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  1. #13
    Community Moderator ger21's Avatar
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    Default Re: Steel Gantry Router

    Looks like it did indeed start with the TinyG, but now uses their own code.

    https://news.ycombinator.com/item?id=17288432

    Gerry

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


  2. #14
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    Default Re: Steel Gantry Router

    Quote Originally Posted by ger21 View Post
    If you want to run analog servos, that limits your options to LinuxCNC, KMotion, or Mach4 with one of the few Analog controllers that work with it.
    Ok, I thought that might be the case. What's your view on how to run the servos? I can only really go off what I've read, and the general consensus I have seen is that Step/Dir is OK, but the preference is to run analogue with encoders back to the drives, then also back to the motion control(for full closed loop) as it's smoother and more accurate..

    If you were setting up servos on this machine what controller would you run and how would you set it up? I'm very flexible at this point as I haven't ordered anything, and very inexperienced - the only motion control I've set up is 4 Nema23 steppers off a Mesa 5i25 > Gecko540


    *edit* Also, does anyone know good suppliers for 5mm GT closed belts and pulleys that would suit my servo reduction? It seems like 60/20T or 72/24T at a 15mm width would work. Still digging through the material above, but no specific suppliers

    Last edited by stuarttaylor00; 08-09-2019 at 02:31 PM.


  3. #15
    Community Moderator ger21's Avatar
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    Default Re: Steel Gantry Router

    I'm using DMM's on the machine I'm building, but running them step/dir.

    Not sure there would be any noticeable difference in smoothness, and accuracy should be exactly the same, as both methods use the same encoder, and the motor is always moving to a specific encoder position.

    Scratch Mach4 from that list, as it's can't close the loop in the control.

    Gerry

    UCCNC 2017 Screenset
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    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  4. #16
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    Default

    Quote Originally Posted by ger21 View Post
    That machine should be able to cut plywood at 10m/min. I'd be looking for 15m/min or more rapids.

    3000rpm motors would give you 30m/min, but you don't want to spin the screws that fast. A better choice would be 2525 screws with a 3:1 reduction. That gives you 25m/min rapids with the screw spinning at 1000 rpm.
    At 1.5 meters length spinning the ballscrew at 1000rpm is looking for trouble, big trouble. At 800 they started vibrating, 2505 that is. And it is 1.5m for 1.25m cut area or thereabouts.
    There are calculators online that can give you a rough idea of what you can spin them.
    You should check that as it has been several years since i did that, but am pretty sure that was it. The Y axis was 2.5m with ballscrews on both sides, had to setle for 2m/m. What a pitty.



  5. #17
    Member peteeng's Avatar
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    Default Re: Steel Gantry Router

    Hi Stuart,
    1) Gerry recommended https://bstmotion.aliexpress.com/store/314742 and I have emailed Fred there a few times with questions and he has been very good
    2) For pulleys etc start at https://www.naismith.com.au/list_products.php?m=42 they have been good to deal with. They currently can't supply ATL belts but I can get these if you want to go that way
    3) Yes the web based thing is my hurdle with BB at the moment. I have a machine in a shed with no web access. BB have sent me 3 options to counter that. I'm working thru them now. I'd like to use it on my next machine.

    Peter

    Re buildbotic controller/driver- I've just go a reply from Doug. To use locally without internet, get an ethernet switch and plug BB into the switch and a computer into the switch and Bobs your Uncle, it works. Peter

    Last edited by peteeng; 08-09-2019 at 07:16 PM.


  6. #18
    Member peteeng's Avatar
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    Default Re: Steel Gantry Router

    Hi Stuart, not so far away... I'd like to play devils advocate on your project.

    1) Your about to buy a manual mill and spend about $8-10k on a half sheet machine. Plus invest 6 months to a year to get it done. You can buy commercial machines for around $10k and your done, on your way?
    2) Your a Maker and good at CAD. You have chosen steel as its convenient and you can probably weld steel yourself. You have started at the usual design space of designing a bench and a gantry but the real effort should be put into the Z axis. That's the crux of the machine and the pointy end that does the work. No value in having an UBER/bench gantry and a wimpy machine holder. Especially when it comes to "aluminium".

    So to discuss the SHS or RHS gantry solution. a) Its convenient but b) it has issues. The corners have large radii so you have to mount the rail a fair way from the corner. The faces of SHS are cupped due to the rolling process, so if you attach to the face, the rails will not be horizontal. Ideally the rail should be mounted to the web (to transfer the loads directly to the SHS) but in this case can't be done. Some people weld a thick plate to the front then machine this to create the mounting surface. But this requires the gantry to be stress relieved as it will definitely change shape when welded/machined. So now you have a rail mounted on a 6mm thin piece of metal that can flex slightly when loaded. This is also the case with other elements using this construction philosophy. All of these flex points add up...

    Moving parts need to be light weight - see the Z axis plate as an example. The same should be considered for the gantry it should be aluminium to allow a very stiff and light structure to be made so it's easily driven. If you make it in Al then you can machine the parts with registers and features that make alignment easier. (using your manual mill or a CNC) Billet machined parts bolted and bonded together is a very successful machine build technique. Use Loctite 290 or 294 to set joints once correctly assembled for instance. (there are many examples in this forum)

    Aligning this large and heavy steel gantry that has no machined features will be a mission and keeping it in line in use as well (cutting aluminium involves large loads that will flex the machine) If you aim at a precise machine to do Al then this will be a bug bear when you put on your machine assembler hat. CAD objects are really easy to move around on the screen!! I move a 360Tonne trailer with my little finger!!

    I suggest the following:
    Since you are interested in servo control and one objective of this machine is to learn about that, make a smaller benchtop machine that can cut Al parts. Use that machine to build the big machine parts. The big machine should be steel bench, aluminium rest. You could also buy a small benchtop CNC that does Al and move along as well I think within my guess at your budget.

    I think you need to write down your objectives and budget and maybe there is a way through this that will result in a better machine then the current "plan".

    I say all of this because I design machinery in the mining, medical and yachting world and see a lot of projects consume time and money that could be better spent. Project inceptions are always enthusiastic and $$$ do not matter. At some point all this changes and reality bites and your well off expectations So do not buy anything until you have fully resolved the design in CAD, sourced everything and costed it. Then at least you have a well understood design and have only spent your time on the project (Hobby time). You may get near to the end and scrap the design due to cost or technical issues. There are a few traps along the way, like designer inertia. This is when you know something has to be changed but you don't because A) you are attached to the sunk time in the design and B) you know it will take more, more time to do the changes. If you don't do the change then you have compromised the work and the result. This approach also will allow the machine to be built in the shortest time as everything will fit and everything is available. The forum is full of projects that replace this and change that and never seem to get to the correct resolution.

    Enjoy the journey, Happy to help... Peter

    Re buildbotic controller/driver- I've just go a reply from Doug. To use locally without internet, get an ethernet switch and plug BB into the switch and a computer into the switch and Bobs your Uncle, it works. Peter

    Last edited by peteeng; 08-09-2019 at 07:14 PM.


  7. #19
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    Default Re: Steel Gantry Router

    Of course someone has to play devils advocate!

    You make some valid points, and I have certainly considered most of your thoughts prior to this.

    1) yep you're right on the money, I'm budgeting AU$10k. I have considered commercial machines, but could not find anything <$10k that would cut half a sheet and also be rigid enough to cut aluminium. Would you mind posting some links for me to investigate? You also mention buying a benchtop CNC and moving on - to which brands are you referring? I feel like I've been looking in the wrong places

    2) Yes steel is easy for me to cut and weld, I can currently machine aluminium on my little router but not to the accuracy that I'd like. A point I'd like to make here is that I understand the Z axis isn't as rigid as it should be. The whole reason I am posting my design here is to get input from people to help me design something that isn't 'wimpy'. Though I am learning, I don't have the knowledge to just come up with the ideal design, that's why I engage you wonderful people. (let me know if you ever need someone to operate an LNG plant for you - now that I can do!)

    I understand your Issue with using SHS/RHS. However I have seen some pretty good designs come out of here and mycncuk.com that use similar techniques and have achieved good results. I have seen several builds where if welded carefully, the bearing rail mount can be machined without needing to stress relieve the box sections. I've also seen guys successfully epoxy pour the mounting locations for the linear rails - this seems to be more popular in the UK than america, but they have good success with it. Again this is my point, I've not come here to show people how to build a machine, I'm asking for input as it's a project I'd like to do I just need a little guidance.

    I have goals of CNC'ing the DM45 benchtop mill, I know thats likely a more simple project than building a CNC router (depending on how far I go with PDB and ATC), and it'd certainly cut aluminium without issue. I don't know if that will come before or after the router.

    I appreciate your comments on the fact that a lot of projects run out of energy/funding, or become so tied up due to design flaws that they don't ever get finished. I have no intention of rushing this, if it takes me 6 months, a year to get the design sorted then I'm ok with that.

    I will get my design brief down so it is more clear. I have a good idea of what my requirements are and I'm just starting to get some rough ideas of costs together now, This sort of comes alongside the design.

    A final note I'll add is: This project for me is as much about building the machine as it is actually using it to do work. I have found with my current CNC machine that I spend as much time, and get as much enjoyment from modifying it, making new parts, upgrading parts, as I do from designing and cutting jobs on it. That being said I do make an income with it, but being locked down to an 800x800 work area makes working with sheetgoods pretty inefficient, and limits the size of my jobs for signage.

    Thankyou for the input



  8. #20
    Member peteeng's Avatar
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    Default Re: Steel Gantry Router

    Hi Stuart - I'm not saying your ideas won't work, I'm trying to say in a project like this it is good to think bigger then the convenient solutions. It's a big task and long journey and there maybe opportunities that result in a better machine for no extra effort other than thinking different. There are all manner of solutions and they all end up working if you persist. It comes down to how good a machine do you need and can you realise it. So far your travelling the right road... and you are brave to put this out there and there will be flack but you and your machine will be better for it.

    1) I think the epoxy levelling thing is a poor solution, sure use epoxy to set a machine but levelling is another matter. I have been involved with concrete leveling and epoxy levelling and it's a tough gig. Wouldn't go there, there are better approaches
    2) Sure welding carefully can get you so far but the bottom line is it's a compromise process for the application. I do recommend brazing vs welding. I have worked as a welder, a welder trainer and a robotic welding programmer and distortion is inevitable and permanent so tread lightly
    3) I understand your a Maker and that's the fun bit, Tally Ho!!


    https://www.gregmach.com/product/woo...0-cnc-machine/ this was $12k AUD at a machine show a years ago. I see the price is removed and the smaller version is $12k.

    What CAD are you using? Peter



  9. #21
    Member peteeng's Avatar
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    Default Re: Steel Gantry Router

    Hi Stuart - So to review. 1) your base and gantry are fine. The 200x200x6 is on the money for the gantry. It took me 4 months of analysis to arrive at that point, Maximus is 210mm high and 175mm deep by 6mm thick. If all of that gets executed properly its a great machine. 2) The z axis needs some deep thought. A small hobby mill is about 5N/0.001mm stiffness at the tool. A typical vertical milling centre is about 150N/0.001mm at the tool. Serious milling machines are way over that. If you have FEA associated with your CAD it's worthwhile using it. Maximus has been aiming at 10N/0.001mm and will probably pull up under that. Its Z is tubular and its equivalent thickness in steel is 76mm so you can now see how stiff this thing may have to be.
    Learn about "whirl", it will be your limiting factor on the long drive screws... if you can measure your mills stiffness then that gives us a benchmark... or you shapeOK that would be good.

    Anyone out there who would measure their machines static stiffness and publish it here would be doing us all a big favour. We need a router stiffness data base!!

    Regards Peter



  10. #22
    Community Moderator ger21's Avatar
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    Default Re: Steel Gantry Router

    There's some very good info on gantry beam design here:
    https://www.cnczone.com/forums/diy-c...cad-posts.html

    Note that it may not agree with Peter.

    Gerry

    UCCNC 2017 Screenset
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    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)


  11. #23
    Member peteeng's Avatar
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    Default Re: Steel Gantry Router

    Hi Gerry - Thanks for the link very good. I flicked through it and they agreed that the steel 200x200x6mm (8"x8"x1/4") gantry was the go and that a lot of work had to be put into the Z axis. Their stiffness target was 50000lbf/in which is 9N/0.001mm I wonder if they got there in reality. Same as Maximus, interesting!! So I think this is a great link for Stuart. Should get him to speed fast.
    Peter



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    Default Re: Steel Gantry Router

    For stuartxx - OP ..
    In this case I agree very much with Peter-nn.
    A bought older machine is much better - as it can produce some profits within a short amount of time.

    And not.
    Stiffer is not much more expensive, and can be added later, especially for a router.

    Making a really good commercial router is quite expensive.

    You certainly *can* make a good commercial router.
    Many people have done so. See mechmate.
    Avg. costs are 10-12.000$ for basic mechmate type stuff.

    Easily add 5-8k$ for proper linear guides,
    proper spindle w. toolchanger, say ISO30 / 10k rpm,
    tables for in/out of cutting material,
    dust vacuums,
    materials handling.



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