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  1. #21
    I think you have one one vid repeated so three shown.
    ..Clive
    The more you know, The better you know, How little you know

  2. The Following User Says Thank You to Clive S For This Useful Post:


  3. #22
    Quote Originally Posted by Clive S View Post
    I think you have one one vid repeated so three shown.
    Fixed. Thanks.

  4. #23
    What has been pointed out is entirely correct.

    If you are just looking for a cheap machine to mill e.g. foam or something then this probably works fine, as pointed out though the bearings on steppers are radial bearings designed for radial loads. They will be experiencing axial loads when trying to drive the screws which is something radial bearings aren't particularly great at... That will result in excessive play, premature wear and eventually failure.

    Given that the drawer slides won't allow you to machine anything hard anyway, you will probably be ok on the X and Y (although they will still wear out and develop slop more quickly, and are more difficult to replace than in a separate fixed bearing block for the screw), but given the weight of the router being pulled up repeatedly the Z-axis will probably suffer more.

    It also means you are relying on a rigid coupling between the motor shaft and screw, which translates vibrations and resonance into the motor, which again isn't great news. With direct drive really the idea is to have a jaw type coupling with a rubber/flexible insert that provides some protection to the motor. You can't do that however unless the screw is supported by its own bearing set.

    I know you think people are being negative or crushing your creativity but there's a reason why things are done a certain way, and it's not creative to go and do things the wrong way just for the sake of being different. To come up with a new solution that actually addresses the reason why things were done in a certain way (e.g. the fact that radial bearings aren't designed for axial loads, and vibration decoupling) whilst doing it better/cheaper/differently is what being creative or innovative would be... just ignoring the issues that cause things to be done a certain way and then doing it poorly to save money is not innovative, it's poor engineering.

    You clearly aim to create a cheap machine, on that front you are succeeding. Though how anyone on here is supposed to know what your end goals are when you haven't stated them is ridiculous. Hopefully it's just a fun project for you, and you enjoy making stuff - which is great imo. If you are expecting any sort of accuracy or ability beyond carving some foam into interesting shapes then you are probably going about it in the wrong way.

    By the way were you actually trying to infer that your creation will be capable of holding 0.001mm over a 12 inch disc or did I misunderstand that?
    Last edited by Zeeflyboy; 03-03-2017 at 12:23 PM.

  5. #24
    For all those who don't read entire threads and have no idea what this machine will be used for, I posted this 2 weeks ago
    "finished off the z axis today, i finally gave up on having supported bearings on the lead screw and mounted it directly to the motor as ill only be using this machine for wood/plastics it wont be a problem"
    Wood and Plastics !!!

    A_Camera, I asked for you to show me a draw slide cnc machine made of STEAL and all you posted was videos of ones made of wood !!!
    "BTW, I seriously doubt you will achieve 1 micron over 12". It was a question not a referral to my cheap draw slide build.

    Zeeflyboy, "You clearly aim to create a cheap machine, on that front you are succeeding" "Hopefully it's just a fun project for you, and you enjoy making stuff - which is great imo". yes your 100 % correct,
    This build is not about saving money its about making something off the top of my head no plans to follow just using parts you wouldn't use in a high end cnc machine.
    "Though how anyone on here is supposed to know what your end goals are when you haven't stated them is ridiculous". read the 5th post i made it clearly states I'm going to cut wood and plastics.
    "By the way were you actually trying to infer that your creation will be capable of holding 0.001mm over a 12 inch disc or did I misunderstand that?". No i was just asking a question if there was a cnc
    machine capable of .001mm as I make telescope mirrors for a hobby and i can produce by hand mirrors with a surface accuracy of 0.000125mm so just wondering if a machine could get anywhere near that.


    As to the Axial loads in Nm on my z axis can anyone tell me what you think it will be lets say cutting pine at a feed rate of say 700mm pm with a 2 flute 6.35mm end mill and a pass depth of 4mm ? just a approximate estimate will do
    Last edited by Steel; 05-03-2017 at 12:32 PM.

  6. #25
    Quote Originally Posted by Steel View Post
    "By the way were you actually trying to infer that your creation will be capable of holding 0.001mm over a 12 inch disc or did I misunderstand that?". No i was just asking a question if there was a cnc
    machine capable of .001mm as I make telescope mirrors for a hobby and i can produce by hand mirrors with a surface accuracy of 0.000125mm so just wondering if a machine could get anywhere near that.
    Please explain/show the equipment you use to measure to that level of accuracy.!

    Quote Originally Posted by Steel View Post
    As to the Axial loads on my z axis can anyone tell me what you think it will be lets say cutting pine at a feed rate of say 700mm pm with a 2 flute 6.35mm end mill and a pass depth of 4mm ? just a approximate estimate will do
    It's no that simple. To calculate accurately you need to know the bearing type and arrangment. Also just saying pine isn't enough as there are many species of pine so each will cut differently and be different Density/Dryness.

    However I wouldn't worry about the bearings failing, which they will sooner rather than later, because this will be the least of your troubles. Between resonance and the shity engineering they'll hardly be working much.

  7. #26
    Jazzcnc just the other day you said "No thanks got better things to do and couldn't give a shit anyway" in referral to my cnc draw slide build so my question for you is why are you still posting on this thread ?, since you are then give me a ballpark figure in Nm of the axial load range i can expect.

    "Please explain/show the equipment you use to measure to that level of accuracy.!" https://en.wikipedia.org/wiki/Foucault_knife-edge_test
    Last edited by Steel; 05-03-2017 at 01:47 PM.

  8. #27
    Quote Originally Posted by Steel View Post
    Jazzcnc just the other day you said "No thanks got better things to do and couldn't give a shit anyway" in referral to my cnc draw slide build so my question for you is why are you still posting on this thread ?, since you are then give me a ballpark figure in Nm of the axial load range i can expect.

    "Please explain/show the equipment you use to measure to that level of accuracy.!" https://en.wikipedia.org/wiki/Foucault_knife-edge_test
    Because it's Free country and Forum so I can and there's sweet FA you can do about it other than not reply.! . . . . . . But It's true I don't give a shit what your doing however I was intrigued to how some one who thinks draw runners are suitable for CNC would go about measuring such fine tolerences.?

    Oh and if going to quote try using the "Reply with Quote" button it's much clearer.

    Regards Axial loads then like I say depends on lots of factors and lifes too short to waste time working it out plus I'm not that clever.

  9. #28
    Ok so you don't really know about what axial loads i will encounter ok fair enough maybe someone else has some idea ?

  10. #29
    Axial force from the plunge is I would say largely irrelevant in the materials you are using and is probably the least of your worries. The weight of the router/mount and travelling parts of the Z-axis are probably higher than the force required from the motor as long as you aren't plunging crazy fast.

    Typical max axial rated load for a double bearing nema23 is in the region of 1.5kg-f (e.g. see data sheet here, last page at the bottom specifically) https://www.anaheimautomation.com/ma...ec%20Sheet.pdf

    So your biggest problem (in terms of Z-axis axial load, I think Jazz would probably contend that it's not your biggest problem lol) is that unless your screw, nut, router, router mount, and all "hung" mass of the mounting plate is less than 1.5kg, you are already exceeding the axial load before you even start moving.

    Let's say you are using a small router that weighs about 3kg, add the weight of the screw, router mount, etc etc and what, maybe 5kg? Simply hanging there before taking into account any dynamic acceleration loads during retracts you are exceeding the rating by over 3 times.

    You could bodge your way around it by counterweighting the Z-axis, but you'd still be subjecting it to axial loads when it does actually hit the material by doing it that way, and it would also be more complicated than just giving it a proper bearing setup which would be superior in every way.

    edit - actually are you using a nema17 there? in that case it'll be more like 1kg-f axial load rating which would change the equation to being 5 times over load just hanging there.

    double edit - I'm not sure why you think a steel framed build like this is innovative or indeed preferable to any of the other extrusion or wood based drawer slide builds? Indeed the only point I can see of doing a drawer slide build is that it's cheap and easy to build without access to any special equipment, which you kind of ruin the point of when you start talking about welding a steel frame. The components you are using don't have the accuracy or rigidity to benefit from the more sturdy steel frame, so it actually seems to be slightly defeating the point of these designs in the first place.

    To me it seems like you're wasting what could be quite a nice little steel frame by then going and fitting it with sub-par components. assuming you've done a semi-decent job of alignment on that frame, if you took that same frame and fitted it out with some proper linear motion components (and stopped hoping that radial bearings could take thrust loads) you'd actually have a half decent machine there.
    Last edited by Zeeflyboy; 05-03-2017 at 04:50 PM.

  11. #30
    I just looked at the z axis on my 3020T and the lead screw is supported with one bearing on the top plate and either a bearing or sleeve on the bottom plate and the motor is connected with a flexi coupler so those bearings are being used to support axial loads even though there radial bearings. I cant see the difference by using the stepper bearings to replace that type of set up. Im using a 420oz nema 23 fitted with 6000z bearings.
    I think i will make a stand to hold a nema 23 to replicate a z axis position with a 10kg weight mounted to a shaft hanging from the motor shaft to replicate what my setup and run the motor till the motor bearings fail !!
    Again the point is to build this machine using using draw slides, I have a new set of 20mm supported rails with ball screws but i dont want to make a mid end machine. If it works great if it doesn't then ill make changes but for now ill do it how i wanted to do it and see how it turns out

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