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  1. #1
    Join Date
    Jun 2009
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    13

    Red face One more DIY first born CNC

    Hello everyone!

    First I want to congratulate pretty much all of you because in every threads I read (mostly in the DIY section) I see a strong demonstration of respect, specially noticeable towards the newbies. I had no intention to post anything but to do my research on my own instead. Everyone's positive attitude convinced me otherwise. I'm confident I can ask for help without fear of judgment.
    I'll just had a little side note to this, I love straightforwardness: If you think something is just a plain bad idea, please tell me. I like to believe that I can handle the truth. That's what I'm looking for.

    Short story:
    I started building a first CNC about 10 years ago and never finished it. The stepper motors and controllers are about all I intend to salvage from my first attempt.

    Goal:
    If I have to choose between precision and working surface area, I'll take precision. I'm aware that my current components are not the best for it, it's just to keep it in mind.

    The components list up to now:
    - Nema23 425oz/in 2.8A stepper motor with KL5056 drivers (it's the analog version, now they are digital)
    - SBR20 supported rail & bearings (300/600/1000mm) + Ballscrews, bearings & nuts ( 350/650/1050mm) Kit is from Amazon.
    - Bosch Colt palm router as spindle

    I'm still in the design phase and I'd love to get your inputs on few questions.

    Q1 - I'll use 8020 extruded aluminium for the base frame. I designed the first draft with 1515 extrusion and it seems a bit bulky for what I consider to be a fairly small machine. Is the 15 serie (1.5" x 1.5") an overkill or does it bring added value in rigidity? And the rail supports are larger than 1.5" so like with the 1" version, the "floating" portion of the bearing rails would be sitting on the transversal frame supports. There is way less unsupported surface with the 1.5" though.

    Q2 - I had in mind to install every rails with the supports parallel to the table. It was easy to do for the Y axis. It a bit more complicated for the X travel (on the gantry). On most of the designs I see, the rails are installed on their side. I'm pretty sure it's less of a problem with the carriage block type rails. Can this be an issue for SBR bearings? Would it better to design the gantry beam with a rail on top and one underneath? I also thought of installing the rails in the back of the gantry but my guess is that if I am to go with a side installation I better get as close as I can from the spindle holder assembly (Z) not to mess with the center of gravity.

    Q3 - I noticed comments on ballscrews accessibility for maintenance. On all axis, I installed the lead screws between the rails and they're all pretty jammed up and surrounded by framing components. Should I consider making them more accessible, like bringing the X axis lead screw behind the gantry per example?

    Q4 - I planned on making the gantry out of 3/4 inch baltic birch because I'm well equipped to work with wood. Could this be too heavy?

    Thank you very much for your help.

  2. #2
    Join Date
    Dec 2003
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    1206

    Re: One more DIY first born CNC

    You seem to have designed for a very big Z-axis.Have you examined the body of the router and determined how much depth you are likely to have to the tip of the tool?Lots of people seem to be designing very tall machines,perhaps without consideration of the limitation imposed by not being able to get into the corner recesses of a tall job.Without knowing what kind of projects you have in mind its a bit hard to make judgements but the brace between the side plates of the gantry will be a much lower barrier to tall jobs and I don't see much advantage to having the tool raising much above this point.

    You could switch the gantry bracing to vertical webs on the outside of the side plates to free up some space and obviously the wider the web-the greater the stiffness.Maybe by extending the vertical and horizontal elements at the top and the piece below the extrusion too and link it all together.I like working with good quality birch plywood and unless you get really aggressive it should be adequate for the loads a small router will impose.I strongly suspect the modest power of the Bosch will be your limiting factor even though it is a lot more powerful than some of the tiny Chinese spindles that come on the small and inexpensive 3020 machines.If you want to see some impressive engineering analysis of router construction you should look in the Australian sub forum for the thread about Maximus.Admittedly a bigger machine but a very thorough job with similar material.

  3. #3
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    Jul 2018
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    6254

    Re: One more DIY first born CNC

    Hi Routalot and F8. Maximus is steel so a bit different to Birch. But the principles are the same. I do some calcs in here that show birch (mdf actually birch will be way stiffer) can be as stiff as aluminium so have a search for that. Peter

  4. #4
    Join Date
    Jun 2009
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    13
    Quote Originally Posted by routalot View Post
    You seem to have designed for a very big Z-axis.Have you examined the body of the router and determined how much depth you are likely to have to the tip of the tool?Lots of people seem to be designing very tall machines,perhaps without consideration of the limitation imposed by not being able to get into the corner recesses of a tall job.Without knowing what kind of projects you have in mind its a bit hard to make judgements but the brace between the side plates of the gantry will be a much lower barrier to tall jobs and I don't see much advantage to having the tool raising much above this point.
    The table is not showing on the images, I think it can be misleading. The table would sit on top of the four aluminium legs. I imagined making it out of birch again where I would put metal inserts to fasten waste boards quickly. I really like the idea of small 8020 channels covering the full surface too though!

    With the current setup, the clearance between the gantry and the table top is about 5".

    I arranged the spacing so the spindle chuck is 1/2" above the table surface when the Z is at it's lowest position. I don't imagine I'll ever be out of reach like that. I mean, the cutting bit will always protrude of at least half a inch from the spindle right? If not, it meens I need to replace it because it broke! At max Z position, the carriage should go high enough to enable the cutting bit to be just under the gantry point.

    With all of that said, I think Z clearance should be tuned after we are sure of where we're going with the rest of structure design.


    Quote Originally Posted by routalot View Post
    You could switch the gantry bracing to vertical webs on the outside of the side plates to free up some space and obviously the wider the web-the greater the stiffness. Maybe by extending the vertical and horizontal elements at the top and the piece below the extrusion too and link it all together. I like working with good quality birch plywood and unless you get really aggressive it should be adequate for the loads a small router will impose.
    I would like clarifications on this as I'm really concerned about stiffness. I'm not sure I understand what you mean though, I'll have to re-read that part in front of the drawings tonight. But I get the idea of linking the top to the bottom of the gantry!

    This brings the weight question back up. Will it be too heavy to build the gantry out of birch. I could also go with thinner plywood and braze everything together to prevent torsion. I think I'm starting to get what you mean!!


    Quote Originally Posted by routalot View Post
    I strongly suspect the modest power of the Bosch will be your limiting factor even though it is a lot more powerful than some of the tiny Chinese spindles that come on the small and inexpensive 3020 machines.If you want to see some impressive engineering analysis of router construction you should look in the Australian sub forum for the thread about Maximus. Admittedly a bigger machine but a very thorough job with similar material.
    I have bigger routers available, that's for sure. At first I wanted to buy a 500w spindle but decided to go with the common Colt option. I agree that the Colt tend to bog down rather quickly under load but that's mainly because my arm is not computer controlled (yet). But I'll keep that in mind and ensure to be able to switch to a bigger router motor eventually.

    I never heard of the Maximus you're mentioning, I'll check it out.

    Thanks for your inputs. Please keep them coming.

  5. #5
    Join Date
    Dec 2014
    Posts
    640

    Re: One more DIY first born CNC

    In terms of your X axis...I did something similar with the round supported rail, but my beam (although made of MDF) is a torsion box and it's super rigid. With your gantry sides so high you might think about a torsion box rather than just the one piece along the back. Also, double the gantry sides as well. I would bet that if you built it as is, you'd be able to push side ways at the top of the gantry and measure a good bit of flex at the other side...even with a gentle push.

  6. #6
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    Jun 2009
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    13

    Re: One more DIY first born CNC

    Quote Originally Posted by peteeng View Post
    Hi Routalot and F8. Maximus is steel so a bit different to Birch. But the principles are the same. I do some calcs in here that show birch (mdf actually birch will be way stiffer) can be as stiff as aluminium so have a search for that. Peter
    Sure will, thanks

  7. #7
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    Jun 2009
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    13

    Re: One more DIY first born CNC

    Quote Originally Posted by fretman_2 View Post
    I would bet that if you built it as is, you'd be able to push side ways at the top of the gantry and measure a good bit of flex at the other side...even with a gentle push.
    I can totally see it happening! Thanks for pointing that out. I like rootalot's idea to have a piece go around the whole thing. I'll try to incorporate that idea when I get home.

  8. #8
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    Jun 2009
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    Re: One more DIY first born CNC

    Hi Peter,
    I had a look at your thread and I got to say I'm trully impressed. (Even if I got lost from the first few posts! )
    When I started to draw, I thought of using that Y rails sitting on top idea... it makes sense, not sure why I switched to underneath the table rails way!?

  9. #9
    Join Date
    Jul 2018
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    6254

    Re: One more DIY first born CNC

    Hi F8 - Designing something is cyclic and you have to be prepared to go around many times to get to where you want to go. Everything is connected so changing one thing could mean changing everything.

    You do need to write down some objectives so you can review against these as you go. Birch (or any plywood or MDF) not being as stiff as metals means that any long flat piece needs a transverse web on it to make it stiffer. Making boxes is even better. I'd also encourage you to make the bench from ply. The extrusion will take you down a certain pathway and is expensive. The birch is more flexible in terms of design and will be as stiff as the extrusion or stiffer. Look up pocket hole construction and glue everything together. Seal with PVA glue mixed with 1:1 with water, say 4 coats or more. It's a very fast way to seal the wood and glue the joints and looks good.

    If you mix al and wood in the bench they will move at different rates as the air moisture changes. So stay with ply for the bench. Use thread inserts to create a grid of hold downs. See photos attached of Scoots bench, they are a 200mm grid of M8 timber thread inserts. Has worked very well and is low cost. I get the inserts in 100's from china vs local ...Have fun... Peter

  10. #10
    Join Date
    Mar 2003
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    35538

    Re: One more DIY first born CNC

    Q1) Most would say that 1.5x1.5 is much too small. Not anywhere near overkill.

    Q2) With round shafts and open bearings, shaft up is the preferred method. If mounted horizontally, the loads are only carried by half of the bearings. But with a small, lightweight machine like this, it probably doesn't matter much.

    Q3) AS long as you can grease them, you don't need any other access.

    Q4) No, not too heavy at all. Weight is not a bad thing. My recommendation would be a torsion box, with 3/8 or 1/2" baltic birch skins. It won't weight too much more, and will be at least 10x more rigid.


    My advice would be to just build it and use it. You'll then find out pretty quickly what needs to be better, when you build the next one.
    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)

  11. #11
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    Dec 2003
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    1206

    Re: One more DIY first born CNC

    I created a quick and fairly rough model to illustrate what I was trying to describe earlier.It does occupy more space and that might be a problem for you.The other thing I did was to leave out the upper horizontal tie-jut below the table-so the parts can be assembled.the other element can be added later,if needed.

    The advice to consider torsion box construction is good and it gives a place for the cables to run.Just be sure you have sufficient access to position any nuts and thats a subject that could embarrass me if asked for details....

  12. #12
    Join Date
    Dec 2014
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    640

    Re: One more DIY first born CNC

    Here's the inside of my gantry beam. The internal structure interlocked so it was easy to align and glue together...

  13. #13
    Join Date
    Jun 2011
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    692

    Re: One more DIY first born CNC

    Right now it looks as if your table will only be connected to the long rails by the 4 corners. They need to be much more tightly coupled. Right now, picture how much flex you would get if the spindle pushes down in the middle of the table. The table will flex down, and the long rails will flex up. When milling with a spiral flute bit the problem will be the opposite, and will pull into your workpiece. Probably not a big problem on wood, but you may find your cut depth varies depending on how far from the corners the cut is and how heavy the cut is.

  14. #14
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    Jun 2009
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    13

    Re: One more DIY first born CNC

    Peter
    Agreed on the cyclic characteristic of machine design. When I started this thread I was at my 3rd redraw from scratch. That's what I love about designing on a computer, you can start over and over, you can build what ever you imagine and all of that without producing any scrap! I remembered why I didn't stick to the "high Y axis" idea and that's because I have only one lead screw. I'm now evaluating the possibility to have a fix gantry and possibly with the X axis longer than the Y. I tried it with a moving gantry setup but it couldn't make it effective to see an advantage to it.
    I didn't think about writing down my objectives! That should have been step 1 and I'll be sure to do so before going any further.
    Like I said in the initial post, I'm well equipped to do woodwork. I've been intensively working wood (as a hobby) for the last 5 years or so. I'm not a fan of pocket screws but in this case, you're right, it would be a great application for it. Considering temperature movements is another great advice, another thing I didn't think off. Your sale's pitch for ply is on point!... and I'm totally okay with low budget projects.
    Thanks again for your help.

    Gerry
    A huge THANK YOU! to you Sir. There's someone who gets me! Bullet points answers to my bullet points questions. What more can I ask for?
    All answers are noted and well received and appreciated.
    Your advice is (in my case) the best you could have given me. I improved a lot over the last few years but I always had a tendency to leave many projects unfinished. But that's why I'm here: finish what I started. Short time... long time... it's all a matter of perspective I guess.

    routalot
    Yeah that's what I finally understood. That's good stuff!

    fretman_2
    That looks massively solid! Thank you very much for sharing!

    skrubol
    The images were there to illustrate my questions, but thanks for the pointers, it's valuable information

    Heading back to the drawing board
    :cheers: all!

  15. #15
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    Jul 2018
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    6254

    Re: One more DIY first born CNC

    Hi F8 - To improve the stiffness of some of your parts consider laminating the plywood with aluminium. This is easy to do with contact cement. Unless you are familiar with epoxy gluing aluminium, which can be difficult, use contact. Cheaper than epoxy and very easy to do. For instance the Z Axis plate needs to be stiff. If you use 3/4" ply with 2mm aluminium skins this is equivalent to a solid 17mm thick aluminium plate! This is very substantial for your machine. Aluminium laminate is easy to work with normal wood working tools so you are OK with that.

    If you go this way you can use MDF as its much cheaper than ply and it's still the same result. Low budget does not necessarily mean low performance. Cheers Peter

    A fixed gantry is inherently stiffer than a moving gantry. But it takes up twice the footprint. If the machine is small and you have the space then a fixed gantry is the go. Machine performance is about rigidity and rigidity should be the guiding light of the design. Every step taken in a machine design should be towards more rigidity.

  16. #16
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    Re: One more DIY first born CNC

    Quote Originally Posted by peteeng View Post
    To improve the stiffness of some of your parts consider laminating the plywood with aluminium... For instance the Z Axis plate needs to be stiff. If you use 3/4" ply with 2mm aluminium skins this is equivalent to a solid 17mm thick aluminium plate! This is very substantial for your machine.
    Thanks again Peter.

    I love to learn stuff like this!! It looks so simple when you know about it but the first discovery is so exciting!
    I'd be curious to know from where are we starting from? What is the "stiffness" value of the ply (or MDF) alone without the AL laminated to it?

    Would it be worth to laminate both side?... or to core the beam with aluminium, (ply-al-ply)?
    Can I use steal instead of aluminium? Oooohh! you got my head running!(flame2)

    Cheers

  17. #17
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    Sep 2005
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    1740

    Re: One more DIY first born CNC

    Instead of re-inventing the wheel you need to look at some successful builds. Ericks is one example. Your Z is way out of proportion to the rest of the machine. Instead of laminating plywood to aluminum with contact cement which is fine for counter tops think about using heavier aluminum extrusions. Wood or MDF expands and contracts at a different rate than aluminum. Or make the frame from steel.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP

  18. #18
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    Re: One more DIY first born CNC

    Would it be worth to laminate both side?... or to core the beam with aluminium, (ply-al-ply)?
    You MUST do both sides, in effect creating a torsion box.

    A wood torsion box will do the same thing, and be easier.

    Here's my gantry beam, with 1/2" baltic birch skins.
    https://www.cnczone.com/forums/cnc-w...html#post67929

    And my table, which uses 1/2" MDF skins.
    https://www.cnczone.com/forums/cnc-w...html#post67933

    Both still stable and flat, after 14 years.
    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)

  19. #19
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    Jun 2009
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    13

    Re: One more DIY first born CNC

    Quote Originally Posted by wmgeorge View Post
    Instead of re-inventing the wheel ...
    I'm not trying to re-invent anything but nowadays there are so many wheels to choose from! I'm just a little overwhelmed with all the options including those I didn't knew about.
    But I humbly get your point: "Keep it simple". A good reminder is always appreciated and I surely need to keep this one in mind. Thank you for it.


    Quote Originally Posted by ger21 View Post
    You MUST do both sides, in effect creating a torsion box.
    A wood torsion box will do the same thing, and be easier.

    Here's my ...
    I went tru the thread you shared with my eyes wide open. You've made a really nice machine... and the result samples are just extrodinary! I'd be extremely happy to be able to get similar results.


    Doing my best to provide updated sketches soon, stay tuned.

  20. #20
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    Jul 2018
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    Re: One more DIY first born CNC

    Hi F8 - It's your first machine so KISS. To clarify the Al/timber/Al construction. MDF has a stiffness of about 3MPa. AL is 70GPa. F17 plywood is about 14GPa which is about birchs stiffness. You mention putting AL in the centre of a laminate, this does not work. A stiff skin has to be placed on the outsides of a less stiff material to make a "sandwich". There is no bending stiffness benefit in MDF/AL/MDF. Sandwich construction is a bit more technical than monolithic or solid construction so stay with solid for now. Sandwich construction using contact cement is far more sophisticated than just for benchtops. There are many buildings and vehicles held together with the same technology. But using KISS keep in the one media; timber, aluminium, steel etc do things your comfortable with but step out a little as well. Boxes are many times stiffer than flats so use boxes. Cheers Peter S

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