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Thread: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

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    Default DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Apologies if this thread seems redundant, but I wasn't able to find a thread on a suitably similar design.

    I have a mechanical background, but very limited exposure to CNC mills/routers. I have cut MDF using a micro mill, but accuracy was not a major concern for the end-use. I am familiar with 3D printers kinematics and structural considerations, but the forces acting on these machines are quite light compared to the forces generated from milling aluminum. Aluminum extrusion profiles are readily available (in only a few sizes) for me, and I've found the bolt-together design to be quite convenient. I posted this on another forum, but CNCZone seems to have many experienced machinists and DIY CNC designers who can offer their expertise. I took a look a DonFrambach's design thread and CatalystGilles design as well, but I don't have easy access to those sizes of extrusion, or a welder.

    I'm planning on building an aluminum extrusion frame CNC mill from scratch that is capable of (slowly) milling 6061 aluminum (ideally faster than a reinforced 3018 engraver, at least as an initial goal). All extrusion pieces are 20mm x40mm and will be secured using aluminum inside corners as well as aluminum corner plates wherever possible. My goal for accuracy is +/-0.1mm. The planned build volume is ~12" x 12" in X & Y, with ~2" of Z travel.

    The two plates at the bottom of the Z-axis supports are planned to be 0.25" aluminum plate with custom drilled holes, very similar to T joining plate that can be purchased. The idea behind this feature is to maximize the stiffness about the Y-axis by maximizing contact area. The piece of extrusion below the X-axis gantry that appears to intersect several of the Y-axis profiles will actually be three separate pieces (one piece in the middle and one piece on the outside of the linear rails' extrusion) to add rigidity to the Y-axis extrusions.

    Linear motion would be controlled by a GRBL controller, driving Nema23 motors, connected to 12mm ballscrews (for all three axis'). Each axis will have two parallel linear rails (15mm Hiwin style seems too flimsy due to the M3 mounting screws, so 20mm rails are currently the top option on my list). The kinematics will be similar to a 3018 CNC where the bed moves in the Y-axis, while the toolhead moves in X and Z


    I have a few questions:

    1) Do you see any mechanical problems with the frame for slowly milling aluminum to within 0.1mm? (such as a lack of stiffness, etc.) I'm open to suggestions.

    2) What is everybody's experience with Chinese linear rails? I've heard mixed reviews, particularly in terms of problems with binding (poorly machined blocks) or lots of play (due to undersized ball bearing sizes)

    3) This design's current cost is below a (Chinese) 3040 or 3020, but do you have any specific recommendations for an alternate below $1000 CAD?

    Thanks in advance.

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    Attached Thumbnails Attached Thumbnails DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum-cnc_frame01-png  


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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    double post for some reason



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi 147 - Whether you mill aluminium fast or slow does not matter. Machine stiffness matters. You are building a small machine with a small Z this is advantageous. I think you may need more than 50mm of Z unless you are just engraving. Now the crux is what you mean by "milling" so you will have to specify a target feed speed and a Depth of cut and a chip load that you want to achieve before anyone can help. I suspect that what a machinist would call "milling" will not be able to be achieved with a machine built from 2040 extrusions. There are many many small routers built from extrusions that claim to cut Al and in videos they do. But they achieve this with very small depths of cuts and small tools and fast speeds. Sure this cuts small bits of Al but you just wear out the ends of the tool really quick and take hours to do a small job. I suggest you find a small commercial mill that does what you want, to establish what it needs to look like, it won't be 2040... You will achieve +/-0.1mm quite easily but you need to understand if this is a tolerance or a repeatability...

    For a small machine I'd triangulate the column not bracket it, it will be stiffer and won't vibrate as much.

    re: quality of parts - you get what you pay for, try to get brand names at a good price and you will need medium or high preloaded cars for a mill... and your spindle is a whole new can of worms...keep at it Peter



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    2040 extrusion would be best thought of as not much stiffer than cooked spaghetti.

    You are not going to achieve 0.1mm tolerances in aluminium (well unless every part takes a year to make)

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


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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi Peter, thanks for the reply. My current design goals are to cut through aluminum sheet/plate up to 0.25" thick, but eventually cut through thicker bar stock to make functional parts. The cutting of the sheets might fit into the 'routing' category of CNC machines more, but the focus of those machines appears to be woodworking and plastics. I'm just getting starting in CNC machines, so I don't have a clear idea of what MRR I am looking to achieve.

    I've found some small desktop mills that say that they can aluminum such as Bantam Tools' desktop mill and the smaller Haas machines, but I was hoping for the 12" x 12" X-Y work area. I agree that the small 'routers' (often marketed as mills) are not well suited for light 'milling', As far as I can tell, some are glorified engravers, which is not useful for me.

    Would larger extrusion like 1.5" x 3" (Model #15QE1530 from a local supplier, I'm not sure what the rules are for posting links) possibly be viable? The moment of inertia is ~ 17x that of the 2040 (about the Y-axis, if looking at the gantry uprights).

    I was definitely considering adding a support connecting the top of the gantry and the end of the rear Y-axis extrusion after I saw some of the designs here. Thanks for the tip.

    I've found some local suppliers for genuine Hiwin linear rails, so I will look into that.



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi 147 - Look up the Katran thread and scale that down. Peter

    Attached Thumbnails Attached Thumbnails DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum-katran-thread-jpg  


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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Thanks Peter. That's a beautiful machine. I'm only halfway through the thread, but at least I know what kind of stiffness I need if aluminum extrusion is used. My local supplier has 3" x 3" extrusion, which is not quite as stiff, (140.645 cm^4 vs 171.6341 cm? for the moment of inertia) but should be OK? Thanks again, I've learned a lot.



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi 147- by extrusion I assume you mean a construction extrusion. Beware with these they are expensive and do not offer great inertia to size ratios. Convenient yes but anything convenient has negatives attached for that convenience. see attached. Peter

    Attached Files Attached Files


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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi Peter,

    Thanks for those documents. Steel tubing is definitely a construction material that I've considered versus aluminum extrusion, but not aluminum tubing only because of convenience. How would you recommend fastening the sections of tubing together? I don't have a welder, so the only method I can think of off the top of my head is drill and bolt together with plates. I've built a 3D printer frame out of 19mm particleboard, and I would consider using the same material for a router frame but definitely not for a mill.



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi 147 - I don't recommend welding steel or aluminium unless you really know what your doing or can get it stress relieved. Consider using square or rectangular heavy wall aluminium glued together at the joints. Construction is a fundamental philosophical question only you can answer. The answer lies in your $$$, your resources and what you want to achieve and your interests. You can use Portland cement, CSA cement (like I'm about to) epoxy granite, steel or Al soldered together, steel or Al brazed together, cast iron, metals bonded together. Fibreglass, carbon fibre, all have been done and all have some threads here. Depends on what facilities are nearby you and how far you want to go with various technologies. You could fully metal 3D print a mill in titanium in the next month.

    steel tubes tend to be thin due to trying to save weight then you hit local distortion issues and vibration issues. Welded components warp and need SR or cold setting or make subassemblies so they can be aligned. I would braze before I welded...
    same with aluminium but because the tubes tend to be thicker local distortion and vibration can be side stepped. I have brazed a lot of aluminium parts
    epoxy granite is very doable but I think there maybe a swing to CSA concrete soon over epoxy. Any of these need moulds so you need to understand how to do this
    cast iron if there is a foundry nearby but why would you do this? then there's post machining needed
    bonded metals are very doable
    composites doable if you know about moulds and fibres
    3D metal printing costs $$$ but is a mature doable pathway

    each have pros and cons - pick your poison

    Many people have made plywood machines that they make their aluminium parts on for the next better machine then use that machine to make better parts for the next machine. If your a Maker there's more then one machine in you. I'm up to No5.

    cheers Peter



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi 147 - Here's a neat little epoxy granite mill. But I'd suggest CSA grout, its much much cheaper and stiffer. Would use same moulds, use formply. Look up PVA (NOT PVA glue! PVA glues correct term is PVAc) release for concrete. Many people use the wrong release agent when casting a machine:

    1) removes the design from std section sizes, welding and to an extent bolting. But bolts are inevitable unless you are clever
    2) allows consolidation of many parts into few parts. Stiffer, less vibration, damper
    3) allows freedom to optimise geometry
    4) has more possibilities to explore

    Look up the Milli thread - its bigger but has to hurdle the same issues as yours...

    Peter

    https://www.instructables.com/CNC-Milling-Machine/

    https://www.americanmachinist.com/ar...-machine-bases

    most of the best machine tools are now made in some sort of composite, look up granitan

    147 - I'm not pushing an agenda here. You are going down a path that 1000's of people have already gone down. Its an opportunity to step up vs doing something that already has been done. You will save 1000's of hours by just copying a steel machine that is somewhere on the forum that has been debugged. Or the Katran machine. Or Milli, Put in 100's of hrs already. So if your dead keen to do something yourself push the envelope fwd. Won't take any longer or be any less painful. Machine designers are somewhat masochistic...

    Last edited by peteeng; 11-30-2020 at 02:58 AM.


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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    New post with timber machine cutting aluminium - excellent Peter
    https://www.cnczone.com/forums/cnc-w...ml#post2416580



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Thanks for all the feedback Peter. I'll try and address the points that you brought up in chronological order:

    After reviewing the theoretical deflection of aluminum extrusion vs steel tube (rectangular or square), I'm probably going to go with the steel tube (0.125" or 0.25" thick) as it is far more rigid for a comparable size and with a lower cost (Thanks for those articles, they were very informative). My preferred method of construction is bolts since they are more forgiving, but sufficiently strong (given the correct grade, etc.)

    I have several FDM 3D printers, that have been made using that progression: use the first machine to build to second machine, to build the third machine. However, as I've learned more, I've tried to make more careful decisions in the design process, rather than down the line, which is why I'm pondering the mill design. An ounce of prevention...

    For the cast frame from the instructable: I like the convenience of a monolithic frame, but I don't think that I will pursue that as a first CNC build, especially given my limited experience with molds and casting. I will definitely bookmark that page for later.

    The Milli design is definitely not what I am used to seeing. I'll keep following your progress, very inspirational! I haven't read through all (12 as of this reply) pages of the thread, but I will be trying the learn as much as possible from that build's progress.

    I'm quite surprised that the wooden frame is able to cut within 0.005". I'm not as confident with my woodworking abilities (and I lack the proper tools), so I would likely not go that route. One of my 3D printers has a wood frame that has been performing well for many years, although it could probably be stiffened by adding some supports. I definitely got my money's worth out of $25 (CAD) of particleboard.

    Closing thought: I was pointed toward the "PrintNC" design, which used linear rails, ballscrews, and rectangular steel tube as the kinematics and frame. 3D printed components make up the custom parts, but these might be feasible in aluminum once the mill/router is operational. It's a moving gantry, which is not preferred in terms of rigidity, but the smaller footprint is tempting. This machine design is often compared to the MPCNC, but as others have pointed out, these are very different machines, and designed for different capabilities and price points. I have access to most of these components and I believe that I have the required tools to make this machine (the PrintNC, not the MPCNC). Any thoughts on this design? Thanks



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    Default Re: DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

    Hi 147 - Sounds like you have a pathway figured. There seems to be lots of PrintNC out there. If plastic connections are printed I'd use the stiffest plastic I could use in the printer. I'll keep watch on your progress. I have a small 3d CNC platform earmarked for a printer haven't got into it yet. So much stuff to do. Peter



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DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum

DIY CNC Aluminum Extrusion Fixed Gantry Frame? - for slowly milling 6061 Aluminum