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Thread: DIY CNC machine on the cheap!

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    Default DIY CNC machine on the cheap!

    Hello everyone,

    This is my first build and I've already gone against most people's advice of making a small first machine. At 600mm x 300mm x 75mm cutting volume, I think it will be a fairly large one, but I'm eager to see what lies ahead. I live in Africa and its really hard to ship things bought off the internet, so my biggest objective will be to source as many of the required parts as possible from local venders. Everything that will require tooling will be done by hand tools besides drilling (drill press), grinding, and perhaps cutting (angle grinder) the steel. The design I came up with doesn't require that much accuracy for drilling, so a drill press will suffice. All the bolts that will hold the machine together will be M8 bolts, besides those I'll use to attach the stepper motors, which will probably be M5. The plan, in short, will be to use a 9mm drill bit for the M8 bolt holes so i have a fair bit of play within the holes, which will help me make minor adjustments when assembling. This will especially come in handy when fixing up the linear slides nice and tight with as little play as possible. Most of the machine will be made up of standard 25mm x 25mmx 6000mm steel box tubing.
    I have bought some of the items I'll need on eBay, just waiting for them to arrive. I hope they reach me by post office *fingers crossed* (like I said, the physical address and mail delivery system in Africa still has a long way to go, so post office is probably my best bet at the moment). For now, a few snapshots of the frame are all I've got. I did the design in Sketch Up and I have attached the file so anyone can have a closer look and do with it what they may. Any ideas (from noobs to pros ) are welcome. I decided on a metal frame for the machine because I don't have the tools to machine MDF or other wood for that matter and hope I don't regret it!

    Isaac.

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    Default Re: DIY CNC machine on the cheap!

    Few more pictures!

    Attached Thumbnails Attached Thumbnails DIY CNC machine on the cheap!-x-axis-linear-bearing-inside-jpg   DIY CNC machine on the cheap!-x-axis-linear-bearing-jpg   DIY CNC machine on the cheap!-y-axis-backside-jpg   DIY CNC machine on the cheap!-y-axis-detail-jpg  

    DIY CNC machine on the cheap!-y-axis-linear-bearing-backview-jpg   DIY CNC machine on the cheap!-z-assembly-apart-jpg   DIY CNC machine on the cheap!-z-assembly-front-view-jpg   DIY CNC machine on the cheap!-z-axis-linear-bearing-jpg  



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    Default Re: DIY CNC machine on the cheap!

    I would be concerned about the leverage exerted on the gantry by the Y axis.That 450mm height gives the forces quite a mechanical advantage and there is a desperate shortage of triangulation,which will be amplified by having bolts pass through holes that are 1mm oversize.I would suggest you increase the distance between the bearings on the Y axis and add some bracing and it would probably be a good thing to extend at least one of the box sections of the gantry so that an external brace can help hold the gantry rails square to the uprights.Good luck with the machine.



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    Default Re: DIY CNC machine on the cheap!

    Whew...I forsee lots of flex in that design. I agree with routalot that there's going to be lots of leverage on that gantry. You could still build your machine economically using other materials like MDF using torsion box design. That would be much more rigid than your current iteration.



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    Default Re: DIY CNC machine on the cheap!

    Hello routalot,

    Thanks for sharing your observation. I kind of realized that the gantry was hanging a little too high and I wasn't sure whether the eight bolts i had assigned the job of holding it up with all the associated weight and cutting forces would work, but i thought I'd build it and check for flex with the frame done. I'm glad you've mentioned that this early, so that's going to change for sure. Increasing the distance between the bearings on the Y axis would most definitely mean i would have to do the same for the X axis, which i really wouldn't mind if it reduced the flex on both axes. Increasing the distance between the bearings on the X axis to facilitate triangulation would increase the overall length of the machine along that axis, which i also wouldn't mind, however, i would have to start thinking about revising that linear mechanism to be fully supported. I haven't had any experience what-so-ever with CNC machines, never actually seen one doing its thing! Only videos on the web, so i haven't a clue what specific design considerations to keep in mind to make the frame rigid. You can't imagine how helpful I find your advice. Thanks again.

    Isaac.



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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by fretman_2 View Post
    Whew...I forsee lots of flex in that design. I agree with routalot that there's going to be lots of leverage on that gantry. You could still build your machine economically using other materials like MDF using torsion box design. That would be much more rigid than your current iteration.
    Thanks for the recommendation to switch to MDF, fretman_2. Unfortunately, I don't access to power saws, or sanding machines to guide me with cuts. Most DIY machines I've seen other hobbyists do using MDF are usually cut by either another (sometimes bigger) CNC router, or a couple of wood working power tools, which I don't have either. If I can cut MDF straight and true using hand tools, I'd gladly consider using MDF. It's interesting that I thought the first concern most CNC'ers would have would be the linear slide design for the Z-axis with the ball bearings running a long the rim edge (because of the small contact area and lateral load on the bearing), but that doesn't seem to bother you guys that much.

    Cheers
    Isaac.



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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by routalot View Post
    I would be concerned about the leverage exerted on the gantry by the Y axis.That 450mm height gives the forces quite a mechanical advantage and there is a desperate shortage of triangulation,which will be amplified by having bolts pass through holes that are 1mm oversize.I would suggest you increase the distance between the bearings on the Y axis and add some bracing and it would probably be a good thing to extend at least one of the box sections of the gantry so that an external brace can help hold the gantry rails square to the uprights.Good luck with the machine.
    I'll make modifications to the design tomorrow (it's getting a little late now) and post them, starting with triangulating the gantry. I'll also try to figure out a way i could support the X axis because lengthening it would most definitely require it.



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    Default Re: DIY CNC machine on the cheap!

    Well...the linear slide could be a concern, but likely less than the flex. A long moment arm is the same as using a long stick to move a big rock...takes less pressure on the other end to do the work. You might ask yourself if you really need all that clearance under the gantry. You didn't really go into what you intend to cut with your machine. I designed mine to cut out guitar necks and bodies. So I limited the Z cutting travel to about 3 or so inches to keep the forces down when I cut. I lacked the engineering skill to project those forces, but I did have an understanding that they could be higher with an excessive amount of Z travel.

    Nothing particularly wrong with using skate bearings the way you have them I suppose. It looks as if you have a cross member under the machine that keeps the two bearing assemblies from spreading. You might have some issues later with using steel on aluminum...depends on how often you use it.






    Quote Originally Posted by imbaine13 View Post
    Thanks for the recommendation to switch to MDF, fretman_2. Unfortunately, I don't access to power saws, or sanding machines to guide me with cuts. Most DIY machines I've seen other hobbyists do using MDF are usually cut by either another (sometimes bigger) CNC router, or a couple of wood working power tools, which I don't have either. If I can cut MDF straight and true using hand tools, I'd gladly consider using MDF. It's interesting that I thought the first concern most CNC'ers would have would be the linear slide design for the Z-axis with the ball bearings running a long the rim edge (because of the small contact area and lateral load on the bearing), but that doesn't seem to bother you guys that much.

    Cheers
    Isaac.




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    Default Re: DIY CNC machine on the cheap!

    I’m not sure what suppliers can do for you in your country, but many around here they can rip sheet goods to size. If you know the width of the boards you need you can have the MDF or plywood pre cut.

    Not having tools can be a huge problem which is where kits come in so handy. The problem with kits. Ring the big jump in parts costs over raw materials and shipping charges. It might not be effective to ship a kit that distance but you might want to look for shops near you with the ability to cut materials to size. Even a wood working shop with a table saw can help with wood or aluminum products.

    It is completely possible to get straight cuts with hand power tools simply by using guides for a saw or router. It is a bit harder to get them parallel. For a guide the edge of factory fresh plywood may do the trick. Parallel cuts require a lot more work on the builders part to align the straight edge.

    I have to agree with others here the gantry will likely be a problem. Gantry are in fact a weak link in many DIY builds. What you want to do here is define the capabilities you need and then design and build to suit.

    Running short on time - hope this helps.



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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by fretman_2 View Post
    Well...the linear slide could be a concern, but likely less than the flex. A long moment arm is the same as using a long stick to move a big rock...takes less pressure on the other end to do the work. You might ask yourself if you really need all that clearance under the gantry. You didn't really go into what you intend to cut with your machine. I designed mine to cut out guitar necks and bodies. So I limited the Z cutting travel to about 3 or so inches to keep the forces down when I cut. I lacked the engineering skill to project those forces, but I did have an understanding that they could be higher with an excessive amount of Z travel.

    Nothing particularly wrong with using skate bearings the way you have them I suppose. It looks as if you have a cross member under the machine that keeps the two bearing assemblies from spreading. You might have some issues later with using steel on aluminum...depends on how often you use it.
    Right,... thanks to you guys, I realised many things of vital importance my gantry lacked that I had completely missed!!! Only after I imagining the machine cut along each axis at a time did I notice how much flex is actually inherent in this particular design, so i came up with a major revision! I intend to use it primarily for engraving lettering in wood and plastic (mostly acrylic for signs although i do sometimes need custom cut parts for small speaker enclosures out of MDF. As i mentioned earlier, I live in Africa and the nearest CNC in 350kms away, and only good for about 150mm x 200mm x 20mm cutting volume, so that's useless! I know for sure I'll get clients for the machine, but I don't want to get ahead of myself just yet. So, in rev 2, solved most of the flexing problems with the gantry as you can see.



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    Default Re: DIY CNC machine on the cheap!

    Well actually I can't see.Its good that you have been visualising the loads on the machine and the additional information suggests to me that a 90mm Z axis travel would do what you need.Which would allow you to reduce the gantry height significantly and by doing so you would reduce the leverage exerted by pushing the tool through the work.The other thing that you might want to consider is that the forces applied to the gantry will tend to twist it and the two lengths of box section in your initial design are sub-optimal.I don't have an easy answer,but you description of how limited the facilities are should be seen as a challenge and not a limitation;a determined man will get the job done.



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    Default Re: DIY CNC machine on the cheap!

    Rev 2 modifications:

    1) Added triangulating bars on both sides of the gantry. that should take care of flexing when cutting along the X-axis alone.

    2) Also added a piece of timber snugly between the each pair of the gantry uprights. That should prevent flexing when cutting along the Y axis alone and finally;

    3) Added another piece of timber whose face runs parallel to that of the cutting table, underneath the table. This should resolve racking (or at least minimize it) of the gantry from side to side probably by keeping the X-axis bearings nice and parallel.

    I can't think of anything else I could possibly add to the gantry to make it any more rigid that it already appears. As an extra precaution, to prevent the X axis rails from sagging under that weight of the gantry, I think I'll add some 2mm L-section steel running along the edges of the table (Not yet added in the pictures). This will serve the purpose of both stiffening the X-axis rails and keeping saw dust from jamming the X-axis linear bearings during operation.

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