Feeback on cnc design


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    Default Feeback on cnc design

    Hi guys,

    I've recently started designing a cnc machine and I would like some feedback on the design before I start ordering parts. I do intend to use it for light metal working. A link to a STEP file can be found below.

    I use 40x40mm aluminium T extrusion for the frame,
    nema 24 (3.1Nm) for x and y and nema 23 for Z. There are 2 nema 24 motors driving the y axis, because I'm afraid the frame will start "pulling" with one motor if there's an offset load. That's one point of concern. Is it doable to sync up those stepper motors so that they run identical, or would it be better to figure out a way to use a single, stronger motor that is centred under the cnc for the y movement? (major design overhaul)


    A chinesium 2.2kW spindle
    HGR20R rails with HGH20CA bearing blocks for x and y
    HGR15R rails with matching bearing blocks for z
    screws are RM1650 en RM1204 for xy and z, respectively.

    All plate material, except for a couple of shim parts here and there is 10mm steel.

    STEP file can be found here. Uploadfiles.io - cnc.stp
    Any feedback is appreciated

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    Default Re: Feeback on cnc design

    Post pictures, rather that a CAD file please.

    Most control software allows you to slave the two motors together, so two motors is not an issue.

    Gerry

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    Default Re: Feeback on cnc design


    Hope this helps.

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    Default Re: Feeback on cnc design

    I'd lower the gantry, and make the gantry sides wider, spreading the bearings apart a bit.

    And use a continuous plate across the full length of the gantry on the back.

    Gerry

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    Default Re: Feeback on cnc design

    Thanks for your answer. I'll make some changes and report back.



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    Default Re: Feeback on cnc design

    What Gerry says...those aluminum extrusions will be a source of flex if you're not mindful of that in your design.



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    Default Re: Feeback on cnc design

    Thanks for all your comments. I lowered the gantry, added a full-length plate to it and widened the gantry supports. As for the frame: I use aluminium because I already have it. These things are expensive - got to cut cost somewhere
    That said: I have 2 types of 40x40mm extruded T profile. I have 3 lengths of 1300mm of good quality stuff (thicker walls, more material) and plenty of 40x40 T profile that's a bit lighter on metal. Where in the frame should I use the heavy Gage stuff: The 2 Profile in the Y direction, the struts holding the 2 Y profiles in place or the gantry? Considering the Y direction will be reinforced with struts and angles on one side, and solid steel rails on the other, I'm thinking gantry.



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    Default Re: Feeback on cnc design

    Sigh.....why does everyone design the same machine using totally different configurations of the material content...........if I've seen one moving gantry router I've seen a million different layouts that all do the same thing......not one is ground breaking or totally breaking out of the mold.



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    Default Re: Feeback on cnc design

    So? Why reinvent the wheel.



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    Default Re: Feeback on cnc design

    It is looking better, but I would get the screws out of harms way. You can place them below the table just as easily I think. It may require larger extrusions on the side and maybe back them up with a vertical steel plate on the inside. Then support the entire machine on the ends.

    Lee


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    Default Re: Feeback on cnc design

    Stiffening the side supports of the gantry would help counteract side forces. That's where I erred a bit on my machine. You'd be surprised at the little bit of flex you'll get by pushing sideways on the gantry.

    Quote Originally Posted by LeeWay View Post
    It is looking better, but I would get the screws out of harms way. You can place them below the table just as easily I think. It may require larger extrusions on the side and maybe back them up with a vertical steel plate on the inside. Then support the entire machine on the ends.




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    Default

    Quote Originally Posted by handlewanker View Post
    Sigh.....why does everyone design the same machine using totally different configurations of the material content...........if I've seen one moving gantry router I've seen a million different layouts that all do the same thing......not one is ground breaking or totally breaking out of the mold.
    For the same reason the square column mill hasn't changed. Maybe instead of whining, you can provide some goundbreaking examples of your own.



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    Default Re: Feeback on cnc design

    Ok how's this. Rails are moved to the bottom, gantry supports are extended downwards. Some height blocks are added (I can add more in the middle of course). There are adjustable feet I can use to get the extra distance.



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    Default Re: Feeback on cnc design

    I see this machine flexing alot, but a few changes could really help you IMO.

    As was mentioned, your gantry risers are flat plates, and flat plates bend easily. Also they are very tall which makes things worse.

    You could make them square and then bolt some heavy duty steel angle iron or square steel tube to each edge. That would wake them stiffer and be easy to do. You could also move the front bearing forward a bit. you could also make them not as tall.

    The T slot profiles you are using to attach the rails to for your long axis are very small, so I would think that you would need to have them bolted securely to some kind of frame that goes under this machine to keep them from twisting / deforming. Or use some bigger extrusions. Moving the rails underneath, this looks like it should be bolted to something more sturdy and now you can't.

    As far as protecting the ballscrews go, you know you could make a chip deflector out of clear plastic or anything else really that will stop chips from being thrown onto your ballscrews, the downside being that it might cost you a few inches of movement.

    I don't really like this design I'm sorry. It just seems too wobbly to me. I'm very much biased against machines with tall plate gantry risers. Of course, you can change it to make it better.

    What I do like is your CAD work in drawing everything out, it's excellent. Spending a bit more time on some additional design iterations will be worth it I think.



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    Default Re: Feeback on cnc design

    Quote Originally Posted by louieatienza View Post
    For the same reason the square column mill hasn't changed. Maybe instead of whining, you can provide some goundbreaking examples of your own.
    Nope.....I don't have any ground breaking moving gantry examples I'd like to expand on......certainly and definitely not a moving gantry type, and this thread is all about someone else's design aspiration not my preference.

    My preference for a gantry type CNC router would be a moving table type.........and all welded in steel.........if you're going to get serious with a machine it's best to get really serious to practical limits.....that interpreted does not mean over engineering just to be sure it wont break.......lumps of metal in the wrong places just weigh more.

    In this design the continuation of suggestions for amendments is gravitating to a conventional build that has been built a thousand times to the same old same old outcome......this is ideal if you want to build a CNC router and don't know how the various interfaces or scaled components interact.

    That it will eventually become a viable design is without doubt..........given enough design variations and you can end up with a design for the Titanic.

    So to close on my criticism.......why not just have a conventional design layout and go on from there.......it's just the size that makes the difference.
    Ian..



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    Default Re: Feeback on cnc design

    If I could suggest some input... Use an end plate for both sides of the table, and purchase flanged bearing blocks (FK, FF) instead. I'd use them on the gantry as well. This will allow for some radial adjustment. You will however need a riser for your steppers, but you can buy solid ones pretty inexpensively on eBay. For the gantry risers, you could bolt extrusions to the riser plates to add stiffness. I would also suggest larger gussets. If you require the larger Z movement I'd also suggest reversing the configuration of the carriage assembly. In the ideal setup, the LM bearings and ballscrews would lie center through the same plane. You may consider putting the ballscrews under the table, inside the side rails, and run a transverse plate spanning the two gantry uprights. You can then mount the ballnut carriers to that.



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    Default Re: Feeback on cnc design

    Hi louieatienza,

    Thanks for your input, although I don't understand everything you said. What's the difference of flanged bearing blocks vs the supports I have now (functionally, that is)
    When you say "reversing the configuration of the carriage assembly" I don't really understand what you mean.

    In the meantime however, I've made some more modifications. I slightly decreased the height of the gantry risers, added double angle plates to them and added a bunch of supports to the bed extrusions, attached them with a boatload of 40x40x40 angle plates. Now I can also mount the feet to those.



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    Default Re: Feeback on cnc design

    Quote Originally Posted by metiz View Post
    Hi louieatienza,

    Thanks for your input, although I don't understand everything you said. What's the difference of flanged bearing blocks vs the supports I have now (functionally, that is)
    When you say "reversing the configuration of the carriage assembly" I don't really understand what you mean.
    If you have end plates on both sides, you can use FK and FF flanged bearing block which will mount flush onto the face of those end plates, instead of having to make an interface bracket for the block style bearing blocks. Which I think would ease assembly and alignment.

    As to the Z axis, if you want to keep that amount of travel, design the saddle with the bearing blocks fixed and have the rails mounted onto the carriage.

    For the gantry risers, you don't really need the angle iron. All you'd need are larger gussets underneath the gantry bridge.

    Finally, you may want to consider modifying the risers that you can mount the bridge toward the back. This would put the cutter more inside the footprint of the riser bearing blocks, put the CG of the whole bridge/carriage assembly more in between the riser bearing blocks, and give you more work area for your gantry travel.



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    Default Re: Feeback on cnc design

    Hi louieatienza,

    Those interface brackets are just some pieces of sheet metal, should be fine I think. What's the difference of moving rails instead of moving bearing blocks? To me that sounds like pushing on one side vs pulling on the other: the end result is the same. I did change the riser plates and spindle mounting somewhat to get the spindle closer to the mounting blocks. I think this is as good as it's going to get without major design changes. I still don't know what you mean with gussets. When I google it, angle plates seem to show up most, but those are already on the riser plates supporting the gantry. I could make them bigger, but otherwise I don't know what you mean.




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    Quote Originally Posted by metiz View Post
    Hi louieatienza,

    Those interface brackets are just some pieces of sheet metal, should be fine I think. What's the difference of moving rails instead of moving bearing blocks? To me that sounds like pushing on one side vs pulling on the other: the end result is the same. I did change the riser plates and spindle mounting somewhat to get the spindle closer to the mounting blocks. I think this is as good as it's going to get without major design changes. I still don't know what you mean with gussets. When I google it, angle plates seem to show up most, but those are already on the riser plates supporting the gantry. I could make them bigger, but otherwise I don't know what you mean.


    Theoretically the lower the lower LM blocks are and the farther they're spread, the more rigidity on the Z axis. Having the rails on the Z carriage allows the lower LM bearing placement. Although they shouldn't be relied upon structurally, having the rails on the Z carriage does stiffen it up some and adds mass. I'm not opposed to fixed Z rail if the travels are relatively low.



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