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  1. #1
    Hi, I have been lurking here for quite a while and am now thinking of taking the plunge (!) and building some form of cnc router. Before I dive in (and probably get it all wrong) I would welcome comments on what I am thinking of doing.

    First though, some background.....
    I have 3 3d printers, one of which I built myself from scratch so think I understand the principles of CNC. I also have a dilapidated single garage as a workshop which is so full of stuff I can hardly move around but there is a lathe, pillar drill, belt sander and a fair selection of hand tools in there. Space though is a problem!
    I also have too many things to do at the moment so, if it is to have any chance of success, I need to keep any build as simple as possible!

    To that end I set a basic spec for a machine:
    - 800x500x500 machine dimensions with the biggest practical work area. Anything over 200 x 300 workable area would be acceptable though.
    - workpieces likely to be more 2.5d rather than 3d, so a small (maybe 100mm?) Z is probably ok. I suspect allowing for tooling and workholding will impact the z height more than the workpiece itself.
    - capable of cutting aluminium and brass. Steel would be a bonus but I have no illusions that that will be sketchy at best with what I am likely to make.
    - cheap! Target cost is around 500 although I am fully aware it is likely to go massively over budget by the time I have made it do what I really want.

    Also, I might upset a few people here with this but, based on my experience with 3d printers, I would rather start cheap and "just about ok" knowing I am likely to upgrade later than go straight in with an over-engineered solution that will do anything. I know this sounds strange but I somehow enjoy the challenge of making things work and finding out what are really the critical things that need to be done right. As an example, I started out with an Anet A8 3d printer. It was only by getting that working as best it could (and having bought an ender3 and also fixed that) I reckoned I knew how to make my own design. I still have the A8 though and it still prints as well as anything else (if a bit slowly).

    Anyway, to the point.....

    Given the small size and need to keep it simple and rigid I am thinking of going with a fixed gantry design. Sensible?

    For rails I am thinking of going with SBR supported rods. Two reasons: 1) cost. 2) tolerance to mounting errors. My custom 3d printer was made using 2040 extrusion with linear rails and I was surprised how difficult it was to make the mounting surfaces coplanar. Even slightly distorted extrusion meant I had to mill then flat to stop binding.
    Given how I am thinking of making the frame (next point) that puts me off linear rails and I certainly don't think unsupported rods will work. Will I regret not going with rails even on this first build?

    Lastly, frame material. Again, this might be controversial - I am thinking of using plywood! My reasoning being that I initially want something quick and easy to build that is rigid enough to start making parts for a mk2 version (there is bound to be one so I might as well plan for it...). Steel would need welding to make it worthwhile (I haven't used my welder in 10 years) and would likely resonate unless filled with epoxy granite or sand. It is also hard to modify and experiment with, as is aluminium (unless I had a working cnc router). Wood is good for stopping noise and resonances, can be stiff if built properly (especially given it is a fixed gantry design) and is cheap an easy to work with. The down side is that it is almost impossible to make things accurately and it likely to distort and move over time. I am thinking that is not really a problem for my first build though as it should be "good enough". This is for the main frame and gantry (and maybe) the moving bed. The z axis assembly is likely to be aluminium. Obviously it will be thick laminations and box sections to get the rigidity, not just flat ply sheets.

    So, am I being silly? ;)

  2. #2
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 13 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,556. Received thanks 1,304 times, giving thanks to others 83 times.
    Quote Originally Posted by brman View Post
    So, am I being silly? ;)
    In a Nutshell Yes.!

    There is no way you can build a machine that can cut aluminum and brass to any reasonable degree from wood and with only a 500 budget.

    I said this to someone else recently also. The plywood alone will cost you more than steel, The only place for MDF in CNC for lighting fires to keep shop warm and using as a spoil board. Don't do it.!

  3. #3
    Quote Originally Posted by JAZZCNC View Post
    In a Nutshell Yes.!

    There is no way you can build a machine that can cut aluminum and brass to any reasonable degree from wood and with only a 500 budget.

    I said this to someone else recently also. The plywood alone will cost you more than steel, The only place for MDF in CNC for lighting fires to keep shop warm and using as a spoil board. Don't do it.!
    Well, to be fair, I did sort of expect that response ;)

    Just to clarify though, I would not use MDF (other than for a spoil board). It is nowhere near rigid and stable enough. Plywood I thought might be if constructed properly but it sounds like you are telling me otherwise.
    Anyway, leaving that aside, any comments on the use of supported rods vs linear rails and fixed vs moving gantry? Am I more on track with those decisions?

  4. #4
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 13 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,556. Received thanks 1,304 times, giving thanks to others 83 times.
    Quote Originally Posted by brman View Post
    Well, to be fair, I did sort of expect that response ;)

    Just to clarify though, I would not use MDF (other than for a spoil board). It is nowhere near rigid and stable enough. Plywood I thought might be if constructed properly but it sounds like you are telling me otherwise.
    Anyway, leaving that aside, any comments on the use of supported rods vs linear rails and fixed vs moving gantry? Am I more on track with those decisions?
    My advice is to price up the steel from a good steel supplier because I think you'll get a shock. To make a machine that is anywhere near strong enough and good enough will require a lot of high-grade plywood which isn't cheap.

    Regards the linear rail question then I'd go with profiled linear rails every time over round type. That said I'm not advising you not to use them and in fact, if you do go down the plywood route then I'd advise you did because it will be easier like you said and the accuracy and strength profiled offers would just be wasted anyways.

    The best advice I can give you is to forget any idea of building it then upgrade as you go along. The upgrade route never works as usually what you find or would like to upgrade to requires a whole need or different machine anyways.
    If it's just to learn on then could say fine build it cheap.! But in reality, it's no more difficult to build it correctly the first time or in such a way that it's very close and not too difficult to improve if needed. Plus if it turns out that you need a completely different type or size of machine you'll get your full money back and if done correctly may even make a profit which you can put to the next machine.
    With a plywood machine it will be worth nothing but firewood when finished with, components like round rails won't be good enough for the next build or correct size even, so very little of the machine will be reusable. So all that time and investment will be wasted.

    Don't do it is my strong advice. Take a little more time and research what you need, ask questions so you find the best components to suit your needs and be patient don't rush to buy components or build it too quickly. Like most things that are built from the ground up there is an order in which it's best to tackle the job. It's also like eating an Elephant.? One small bite at a time so no rushing.

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  6. #5
    Thanks, that is very useful and definitely gives me food for thought.

    It does give me a problem though. From my experience with aluminium I don't think a basic extruded design is going to ideal either. Which is probably why you recommend steel?

    My problem is that I am concerned how I would make a decent steel frame with the tools I have available and without excessive work. Specifically, steel sections are not generally dimensionally accurate so getting rails coplanar without milling or resin leveling. I am also concerned that if I weld then things will distort (I am very much an amateur welder!).
    What I don't want to do it invest time in a steel frame which ultimately ends up looking like a pringle ;(
    I realise this might sound contradictory when I was earlier talking about plywood but at least with plywood I can easily adjust with files, planes and sanding.

    Maybe that should have been the question? How best to make a steel frame that is accurate enough?

  7. #6
    Quote Originally Posted by brman View Post
    Maybe that should have been the question? How best to make a steel frame that is accurate enough?
    Tack weld opposite points. Progress slowly and methodically, setting up as accurately as you can and measuring as you go. All you need is a stick welder, a grinder, and a tape measure.

    Then level with epoxy. It's completely doable, loads of people on here have written about their experiences and how to do it. If you screw it up (like I did my first time) chip it off and try again.

    Alternatively, skip the hard stuff and use aluminium profile. You'll be bolting your rails on in minutes rather than days or weeks (or you know, in my case, months).

  8. #7
    If you want to cut metal on the machine,just find an old mill and add ballscrews and steppers.It may go over budget but it will work.Cutting metal on a woodworking machine may,just,sort of,be possible.That doesn't mean its a really good idea and trying to do it on a machine with a lot of Z travel, with all the consequent magnified play in the system won't help.For a hobby machine that just cuts wood you can do some stuff with a wooden machine.There are some extremely lightweight machines all over youtube delighting their owners,even if they wouldn't be much use in an industrial environment.You just have to be realistic about balancing budget,usage and building ability.The answer is out there once you carefully consider which features matter most.

  9. #8
    Quote Originally Posted by AndyUK View Post
    Tack weld opposite points. Progress slowly and methodically, setting up as accurately as you can and measuring as you go. All you need is a stick welder, a grinder, and a tape measure.

    Then level with epoxy. It's completely doable, loads of people on here have written about their experiences and how to do it. If you screw it up (like I did my first time) chip it off and try again.

    Alternatively, skip the hard stuff and use aluminium profile. You'll be bolting your rails on in minutes rather than days or weeks (or you know, in my case, months).
    Which I think highlights my problem. careful welding (with lots of practice first), epoxy levelling. It just isn't going to happen. I need to find a easier route or just not bother.

    Quote Originally Posted by routerdriver View Post
    If you want to cut metal on the machine,just find an old mill and add ballscrews and steppers.It may go over budget but it will work.Cutting metal on a woodworking machine may,just,sort of,be possible.That doesn't mean its a really good idea and trying to do it on a machine with a lot of Z travel, with all the consequent magnified play in the system won't help.For a hobby machine that just cuts wood you can do some stuff with a wooden machine.There are some extremely lightweight machines all over youtube delighting their owners,even if they wouldn't be much use in an industrial environment.You just have to be realistic about balancing budget,usage and building ability.The answer is out there once you carefully consider which features matter most.
    Which is where I am at the moment, trying to balance time, budget and quality. I've seen pictures of high quality machines and, while I probably have the ability to make one, I don't have the time (or inclination). I have also seen MPCNC cutting ally acceptably (to me, not a production engineer) on youtube. So the question is really how low can I go without wasting my time?
    I am tempting to try and see but I just know that will be followed by a lot of people saying I told you so...... ;)

  10. #9
    I won't criticise anybody for doing their best to make something work.I started with an MDF machine and drawer runners,which gradually got changed to SBR12 rails.I also use a much derided breakout board off a parallel port running LinuxCNC and it has never let me down.The crux of the matter is that we have the freedom to build with materials we are comfortable with and running software of our choice.If it doesn't meet our hopes,then clearly we made at least one wrong choice-at which point we get to decide what we do about it.

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  12. #10
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 13 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,556. Received thanks 1,304 times, giving thanks to others 83 times.
    Quote Originally Posted by brman View Post
    while I probably have the ability to make one, I don't have the time (or inclination).
    That one statement right there is why you should give up right now.!

    If you don't have the budget to buy one and you don't the time or inclination to build one then just call it a day and save your money for when you do. If you proceed then it's highly likely you'll just blow money or as often the case when taken on half-hearted you'll fail and give it up.

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