New Machine Build CNC bench mill design for feedback - Page 2


Page 2 of 2 FirstFirst 12
Results 13 to 22 of 22

Thread: CNC bench mill design for feedback

  1. #13
    Registered
    Join Date
    Feb 2017
    Location
    Finland
    Posts
    2
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by oxomoxo View Post
    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.



    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.



    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
    Not sure about your table size but you can get nice steel t-slotted tables quite cheeply:

    https://rover.ebay.com/rover/0/0/0?m...2F370753429171

    C6 Milling Table 240x110mm - Arc Euro Trade

    X3-160 Milling Table - Arc Euro Trade

    https://rover.ebay.com/rover/0/0/0?m...2F273088730958



    Sent from my XT1562 using Tapatalk



  2. #14
    Registered
    Join Date
    Jun 2011
    Location
    US
    Posts
    219
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by oxomoxo View Post
    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
    Basic simulations will just show linear deflection, so it doesn't matter all that much how much force you're applying, if you double it, the deflection will double. It's more useful in the design phase for seeing where your highest stresses are and reinforcing those areas. For a feasibility study you would need to know pretty close how much force you will have.
    Simulating failures are more complicated simulations I believe, as they are in the nonlinear realm.

    Edit: Also it's really hard to figure out machining linear force values. You'd think there would be a simple formula to estimate (with spindle torque, tool size, radial engagement as inputs,) but I've never been able to find one.



  3. #15
    Registered
    Join Date
    Apr 2018
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by jkkmobile View Post
    Not sure about your table size but you can get nice steel t-slotted tables quite cheeply
    Thanks for the links @jkkmobile the last two are quite in the range (somewhat too long though)

    The aluminum t-slot table I mentioned earlier is this one
    https://www.ebay.com/itm/T-Slot-plat...m/183221484635
    Which would be the exact size of the XY travels

    Quote Originally Posted by skrubol View Post
    Simulating failures are more complicated simulations I believe, as they are in the nonlinear realm.
    I guess I spent too much time around game engines where physics and simulation basically means "ability to bump around and shatter stuff" haha ... :P

    Quote Originally Posted by skrubol View Post
    Edit: Also it's really hard to figure out machining linear force values. You'd think there would be a simple formula to estimate (with spindle torque, tool size, radial engagement as inputs,) but I've never been able to find one.
    This one I stumbled upon ... but I still have to take a dive and skim out what I need (not much on cutting tools, more structural stuff).
    http://160592857366.free.fr/joe/eboo...am%20Tolly.pdf

    Still no cutting tools on this one but more diversity of problems :
    http://www.dbc.wroc.pl/Content/7154/...e%20Design.pdf

    I'm not sure but maybe considering the cutting tool as a simple rod in a compound action (like a spiral plunge cut) could give a close enough idea ? I'm not saying I'd be able to derive an actual formula but maybe setting up a simulation scenario ... I apparently need to dig this further ..



  4. #16
    Registered
    Join Date
    Jun 2011
    Location
    US
    Posts
    219
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by oxomoxo View Post
    Which would be the exact size of the XY travels
    You usually want the table a little bit longer in at least one axis (usually the long axis) to give more fixturing flexibility when working on a piece at the limits of your machine (a place to fit clamps or whatever.)



  5. #17
    Registered
    Join Date
    Apr 2018
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by skrubol View Post
    You usually want the table a little bit longer in at least one axis (usually the long axis) to give more fixturing flexibility when working on a piece at the limits of your machine (a place to fit clamps or whatever.)
    Yes, especially since I'm considering designing a fourth axis (A), I'd add at least a couple of inches on the sides ... but the spindle part of the fourth axis design is kind of touchy to me, it's a pity there is no standard part aimed at housing bearings for quick and simple spindle assemblies (something like the LM series linear bearings housing but with a tight fit), that would ease up so many projects (I can think of a few reasons why though) ...

    Last edited by oxomoxo; 05-18-2018 at 03:15 AM.


  6. #18
    Registered
    Join Date
    Jun 2011
    Location
    US
    Posts
    219
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Littlemachineshop sells parts for mini (7x) lathes including headstocks.
    https://littlemachineshop.com/produc...ory=1023914534



  7. #19
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    United States
    Posts
    31697
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Corian is very brittle, and can easily crack if the forces are in the right place.

    It also expands and contracts a LOT with temperature changes.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  8. #20
    Registered
    Join Date
    Apr 2018
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by ger21 View Post
    Corian is very brittle, and can easily crack if the forces are in the right place.
    It also expands and contracts a LOT with temperature changes.
    The very purpose of engineering being to determine fitness of material/process to the purpose, "very" and "a LOT" doesn't carry much signification : with the right forces in the right place one could tear down the building the mill will be into.

    However, thanks for your concern, both questions (material strength and thermal stability) are to be considered, and I'm discussing them with Corian's technical staff atm.

    WRT strength, the purpose (and expectations) of the machine is crucial :
    Quote Originally Posted by oxomoxo View Post
    Essentially it's an overbuilt yet not too big bench mill for a home shop intended at small mechanical parts, plastics, and brass / aluminum involved in animatronics projects.
    The thickness of all ''flat'' frame components is about 40mm (to be exact : 38=2x19mm press laminated).
    With a 70x65x60 cm overall size it's not a toy, Fusion tells me the weight of all Corian parts will be around 90Kg ..
    But still, I want to run some simulation to confirm that everything is right as my intuition says, especially at dowel nuts assembly points.

    There are multiple things to consider when it comes to thermal expansion : dimensional precision and geometry (squareness/parallelism)
    Here is some meaningful data I have :

    * the mill will be operated in a somewhat thermally stable environment (home shop)
    * the thermal expansion factor of Corian is 39*10^-6/L(mm)/°C which builds up to 0.025mm/°C on the longest dimension (Z Axis) or 0.00156mm/°C across the thickness of the material.
    * the mass of the mill (Corian parts weights about 90kg) "should" give ''a lot'' of (sorry no data available on conductivity right now) thermal inertia to flatten out transients if any.
    * the topology of the mill (open frame) means dimensional precision is essentially a mater of relative movement/positioning of spindle and table. No ATC so tool origin will have to be checked at change and tends to correct error/variation along the machining.
    * to hinder geometry the mill would have to be heated in such a way that there would be large temperature gradients across the frame (non uniform expansion) and for that purpose possible heat points (motors) are thermally insulated from the frame besides being mechanically insulated (plum couplers).

    That's the state of my research so far ..
    What do you think ?

    Last edited by oxomoxo; 05-19-2018 at 08:43 AM.


  9. #21
    Gold Member
    Join Date
    May 2005
    Location
    USA
    Posts
    3473
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    You have a most interesting design here. I don't get to this side of the forum much so it is good to see a fresh design.


    Quote Originally Posted by oxomoxo View Post
    Hi @skrubol, lots of good questions :



    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.
    This is the unfortunate part as I think your design will be crippled by the choice of materials to build the machine. Imagine the same machine with Aluminum as the base material. You mentioned that there are plenty of CNC shops to do this in Corian, but most of those shops could do the work in Aluminum if they really wanted to. However you might be surprised how many machine shop out there would be willing to do your design in aluminum. The only difference being that they would a bit harder to find for somebody not tuned into the locals machining industry. A machine shop would also likely start with correctly sized pieces instead of gluing up flat stock for the thicker sections of your design.


    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 wouldn't call it a toy no matter what is made of. I actually like the mechanical layout of the parts. Personally I'm really bothered by the Corian as the structural material. Just imagine what you would get if the machine was made out of aluminum. Or take it a step further and make it out of steel. If you go aluminum I really doubt that the machining time and cost would be excessively different.
    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) ..
    I've learned to be careful about what people mean by machining steel but I really doubt that you would get anywhere near desirable results in a timely manner. It may even have trouble with some of the more difficult aluminum and brass alloys. It really comes down to how badly the machine vibrates under load in these materials. I have no experience for a definitive answer but I'd strongly suggest that it would have a difficult time.


    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 :



    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.
    Good mechanical design won't make up for weak material. If your goal was wood or plastics I wouln't be too concerned. The fact is many routers/mills are in fact made out of wood and do just fine for what their owners intended. In this case you want to build a machine out of a material that is structurally similar to wood and the expect it to machine materials beyond aluminum. It might meet your expectations or it might not, I can't say because I don't know what your expectations are.
    Anyhow, that's a good (crucial) point, to be considered with due diligence (including design time).



    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 ).
    Well we have your parents to thank for fresh design then!!!!!!
    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 ...
    Maybe locally the counter top shops are large in number but I suspect that around here there is a 3 to 1 or better advantage for machine shops. By the way it helps to widen your search beyond toomakers shops. There are all sorts of metal working enterprises that can offer up services that might be employed by a tool builder. Not to advertise but one example locally is Nifty Bar, a business that specializes in processing steel plate. The point is you can literally order many parts needed for a machine build, example: http://www.niftybar.com/files/2314/8...000_1_2017.pdf. That material may be of no interest to this specific build but the point is a lot of stuff can be purchased these days. I know some of this stuff looks "expensive" but a sheet of Corian is not cheap either and that is before machining.

    As for not having "a Bridgeport to build it" that is actually a common problem so people are always looking for new ways to do things. As I've said the only real issue I see is the material choice. Have you considered fiberglass sheet goods, wood composite structures, aluminum extrusions or even bolted together steel? Aluminum sheet goods such as MIC6 can be had at prices that aren't that much different than Corian.
    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
    Well lets look at it this way you can always build it as part of a learning process. Since there are few if any metal working machines built this way in the end you really need a prototype to see how it will work.

    I do have one other concern though, the actual table needs to have parts bolted or clamped to it. Corian would be terrible in such an application. Why not spend some money here on a tee slotted table which can be had online. IF those are too rich for you tooling plate can be had and is fairly accurate raw. I just see a corian table getting very ugly very quickly due the stress of threaded holes, clamps, swarf and what have you.



  10. #22
    Gold Member
    Join Date
    May 2005
    Location
    USA
    Posts
    3473
    Downloads
    0
    Uploads
    0

    Default Re: CNC bench mill design for feedback

    Quote Originally Posted by oxomoxo View Post
    The very purpose of engineering being to determine fitness of material/process to the purpose, "very" and "a LOT" doesn't carry much signification : with the right forces in the right place one could tear down the building the mill will be into.
    How about too much?
    However, thanks for your concern, both questions (material strength and thermal stability) are to be considered, and I'm discussing them with Corian's technical staff atm.

    WRT strength, the purpose (and expectations) of the machine is crucial :

    But still, I want to run some simulation to confirm that everything is right as my intuition says, especially at dowel nuts assembly points.
    One thing to consider is unintentional damage that is a machine crash.
    There are multiple things to consider when it comes to thermal expansion : dimensional precision and geometry (squareness/parallelism)
    Here is some meaningful data I have :

    * the mill will be operated in a somewhat thermally stable environment (home shop)
    * the thermal expansion factor of Corian is 39*10^-6/L(mm)/°C which builds up to 0.025mm/°C on the longest dimension (Z Axis) or 0.00156mm/°C across the thickness of the material.
    * the mass of the mill (Corian parts weights about 90kg) "should" give ''a lot'' of (sorry no data available on conductivity right now) thermal inertia to flatten out transients if any.
    * the topology of the mill (open frame) means dimensional precision is essentially a mater of relative movement/positioning of spindle and table. No ATC so tool origin will have to be checked at change and tends to correct error/variation along the machining.
    * to hinder geometry the mill would have to be heated in such a way that there would be large temperature gradients across the frame (non uniform expansion) and for that purpose possible heat points (motors) are thermally insulated from the frame besides being mechanically insulated (plum couplers).

    That's the state of my research so far ..
    What do you think ?
    One gotcha with thermal issues is that it can be very localized especially if the material doesn't conduct heat well. The end result is expansion in one place resisted by cool parts else where. So you get twisting and binding as thing move out of alignment. This can by the way be a problem on any type of machine built in any manner. If you get enough expansion in one part of the frame you will either have your linear rails bind or the expansion will cause them to attempt to rock on the corian mounting surfaces. So yeah thermal isolation of hot parts would be a requirement. My general experience here has been on high precision lathes that never saw a piece of Corian, however that doens't mean that it wasn't a problem.

    In any event it will be interesting to see this machine in operation. Best of luck with it!



Page 2 of 2 FirstFirst 12

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

CNC bench mill design for feedback

CNC bench mill design for feedback