New Machine Build Help a Newb Build an 8x4 Machine ????


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    Default Help a Newb Build an 8x4 Machine ????

    Hi All,

    I’m new here, given myself a 2 week crash course with a 3018, done 4 jobs, now ready to build a decent size machine. I only learn by ‘doing’, so in the deep end suits me fine.

    I have in my workshop an 8x4 welded steel table, I use it for all sorts, the idea is for the CNC machine to be suspended from the roof when not in use, and lowered onto the steel table when I need it.
    I will make the CNC frame height adjustable from the steel table, so I can raise or lower it depending on the height of the work piece.

    I’m planning on mostly using it for cutting wood. For example, my next job is to build 2 pairs of Oak Gates, 85mm thick, 1750 wide, and big curved top rails, usually id cut this out on the bandsaw, hand plane, belt sander.. but it’d be a lot easier if I could spit these out on a CNC..
    I also want to be able to load 6x6, 8x8, 10x10 etc Oak Beams for shaping, cutting mortise and tenons, engrave, etc..

    I’d also like to use it for Laser’ing stuff.. And cutting metal, mostly Alu, possible steel sheet too if I can?!

    I have a bunch of questions.. If you’ll humour me..

    1. Control Box/Board
    Iv had a look and only seen really cheap eBay stuff or really expensive.
    Can I run a £20 GRBL(or similar) board with a big machine? I’m not entirely clear on the drivers, breakout boards, etc, and what board they work with, and what steppers I’d need.
    The computer side of things is where I really struggle. Been using Onshape CAD. Tried MeshCam, don’t like. Using Easle CAM now. Used GRBL Goode sender or whatever it is. Also DLd UGS but could get it to load my file. I’m looking for simple, idiot proof, no bells or whistles.

    2. With target of machinable area of 8x4, I’m hoping a 1500mm leadscrew will be ok for the gantry. I’m assuming 2700-2800mm is to long for an unsupported leadscrew, or is it possible? How fat would it need to be not to defect and/or whip? What’s the alternative, rack and pinion?

    3. What’s the best type of linear motion rails? I’ll probably be going eBay for these, Round SBR20 or SBR25, or, HGR Series 20-25mm?

    Any help would be very much appreciated, try to hide your laughter ????
    Thanks
    LondonBoards

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    Default Re: Help a Newb Build an 8x4 Machine ????

    I've never seen a setup like you describe, where the CNC parts hang from the ceiling until you want to use them. It sounds like you'd have problems getting everything to work right each time you did that. Maybe if there were solid bolted connections that were repeatable you could make it work, but it seems that if I had a rig like that I'd probably tend to leave it in place rather than go through all the trouble of re-connecting everything each time.

    It also seems that for the sort of projects you're talking about, conventional woodworking equipment like tablesaws, bandsaws and chisels, etc. would be faster and work better than CNC. Remember that with a router table, you can only work on one side at a time, but for putting tenons on beams you want them positioned end-up. With fancy engraving and carving, you're more in the realm of where CNC router save you time.

    All the GRBL setups I've seen have been low-powered, suitable for smaller machines perhaps, but nothing as large as the one you're proposing.

    Take a look at DeskProto for simple, powerful CAM intended for non-machinists.

    Lots of machines use ball screws over an 8 foot span, but they tend to be fat ones. However, rack and pinion is a viable alternative.

    The HGR type of rails, with a basically square shape, are vastly superior to the round rail type.



    Only the most solid CNC routers can do an effective job on aluminum, and none of them cut steel well.



    Laser cutters are entirely different machines that only superficially resemble CNC routers. Most importantly, they are totally enclosed with eye-safe material and won't fire until the doors are closed and it's safe to do so. I know there are videos of people who strap a laser onto their CNC machines, but people do lots of stupid stuff on the internet.

    Andrew Werby
    https://computersculpture.com/


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    Default Re: Help a Newb Build an 8x4 Machine ????

    I use a cnc router for my mortise joints and they are absolutely perfect. Nothing compares. Also use it for anything that needs to be repeated or is round. It gets used in my Joinery business about as much as my spindle molder.

    Totally agree with the last post. It took me a whole bunch of work including a whole new Z assy before I could be honest and say I can mill alloy properly. Especially accurately as it does not have a +/- 0.25mm tolerance that timber does.

    I say build it. And you will see for yourself it's not the best idea to dismantle and raise. But..... do build it. And lots of help here when you get stuck.

    Oh. And I use a very cheap breakout board and apart from the lack of about another 3 or so inputs can't fault it. B

    Sent from my SM-N970F using Tapatalk



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Quote Originally Posted by awerby View Post
    .
    Quote Originally Posted by boydage View Post
    .
    Thank you both, much appreciated.
    I can assure you it will be firmly fixed each and every time I come to use it. My workshop is a reasonable size but I can not afford an 8x4 area to be solely for this machine. I’m confident in making it firm, thats one thing I’m not worried about.

    You’re right, Andrew, I probably could do my Gates job quicker and cheaper by hand factoring in the costs and time to build the machine, but I only need to build the CNC once, I’ll find more and more uses for it.
    I probably wouldn’t do things like tenons, I have an old Wadkin Spindle Moulder with a custom fitted Axminster sliding table, custom made spindle and rebate block with flush top, so I can smash out a 5inch wide tenon in seconds.
    Id like to get away from doing site work and do more workshop work, my knees are fu bar’d.. I have a ton of ideas I want to machine, so it’s definitely worth the initial setup. designed a shelving system which I could smash out 8x4 sheets of components in an hour rather than days on the bandsaw + sander, less time, less consumables, less dust, less wastage, more profit.
    I’ll probably CNC my old Myford Lathe too after this project..lol

    So, just to clear up a simple thing, is Breakout board and Control board the same thing?

    Which Board do you use Boydage?

    I need to decide on what size steppers I need, and drivers, etc. Obviously there is variables that dictate the specs, is there a calculator online somewhere or a document on how to workout what I need?

    Do Rack and Pinion systems use the same Steppers as Leadscrews?

    Thanks chaps



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    Default Re: Help a Newb Build an 8x4 Machine ????

    That does sound like the right tool for tenons, but I agree, you'll probably find a lot of uses for your CNC once you get going with it - so much so that you won't be boosting it up to the ceiling too often.

    No, a breakout board is just one component of a controller, which can consist of one or multiple circuit boards. All it does is give you terminals for your logic functions. Actually doing things with the signals and outputs is the function of the controller, which can host the drives, generate analog signals to control the VFD, use logic signals from software commands to do work like triggering relays, and similar things. The BOB is just a pass-through.

    To choose your steppers, figure out how much torque you'll need at what speeds, and look up the torque/speed curve of the motor to see what it will deliver. Don't just go by the holding torque (the most common number you'll see advertised) since that's measured when it's standing still, but torque falls off rapidly as the motors go faster. Make sure that the voltage required won't kill your drives; this usually favors motors with less inductance.

    Yes, R&P systems can use the same steppers,as ball or leadscrews, but they may need to go faster or provide more torque at a given speed, depending on how the threads and teeth compare.. If you're going with R&P you need to figure out a way to preload the pinion against the rack, that's the main mechanical problem they face.

    Andrew Werby
    https://computersculpture.com/


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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi Andrew, thanks for taking the time to reply. Iv done a few more evenings of reading/youtubing, there is so many variables I don’t know where to start in spec’ing the components, so many articles and videos are contradictory of each other it’s hard to know who to listen too.
    I’m yet to find a proper guide in working out all these variables. More reading required.. unless someone fancies telling me what I need..lol



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    Default Re: Help a Newb Build an 8x4 Machine ????

    The smaller and more specific your question, the more likely you are to get a useful answer.

    Andrew Werby
    https://computersculpture.com/


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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi Andrew, I shall bare that in mind.
    Iv decided to scrap the adjustable hight mounting method I had planned, and decided to make end plates for the gantry to be adjustable. I’m designing it to have 250mm Z axis travel, so I’ll be able to machine 8x8” beams and be able to get all the way down to base board, and still have room to adjust up or down.

    Iv been trying to workout Ballscrew sizes. I’d like to use Non Captive steppers, Idea being the stepper is fixed to Y axis gantry plate, ball screw clamped tight at each end.. but, I can’t find any steppers big enough, or fast enough, or that have the correct ball screw internals.
    I’m thinking 25mm ball screws for the Y axis, if they whip, I’ll just have to go slower. The cost gets to crazy to go bigger.



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    Default Re: Help a Newb Build an 8x4 Machine ????

    I need to workout the following..Ball Screw Pitch, Stepper Motor Spec, Drivers Spec..

    How do I work this out? Is there a guide somewhere on how to equate the variables?

    Considering the Ball screws are going to be 2600-2700mm long, am I better off with a 10mmPR pitch, rather than a 5mm pitch? ie spin the shaft half the speed to achieve same travel.
    Would this affect accuracy? If so, how much? Negligible amount or considerable?

    Also, I’m now going to make it fully welded steel construction. I want the rigidity/accuracy.
    On the fence whether to get a auto tool change Spindle, or maybe just upgrade to one in the future. Will have to see how my budget stretches.



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    Default Re: Help a Newb Build an 8x4 Machine ????

    All these things - Ball Screw Pitch, Stepper Motor Spec, Drivers Spec. - are interdependent. Start with a high-quality driver that can tolerate significant voltage, since that's often a limiting factor. This isn't the place to save money; better drivers cost more than crappy ones. Look for motors with low inductance, since high inductance will keep them from achieving their top speeds.

    If you're worried about screw whipping, then yes - spinning them slower cuts down on that. But it sounded like you wanted to go with a fixed screw and driven nut. This is a rarer configuration, but I've seen it done. I'm not sure who supplies the hardware, but above a certain size you don't see self-contained ball screw/stepper combos; look for a belt-driven nut assembly to bolt to your moving stage.

    Welded steel makes a lot of sense, but be careful to constrain the parts as much as possible and avoid overheating any one area to keep things from warping too badly.

    Andrew Werby
    https://computersculpture.com/


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    Default Re: Help a Newb Build an 8x4 Machine ????

    That’s a great idea, Iv just had a quick look at driven ball nuts, they are expensive to buy, but easy enough to make. Most are smooth for flat belts, I’d like them with teeth/notched belt, or better still, mechanical gears. Either way, it’s very much a route I’m going to explore.

    What can you tell me about target feed speed? 30mm/sec has been said online for hardwoods, I’d like to be able to go that sort of speed, but also double that for when I’m removing less material or working with softer materials.

    Obviously I’ll need to work out gearing of whatever pulley system I end up with. I’m still no closer to working out what speed/torque motors I’ll need though.



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi London - If you weld the steel frame be prepared to have it machine true. Its unlikely a welded structure will be flat and level after welding. There are many threads here that work through the build process. I suggest you find a couple of those and read them through. 30mm/sec is 1800mm/min. This is slow for some machines fast for others. My M23 motors with 10mm pitch can cut timber at that speed easily and its only got a 600W spindle. Your on a steep learning curve. Peter



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi Peter, thanks for your thoughts, I take on board what you’re saying about a flat bed, I’ll do my best, I have a Fab shop behind my unit, they have a big engineers flat table I can use, hopefully be good enough.

    Just done a quick sketch of how I envisage this layout.. I couldn’t be arsed with anymore detail at this stage so excuse the primitive sketch.

    Attached Thumbnails Attached Thumbnails Help a Newb Build an 8x4 Machine ????-72b0e7d0-a408-46d3-a07a-deb4eeb099a1-jpg  


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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi London - Doesn't matter how flat the welding table is, welds shrink and frames move.... find out if there is a heat treater nearby that can stress relieve it. Then you will have to finish machine it (with or without SR) Peter



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi London - You have your gantry mounted on angle iron. This will twist and vibrate. Keep working at it and drop cutting steel form the wish list, maybe AL as well. Peter



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi Peter, angle iron Iv drawn is 100mm x 100mm x 14mm, in reality, I think 12mm thick will suffice. 12mm stuff is tough as hell, welded to the legs every ~500mm or so.
    Idea of the angle iron was to try and keep the ball screw protected from debris, it would make for an easier design if it was 100mm box, and box is cheaper than 12mm Angle.

    Regarding motor Spec. If most setups are direct drive with stepper at end of ball screw... And if I use 1:1 gearing from stepper to driven ball nut.. I can assume calculating the speed will be the same. I’m unsure how torque is affected with this setup. Whether I use belt drive or mechanical gears will have a bearing on this aswell maybe?

    If my gantry ends up being around 200kg, and I want to be able to machine 3500mm/min, using a 2005 ball screw, with double back to back ball nuts spring loaded, running on Hiwin blocks, how do I calculate what motors I need? And what drivers?



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi London -100x100x14 is very sturdy but still may vibrate. If your feed is 3500mm/min and your pitch is 5mm then the motor is doing 3500/5= 700rpm. This is near a point with a stepper of no torque. You need to look at the torque /rpm curve to determine if the motor can do what you want. Steppers lose torque linearly from 0rpm (stall torque & max torque) to about 1000rpm or less. Hybrids do a little more torque above 1000rpm but say you use the biggest N23/N24 motor with 4Nm of torque it will only have about 2Nm at 500rpm. I usually design systems at 500rpm. The sort of machine your talking about would benefit from using servos. They have a flat torque curve from 0-3000rpm. So you will achieve your feed of 3500mm/min easily and have a rapid of 3000x5= 15m/min which is a good speed.

    You will need support bearings to protect the motor from thrust. If you use belts or gears you also have to protect it from radial loads. By the time you go belts gears brackets space I'd look at servos. Re: box sections they are not flat enough or level enough to bolt rails to directly. The cars will jam. The sides are cupped or crowned. There's lots of threads that get stuck on this approach. Usually a flat bar is welded to the hollow section and that is machined flat. You may have the same issue with the angle.

    Hiwin publish the calculations for figuring out the loads created by ballscrews, also buckling and whip. Look at their site. 5mm pitch at 2Nm will move 200kg easily. Its the target acceleration that you want that will drive the motor size. Nema34 are commonly used but they can be slow due to their extra inertia and inductance. Biggest N23 or N24 will do fine for now... A 20mm ballscrew has heaps of inertia the motor will use half its torque accelerating the screw and half driving the system...Peter



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Quote Originally Posted by peteeng View Post
    You need to look at the torque /rpm curve to determine if the motor can do what you want. Steppers lose torque linearly from 0rpm (stall torque & max torque) to about 1000rpm or less.
    This is what I’m getting at, this is where Iv been struggling to spec the appropriate motor.

    Thank you for taking the time to explain this, exactly the sort of info Iv been after, very much appreciated.

    Going for a read up on servos now, I get what you’re saying about the thrust, I thought about this being a problem last night when I went to bed.. yes the rotation of the ball nut will give me linear movement, but how do I retain it and stop it flapping in the wind, a belt would flex, gears would un-mesh.
    A non captive motor would certainly make life easier.



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi London - I'm not sure what you mean by a non captive motor. The usual workflow for machine design is 1) decide the working envelope you need 2) design the structure and bearing system to the stiffness you need 3) Now you know the weight of everything 4) Now you can add the drive system, which usually means shuffling some of the structure to get stack heights of support bearings and motors and rails etc correct 5) now you can address the required pitch to achieve your target feed speeds and rapids 6) from this you can calculate your screw diameter to check it does not buckle or whip 7) Now your close to reviewing what you have and you move to Round 2 and then refine what you have 8) you go through Round 3 polishing what you have 9) you finalise the design. But if your thorough you will have about 10 Rounds at the task maybe more. Peter

    Look at Asian servos they are a reasonable price and will perform so much better then steppers. Its an area that is worth the $$$ spent.

    If your screws are 2700mm long they will be large. Gravity is your enemy here and a mid support can save the day. Its a plastic block that can move out of the way as the nut goes by. This block stops the screw from sagging which is the initiator of the whip. If the screw does whip the block dampens the motion. There's a few examples of this strategy in the forum... and don't place it dead middle as then you are at a node and the screw can move in a second order wave. Place it at 60% say or use 2 uneven supports

    If you remove steel and Al from your list then consider belt drives, a 25mm belt will do the job easily, no concern over length and will run very fast compared to big ballscrews as they have hardly any inertia....



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    Default Re: Help a Newb Build an 8x4 Machine ????

    Hi Peter,

    Screen shot and link below is what I mean by non captive motor. These particle ones range from 460N to 900N force(assuming they mean Nm), that’s wildly different to the 4nm and 2nm you quoted in your example. These ones only cater for small dia screws, so not sure they’d be suitable at all.

    https://en.nanotec.com/products/2916...-actuator-la56

    I am beginning to rethink the Driven Ball Nut route.. Just seen/heard the noise a 5mm pitch ball nut makes spinning to achieve 1500mm/min.

    Will investigate belt drive..lol

    Thank you again for your detailed replies.

    Attached Thumbnails Attached Thumbnails Help a Newb Build an 8x4 Machine ????-b2876be1-7754-4104-a193-e268dde65bb9-jpg  


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