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What' the basis of a new CNC design ? ............ ACME lead screw length ?

Discussion in 'CNC Mills/Routers' started by T4Concepts, Dec 7, 2017.

  1. T4Concepts

    T4Concepts Well-Known
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    Hi all,

    After searching around for a CNC machine that will allow me to perform a particular task, it's becoming apparent that I'm going to have to build one myself. The 'C-Beam' and 'V-Slot' system is absolutely brilliant, virtually any combination exists. But where to begin ? How do you base the dimensions of your intended machine ?

    I know the maximum dimensions of the parts I need to create and machine, but is my new cnc build restricted to the length of the available acme lead screws ?



    TURK
     
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  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    It's based on the cutting area desired. Don't oversize any more than absolutely necessary.
    The TR8*8 screws useful length maxes out around 1 meter so that's the max length they are sold at. Beyond that you get into issues with bowing/whipping. If you wish to go longer you need to find larger diameter screws or go with belts or rack & pinion drive.
     
  3. T4Concepts

    T4Concepts Well-Known
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    Hi Rick,

    According to ooznest, the lead screw' available lengths are 250mm, 500mm and 1000mm

    Sorry, don't do belts, don't like the idea .............. just a personal thing :rolleyes:

    What if you intend designing your own CNC ? ................ ideal dimensions for me would be 600x600mm. I take it it's not just a case of sawing the end off a lead screw !? For that I would have to buy x3 1000mm lengths and cut them down. Doesn't mean a great deal of sense to me that.



    TURK
     
  4. Jonathon Duerig

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    Usually you want to think about the dimensions of your work envelope and work outwards. Let's say you need to be able to cut things that are 600mm x 600mm. That means that you need axes that are at least the size of your work envelope plus the length of your gantry plates (they will run into the edges) plus the size of any other obstructions that might happen at either end. So if you want to make a machine that has a working envelope of 600mm x 600mm, then the 1000mm lengths will actually work pretty well. They give you plenty of extra space so that you can always do things the easy way at the expense of a little bit of travel.

    For example, it is usually easier if your Y gantry plates are mounted on the outside. This means your lead screws aren't going to be be exposed to dust and swarf as much. But that cuts at least an extra 50mm of travel off each end. And it is easy to mount a homing switch if you are willing to give up a bit of travel but it is a tricky puzzle if you are not. This will be true for a lot of things. So I'd recommend that you figure out the travel you want, look at the options and estimate the max travel you'd get. Then round up to the nearest standard size.

    -D
     
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  5. T4Concepts

    T4Concepts Well-Known
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    Thanks Jonathon :thumbsup:

    Makes a great deal of sense.

    I read somewhere that when designing your own CNC it's usually recommended to begin at the bottom .................. work out the bed size, side rails, the gantry and finally the Z axis. All this makes a great deal of sense also. But my issue is with my Z axis, I really do need to get as much clearance under my chosen spindle. Also, how much space is really required around the workpiece to consider it a safe distance ?

    The Workbee does really look like the sort of machine I'm going to buy ( or even modify ), just wish the Y plates were higher so the X gantry would also be higher. That would increase the clearance from my bit to the bed quite considerably.


    TURK
     
  6. Jonathon Duerig

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    You can make the bed any height you want. The limitation on Z is the amount of Z-axis travel not where the bed is. If you look at any of these machines, don't imagine putting it on a kitchen table. Your 'table' can have sides that are higher up than the middle for example. Or the table 'bed' might be a platform you crank up and down. Or whatever. So don't make the gantry plates higher. Just make the machine higher or the bed lower. As long as you have Z-travel it will work out fine.

    And you can set your table up for whatever carving you need to do. If you think you might need to carve the end grain of long logs, just have one end of your table with a vise for holding the log and no table top at all.

    In terms of safety, the important thing is that your 'safe Z-travel' be higher than any clamps or other protrusions and above any part of the workpiece. And you want to wear safety glasses, especially if you don't have some way of controlling the debris that comes out. Also, bits may go flying if they break as well.

    -D
     
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  7. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Would cutting a blockout in the base board of the Workbee and dropping your blanks down into it be workable?
     
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  8. T4Concepts

    T4Concepts Well-Known
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    Best if I post a picture of what I'm working on guys, otherwise we're all working in the dark here.

    Actually, I'm not working with wood .................. I'm profiling 3mm thick ABS thermo plastics.



    Back soon with pictures ! :thumbsup: :D



    TURK
     
  9. Jonathon Duerig

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    Just FYI, I cut 3mm thick ABS plastic all the time. Because of one thing and another, my Z-travel ended up being only 40mm or so. This turns out to be plenty when you are cutting thin sheets of material.
     
  10. T4Concepts

    T4Concepts Well-Known
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    Hi guys,


    Here's one of the vacuum formed parts that I need to profile >>

    1960_IMG_3585.jpg


    And here's one I finished off by hand >>

    1952_IMG_3530.jpg


    The two 92mm holes are for the headlight units, the 12mm holes are for the adjuster screws to adjust the beam on the headlights, and the smaller 8mm holes are to mount the metal headlight mounting frames to the assembly. That's the part I need to machine. I have literally hundreds of these to make ! Only a CNC machine will guarantee precise alignment of all these holes. The grey thing that ABS part is sitting on is, a resin tooling plug that I use for vacuum forming the parts.

    Now you can see the problem I'm having, buying a CNC machine isn't as straight forward as it seems ...................... fine if your intention is to machine flat pieces of wood and your making jigsaw puzzles, but that's not always the case. The spindle would also have to travel onto 2 different levels.

    So, am I trying to accomplish the impossible ? I don't think so, the 'C-Beam' and 'V-section' modular system I think is the answer. But where to begin !? o_O




    TURK
     
  11. Jonathon Duerig

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    If this is an example of the kind of thing you want to do, then you need a CNC machine. But if this is exactly what you want to do, a CNC machine is probably not going to save you much. What I mean is that you could create a custom jig and crank out a lot of these on a drill press (or two drill presses). There is only marginal benefit in a CNC if you are doing the exact same pattern over and over. But if you are doing a bunch of similar patterns that are all different, then a CNC is more likely to be worthwhile.

    But suppose you do need a CNC. What you want to do is just like @Rick 2.0 suggests and which I alluded to. You will have a cutout on your bed that lets you place one of these securely so that most of it is below the bed with only the parts you need to cut above the table. As long as your z-travel can go down to the lowest part you need to cut and up to at least 5mm or so above the top 'peak', you should be fine. Note that you will still need secondary operations after you CNC to get those side holes.

    You might also have some luck doing the drilling before the vacuum forming. If you could do that, then everything would be easier and there would be no secondary operations. But the two problems you'd have to solve would be precise registration and figuring out how to block up the holes in a temporary way to still let you vacuum form.

    Assuming the workbee has enough z-travel for you, it will work even your jig for holding it is cut out of the bed. But you will have to think very hard about workholding. The key to making this useful will be to minimize setup/teardown time and maximize the number of units that can be cut in one cycle.
     
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  12. SugarJ

    SugarJ Journeyman
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    I agree. If the purpose is to crank out hundreds of identical parts, your effort would be better spent on creating a jig and doing it on a drill press. The process will be faster than doing it on a leadscrew CNC.
     
  13. GrayUK

    GrayUK Master
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    Hi Turk.
    Perhaps if it is just the holes on the side that you are concerned about, then as the other guys have suggested, you create a cavity in the bed of your CNC, in the bottom of which, you have fixed a side profile plug, allowing your headlight fixture, complete with its own plug to fit in snugly about half it's depth. This method would require two plugs, one for each side. If you know what I mean.
     
  14. T4Concepts

    T4Concepts Well-Known
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    many thanks for your help and suggestions guys ................... all taken onboard :thumbsup:

    I particularly like the idea of the cut-out in the cnc bed, excellent idea in terms of lowering the ABS part but also to secure it. An idea I will undoubtedly use in the future.

    A wooden jig is currently what I'm using right now, it's fine for the smaller holes that can be drilled out with conventional drill bits, but drilling out the 92mm holes is a different story ! No holesaw available will cut 3mm ABS effectively, and a router bit just tears it to pieces :jawdrop: But a milling bit will 'cut' that hole out very effectively.

    And there's also another reason why I'm looking at a CNC machine.

    When making the original moulds, the original concept ( or form ) is created using PU foam. It's quite dense but soft enough to form by hand, like the one in the picture below. But a CNC machine would make light work of this, and much more precise than I can ever make it. And another thing to consider, as you're designing headlights assemblies, the off-side and near-side are a direct reversal of one another. To do that simply by eye is very very difficult. With G-Code the entire process would eliminate any errors. So, it's not as if I need to build a CNC machine that will mill very hard materials where structure is vitally important, as the materials I'm working with are quite soft in nature.

    Hand sanded PU foam plug >>

    1636_IMG_1857-1.jpg




    TURK
     
  15. GrayUK

    GrayUK Master
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    You would design the plug to sit the item flat and square to the cutter. I think your main problem is going to be the length of the bit you use. To cut A, you will need to get down the side of B, that is going to be the sticky bit. However, you are not attempting to cut aluminium, or a hard wood, so maybe a longer bit may work, without flex, if used with care and many light cuts. Considering the size of hole you intend to cut, you could go to quite a large bit, but still not be greedy.
    P.S. Structure is always very important in the CNC game. Stress and flex are always your enemy.
     
  16. T4Concepts

    T4Concepts Well-Known
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    I'm not really fussed about speed and cranking out these out by their hundreds, I'm more concerned about the quality of the completed part. They're bespoke custom headlight units, that perform very well. And not really intended for mass production type of thing. So I won't be churning these out if that what you mean.


    No, it's not the small 8mm holes in the side I'm concerned about GrayUK, but the accurate positioning the holes in the top of the part. After all, that's the mounting points for the headlight units, so they must be precise every time.

    The small holes in the side I drill out manually when I assemble the assemblies.


    I have a small Proxxon milling machine, so doing a quick mock-up of what is needed, shows the sort of issues you would encounter. Forgetting about the two level milling/drilling thing for the time being, you can quite clearly see that the bottom edge of the 'Z' axis would touch the part. You guys who already have a CNC machine would know this, and with most ( if not all ) the CNC machines I've seen so far, the bottom of the spindle motor always lines-up with the bottom edge of the 'Z' axis assembly.

    Would it be possible to mount the spindle motor lower down d'you know ?

    Many DIY cnc builders use different types of spindles, 'spindles' not really intended for CNC ....... like the DeWalts for instance, or the Makita C0700 ( which I also own ), but I'm intending to use this spindle, the Proxxon BFW 40/E >>

    IMG_4070.jpg

    Either way you look at it, the part would have to be oriented as in the picture >>

    IMG_4072.jpg


    I've been measuring stuff ( cnc bed area ), and it's beginning to look as though the Workbee at 500mm square will do the job, and lowering my part in the MDF bed as suggested earlier, it's just that 'Z' axis travel I'm worried about.

    Anyway guys, I did notice that that Ryan Lock from 'Ooznest' in the UK is on here, so I'll direct him to this post, as I emailed him yesterday explaining what I was trying to do. At the very least this post ( and the images ) will help him understand my situation.




    TURK
     
  17. GrayUK

    GrayUK Master
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    Sorry Turk, we had a cross threading event there :banghead:
    By the way, they look very professional.
    Good job
     
  18. T4Concepts

    T4Concepts Well-Known
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    Thanks mate :thumbsup: :D

    High performance with a high quality build is what I'm after, I just got tired of paying extortionate amounts of money for inferior mass produced headlight units. It seems I'm not the only one, as my order book is already full and I'm still at the prototyping stage ! :D >>

    1986_IMG_3731.jpg


    I really just have to work on my workflow and 'production' method.




    TURK
     
  19. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Sorry, I've been out for a few hours and am just now catching up on the conversation. Based on what you are showing you might consider up-sizing a minimill to do the job, increasing the length of X and Y and reversing the Z to a full axis plunge rather than just a router plunge.
     
  20. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Here is a better idea of where I was going with the previous comment:

    Concept Mill.jpg

    Sketchup file attached.
     

    Attached Files:

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  21. T4Concepts

    T4Concepts Well-Known
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    Absolutely bang on Rick ! :thumbsup: What fantastic feed back ;)

    I watched that entire video, all 1 hour and 45 minutes of it ................ and that's exactly what I need. I did the mistake of thinking that I really needed a CNC machine, but they do indeed come in all guises. A CNC machine doesn't have to be box shaped with an over hanging gantry travelling left to right, that MiniMill you show in your post is still a CNC as it's computer controlled.

    I just took a look at 'ooznest.co.uk' website, but they don't list it .......................... no doubt they'll stock all the parts to construct one though. When I checked 'Openbuilds' webstore, they list it as a third of the price than the CNC machine I was looking at originally. And that's including the Nema23 stepper motors and a 24 volt power supply, great value I think.

    Many thanks for all your help guys ................. as it's 7Am over here in France now, and I've been at this since yesterday midday, I'm getting rather tired now so I'm off to my flea pit ! :D



    TURK
     
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  22. Giarc

    Giarc Master
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  23. T4Concepts

    T4Concepts Well-Known
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    Hi guys,

    Well that's a first ! ................... Never seen that before. Website blocked 'Geolocation IP Alert' recognised as being initiated from FRANCE !

    Seems that 'Kodiakcuttingtools' don't want us French guys seeing what they're selling ! :cool: Never mind, Google search to the rescue .................. and found some elsewhere. I wasn't aware you could get extra long milling bits, so I'm grateful for the link anyhow, Giarc. :thumbsup: That should sort out my issue with cut depth.



    TURK
     
  24. GrayUK

    GrayUK Master
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    Well Turk, that should be you all ready to go!! :thumbsup::thumbsup::thumbsup:
     
  25. T4Concepts

    T4Concepts Well-Known
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    Well, almost GrayUK ..................... now I've just noticed something :cool: Mmmmmmmmmmmmm .................

    Before I dive in, I decided to look back on this > OpenBuilds MiniMill

    Pretty much the same machine I need to build. So I've already put in my basket at RepRap 3D Printer Parts Supplier - V-Slot CNC - Ooznest
    the following:

    500mm C-BEAM LINEAR ACTUATOR KIT - for Y axis
    500mm C-BEAM LINEAR ACTUATOR KIT - for X axis
    250mm C-BEAM LINEAR ACTUATOR KIT - for Z axis

    So, pretty much the same as the MiniMill in the link above, except I've chosen a longer 500mm X axis.


    The MiniMill spec states the travel as following:

    X Axis Travel: 120mm - (4.5")
    Y Axis Travel: 195mm - (7.5")
    Z Axis Travel: 80mm - (3")


    How do you work out the amount of travel you need ? For instance ................. the Y axis in the spec above is 195mm, would this mean you need to divide 195mm by 2 ( the middle ), so basically the maximum travel is 97.5mm to the left and 97.5mm to the right ?



    TURK
     
  26. Scotty Orr

    Scotty Orr Veteran
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    That's basically the idea, but on the MiniMill (for example), the support post in the rear on the y-axis is closer to the mill head than the front of the y-axis. On the MiniMill, you indeed have 7.5" of travel, but only about 5.75" of usable "build length". The rest of the travel takes the work piece further foward for easy removal. (So you have about 2.8" rearward travel, and 4.7" forward travel - from mill center..)
     
  27. T4Concepts

    T4Concepts Well-Known
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    That's what I was afraid of .................. lack of work space !

    The parts I need to work on are 292mm L x 164mm W x 100mm H been doing some mock-ups with wood and sliding them about. It's getting to the point now, where I realise that the 'minimill' configuration would become unstable as a work platform, so maybe I should go back to my original idea of the conventional CNC machine layout, like the WorkBee.

    Hopefully I can have a chat with Ryan Lock from Ooznest tomorrow, and he can advise me.



    TURK
     
  28. Scotty Orr

    Scotty Orr Veteran
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    Yeah, I ran into the "limited area" problem with my MiniMill, so I upgraded it with about $200 in parts to give me a expanded X and Y build area. (See MMXL - A MiniMill Conversion ). Then you might be able to do what Rick 2.0 mentioned above to get increased height for Z.
     
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  29. T4Concepts

    T4Concepts Well-Known
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    Thanks Scotty, that's a good idea that ......... I hadn't thought of an extended Y axis like that. But that would only work as you have done by moving the centre posts to two side mounting positions for the X axis. So we really are talking about a more conventional way then. I've already seen many many member builds, CNC machines 'off the shelf' and what not, and I'm trying to get it right first time round as opposed to have to 'upgrade' in the future. I guess part of the fun is the research anyway :D

    Really enjoyed watching your video, first time I'd seen a minimill in action. Thanks for taking the time to share :thumbsup:

    That's the router I've got as well, Makita C0700, nice machine, but I'm going to use my Proxxon BFW40/E as my main spindle motor on this, with the option of the Makita as well.



    TURK
     
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  30. GrayUK

    GrayUK Master
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    There really are sooo many variations on a theme nowadays. For my two penneth, I would use two CBeams as the Y axis, and mount my two CBeam gantry posts on top of the Y CBeams, therefore gaining full width, and importantly, full length of the bed. A centre Y Linear Actuator down the centre like Scotties, but have outriggers left and right on the bed which will locate into the CBeams. This eliminates any chance of wobble from side to side. Simple but effective variations.
     
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