New Machine Build DIY regrets


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  1. #1
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    Default DIY regrets

    Hi all,

    What would you change about your own builds? I'd love to learn from mistakes made, best way to learn IMHO. I will continue my research of course but there's no substitute for reports from the coal face as it were.

    It has been my experience that no matter what project I'm working on, I end up finding things I'd do very differently if I started over. It just so happens I've begun the journey into making my own CNC Laser. So far I've decided that I need the power of a CO2 unit for cutting at decent feedrates, and all the optics that implies. Next is to decide on the type of linear rails. V-slot, guide/carriage (and sundry sub-types) etc

    I have an industrial laser cutting background so am very familiar with the larger scale machines, but of course building my own is a different thing entirely.

    Thanks in advance everyone. I appreciate your time if you're able to reply.

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    Default Re: DIY regrets

    Well i will chime in

    I have built 3 3d printers and a CNC Router from a kit by XZero CNC. I am as well building a Laser cutter and experienses from my previous builds are:

    Steppers are fine! REALLY they are. I love them om my 3d printers and also on my router. Provided with high quality drivers they are great BUT for a laser thats an other buisness entirely... if you are engraving using scanning method that is... My calculations tell me that in the extreme case of engraving paper with 150W laser you will need about 1200mm/s at 30% power. This is servo territory and hopefully the Laser source can handle switching at that speed. This is why RF is preferred over DC tubes ( of course also a lot of other reasons). On my build i am thinking of combining servos and steppers to keep cost down. Servo for the laser head and steppers for the gantry. So lesson one Steppers are good if combined with good drivers. High speeds - go for servos. I started with cheap drivers and learned the lesson.

    Belts are good if correctly dimensioned. They can cause vibration if the setup is weak but with a proper build they are great. they do require more horsepower however. as i built my second 3d printer i wanted to increase speed and had to increase the tension on the belts but the machine was to weak and axes where no longer straight when i had the desired tension on the belts. Ballscrews require proper installation and this is a lot harder than one might imagine as they deform easily. Align, align and align again. If done improperly they break, have non linear force curve and vibrate/shake at higher speeds. They also have a speed limit determined on quality and preload etc.

    Linear rails: I have had real Hiwin, Fake Hiwin, SBC, and THK setups and China knockoffs are crap. If you need linear rails with blocks chinese fakes wont do. V-slots etc are great if you want to go cheap but require big spacing resulting in a not so compact build but can take high speeds. Linear guides are not the best for super high speeds but normal and fast cnc machines are within the scope for what they can handle. Take note on different models though as preload and tolerances differ a lot between models.

    With all my builds i have had issues with the original and intended wireing. Bad wireing can do a lot of damage! (endstop switch not signaling -> crash or noise/crosstalk/inductive load killing motor drivers or other sensitive electronics. Always use proper cables and schielded wires where needed. Bad wires are one of the worst issues to debug and cause headache! And it is not fun ripping an entire machine apart jus due to cheapo cabels for next to no money saved.

    Align the machine properly from the beginning and take the time it needs to get it right. If you are doing any kind of precision work where pieces need to fit together, dimensional accuracy is vital.
    Tilting tables, twisted gantrys and machines not properly leveled cause wired issues and cost time and most of the time if it is not straight from the beginning - it never ever will be. Use rigid components to set up mirrors, properly schim everything to get it perfect. A straight machine preforms consistently. if not straight wired issues like "upper left is fine and lower right does not even cut" may occur.

    Monitor everything! Make sure you can control an monitor everything you need. Like for example cooling pump, airpressure, fireguard and supply power and place alarms for each! Safety equipment can often be built on the cheap and still work well but omitting them can cause your house to burn up. I have fillament monitoring and smoke alarm on my printers (which can take up to 24 hrs for one print) which has saved me a lot of time and money. On my router i have four E-Stop´s which all have come to good use in my novice days learning to handle the machine but also for unexpected events such as failing clamps... Be safe!

    My only current issue is finding out how powerful a servo needs to be to control my laser head on my intended machine...

    Still Learning..... :D


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    Default Re: DIY regrets

    Thanks for taking the time to reply Bx3mE. That's a great help. I'm in the process of design, and need to decide on steppers and mounting hardware, idlers etc.. Also belt orientation. I've heard people mention they get crap stuck in the teeth and I was thinking running the belt vertically may help debris drop away. When I can, I'll post a link to the linear rails I'm going with too. LGD6 if you care to google. I'm not at my usual PC. I'm aiming for a 40W laser and I was expecting 100mm/s would cover most of my hobby needs? Perhaps I'm way off on that one. More research required lol.



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    Default Re: DIY regrets

    I would not go for the lgd6 as for my taste i dont like the design with just one row of balls on each side of the block - it makes it sensitive to radial forces of the head no matter if you mount it vertical or not.

    On the belts i think it is smart to mount them vertically. I have them vertically in my 3d printer for that reason.

    100mm/s is not a problem if you keep your head light. and 40W will take you a long way. As long as you are not engraving photos, speed is rarely a problem for hobby needs. Adding some time to occasional jobs i think is fine if you get quality in return...

    While you are at the mechanical setup think twice och which bearings you use with the idlers. Some are noisy and imprecise. If you buy complete assemblys look at bearing dimensions and check if they are cheap to replace. and do yourself a favor and replace the right away with quality bearings.

    Be aware of bad belts to. there is a big differense in china belts and precision belts. If you need precision, correctly reinforced belts make a difference and are quite cheap.

    I know that saying look at quality components for every part will make a better machine in preformance. On the other hand, choosing cheap and low quality parts in the right places by doing concious choises will give you the performance you need at the best cost...

    What kind of controller are you looking at?

    Still Learning..... :D


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    Default Re: DIY regrets

    I have a DIY CNC router that was mostly a kit from EBay. The biggest regret was starting with acme screws instead of going with ballscrews. I tried several attempts at anti-backlash before switching over to ballscrews. Even with chinese ballscrews, I can drive twice as fast with 1/5 the backlash.

    My next regret is having unsupported rails. My X axis has two 42" by 1" diameter rails mounted 3' apart. They are tolerable, but I can flex them with a bit of pressure. The Y axis uses two 36" by 1" diameter rails about 5" apart that the Z axis rides on. It is super easy to twist the Z axis carriage because the Y axis rails are so close. I added a 3rd supported Y axis rail to prevent twisting and live with the X axis flex.

    Steve



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    Default Re: DIY regrets

    Steve, good to know about the unsupported rails. I intend to use a single short length (approx 20"/500mm) for the gantry axis. But it's a laser so there's less mass to shift around than a router.I know of commercial 3D printers using the same rails unsupported.

    Bx3mE, the rails in question: https://tinyurl.com/yctmxlcf . Not sure what you mean about the bearings. I don't like the available carriages anyway, so I'm making my own. Cuts down on weight when the carriage forms the gantry riser too IMHO. What feeds do you feel are required for photo etching?

    Cheers



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    Default Re: DIY regrets

    Haven't decided on a controller yet. I've had a look at Smoothieboards and they look ok, but haven't really looked into it thoroughly



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    Default Re: DIY regrets

    Quote Originally Posted by Blackened View Post
    Steve, good to know about the unsupported rails. I intend to use a single short length (approx 20"/500mm) for the gantry axis. But it's a laser so there's less mass to shift around than a router.I know of commercial 3D printers using the same rails unsupported.

    Bx3mE, the rails in question: https://tinyurl.com/yctmxlcf . Not sure what you mean about the bearings. I don't like the available carriages anyway, so I'm making my own. Cuts down on weight when the carriage forms the gantry riser too IMHO. What feeds do you feel are required for photo etching?

    Cheers
    You are correct that a laser might be OK with a lighter structure. Those rails can be fully supported if needed. Are you planning to use a single rail or a pair of rails for the gantry axis? If it is a single rail, then a small amount of bearing slop could allow the entire head to twist because the bearing surfaces are very close to each other. There isn't much force, but there is still inertia when the axis changes direction at high speed. They look like they would be great for the long axis when used in pairs.

    Sorry, no idea about photo etching.

    Steve



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    Default Re: DIY regrets

    Quote Originally Posted by Blackened View Post
    Haven't decided on a controller yet. I've had a look at Smoothieboards and they look ok, but haven't really looked into it thoroughly
    I've been running a k40 laser for about a year. One of the more popular upgrades is to change out the controller to one that will run gcode.

    I use a smoothieware compatible controller from Cohesion3d. They sell a drop in replacement board for the k40 but it can be used to run other lasers too.

    I don't run smoothieware since that firmware runs slow for raster engravings. Instead I use the much faster grbl-lpc firmware. It compatible firmware that will run on smoothieboard and clones.



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    Default Re: DIY regrets

    Quote Originally Posted by steve323 View Post
    *snip* Are you planning to use a single rail or a pair of rails for the gantry axis? If it is a single rail, then a small amount of bearing slop could allow the entire head to twist because the bearing surfaces are very close to each other. There isn't much force, but there is still inertia when the axis changes direction at high speed. They look like they would be great for the long axis when used in pairs.
    Steve
    Yeah was planning on a single vertically mounted unsupported rail for the gantry, with a pair for the main bed (also vertical). But now I'm concerned about play. I'm making the carriages because the existing ones have the bearings spaced too close together and won't be as stable as they could be. And also If I make the carriages, I can incorporate all mounting holes etc into a single piece to save on weight. Wasn't easy to find bearings. The 6mm radial groove needs to be very shallow so the rim doesn't run on the aluminium extrusion and only contact the hardened steel rails. The supplier (where I plan to get the rails) was extremely helpful when I told them what I was doing and gave me an offcut of the rail. I got datasheets online that don't agree in some of the dimensions to the real product.

    Double rails seem way overkill for this, so if a single one won't do, I'll have to consider alternatives.



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    Default Re: DIY regrets

    Quote Originally Posted by jfong View Post
    *snip*
    I don't run smoothieware since that firmware runs slow for raster engravings. Instead I use the much faster grbl-lpc firmware. It compatible firmware that will run on smoothieboard and clones.
    Oh that's great. So when I commit to hardware I still retain some software options. I didn't realize smoothieboards had other possible firmware



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    Default Re: DIY regrets

    I would definitly use long version of blocks for the gantry axis due to inertia as Steve implies. The head is likely to experience 5G when accelerating and decellerating. If you do the math you will see that for 600dpi you will need to do 600 passes per inch, for us metric people that is roughly 23000 passes every meter and if you bump the resolution to 1200 dpi you can double that to 46000. If you have a 50x50cm job you are looking at 23000 passes which are 50 cm long Your head will need to move atleast 5 cm outside that area giving 60cm travel each pass times 23000 equals close to 14km of head travel during the operation. You will need close to 4m/s travel speed to do this job in 1 hour not taking into consideration time added for acceleration and decelleration. That would be 150 ips. Of course this is not possible but more to illustrate what to expect. Anyone correct me if i am wrong! Checking in on epilog and trotec it seems they do 1500-3000mm/s on the gantry axis when scanning/photoengraving. For this reason i recommend servos.
    This is also why i prefer caged ball style linear guides like THK SHS Series.

    I am running Smoothie using a Azteeg board from panucatt devices with great sucess and the board has developed two versions since i bought mine. But you should be comfortable with computers to go this route as it requires skills to follow some guides on setting up the config files and possibly some linux tutorials to set up Raspberry pi with Octoprint and or laserweb to get a smooth solution.
    I have had stabillity issues with grbl firmwares but that might be my bad... Cohesion3d has been mentioned to me several tines but i have no experience.
    I have done this several times and it takes some long nights to get comfortable with and to set up good security with cooling and exaust fan but other than that is great.

    Still Learning..... :D


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