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  1. #13
    Member peteeng's Avatar
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    Default Re: Student organization looking to build CNC milling machine for school donation

    Hi 308 - don't fly too close to the sun or make the labyrinth too hard KISS... Here's some more reading matter. You or the team will have to get on top of FEA quickly. I suggest you talk to Altair about simsolid. They usually are happy to provide software to Unis free. Where are you in the big old USA? Peter



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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by peteeng View Post
    Hi 308 - As far as a machine goes you cannot make many things adjustable. Adjustability is a two edge sword. What you are aiming at and talking about requires machined fits, adjustability will work against you in the long term.

    Fusion 360 has FEA especially for students. Being engineering students I imagine they and you have studied structures and am familiar with manual beam calculations. I spent the early part of my career pre FEA so did all of this by hand, I've even calculated FE meshes by hand pre auto meshing. Building something is one thing but also designing something the way you will do it as a professional is important. Every part in a mill should have a calculation behind it, even the nuts and bolts and oil. Its ambitious, keep us posted and aim high gravity sucks. Peter

    Hi 308 - As an aside. I suggest you work on your language as well. If you used words and expressions as you have done at management levels you will never get the funds approved for your project. Words like "hope" and "adjustability (as a solution)" send shivers up management spines!! You have to have clear objectives, non conflicting ideas and reasonable solutions in the pitch. Publish some images here we'd like to see them... Good luck

    and tell me briefly why the twin gantry is a good idea?
    You're right about FEA in fusion! i need to look into that. As far as manual beam calculations, I do not recall doing them in any of my classes so I suppose I may be lacking in that regard. I see your point about the calculations and speech methods. I will be sure to take a more organized, formal approach



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    Member peteeng's Avatar
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    Default Re: Student organization looking to build CNC milling machine for school donation

    Hi 308 - Then what is your engineering background? Are you on the electrical/electronic side? Peter



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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by peteeng View Post
    Answers:
    1) That was 20 years ago and everyone would have moved on by now. Call Ted Hall I'm sure he has time for students or someone there can help. He has a successful business so the users must like them
    2)Please publish some images to ensure we are on the same page
    3) An "I" beam consists of flanges and a web. The web transfers shear between the flanges, the web is the shear structure. We make I beams to improve the structural efficiency of the material. In a twin gantry design as I think you are designing you are using two tubes as the flanges but you do not have a web. I think you expect that two widely spaced tubes are stiffer then one large central tube. This is incorrect thinking. If you do the correct math this will become apparent

    Mind experiment : You have two parallel beams well supported at the ends (your twin gantry). There is a stick in the middle that slips in between. You push on the lead beam, how much load gets transferred to the lagging beam via the stick? If the lead beam is very stiff not much, so the lagging beam is redundant. So in the twin beam approach you eventually have to have two beams the size of the correct beam. The twin gantry is actually evaluated in Bambergs thesis and rejected for being less stiff. I rest this issue here.

    4) Speak to HAAS and ask them the stiffness of their minimill. HAAS is a philanthropic organisation with great student interest. The stiffness number will scare you I think... Plus look up accuracy and repeatability they are different.

    I think you need to define what this machines real reason to exist is. A HAAS is a venerable machine to emulate but so far I can't see you getting there. A machine has to have a strong reason to exist otherwise it will rust in a corner, if in fact it gets built. You need to expand the vision. Companies and people are happy to help and money is not the issue, there is more money in the world now then there ever has been. For instance why do you want to cut tool steel? Make the machine out of carbon fibre? do you realise that by the time you are a good engineer, mills maybe dinosaurs? taken over by 3D printers? Companies like HAAS are looking for the next stuff not the stuff that was done 20 years ago. If you where tasked to take a mill to the moon to cut some moonium would you make it out of 2T of steel? What does your sponsor want? Think beyond your thinking... that opens doors

    I'm not invalidating your current trajectory I think there's an opportunity here bigger than you think...
    There are a million reasons to halt this project, you only need one really good reason to have it happen Peter
    1) Is Ted Hall an employee at shop bot CNC? if so I will make an effort to contact him!
    2) our modeling is at a very early stage right now but I will post an image of what I am referring to by dual gantry. (please disregard any other concepts in the design, it was a very early design point) https://imgur.com/a/JhBX06k
    3) Thank you for the definition! I think i can see in your own design, maximus, where you utilized a shear damper as shown in bamberg's work. Bamberg's Thesis is lengthy, however,and may take me a week or two to fully read through (I promise i fully intend on doing so), do you know where he denounces the dual gantry within the thesis (general page range or section)? please don't regard this as laziness on my part, I am simply trying to forward our conversation without delaying until I have fully read the material.
    4) you're right! I will try to do that this upcoming week! I've been trying to contact organizations for sponsorship and knowledge but so few actually respond via email... I do see what you're saying about defining purpose and forward thinking. I will make a point to do a write-up on purpose. Thankfully, our current sponsor doesn't have any requirements for us other than our use of their software.... perhaps other potential sponsors may have stricter requirements. I will do what I can to be forward thinking in my design, and application

    Also, I am a mechanical engineering student with a manufacturing background. We do have a couple of EEs on our team however!

    As always thank you for the thoughtful response, I really appreciate the amount of effort you are putting in to help me out!

    Last edited by Daedalus308; 06-08-2019 at 08:54 PM.


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    Default Re: Student organization looking to build CNC milling machine for school donation

    1) Is Ted Hall an employee at shop bot CNC? if so I will make an effort to contact him!
    He's the founder of Shopbot.

    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)


  6. #18
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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by hanermo View Post
    Please point to a twin gantry machine picture so we know what you mean ... ??

    The most rigid machine possible is a twin-column milling machine using a moving table, usually y moves.

    The two fixed columns have half the unsupported distance vs a c-frame, thus are 8x more rigid, each.
    And there are 2, they can be anchored to the floor, the bridge can be heavy as it is clear of stuff.

    Drawback of moving table is needing double the table size for the support below.
    Larger footprint in y, but much more rigid (anchored to floor), easy, simple, cheap.

    I suggest defining a plan and wants/desires/abilities diagram, with time/costs somewhat marked in.
    Making the machine mechanically is trivial, given you have people with skills and can get secondary bits like motor mounts/brackets machined locally (school) for free and have measuring stuff.

    Imo, the better you make the machine mechanically, exceeding common VMCs specs, the more successful it will be.

    There are endless complex challenges, most of which cannot be solved well in less than 6 months, even with many clever people working on each one.
    Toolchanger will be an issue.
    IO will be an issue.
    Sensors will be an issue.
    Controller will be an issue. The issue.
    Docs will be a big issue.

    Gcode implementation and features and proofs will be a big issue, will depend on the controller, and are about 10.000x more complex than you probably think.
    SW:
    You probably want css/inverse mode or feed/rev, rigid tapping.
    Probing. How ?
    Look into this. It won´t be pretty.
    Toolsetter.
    Test it, prove it, a wood tester machine of 500$ is fine for 99% of proofs.

    IO for mechanical tests of oil, air pressures, any interlocks, servo faults, axis enables, etc.
    Toolchanger IO, spindle IO.

    A basic 3 axis servo lathe needs about 130 wires and 40+ IO.
    (Like mine).

    At the low end, a chinese 4-axis offline controller wired to some mechanicals gets you a machine.
    Using better mechanicals and a stiffer frame gets you a better machine than most here. Very basic.
    Next come the 5 serious problems I outlined.
    I just added an imgur link to an early model picture of our design to a reply to Peteeng

    Your point on rigidity are noted and I'm glad you pointed them out to me!

    While I would love to exceed VMC specs, I will be happy to achieve Haas minimill specs.

    Due to the nature of the dual axis gantry, I knew a tool changer would be difficult. I believe, however, that a rack style tool changer (with simple coordinate based locations for each tool) will be doable for this design.
    When you say docs, what are you referring to?
    sensors, IO... I agree. lots of things to consider and thats why we're working on it. if it was easy It wouldn't be worth our time right?

    I think we will stay away from probes and tool setters for now, I don't see this as being a professional quality workhorse. We have enough on our plate just speccing out something that works, let alone such a professional quality situation.

    Thanks for the reference on controls, wires, and IO numbers, It will help me to understand the scope of the task at hand!



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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by ger21 View Post
    Do you have a complete machine shop at your disposal, and the knowledge and abilities to use it?
    If not, you'll most likely not only spend more, but also have a far LESS effective machine than had you purchased one. A far better option for students would be to buy a HAAS, and teach the students how to use it, and how to make parts and products.

    We have been told that we should have access to a manual milling machine, a manual lathe, and a tormach pcnc. not much, but hopefully enough. I actually am a certified machinist (although still a newbie compared to some of the wizards on this forum!). As one of the main goals of this project is to get student's hands dirty and give them engineering experience rather than just manufacturing experience, I think even making a machine that only just barely works will be a valuable experience (although that is not the preferred outcome, I fully intend on making a capable machine)



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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by peteeng View Post
    Hi 308 - don't fly too close to the sun or make the labyrinth too hard KISS... Here's some more reading matter. You or the team will have to get on top of FEA quickly. I suggest you talk to Altair about simsolid. They usually are happy to provide software to Unis free. Where are you in the big old USA? Peter
    Peteeng! you are a lifesaver with this reading material. Looks like i have my free time booked for a while !

    Quote Originally Posted by ger21 View Post
    He's the founder of Shopbot.
    Thanks for the info!



  9. #21
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    Default Re: Student organization looking to build CNC milling machine for school donation

    Hi 308 - If you have an ATC its best to have a tool setter, there are many flow on effects from seemingly simple design wants. KISS says no ATC to me for a training machine.

    I used to train people to use welding robots and any machine training needs to be really, really simple in the beginning. This is not only for the single person that can use/train a mill at any point in time but the que of people behind that will get frustrated because someone assumed the tool was set then crashed the machine, not pretty. Future people can develop the ATC if needed. ATC is really only useful for production machines.

    Gerry has answered the shopbot Q and here's the excerpt from Bamberg. Its unwise to have rails "facing" each other, can be very difficult to adjust. Better to be on the same plane (and same structural element) for your purposes. Peter

    Seems you have access to machinery and skills to fit. So now you need lots of time. You learn more from your failures then your successes so sit tight and buckle up. Your going to get a lot of flack here and from where-ever you are. Be prepared to be scarred for life!!

    Attached Thumbnails Attached Thumbnails Student organization looking to build CNC milling machine for school donation-twin-gantry-jpg  


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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by peteeng View Post
    Hi 308 - If you have an ATC its best to have a tool setter, there are many flow on effects from seemingly simple design wants. KISS says no ATC to me for a training machine.

    I used to train people to use welding robots and any machine training needs to be really really simple in the beginning.

    Gerry has answered the shopbot Q and here's the excerpt from Bamberg. Its unwise to have rails "facing" each other, can be very difficult to adjust. Better to be on the same plane (and same structural element) for your purposes. Peter
    Thanks for the quick reply! i see it now! My thought process was to do more like the design on the rightmost side of the chaart, but mirror the gantry so across the X axis so its doubly supported. My intent was not to get two small gantries rather than 1 large one, but rather 2 of the largest we could readily obtain and fit within a given footprint/price. If you believe that is still an unwise direction, I will take that heavily into consideration and will (immediately upon figuring out how) do some FEA on it to help me understand it even better!

    Thanks again for the assistance!



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    Default Re: Student organization looking to build CNC milling machine for school donation

    Hi 308 - No its not doubly supported. The second beam is structurally redundant (as they are not actually connected, this thought bubble is an illusion) and makes it overly complex from many angles.. One correctly sized beam is best.

    Your model seems to indicate that you are going down the welded tube rabbit hole. Since you have access to lathes and mills I strongly suggest you go down the path of billet machined elements (Al or steel) . They will be as stiff, easier to assemble and disassemble and align and size. There is a lot more design freedom in this approach then a tubular one. There are lots of examples in this forum if you dig around. And they achieve rigid mill stiffness. Once you weld something you have a very very large bucket of worms to deal with. Peter



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    Default Re: Student organization looking to build CNC milling machine for school donation

    Quote Originally Posted by peteeng View Post
    Hi 308 - No its not doubly supported. The second beam is structurally redundant (as they are not actually connected, this thought bubble is an illusion) and makes it overly complex from many angles.. One correctly sized beam is best.

    Your model seems to indicate that you are going down the welded tube rabbit hole. Since you have access to lathes and mills I strongly suggest you go down the path of billet machined elements (Al or steel) . They will be as stiff, easier to assemble and disassemble and align and size. There is a lot more design freedom in this approach then a tubular one. There are lots of examples in this forum if you dig around. And they achieve rigid mill stiffness. Once you weld something you have a very very large bucket of worms to deal with. Peter
    I'm sorry, i guess im having some trouble understanding how it wouldn't be doubly supported. Would not an extra set of linear rails and trucks count as a connection?

    As far as welded tube, we intended to weld brackets to the ends, and connect each tube/bracket combo to each other with bolts. I would love to use solid steel, but solid steel of the same size as these tubes is extremely expensive (not to mention would require a crane to hoist into place). Unless you meant using a lot of smaller sized steel billet stock



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Student organization looking to build CNC milling machine for school donation

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