Thread: 1220 2440 build

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  1. #1
    Hi all, I'm Mark. I know many of you have probably heard it all before, but I'm hoping to build a CNC router big enough to take full sheets of ply or MDF and be able to cut nested parts. I'm in the process of enlisting the help of a local engineering firm to take care of the welding and fabrication, they will just work off of my drawings, I'm waiting to hear back from them after today.

    I have a few grand to spend, hoping to keep the costs down as much as possible but don't want to compromise on the design. It needs to be strong, last the test of time and also be fairly fast and accurate. This is a business venture so it needs to cock on, no way am i paying 10k plus, not that id mind if I had the money, if I can build one for a fraction of the cost.

    I have some design ideas and have been working on a basic draft, mostly incorporating ideas I've seen (will post a couple of pics later, if necessary),
    but thought it best really if I get the advice from the pros. I've spent hours (days) trawling the forums and have read some great and useful stuff, the only problem is I've forgotten half of it and the other half is buried somewhere in fragments throughout different pages.

    FYI I am completely new to CNC, but have some experience coding and can draw (a little) in CAD. Can't be much different to building a computer, can it? Hardware and software.

    I have a few questions...

    What pitfalls do you foresee with a machine this size? (1220 x 2440 x 100mm working area).

    The steel and aluminium costs I have covered, it's the cost of the rest of the hardware and software I'm not 100% sure of. Can anyone direct me to a kit or the parts I need?

    If you had 2-3k (2) to spend and you needed a machine this size, how would you go about designing and building it? Materials and hardware etc. Can it be done?

    If there's any relevant (completed) builds you know of please send me the link.

    Thank you.

  2. #2
    Hi Mark,

    There are a few machines here, all self built. But they are not as large as you are planning:
    http://www.mycncuk.com/threads/10066...s-picture-menu

    When the machine is that big (1220x2440) there are many things that come into play:
    1. Ensuring the gantry is stiff enough to cope with the span
    2. Ballscrews may want to whip at that length - I've not built anything that large but either look at fully tensioned ballscrews, rotating ballnut type, or rack and pinion drive.
    3. Costs start to build as things get heavy and better motors are need to drive it
    4. Be careful buying motor kits - they may boast Nema34 8Nm etc. motors but they throw in lowly 48V drivers and you would get more performance with Nema23 3Nm believe it or not.
    4. Ensuring general alignment and straightness

    I know Jazz and others have commented on big machines in the past based on first hand experience so I'm sure they will be here with some better specifics. Also some people settle for 1/2 sheets in the end to make something more manageable.


    Another machine here but unclear if it ever went anywhere:
    http://www.mycncuk.com/threads/6952-...-area%21/page5
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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  4. #3
    Hi thanks for replying.

    1. Hopefully the gantry won't be an issue as the design uses 50mm by 100mm mild steel side rails for the x axis, with 50mm support structures welded to the bottom. I'd seen somewhere that dropping the bed instead of raising the gantry makes the structure stronger, makes sense. 10mm aluminium plate for the gantry in an L shape. In theory, this is sound I think?

    2. Backlash, which sounds similar to slop in a drivetrain, was one of my worries here too. In my design I was looking at using ballscrews, I guess I need to keep reading some more on that issue. Are you saying that backlash can be eliminated by using those methods? I'm sure I've read somewhere it can. The structure itself I think should be ok, I tried uploading a picture from my phone a few tims but it failed.

    3) Most of the weight would be in the bed and support structure below made from mild steel, the only moving parts would be made from 10mm aluminium plate to keep the weight down.

    4.Again this is an area I need to look into more, but I'm thinking I need to finalise my design and see how much it's going to weigh before I decide.

    4. Hopefully this won't be an issue and is why I'm not even going to attempt to weld this myself. The lower supporting structure will be separate from the bed, bolting together so I can use shims to get the bed as level as possible. Not 100% decided on whether the resin route will be needed, probably, Hopefully someone else will come and clear this up.

    You mean that rather than having 100mm travel they leave it at just having 2 axis and using different router bits? I could make that work for some things, but not others.

    Many thanks

    Ps sorry if I've posted this multiple times!
    Last edited by HullMark; 26-02-2018 at 09:45 PM.

  5. #4
    Thanks for that link too, I have seen this and was thinking very similar, I was hoping though as you'll see from the dimensions I've given, mine doesn't need to be as robust for cutting just wood ... or am I wrong?

  6. #5
    If you had 2-3k (2) to spend and you needed a machine this size, how would you go about designing and building it? Materials and hardware etc. Can it be done?
    With this budget you would be lucky to build a machine half the size you are after. I would suggest that you put some of your design idears up for other to critique. Also I would advise not to buy any parts or kits of parts until you have until you hav a good idear of what you require. Sorry for the doom and gloom but many have made the mistake of jumping in with both feet.
    ..Clive
    The more you know, The better you know, How little you know

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  8. #6
    Hi Mark,

    Ok first off let me say straight away that Clive is correct with 3K you cannot build the machine you describe or one that is any good.

    When you get into 8x4 or above the game changes in lots of respects and cost is one of them.

    Now regards your idea of farming out the welding to engineering firm then be careful because I've seen this done many times and fail.?
    The problem comes from the fact most welding firms will weld the frame up as thou it's just workbench and CNC frame requires more careful approach.
    They won't take the time or care to spread the welding so as to keep distortion to minimum. They also won't constantly monitor any twisting that might occur from the heat. And most certainly won't take the time to make sure the Rails surfaces are on the same plane.
    Any distortion or twist will have to be dealt with later otherwise it will affect how the machine performs. So anything that can be done to lower this the better and this takes time and most welders haven't got the time to wait for welds cooling etc so will just weld it up in one go which will cause you issues down the line.

    The rail surfaces must be on the same plane and will need careful attention when welding or they will cause you lot more work. Even then if carefully done your still going to have either Epoxy level or have the surfaces machined flat.
    Don't be fooled into thinking Box section is flat because I've yet to see one that is and certainly not one nearly 3mtr long.!

    Now regards Gantry and 10mm plate in L shape layout then forget it.! That's just not going to be strong enough for gantry that will be 1600mm wide.
    To give some idea the last 8x4 I built which you'll see in pics uses 120x80 HD Aluminium Profile arranged in L shape and I consider that a Minimum for a machine this size.
    It's not just the weight it's carrying but got to also think about resonance/vibrations that will occur from the cutting. Resonance will give poor finish, cause excess tool wear and shorten component life.

    Next comes linear motion. If your wanting Ballscrews then you really need to know what you're doing and what to buy because when you get past 1500mm things get wobbly real quick.
    First, you have the obvious thing to deal with which is screw Whip from the long length. But you also have to think about alignment because long screws are merciless when comes to alignment. The slightest misalignment and they'll turn into gyrating skipping rope which will cripple the machine performance.
    Getting this right is a careful balance of selecting the correct ballscrew with regards pitch and diameter along with correct tensioning and alignment. Get anyone one wrong and your in for world of pain.

    This why Rotating ballnuts are often used for long lengths but this gets expensive and complicated unless you can make them your self.
    Rack & pinion is the common solution for machine this length but again this brings with it's own challenges and problems/costs.

    Coupled with all these solutions comes correct selection Motors/drives etc and is one of the reasons why you cannot build a machine this size for 3k.
    Long, large diameter screws require bigger motors which along with high power drives get expensive quickly.
    Ballscrew or R&P there is no difference really here because R&P is less efficient so still requires large motors to compensate. You also then have more backlash to deal with from R&P. Also R&P will require gearing to give you the Torque and resolution required which adds another layer of costs/complexitys.

    I Strongly advise you to think long and hard before you take this project one with No experience because it's very very easy to get it wrong and all the research in the world won't prepare you for just how much more of challenge it is building an 8x4 than say 4x4.
    The extra length really does change things that much and the slightest errors get magnified.

    But one thing I can 200% tell you is that cannot be done properly or legally for 3k.!!

    Here's two for you one with R&P and other with Ballscrews and mounted vertical.!

    Click image for larger version. 

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  10. #7
    Quote Originally Posted by HullMark View Post
    Thanks for that link too, I have seen this and was thinking very similar, I was hoping though as you'll see from the dimensions I've given, mine doesn't need to be as robust for cutting just wood ... or am I wrong?
    Yes your wrong.!!
    Don't under estimate wood because while it's softer than aluminium you have to cut it faster and often much deeper which requires strength/power.
    Also don't just think strength but also think in terms of vibrations because resonance really does affect the machine in many ways, performance, quality of finish, tool wear and component wear.

    Also just bare in mind CNC tends to open up other avenues and if machine is weak to start with then limits these avenues.!!

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  12. #8
    It's not all doom and gloom at all, I appreciate the honest replies and is why I'm here. I don't want this machine building yesterday, sure it's going to take time, I'm not in a major rush but would like It to be complete in 6 - 12 months. It will take as long as it takes, any sooner the better, this is a side venture/ hobby and the time will give me the chance to research more and work on my CAD.

    This is all sound advice, I won't be purchasing anything until until I have a fully itemised bill of materials, and like you say that will come once I have worked out a suitable design Clive. I've tried attaching photos to the posts I'm sending, but it says failed to upload.

    It seems like The first and maybe most important things to consider are the strength and accuracy of all parts. The two companies I have in mind, I know someone who builds conveyors at one, and i know the owner of the other one. The other company manufactures all sorts of precision parts. There's no doubt in my mind that both of them will be able to achieve the accuracy, they both have decades of fabrication experience each. It's like jazz said though they are always busy so it'll be a case of finalising a design first, then fitting in the welding and fabrication around what they've got going on when I'm ready.

    I thought first of all i'd draw a rough idea, get the structure looking solid for the bed, base and gantry before I go into any of the finer detail stuff. Then from there we can look at motors etc. I will look again at posting some pictures.

    If it can't be done for that price, how much is more realistic Jazz? There's a few machines this kind of size on eBay for 7.5-11.5k with some offering training. I figure if they can sell them for that surely I can build one for less (hopefully, that's usually the case when you DIY as much you can) with the right kind of guidance and outside expertise. Maybe I don't know what I'm talking about? But that's why I'm here.

    This thread as much as anything will serve as a reference for me so I can have everything I need in one place. Any links and information are much appreciated, I'm keen to learn as much as I can from the experts here and am not expecting things to happen over night.

    Cheers guys for the comments, you've given me a lot to think about.

  13. #9
    Quote Originally Posted by HullMark View Post
    It seems like The first and maybe most important things to consider are the strength and accuracy of all parts. The two companies I have in mind, I know someone who builds conveyors at one, and i know the owner of the other one. The other company manufactures all sorts of precision parts. There's no doubt in my mind that both of them will be able to achieve the accuracy, they both have decades of fabrication experience each. It's like jazz said though they are always busy so it'll be a case of finalising a design first, then fitting in the welding and fabrication around what they've got going on when I'm ready.


    Quote Originally Posted by HullMark View Post
    If it can't be done for that price, how much is more realistic Jazz? There's a few machines this kind of size on eBay for 7.5-11.5k with some offering training. I figure if they can sell them for that surely I can build one for less (hopefully, that's usually the case when you DIY as much you can) with the right kind of guidance and outside expertise.
    Ok well obvioulsy depends on lots of factors and how good job you want to do but 4k will be more realistic figure and that is doing everything your self, welding machine work for aluminium parts the job lot.
    So straight off the bat your backs against the wall if paying these companys or even if working on mates rates you haven't got much room to play with.

    Also you'll all most certainly have to buy all the major components ie: linear rails, ballscrews etc from china to do this for 4k- 4.5K.
    Here's Little break done for you.

    The Linear rails & bearings, ballscrews & end bearings will cost about 2k and that's working on 20mm rails. Really 25mm would be better for long axis. Then throw another 300-400 into things like Timing belts, pulleys, Cable chains, nut's bolts etc.

    Frame materials will depend on design but You'll not have any change from 500 and that's working on steel prices at wholesale not retail. By the time throw aluminium into mix for Z axis and brackets etc and you'll be at 750+.
    If you use Profile type gantry like I do then will be easily over 1000.

    The electronics will cost best part of 1000 to be done properly. That's working on using Closed loop steepers and using Motion control card all done correctly in Steel cabinet. Including all cables relays, e-stops, limit switches etc.
    Wouldn't use open loop steppers for machine this size because using slaved motors as there is lot of inertia and easy to loose position. Plus the difference is cost isn't massive so well worth little extra.

    So
    Rails/screws etc 2000
    Rail/screw sundries 400
    Steel/Ali 750
    Electrics/Motors etc 1000

    These prices are not OTT and based off prices I've paid from China so you don't have massive wiggle room. Plus there will be extra hidden costs like paint,Drills etc which could easily account for another 200-300.

    So you see 4K soon gets eaten up and that's allowing for someone who knows what there doing and doesn't screw up. Which is very easy to do for resonably experienced builder and almost guaranted for new builder.!!

    Regards the Ebay machines then I've yet to see one that is any good for under 10K and most are Chinese machines which have there problems like coming with DSP controllers which expire quickly and limiting to use or cheap nasty electronics which will need some fetteling costing more money still. Most 8x 4 that are any good are between 15K-20k.

    If you expect to spend 5K you'll end up with machine that will last for years cut everything you want and be very reliable. The same would cost you 20K+ to buy.
    Last edited by JAZZCNC; 27-02-2018 at 05:19 PM.

  14. #10
    5k sounds reasonable to me, thanks for the break down Jazz, that's helpful and exactly what I needed, a ballpark figure ... have you seen CKJCNC on eBay? They seem to be doing a lot of business selling CNC machines, sub 10k plus VAT for the 1325 model (1300 x 2500 x 200 working area). Certainly looks the part, at least to my untrained eye! About 11.5k inc VAT.

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