1. #1
    After happily reading on another cnc forum that with a bit of cardboard and gaffer tape and a spare 20 minutes I could make a 27-axis robot that would cut me a QE2 sized spacecraft out of tungsten carbide, I decided to come here for a bit of bubble bursting by Jazz and Jonanthan (i'm calling you out sirs...)and the likes.

    Much to my girlfriend's pleasure, I am now living, breathing and sleeping CNC build logs. She now knows what backlash is and why a lovely ballscrew is going to bring more pleasure into our lives than some rubbish holiday to the Carribean (on a side note: she is still finding 'flanges' genuinely funny...be they on bearings or nuts). I think its the way I have decided to use the one and only telly in our flat as my big screen monitor for reviewing designs (extra few inches always helps)...its helped speed up the immersion process. I know when she says she will leave me and hopes I get splinters in my bits, its her way of showing support. (Does anyone have the g-code for Kelly LeBrock (circa 1985) as a back up?)

    Right...so MDF out. SHS and RHS in. I can't weld so I want to go for epoxy/bolt fixing. I would invest the time and expense to learn but I don't have a suitable shop to weld in so its not the most productive investment at this stage.

    I would like to look at a cutting area of 1m*0.5m but that is just an inital thought rather than a fixed requirement. I feel that will get squeezed down somewhat. I predominantly want to work wood to make toys and design items but the ability to stick a weeny bit of aly in there once in a blue moon would be great.

    Now..much as I hate to, lets talk money. I've got none. Near enough anyways. What I would like to do is first work on the frame before putting in orders to Chai and Zapp. I'd sooner spread the build over time and save up for parts that are somewhere close to doing the job rather than buying a load of cheap stuff that will soon be ready for scrapping.

    So onto my initial lines of enquiry...mainly regarding the relationships between your frame and your finished machine.

    What are the best/worst amounts of useable space people end up with as a proportion of machine size?

    How true must the frame be? Can I make up for small inaccuracies in the frame via the positioning of my rails?

    Why do people so often go with tallish gantries rather than building up the sides of the frame and running a much flatter gantry?

    If I commit to building a certain size frame, am I commited on what length of rails and screw to use? I assume that not using the full length of frame for x-axis wouldn't present too much problem. But how about y? Would I need to span the full distance between the x rails or could I leave gaps on either side? e.g. a gantry that is 50cm wide but with 30 cm of rail? Essentially I'm asking to see if I can get away with making my frame to an approximate size, then buy screws and rails off the shelf that are close in size and mount them? Or should I have precise measurements before starting? Reason being, I would quite like to have fun gluing bits of steel together in the near future but I can see that designing a whole machine will be a very lengthy process.

    Any advice appreciated. Flame away.

    Thanks,

    Andy

  2. #2
    Quote Originally Posted by andy586 View Post
    After happily reading on another cnc forum that with a bit of cardboard and gaffer tape and a spare 20 minutes I could make a 27-axis robot that would cut me a QE2 sized spacecraft out of tungsten carbide, I decided to come here for a bit of bubble bursting by Jazz and Jonanthan (i'm calling you out sirs...)and the likes.

    Much to my girlfriend's pleasure, I am now living, breathing and sleeping CNC build logs. She now knows what backlash is and why a lovely ballscrew is going to bring more pleasure into our lives than some rubbish holiday to the Carribean (on a side note: she is still finding 'flanges' genuinely funny...be they on bearings or nuts). I think its the way I have decided to use the one and only telly in our flat as my big screen monitor for reviewing designs (extra few inches always helps)...its helped speed up the immersion process. I know when she says she will leave me and hopes I get splinters in my bits, its her way of showing support. (Does anyone have the g-code for Kelly LeBrock (circa 1985) as a back up?)

    Right...so MDF out. SHS and RHS in. I can't weld so I want to go for epoxy/bolt fixing. I would invest the time and expense to learn but I don't have a suitable shop to weld in so its not the most productive investment at this stage.

    I would like to look at a cutting area of 1m*0.5m but that is just an inital thought rather than a fixed requirement. I feel that will get squeezed down somewhat. I predominantly want to work wood to make toys and design items but the ability to stick a weeny bit of aly in there once in a blue moon would be great.

    Now..much as I hate to, lets talk money. I've got none. Near enough anyways. What I would like to do is first work on the frame before putting in orders to Chai and Zapp. I'd sooner spread the build over time and save up for parts that are somewhere close to doing the job rather than buying a load of cheap stuff that will soon be ready for scrapping.

    So onto my initial lines of enquiry...mainly regarding the relationships between your frame and your finished machine.

    What are the best/worst amounts of useable space people end up with as a proportion of machine size?

    How true must the frame be? Can I make up for small inaccuracies in the frame via the positioning of my rails?

    Why do people so often go with tallish gantries rather than building up the sides of the frame and running a much flatter gantry?

    If I commit to building a certain size frame, am I commited on what length of rails and screw to use? I assume that not using the full length of frame for x-axis wouldn't present too much problem. But how about y? Would I need to span the full distance between the x rails or could I leave gaps on either side? e.g. a gantry that is 50cm wide but with 30 cm of rail? Essentially I'm asking to see if I can get away with making my frame to an approximate size, then buy screws and rails off the shelf that are close in size and mount them? Or should I have precise measurements before starting? Reason being, I would quite like to have fun gluing bits of steel together in the near future but I can see that designing a whole machine will be a very lengthy process.

    Any advice appreciated. Flame away.

    Thanks,

    Andy
    Ok Andy, Welcome to the forum, Its nice to see someone who has been doing their homework on the dynamics of the site. Its plain to see you have been reading large amounts of posts/Threads. The thing is, Usually people submit a design and watch it evolve with lengthy constructive, and sometimes not so constructive debate.

    When you arrive at a design, your build will progress at a speed dictated by you and your ability to produce/procure the parts you need based on your finances and spare time.

    If you wish to machine ali then the design will be based on that, with the side effect that the machine could be used for other materials like MDF but as i have found out, a multi purpose machine will present its own set of challenges, and with that comes extra expence.

    If you are only going to be machining the odd bit of ali here and there why dont you just get the guys who have ali cutting machines to do it for you, and build a better wood machine.

    Just My Opinion though.

    Rick
    Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln

  3. #3
    Get your umbrella out because it's Bubble bursting time.!!!!!!!!! . . . It's "Flange" not "Flanges" but must admit "Flanges" are much more fun to slap your nuts on. Don't worry Jonathan won't Flame you regards your Flanges he's no experience in this area he's never been near one . .

    Welcome Andy

    Your plan to build frame first before buying rails/screws etc is actually a good idea and something I tell people to do if they can wait.
    Often I see people order screws & rails etc then set about building frame while they arrive only to find they either built the frame too short/narrow or vise versa much too long/wide. Often they will buy screws too long and rails too short realising if the rails where just that bit longer they could use all the screw.!!
    Doing it your way then you'll know exactly whats required has you can measure direct off the frame.

    Best advise is make a clear plan and stick to it. Pick a cutting area that is reasonable and don't chop and change.
    Drawing in Cad is good for giving a general idea of the machine and to see if things catch etc but don't get carried away, Better to do it rather than not has it can highlight things you wouldn't other wise see but taking it to the emph degree just wastes time so just use it to rough out the design.

    The single most important area of the frame are the Rail mountings. If you build in some adjustment for the rails then they can be shimmed and tweaked into alignment or parallelism without too much problem. The bed can be surfaced flat and true after it's built and so long has the rest of the frame is some where near square and true then you'll be fine.
    Very important is strength and ability to resist resonance. Resonance is the enemy of finish quality so anything to reduce it helps.

    Reason you see tall gantry sides on wood machines is because it leaves the bed relatively free for loading from all sides where has tall sides limit loading material from front or rear.
    To be honest on Wood machines then it's not really a problem having tall-ish gantry sides has it doesn't need to hold high tolorences compared to machine for harder materials like Aluminium. Obviously there's a limit just like having too much Z axis extension will affect quality of finish but so long has they are strong and well braced tall gantry sides are ok for wood.

    Slowly slowly will always workout better than rushed so take your time and keep your eye out for bargains, they do come up.
    That said don't rush out and buy the first thing you see, esp on the electronics side. Check back here and ask questions before you buy if just 2% unsure.!

    Good luck.

  4. #4
    > Does anyone have the g-code for Kelly LeBrock (circa 1985) as a back up?

    I doubt many have machines beg enough for that. Those. Whatever. Anyone else reminiscing over the designer-a-bird scene in Weird Science ?

    Adrian.

  5. #5
    Thanks all for your replies.

    Rick...you have a good point about outsourcing aly jobs if demand isn't frequent but I think I'm prepared to go the extra expense and time with the build if it means i can keep as much possible in house once i'm finished. I have seen some of the parts people have produced here and have been absolutely blown away by the quality. I certainly might try my luck with the fine folk here for the occasional part when it comes to the build itself.

    Jazz...you don't disappoint. I will work on frame first and then order rails and screws. I'm fixed on my cutting area (1m x 0.5m), just enough for what I have in mind. My first designs are still on the back of an envelope at the moment so some cad is definitely in order. Regarding rail mountings, is there any SOP for incorporating adjustment? I had a look into epoxy leveling too (i saw a guy building a dam on each side...could you build it all the way round so the two sides are level in relation to each other?) Thanks for clearing up gantry thing...it actually made me reconsider where my machine will eventually be sitting. I've also quadrupled my build time so I can spend a bit more too...just need to break it to the other half...i'm sure it will be fine

    Adrian...i have a very sad commodore 64 somewhere...it regrets the day i ever saw that film, as did the antiquated wiring system we had at home.

    I have a few more questions if anyone has any thoughts...

    How does aly box section fare as a frame material? And something like durafix to hold it together (presumably less warping issues than welding steel as the temps are lower?)?

    Y and Z axis conventions...forgive me if this is covered elsewhere and these questions seem silly...I need to break it all down before I can build it up in my head. Why always have the y axis rails one above each other with the z axis on the front? Could you not have the y rails at the same height with the z axis travelling between them? And then finally, the Z-axis itelf, similar thing with y, could you not mount so rails/bearings are opposite faces rather than both next to each other on same face?

    Thanks again.

    Happy CNCing!

  6. #6
    > durafix to hold it together (presumably less warping issues than welding steel as the temps are lower)

    I've had some success and some failures with durafix type rods.

    I did try and "weld" some 3mm sheets together to make up a model tank hull, but the time it took to get the area up to the right temperature meant I ended up with some warping.

    I was using a MAPP torch, as that was the hottest heat source I had available. In future I'm going to stick to getting things professionally MIG/TIG welded for taht sort of thing.

    Adrian.

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