Page 3 of 4 FirstFirst 1234 LastLast
  1. #21
    Quote Originally Posted by brumster View Post

    These are really nothing more than stepper driver ICs, of which obviously there are a plethora out there with various ratings in terms of voltage, current, stepping capability and safety features. Bolted on to that are the relevant amount of heatsinking, protection/filtering but ultimately they take a low-voltage signal from a microcontroller or parallel port - with appropriate optical isolation - and move the motors as requested. One tick = one unit of movement (in the appropriate direction, of course).
    In simplistic terms yes but in reality then theres much more to good drives than this. How it handles resonance is very important and what makes the difference between poor and good working motors. Resonance cripples Steppers and the drive needs to be able to deal with this.
    Making your own is an option but not one I'd recommend and I've seen many people take this route only to end up buying drives after much frustration.


    Quote Originally Posted by brumster View Post
    You can get ones with direct parallel port drive (so no motion control; driven straight from PC) but then the honus is on the PC as the controller, hence all the requirements in terms of it being able to keep up. Each pin on the parallel port controls a function, which limits you somewhat to the number of axes/functions you can make use of.

    Other alternatively you can get drives controlled from a separate motion controller in between the drivers and the PC.
    Not exactly correct. You can get drives with built in Pulse engine so they don't need a PC Parallel port or External Motion controller. IE Stand alone
    People often get the wrong idea about how Mach3 or Control software works. The control software doesn't create pulses it plots a trajectory data based from G-code and then hands this to Pulse engine which then does the Motion control side of creating pulses.
    In standard trim Mach3 uses a Driver to do this function (paralllel port Driver) which then crunches some numbers and outputs the required pulses thru the parallel port to the drives directly (Usualy Via distribution board called a BOB).
    If using an External Motion controller then it hands the trajectory data to The Plug-in for that Motion controller. The controller then does all the number crunching and send the pulses to the drives. The difference being External motion controllers can crunch numbers much faster and output much cleaner pulse stream which makes BIG difference to performance and reliablty.




    Quote Originally Posted by brumster View Post
    When you guys refer to BOBs (Breakout Boards) you're generally talking about motion controllers, although you can get BOBs that combine both of the above.

    It strikes me that keeping them separate gives more flexibility as the drivers need to match the motors; if you get a combo BOB you'd need to be sure that the drivers side of it matched your requirements and they weren't going to change.
    No BOB is just a Distribution board for the I/O signals. Often Optoisolated for protection. Commonly you'll have Motion control board and connect to this 1 or more BOB's for Distribution of the signals.
    Better Motion controllers Like those from Cslabs provide direct connection and remove the BOB from the picture.

    BOB's, or should say Cheap BOB's are a common cause of many troubles with CNC machines and often under estimated to there importance.
    They take all the Signals then distribute them to where needed so if the components used are slow or low spec then any signals going out will be degraded or slowed down.
    Often you'll see people use External motion controllers with MHZ frequency capabilty and connect to BOB with 100Khz bottle neck components.
    Like wise you'll see drives with Max frequency of 200Khz and people using Ex controller with much higher Frequency capabilty connected to 100khz strangling BOB so all that power is totaly wasted.

    So what I'm saying is BOB is very important and while cheap works at the slower end it's pointless getting a External Motion controller for the speed and quality pulses and connecting to Cheap nasty BOB's.

    A Good machine needs to have a balanced system with no weak link.
    Last edited by JAZZCNC; 21-01-2016 at 11:06 PM.

  2. The Following User Says Thank You to JAZZCNC For This Useful Post:


  3. #22
    Thanks everyone; really good input. Got a good understanding now :) going to run some numbers tomorrow and come up with a "high level plan".... :D

  4. #23
    Right then!

    Dismissing the idea of a large, steel-constructed machine with serious aluminium milling capability. (1) I don't have the space to do it justice, (2) I strongly suspect a converted Bridgeport would be a far more sensible option.

    So I've downgraded to a desktop-sized machine, and I'll focus on doing PCBs with that. When I move house and have more space, I'll contemplate the bigger build. So I'll use the desktop as a learning exercise. Which leaves 3 flavours to go for :
    1) The aforementioned "bugger it and just get a Chinese 6040" for 900.
    2) Build something completely on par with the 6040 myself, like-for-like.
    3) Build an overspec 6040-like machine, mainly to learn on construction but also invested in the parts so they can be re-used on a bigger machine in the future.

    I've been bouncing around CNC4YOU and eBay today, making a spreadsheet up to price these.

    Option 1 we all know will do a minimal job, but I'll be replacing the electronics more than likely fairly soon. But it's a baseline, 900 for a rather average machine.
    Option 2 I've worked out, CNC4YOU don't come out that well in this regard, and going eBay for the majority of it I've got a very high level ballpark price of 768... that's with the same spec ballscrews, supported rails, 1.2Nm NEMA23s, cheapo TB6560 drivers (the motor/drivers come in a 3-axis pack for 95). 175 on a spindle, 1605-C7 ballscrews for a 600x500mm working area. That price includes 130 on aluminium extrusion but there would undoubtedly be more cost on getting the relevant plates/etc for the Z-axis and so forth. So, to cut a long story short, I see no point in trying to build a 6040-like machine yourself for less money; I don't think it can be realistically done. They are great value for what they are.
    Option 3, then, comes out at a 1262 plus the frame material, so if I bank on 1400-1500 I think that would cover it. This would be same size as a 6040, but like I said overspecced on the components - HGR15 linear rails, 4Nm NEMA23's, Leadshine DM556 digital drivers, the same old 2.2kw ER20 spindle and VFD, a 48v PSU, same 1605-C7 ballscrews (contemplating C5s, they're not much more), and then some guesswork on the Z-axis, cable, rails and so forth. Most of it UK sourced seems just as cheap, if not cheaper, than China. I guess the quality stuff is the same price wherever you source it from, and China has no interest flogging it!

    Option 2 to me seems pointless. So it's a choice between option 1 and just get started playing with it, or option 3 and long-term investment.

    I understand that 1500 buys a much larger machine but the reality is the costs are kind of irrespective of size; I know aspects of that don't make sense (do you really need 4Nm motors to mill PCBs?!) but I'm thinking re-use in the long term on the next project... and doing the construction with the components I'd use on a large build, so I can get savvy with them.

    Because if I don't do that, then I really might as well just buy a 6040 and be done with it, given my size limits.

    Question - by my calculations a 5mm pitch ballscrew, 200 step motor and no microstepping would give me a 0.025mm per step movement, which is just under 1 thou... and with microstepping obviously could chop that in half a few more times if need be. There would be no reason for me to gear this down would there, given worst (toughest) case the most resolution I'd need on a PCB would be half a thou... (excluding backlash and rigidity issues, I know).

    Am I right in thinking that to maximise accuracy, I need to keep the thing as rigid as possible, run it at appropriate speeds, but ultimately the ballscrews will define that resolution. So the quality of drive, the ballscrews, that's all just a case of how deep your pockets are - the bit that *I* can f**k up is not making the machine square/rigid.... anything else? I know accuracy is more than just resolution, it's about repeatability as well, but go easy on me, I'm learning... :D

    Basically if I go NEMA23 4Nm, Leadshine digital drivers, a capable 48V 600W power supply, C5 (let's say that for now, given the price difference to C7's) 1605 ballscrews with anti-backlash nuts... the only other bits that are going to limit the accuracy/repeatability of the machine are my fudged-up design, or bad software/CAM....?

    If I can accurately mill SMD boards (typically a pad spacing of 0.25mm between pads) then I'd be happy as larry.
    If that's pie in the sky then you're really falling back to through-hold DIP stuff, which really could be 0.5mm or worse, and I then wonder whether it's worth all the bother, apart from as a learning exercise and investment for future upgrades. I guess it could probably do *some* aluminium work if I was careful/slow, but I'm kind of dropping the focus on that now.

    Basically, 1500 on an over-specced DIY build the same size as a 6040 (but obviously better quality).... or spend 900 on a 6040, use it for a year or two, accept it's limitations, fix it as needed, then flog it on for 400 and consider it a learning exercise... or salvage it for the spindle if nothing else :)

    I'm thinking the DIY route but happy for someone to tell me I'm mad for doing it/it makes no sense :)

    P.S. Sorry for the clearly indecisive warblings... I do value your feedback though :)
    Last edited by brumster; 22-01-2016 at 07:57 PM.

  5. #24
    Oh, and spindle run-out, I forgot that. Best I can make out from reading, the usual spindles have a mixed bag in terms of specs and it's probably just a case of cross my fingers and hope I don't get a Friday one...?

    I've started designing anyway; when I get it to somewhere sensible I'll share for comment...

    What are the merits for move the platform and fixing the gantry on the X, versus fixed platform and moving gantry? It strikes me the moving platform will be easier to design and construct but I'll have to accept a larger keep-clear space at the sides of the machine?

  6. #25
    Quote Originally Posted by brumster View Post
    Basically, 1500 on an over-specced DIY build the same size as a 6040 (but obviously better quality).... or spend 900 on a 6040, use it for a year or two, accept it's limitations, fix it as needed, then flog it on for 400 and consider it a learning exercise... or salvage it for the spindle if nothing else :)
    Better Still spend 1500 use it for Two yrs hassle free and then sell it for 2000.!!. . . . .Make a Proper Job using correct components and that is perfectly feasible.

  7. #26
    Aye, true :)

  8. #27
    Not much replies to questions, which is fine we're all busy people, so I wonder whether this now needs moving to a new build thread? Would that make more sense? I'm not saying it's definitely going to happen yet but maybe that will get it better visibility....?

    I made a start on the design anyway, made some assumptions....



    80x40x4 steel box welded frame, X on the platform and a fixed gantry (Y and Z), single central C5 ballscrew, external size 600x500. BGR15 linear rail (why not), NEMA23 motor, big design question at the moment is direct drive or pulleys/belts? I know some of you seem to be fans of pulleys/belts; any reason to go that route? I don't need it for the gearing-down/accuracy as by my measure, even direct will give me the resolution I need (and microstepping, even better). Are there other good reasons to belt-drive?

    Appreciate it needs bracing...

    I need to get some ballscrew dimensions to understand how the motor/linkage needs to be spaced... when you spec a ballscrew are the "unscrewed" parts of the ends always a fixed dimension or will it vary from one manufacturer to another? I took a quick look at one datasheet I found but there were no dimensions on there (from Zapp Automation). CNC4YOU have some specs up for C7 ballscrews but would my C5's be any different?
    Last edited by brumster; 24-01-2016 at 12:30 PM.

  9. #28
    Quote Originally Posted by brumster View Post
    I know some of you seem to be fans of pulleys/belts; any reason to go that route? I don't need it for the gearing-down/accuracy as by my measure, even direct will give me the resolution I need (and microstepping, even better). Are there other good reasons to belt-drive?
    The main advantage of belts other than gearing is to reduce resonance and smoothen motor performance. This is why most use it.
    Resonance cripples the performance of steppers so anything to help reduce it is welcome. Using Digital drives makes huge difference to stepper performance and smoothness.
    Also regards Micro stepping don't think of it to increase resolution because while it does up to a point it's main purpose is to smooth motor performance. Noticed you also mentioned running Steppers at 200 steps (Full step) this would make them run awful so expect to use Micro stepping.


    Quote Originally Posted by brumster View Post
    but would my C5's be any different?
    They are exactly the same regards end dimensions. But C5 screws require higher spec end fixings hence why they sell C5 end bearings other wise there's no point using C5 screws.

  10. #29
    Quote Originally Posted by JAZZCNC View Post
    The main advantage of belts other than gearing is to reduce resonance and smoothen motor performance. This is why most use it.
    Right, that's what I needed to know! Ok, I'll go with belts, albeit on a 1:1....! Thanks.

    Resonance cripples the performance of steppers so anything to help reduce it is welcome. Using Digital drives makes huge difference to stepper performance and smoothness.
    I will be going digital, yes, there seems only a marginal increase in cost of the drivers and like I said, this is an investment/reuse later so no need to buy cheap first off. There's no point; if I just want to do cheap then I might as well buy a 6040 :)

    Also regards Micro stepping don't think of it to increase resolution because while it does up to a point it's main purpose is to smooth motor performance. Noticed you also mentioned running Steppers at 200 steps (Full step) this would make them run awful so expect to use Micro stepping.
    Yep, my point was that I didn't *need* microstepping for any resolution aspect; naturally I'd use it.

    They are exactly the same regards end dimensions. But C5 screws require higher spec end fixings hence why they sell C5 end bearings other wise there's no point using C5 screws.
    Yes, I'd noticed on the website, that's fine. Wasn't going to attempt to mix ;) but to know the end dimensions are the same is just what I needed to know. I'll model off C7 drawings/dimensions, but just spec everything at C5.

    Perfect, thank you!

  11. #30
    Quote Originally Posted by brumster View Post

    I made a start on the design anyway, made some assumptions....


    Fasten the 4 fixed bearings to the lower and the rails on the underside of the component above, your support is then always optimally positioned for the point being machined.

    - Nick
    Last edited by magicniner; 25-01-2016 at 01:38 AM.

Page 3 of 4 FirstFirst 1234 LastLast

Similar Threads

  1. "Hacking" and "Modding"
    By magicniner in forum General Discussion
    Replies: 15
    Last Post: 07-01-2015, 08:59 PM
  2. CNC machine "Spanish" model . Advice and opinions needed!
    By shapebusters in forum Machine Discussion
    Replies: 17
    Last Post: 12-03-2014, 06:21 AM
  3. Replies: 4
    Last Post: 28-09-2012, 12:06 PM
  4. "Racks" VS "ball screw"
    By C.AlveSilva in forum Linear & Rotary Motion
    Replies: 1
    Last Post: 17-04-2012, 11:53 PM
  5. Replies: 1
    Last Post: 25-12-2010, 06:05 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •