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  1. #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



  2. #22
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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
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

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

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


  3. #23
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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.



  5. #25
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    Default Re: Steel Gantry Router

    Your design looks like it would lend itself well to an idea I have had in the back of my head for a while. Think about this idea for a sec.

    Use a Fab Block as the basis for your table design. https://weldtables.com/collections/f...48x48-fabblock
    It is a welding table base that is constructed from tab and slot pieces. I think it would be a great starting point for a flat surface that has parallel sides and will allow you to build any base on it that you want.

    I think that a welded frame will give you good rigidity the problem is warping introduced by the welding process. These tables are designed to stay flat during welding.



  6. #26
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    Default Re: Steel Gantry Router

    Hi Max - They are good but getting them to OZ is a killer cost! Peter



  7. #27
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    Default Re: Steel Gantry Router

    Gerry,
    - Thanks for the link, I had read that thread about a month ago, maybe will run through it again and compare the findings, there is a huge amount of info in there.
    - Good to know about the DMM's in Step/Dir, I will do some more research into that, Unless there is evidence one way is better I'll likely go with whatever is easiest to set up.

    Peteeng,
    - I missed the question before - I am using Solidworks 2018, which is available to me through work, I also use Fusion360 but it frustrates me a little, though it also has FEA. I haven't done a lot of FEA in Solidworks but will get up to speed in it and try and get some numbers - I will run over your build thread and the one Gerry posted, but what forces exactly should I be checking? i.e a 10n force on the cutter perpendicular to the endmill, tested in each direction?
    - I agree the Z-axis needs a lot of work, I will spend some time studying principles and other designs then get right into it. It's only in very early draft stage at this point - maybe an hours work total so far on the Z axis itself. - it has a long way to go.
    - Thankyou for the link on the commercial router, though it looks like the 600x900 model is $12k, I have emailed to get the price on a 1212, I'm guessing it'll be in the 16-20k area. I have attached some photos of the Z on that machine - the design does not look particularly rigid compared to the advice I've had here, maybe I am missing something? though the design is quite similar to my early draft.

    Hanermo,
    - Thanks for the advice, I live in Australia and the second hand machine market is not great, to get any commercial machine second hand is still $25k+ maybe I need to set up some alerts on ebay and other marketplaces for used machines.

    Tommylight,
    I checked a 1500mm ballscrew at 20mm root diameter (i'll be using 2525 screws) and it came back at 1075rpm as the critical speed. this is using Metric Critical Speed Calculator | Nook Industries
    what are your thoughts?


    Thanks all for your input

    Attached Thumbnails Attached Thumbnails Steel Gantry Router-z1-jpg   Steel Gantry Router-z2-jpg  


  8. #28
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    Default Re: Steel Gantry Router

    Hi Stuart - the machine you are designing will be much more rigid then many commercial machines. That's one reason you are doing it I'll reread the Sapele thread. They concluded that the 200x200x6mm is the go for the gantry but they didn't seem to be clear on the conclusion for the Z axis. If you have a design I'm happy to run it in FE, I'd need a step file from SW. The worse case for bending is a push or pull perpendicular to the gantry with the Z axis down. I use a design load of 1000N and the target stiffness is 10N/um ie at 1000N applied the spindle should deflect <1.0mm. If you do not include the bearing stiffness and other contact conditions then I'd aim at 20N/um as your structure will be about 50% efficient. The Sapele thread did mention that they used SHS and when bolted up the linear bearings jammed due to the cupped surface. They had to scrape and fill to get flat. So maybe work with the SHS supplier to get a flat piece or get two tracks milled on it, or at least have a plan B if you can;t get the linears to work. Peter



  9. #29
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    Default Re: Steel Gantry Router

    When I get a minute to sit down I’ll take a look at the FEA, I’ve done it for single parts, but not assemblies so will have to have a play with it.

    I am going to start putting prices together for the frame, a have a friend who works for a fabricator that might be able to weld the frame up and heat treat it, which would be a big win.

    I figure I’ll continue with the design, while getting rough quotes for all the parts, then go from there. I’ve had a look at a lot of commercial Z axis designs over the last few days and am pretty confident I can get something together that will work well. A lot of the big names just use two bits of plate with 25mm linear rails between them... As Peter said, I think I can do better than that.

    For the X Carriage I’m looking at a 2” 6061 block, milled flat potentially with a groove milled in it for Z ballnut clearance. Then maybe 1.5” 6061 milled flat for the Z. I’m yet to draw it up. But will see how it looks.

    Having read up a bit on Z-axis design, It sounds like the rails on the Z can be quite close together without any negative effect, as long as there is as much distance between bearing blocks as possible.



  10. #30
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    Default Re: Steel Gantry Router

    Hi Stuart - Seems there are a couple of treaters in Newcastle or is the oven near Armidale? Peter

    The carriage does not have to be very stiff I've found, But the bearings have to be very close together. In this case you need shear stiffness not bending stiffness. For instance if you put the bearings on top of each other that's great but how do you assemble it or adjust it? A few nightmares in there for you.

    The Z axis is however a cantilever and bending stiffness is king in this part. A typical commercial machine uses 25mm steel plate and its not stiff enough to match your gantry or get to 10N/um. Get some budget figures and concepts and geometry along the way to get a feel for where your going. Everything in the machine is connected and changing something may have far reaching consequences so you need to get thru some design rounds to figure out a few things. Your first objective is to get a functional general arrangement going. By functional I mean you can look at it and say there are no fatal errors that you can see in the design. Then it will be another few rounds to get it really good. Peter

    It would be interesting to know how stiff your ShapeOK is, you'll need a dial gauge and spring scale...

    Last edited by peteeng; 08-12-2019 at 06:40 AM.


  11. #31

    Default Re: Steel Gantry Router

    Quote Originally Posted by ger21 View Post
    Looks like it did indeed start with the TinyG, but now uses their own code.

    https://news.ycombinator.com/item?id=17288432
    I'm Doug Coffland at Buildbotics. We did indeed start with TinyG. After three years of development, there is very little of the TinyG code left. Our controller has 4 stepper motor drivers built in. We do not interface with servo motors. On the web interface, the Buildbotics Controller offers the ability to plug a monitor, keyboard, and mouse directly into the back of the controller, this eliminates the need to connect across a network if you don't want to do that. I use a touchscreen monitor in my shop, so I don't need the keyboard or mouse either.

    I appreciate that you have looked at our product. If you decide that steppers will do the job, feel free to send me an email a t dougcoffland@gmail.com. I'd be happy to answer all of your questions.



  12. #32
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    Default Re: Steel Gantry Router

    Hi Stuart - Looking at your drive speed. If the critical speed is ~1000rpm and your pitch is 5mm (I'll assume the 2525 mentioned is actually 2505) this means your max feed rate is 5000mm/min which is quite slow for a rapid for instance. But if your happy with 5m/min max then that's fine. Cheers Peter



  13. #33
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    Default Re: Steel Gantry Router

    Family holidays always slow down the progress!

    Peter, it was no typo, I am indeed looking at 2525 ballscrews, which should give me around 25m/min rapids with the screw at 1000rpm, and realistically it'll be reduced to about 75% of that.

    The servos will be running a 3:1 reduction so at the servos max rpm of 3000 I should have the ~1500mm ballscrew at its critical speed.

    I haven't done the models or calcs on the z yet but I can likely get away with a 2020 ballscrew on the z due to the shorter length of screw and the fact that the higher rapid speeds will not be as important on that axis.


    I'm progressing with the models of the z axis, however time will be pretty limited over the next month or so. I'm fairly confident in my design, however the cost of aluminium stock may impact the design choices - I will send off for early quotes shortly to see where I'm sitting.

    I may have a couple of jobs coming in for my recently purchased laser cutter which will bump up the budget for the router somewhat. Those things print money!



  14. #34
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    Default Re: Steel Gantry Router

    Ok - Makes sense now.

    Something to think about if your comfortable in epoxying steel and aluminium together is to make a composite Z axis or carriage. Say you glue 2mm skins on the outside of an aluminium plate. It gains a small amount of weight but gains lots of stiffness, as steel is 3x stiffer then the Al. Once you get more geometry settled and costs you may want to optimise this a bit better. I'll figure out webs vs composite soon. Maybe better then using webs (no). Peter

    Edit - Seems the webs are the go. They gain rigidity far quicker then the sandwich does and the main plate will be thinner as well. If we use a 25mm thick plate as a reference then if we add 20mm thick webs 50mm high it will be 10X stiffer then the 25mm plate. An Al plate 36mm thick with 20x50 webs will be 5.5X stiffer then the 25mm steel plate but less then half the weight of the web steel plate. So need to establish rigidity target and tune the webs to get the min weight and max stiffness. Cheers peter S

    Attached Thumbnails Attached Thumbnails Steel Gantry Router-composite-jpg   Steel Gantry Router-z-axis-jpg  
    Last edited by peteeng; 08-18-2019 at 04:42 AM.


  15. #35
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    Default Re: Steel Gantry Router

    What happened with this build?

    Sent from my SM-G970F using Tapatalk



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