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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > RRcnc aka reasonably rigid cnc (build log)
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  1. #1

    Join Date
    Jun 2022
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    6

    Post RRcnc aka reasonably rigid cnc (build log)

    Hello good people of the internet.
    im starting a thread where i will be posting cad models of the cnc i will be building in the next couple of months, it will be used for machining wood to hopefully pay it off at least partially. i plan on cutting wood with it and doing some light cutting of alu or maybe even steel if possible, i will be upgrading it in the future when i save enough as im only a broke student. its a budget cnc that will be under 2500e, i hope xd. made out of steel square pipes 100x100x4 or 80x80 as the base and 200x100 for the x gantry( smaller one). this is going to be my first cnc so be gently with critique lol, im still in the planning stage of it all as i have another 2 months of working to be able to buy all of the material needed. i will post the pic for you to critique and explain more about the design.



    https://i.imgur.com/zLSNYwf.png
    https://i.imgur.com/QTwbFgl.png
    https://i.imgur.com/ZhOmEiv.png btw y gantry isnt connected to the base properly dont mind that just forgot to extend those when i was redesigning
    Dont mind the model, obviously its not finished yet. you might see that i have 2 different z axis, just wanted to see how it looks and im liking the first 1 as it gives me same travel either way. unless i get bigger pipes to raise the y axis to get more clearance. only possible problem is that while it should give me more rigidity and clearence by having smaller distance between bottom carriage and bottom of the spindle it is still 107 mm from the bottom spindle holder to the bottom carriage. the x gantry will be connected to y carriages with 18mm thich alu or steel if i find some. im using 25mm rails on y axis and might do the same for x and z as i decided to not use the alu profile made by vallder made for cnc machine as i heard that steel for same weight is 7 times stronger so yea plus i save around 90$ on the gantry. distance between bed of the machine is 40mm, 15mm between bed and spindle for the smallest plate i would cut on it and 25mm for the smaller bit i found, total travel is around 210mm and clearence between bed and gantry is 207mm. already bought belt reduction for nema 23s for cutting alu and steel i will make a design where its possible to just move the steppers around to use direct drive for more speed when im cutting wood. the spindle im using is 2.2kw cheap chinese. ballscrews 25mm 10mm lead im hoping i can make the machine with 2000mmx1000mm but i now realise how hard it is. ballscrews and rails are actually kinda cheap compared to the rest of the stuff so thats why i wanted to make a bigger machine because there wasnt a big difference in price. the ballscrews are c7 so y axis will have a precision of 0.35mm over the whole 2m length which is fine with me. rails are either legit unprecise hiwin, which i doubt, or a cheap copy. it is very hard to get stuff in south eastern eu so yea. down the line i plan on selling it for a profit and building a metal cutting cnc around 1000x1000 with expensive ballscrews and beefy rails and a nice toolchanger but will see. i have been reading a lot on this forum and im hoping this is what an optimal gantry placment would look like, if not i will change with the advice i get from here. for the people saying that this is gonna turn out like **** because of welded stuff ik it probably will but i will get most surfaces machined by a friend of mine. the second half of the machine is what it would look like if i used a different z axis design btw. i tried calculating the critical speed for the y axis but i dont think i did it right i would be more then happy with 3-4m per minute which is 300 to 400 rpm on a 10mm lead, prob will use 5mm on x and z. critical speed is apparently, i calculated this with minimal info and knowledge btw, 700rpm which is more then enough so around 400 atleast working without prob i guess, 700rpm if both sides are fixed which i have to ask if that means that end machining is different or im just using different ball screw support units. i dont want to use rack and pinion because of poor precision. so yea. if theres anything else you would like to know feel free to ask thanks for your time, cya

  2. #2

    Join Date
    Jun 2022
    Posts
    6

    Re: RRcnc aka reasonably rigid cnc (build log)

    things i need advice on are
    X gantry placment ( currenctly it is pushed way back so that the front carriage holds some of the weight of the z axis, that is my logic behind it)
    z axis i like the current design, the first 1, but if anything would perform better i would be more then happy to change it
    ball screws, advice on speed needed to cut wood, diameter, lead and calculating the rpm it could work with.
    spindle cooling, i would like to cool it actively with a computer water cooling radiator pump and some fans just not sure how to do it exactly. ive heard that spindles are around 75-80% efficient so around 25% lets say of 2.2kw is going to be heat and i think i would be find with 240mm radiator, 2 fans cooling it
    i would like to add a small vacuum plate but not sure how expensive it would be so i will expand on that topic later as already im at the top of my budget,
    cya lads

  3. #3
    Registered
    Join Date
    Dec 2003
    Posts
    1132

    Re: RRcnc aka reasonably rigid cnc (build log)

    I'd put the steppers on the long axis on the other end of the machine as it will make loading whole sheets less difficult.I think you ought to go a bit further with your preliminary design and include a table that allows workholding.If you search this forum there are several threads about rigidity and how much more of it you will need to cut steel,I suggest you seek them out.

  4. #4

    Join Date
    Jun 2022
    Posts
    6

    Re: RRcnc aka reasonably rigid cnc (build log)

    Hello, already placed the steppers on the other end of the machine, decided that a stepper to the rib cage isnt something i would like. i still have around 2 or 3 months before the build even starts so im fine right now, added a table design( fixture) which is just a peice of mdf. i would change it to an alu plate if i find a big one for a fine price. thanks for help i definitely have to do quite a bit more research before i get started.
    this is the design for fixture plate i would like to copy https://i.imgur.com/MvhXQJW.png
    not most optimal but plates get quite expensive tho i would add a square pipe under to support it better unless i save enough for the full plate. thanks

  5. #5

    Join Date
    Jun 2022
    Posts
    6
    Hello, small update make a decision to ditch the idea of using ballscrews for y axis after my suplier said they dont machine the ends, within 15 days or so i will be buying everything i need for a rotating nut design. Im hoping i can get nice accelerations and max sped of 8-9000mm/min and cut speed of 6m/min. I will be buying steppers and drivers from stepperonline. They are closed loop nema 34 9nm model, the ball screw i will be using for the y axis is sfu2510 so 600 rpm will be more then enough and the steppers will be able to handle it. Im fine with paying more for them sense i already had it priced in the budget as i would have payed a bit less for ones of questionable quality. The build volume is still 2000x1000x180 so im quite happy.i will be testing the rotating nut design with 3d printed gears as that is the easiest way for me to do it plus its quite hard for me to visualize their size and i dont want them to look small xD . I will also not be welding the frame but just screwind it together, unless i need to weld it. Changed some stuff like pipe size. I will be using 80x80 for the bed frame and 160x100 (that still might change) for the y axis and x gantry. My current budget sadly wont allow for a vacuum table flood cooling or a good table so i guess ill just run it on the floor until i get one. I will upload some pics later when i get to ordering stuff for rotating nut. Sadly stepperonline hasnt answered my email about shipping as shipping to serbia isnt officially supported idk why. I plan on using 2 angular bearings that go on a smaller pipe (to save cash as big bearings are expensive) and the nut bolted to it. The gear will be on the smaller pipe to make finding actual metal gears easier later on. The x gantry shouldnt be more then 40kg so i should be more then fine. Cya later guys

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