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Thread: CNC bench mill design for feedback

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    Default CNC bench mill design for feedback

    Hello,

    I've been doing some design lately on a bench mill (I call it the C-Mill) I'd like to build ...


    Some data :

    * Designed for flat material (Corian)
    * Barrel bolts assembly
    * 30x15x18 cm work envelope
    * 70x65x60 cm overall size
    Hardware is pretty standard
    * 80mm spindle
    * HGR20 Rails
    * Steppers NEMA23 TBD ...


    Here are some very early and quick renders for feedback :
    structure ? assembly ? material ? components ? steppers ?

    I'm considering open-sourcing the project.

    What do you think ?

    CNC bench mill design for feedback-draft-v86-ltf-jpg
    CNC bench mill design for feedback-draft-v86-left-jpg
    CNC bench mill design for feedback-draft-v86-front-jpg
    CNC bench mill design for feedback-draft-v86-top-jpg



    Thanks for your reading.
    PS: being my first post, if it needs to be moved elsewhere please do so.

    Similar Threads:
    Attached Thumbnails Attached Thumbnails CNC bench mill design for feedback-draft-v86-ltf-jpg   CNC bench mill design for feedback-draft-v86-left-jpg   CNC bench mill design for feedback-draft-v86-front-jpg   CNC bench mill design for feedback-draft-v86-top-jpg  



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    Default Re: CNC bench mill design for feedback

    So it's made from Corian?

    Corian can be brittle, particularly problematic with threaded holes near material edge.

    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)


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    Default Re: CNC bench mill design for feedback

    I wonder if a limiting factor will be the head itself and its attachment to relatively short rails?



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    Default Re: CNC bench mill design for feedback

    Hi guys, thanks for you replies,

    Quote Originally Posted by pippin88 View Post
    So it's made from Corian?

    Corian can be brittle, particularly problematic with threaded holes near material edge.
    Yep Corian or another solid surface material, the point is I don't have a way of producing the Corian parts myself, and there are a lot of Corian shops with big CNCs to order parts from.

    WRT brittleness, I accounted for that issue in the design, there are no (zero) "traction" mode fasteners, all barrel bolts and inserts are in "compression" (sandwich / clamp) through the material.

    Quote Originally Posted by hackish View Post
    I wonder if a limiting factor will be the head itself and its attachment to relatively short rails?
    For now the head is the least "stable" part (in terms of design). Currently the Z work range is 180mm (~7") and the rails account for that movement. The model being full parametric, extending that length would be a piece of cake

    There has been other comments and discussion (DYI-CNC group @FB) on the whole head design, some were suggesting a higher C frame with a downward plate holding the spindle (to prevent gravitational cantilever / nose bob issues) instead of the current more "classic" bench mill L layout.

    For now, my position is that C frame layout w/ plunger plate adds a lot of flex upon lateral strain (X/Y cuts) or would impose a stupidly overbuilt assembly to stay straight, adding much weight and complexity.

    I'd like to maintain the spindle nose as close as possible to a rigid horizontal plane, but I have some ideas about making the spindle support higher and doubling the spindle mount. This would make the head a complete square instead of the current triangle.

    What do you think ?

    Last edited by oxomoxo; 05-01-2018 at 03:42 AM.


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    Default Re: CNC bench mill design for feedback

    Hi there,

    I have finally had some time to push this project ahead ...
    Here are some updated pictures, I've notably modified the head and extended Z rails for increased rigidity.

    CNC bench mill design for feedback-draft-doublemount-v8-head-jpg

    And fitted the stepper mounts, balls crews etc.

    CNC bench mill design for feedback-draft-doublemount-v8-detail-jpg

    A general view :

    CNC bench mill design for feedback-draft-doublemount-v8-ltf-jpg
    CNC bench mill design for feedback-draft-doublemount-v8-right-jpg
    CNC bench mill design for feedback-draft-doublemount-v8-front-jpg

    Thanks for your comments and feedback ...

    Attached Thumbnails Attached Thumbnails CNC bench mill design for feedback-draft-doublemount-v8-head-jpg   CNC bench mill design for feedback-draft-doublemount-v8-detail-jpg   CNC bench mill design for feedback-draft-doublemount-v8-ltf-jpg   CNC bench mill design for feedback-draft-doublemount-v8-right-jpg  

    CNC bench mill design for feedback-draft-doublemount-v8-front-jpg  


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    Default Re: CNC bench mill design for feedback

    What are you hoping to be able to cut with this?
    Corian is not very stiff. Flextural modulus of 1.2 MPSI, Aluminum is 10. Better than most plastics anyway (and I have owned a router made of PVC thinner than the sections it looks like you're planning, 12mm I assume?)
    Do you have any spec on flatness? The material data sheet doesn't mention that. Also, what's the precision a countertop place holds? It may be good enough to line up a sink, but not be good enough for a mill.
    Any particular reason for the Y axis on the X rather than vice versa?



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    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by skrubol View Post
    Any particular reason for the Y axis on the X rather than vice versa?
    Actually, this is what I like the most in this design. This way the foot print of the machine is a real foot print, not like in some other bench mills. I also think this design is more rigid and less prone to vibrations this way. Is there any disadvantage you can see in his design of X/Y?

    I don't like the choice of material, would not build a machine out of Corian. It is suitable as waste board, table top or similar, but not a machine. Perhaps a 3D printer would look nice if made out of Corian, but for a CNC I would chose steel or aluminium.



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    Default Re: CNC bench mill design for feedback

    Hi @skrubol, lots of good questions :

    Quote Originally Posted by skrubol View Post
    What are you hoping to be able to cut with this?
    Yep, that's the central question !!

    Essentially it's an overbuilt (see below) yet not too big bench mill for a home shop intended at small mechanical parts, plastics, and brass / aluminum involved in animatronics projects.

    Quote Originally Posted by skrubol View Post
    it looks like you're planning, 12mm I assume ?
    You assume quite smaller than it is :P .. The thickness of all ''flat'' frame components is about 40mm (to be exact : 38=2x19mm press laminated).

    I know the pictures make scale hard to judge for lack of reference, and the rendered aspect of the material gives it a toyish look but with a 70x65x60 cm overall size it's not a toy, Fusion tells me the weight of all Corian parts will be around 90Kg ..

    I sure won't be hogging steel at crazy feeds but I believe with some care I could do some small steel parts too (if needed) ..

    Quote Originally Posted by skrubol View Post
    Do you have any spec on flatness? The material data sheet doesn't mention that.
    That's a question I have too, I'm in relation with the material manufacturer to clear out the feasibility and a lot of technical questions, I will keep you updated.

    But, please consider that the chain of contacts are all on machined surfaces so, unless I miss something, that brings us to your next question :

    Quote Originally Posted by skrubol View Post
    Also, what's the precision a countertop place holds? It may be good enough to line up a sink, but not be good enough for a mill.
    The way the mill is designed does not require a massive dimensional precision : that may influence in size or give some slight offsets to the build envelope but as long as X/Y squareness and Z parallelism (which are way more common than dimensional precision) are tight on the machine building the machine, the geometry should stay unharmed.

    Anyhow, that's a good (crucial) point, to be considered with due diligence (including design time).

    Quote Originally Posted by skrubol View Post
    Any particular reason for the Y axis on the X rather than vice versa?
    The Y axis being about half the size of X axis, it substantially reduces the weight of moving parts and the global intent is to make the forces go down to the bench thus the overall "triangle/pyramid/cathedral" shape (in that one having both my parent be architects must have played a role :P ).

    Also one reason is benches are usually longer than deep, so the footprint is in relation with that to keep the machine facing the user.

    Again, this project is aimed at solving the "I want a serious yet affordable CNC mill but I don't have a Bridgeport to build it" type of situation, which is my case but I believe is quite common. So I try to leverage what's around and countertop shops outnumber the toomakers shops by far ...

    Also, I try to think upfront the best I can but that's still a WIP, haven't built it yet and all questions / concerns / feedback are welcome for that reason

    Last edited by oxomoxo; 05-17-2018 at 10:23 AM.


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    Default Re: CNC bench mill design for feedback

    Oxomoxo,

    As I said, I like your design, and especially the fact that you try to keep the moving weight down, this is definitely very good. That's why I also designed my CNC with moving table and not moving gantry, which is more popular and sexy looking, but less rigid.

    One thing I haven't seen touched here is the actual table. Which sort of fixtures are you planning to use? Or will you add a T-slot table on top? Also, depending on the materials you plan to work with, be aware that especially aluminium requires some serious hold down, so a heavy wise is needed. Those are normally also pretty high, so before you start you need to consider Z clearance. In any case, even if you like Corian, I'd reconsider the material, especially for the table. There is no point in using Corian for the table which you have to hide under a sheet of T-slot aluminium. Better to use that from the start and save you some extra height waste.



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    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by A_Camera View Post
    Oxomoxo,

    As I said, I like your design, and especially the fact that you try to keep the moving weight down, this is definitely very good. That's why I also designed my CNC with moving table and not moving gantry, which is more popular and sexy looking, but less rigid.
    @A_Camera thanks for your comments, to reply on the material choice I'd say it's a mitigation of convenience (mainly access to tools and materials) and fit for the job, sure this design and material won't fit "any" job you could clamp to the table but it surely could prove quite capable in the end considering the thickness of the material.

    I'm not completely sure I have the all knowledge to run proper simulations but I'll try to, since they are available in fusion.

    Quote Originally Posted by A_Camera View Post
    One thing I haven't seen touched here is the actual table. [..] I'd reconsider the material, especially for the table. There is no point in using Corian for the table which you have to hide under a sheet of T-slot aluminium. Better to use that from the start and save you some extra height waste.
    And, you point this right ... workholding is pretty much unaddressed right now, the only thing I now for sure is Z travel is 180mm so it could accommodate a vise, and if I have a corian plate made it will be covered in threaded inserts.

    I've been looking at T-slot aluminum (machined, not extrusions) on alibay and small screwless vises, checking the Luiz Ally style vise ... lots of options.

    I'll probably also end up with a vacuum plate for flat material which could stay not too high ...

    But for proper clamping I'm open to any suggestion in the 100mm (width) range, low profile, allowing me to keep both my kidneys ... I'm also checking the local second hand market.

    Here is a render along with a familiar object (soda can) for scale :

    CNC bench mill design for feedback-draft-doublemount-v33-scale-jpg

    Attached Thumbnails Attached Thumbnails CNC bench mill design for feedback-draft-doublemount-v33-scale-jpg  


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    Default Re: CNC bench mill design for feedback

    The Y over X is interesting, probably makes sense here given how wide the column flares. Typical mills have narrow columns, so the most efficient use of material is probably to have a narrow base.
    Only reason I assumed 12mm is it's the largest thickness I've seen Corian in. (I've only seen 6 and 12mm.) Are you planning to have the machining done after the material is glued up?
    Just a warning, I'm not a Mech E, but if I were going to do FEA, the basic simulations I would run run are to ground a part to the table, apply your load to the end of the spindle (or vise versa,) and simulate with a load in the X, Y and Z direction (3 different simulations.) There are many more to run, but those will give you a good start on where your weaknesses are. If it's not going to be rigidly mounted down to something, the base should be left unconstrained I think.



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    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by skrubol View Post
    The Y over X is interesting, probably makes sense here given how wide the column flares. Typical mills have narrow columns, so the most efficient use of material is probably to have a narrow base.
    For now, material usage efficiency is ... not assessed, and that could be worth the effort because Corian is not cheap, and it's probably optimisable, I'll be able to see where after I run some simulations, there's a whole branch of the software that does exactly that.

    Quote Originally Posted by skrubol View Post
    Only reason I assumed 12mm is it's the largest thickness I've seen Corian in. (I've only seen 6 and 12mm.) Are you planning to have the machining done after the material is glued up?
    Corian makes a 19mm but it's only available in (off) white (thus the white renders, to get used to it).
    And yes, laminate first then cut. Having to press/glue precision parts multiple times after cut sounds like a lot of parameters to handle and possible fails.

    Quote Originally Posted by skrubol View Post
    Just a warning, I'm not a Mech E, but if I were going to do FEA, the basic simulations I would run run are to ground a part to the table, apply your load to the end of the spindle (or vise versa,) and simulate with a load in the X, Y and Z direction (3 different simulations.) There are many more to run, but those will give you a good start on where your weaknesses are. If it's not going to be rigidly mounted down to something, the base should be left unconstrained I think.
    I take note, thanks for the tip.

    I guess I'll need to know how much toque the steppers can actually deliver and how they do add up in typical usage.
    I also need to test the fastening method (dowel nuts) to rupture point and I'll try to virtually break the column if that's possible .. to see where that goes ... could be fun :P



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CNC bench mill design for feedback

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