . . .
    but it's a lot cheaper than aluminium and ideal for the base.
    Last edited by EddyCurrent; 13-11-2014 at 11:40 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  5. #5
    Quote Originally Posted by Christian Knuell View Post
    Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.
    No sorry can't agree on this. Unsealed MDF changes shape if you so much as show it a cup of coffee let alone any decent amount of moisture. Ply wood will take much more moisture before swelling.

    BUT to IMO both have only two places in CNC.? . . .Spoil board or to keep the workshop warm.!!

    Steel is cheap and easier to work than people realise. Profile is fine but to get the best from it you need all the connection elements, T-nuts etc, and this makes it much more expensive. It's also harder to work than people realise, it's awkward drill/Tap and unless slots used then it can be difficult for mounting things too it with out adaptor plates.

    Combination of steel and Profile works well IME, gives a good balance of strength and ease of build without getting silly expensive.

  6. #6
    I've used MDF for templates which it's great for but does deform and swell if it gets wet. Decent marine quality ply wouldn't have this problem so I had thought of using a combination of that and hardwood to build a strong structure but it could just become a bit cumbersome.

    I can weld and it has to fit in a shed so steel makes more sense when I think about it.

    I'm thinking 1" box section for the main frame.

    Best get drawing.

  7. #7
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 4-5 years. Has a total post count of 1,005. Received thanks 170 times, giving thanks to others 5 times.
    Let me add my twopennorth as someone who has built and used an MDF CNC router, essentially to the JGRO design. There aren't many people prepared to admit that...
    I have a cutting area of about 800x400, from memory. It uses skate bearings on steel tubes and threaded rod. On the plus side - it works. On the down side - only just. It's difficult to get a flat bed, to adjust the bearings and keep them adjusted, and generally to maintain any kind of consistent accuracy. There are better MDF designs but I doubt that they will entirely remove all these problems. As Jazz has said, show this stuff a cup of coffee and it distorts. Take the coffee away, and it will sulk and distort again, but probably not back to where it was. Warm/cold/damp/dry - any change in weather and you will be re-tweaking. All that, actually, might be bearable except that you have to keep cutting speeds so low to avoid major structural distortion - or failure - that big jobs can take hours rather than minutes. OK, I use threaded rod as leadscrew material which limits X axis speed to about 800mm/min, but frankly the thing couldn't take much more anyway.

    As far as accuracy is concerned, I cut a series of interlocking 9mm ply panels for an architecture project and had reasonable repeatability, although not absolute accuracy - that is, I cut some samples, tweaked the dimensions slightly, and then cut a series of pieces that fitted reasonably well. It works pretty well for engraving, as long as you can level the work.

    I'm halfway through a build of a steel framed machine using profile rails and ballscrews. Is there a message in that?
    Last edited by Neale; 14-11-2014 at 11:58 AM.

  8. #8
    Quote Originally Posted by Hopey View Post
    I'm thinking 1" box section for the main frame.
    No 50x50x3 Minimum for a decent strength machine. Steel is cheap if bought in full length sizes so don't compromise the machine with 1" for the little extra 2" would cost.

  9. #9
    Quote Originally Posted by Hopey View Post
    I'm thinking 1" box section for the main frame.
    This machine was built for hardwood cutting, similar size to your proposal, it works great and is very accurate.
    First part of the thread is just random ideas, it should give you some idea of what is required.

    http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy

    The frame; http://www.mycncuk.com/threads/6565-...2425#post52425
    Last edited by EddyCurrent; 14-11-2014 at 12:41 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  10. #10
    Thanks for the input guys, I was thinking I would build a bench in the shed and simply sit it on that or bolt it down but now I'm thinking it needs a solid frame too.

    Great build thread Eddycurrent, I'm a bit dyslexic so it takes me a while to read it all and take it all in. I've skipped over a lot of the electronics bit for now but finding the epoxy levelling really interesting.

    Bear with me and I'll finish the reading and get some drawing done.

    I was looking at Chinese rails and lead screws on ebay, are the Hiwin type worth the extra cash?

    Thanks again for your assistance.

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