A few questions before I start building one

This topic contains 87 replies, has 6 voices, and was last updated by  gera229 8 years, 8 months ago.

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    Yeah, servos are far more complex and expensive, but they do not lose torque at higher speeds and travel faster. But I do not think that speed is necessary anyway or you would end up breaking drill bits.

    I wanted to ask, do the stepper motors lose steps if too much load is put on them? Or are those by HobbyCNC just so strong that it’s the least of your worries?




    Steppers do lose steps if too much load is put on them (or not enough voltage/current), but usually you can tell by the sound and “feel” of the motor when it happens. A good motor that is rated for a decent voltage/current can make all the difference between a great CNC build and a frustrating experience.




    Checked all my computers and none of the have a parallel port. (Should have kept my really old windows 98 PC lol).

    Anyway, after reading over this forum I’ve learned that a USB to parallel conversion would not work. And a laptop parallel port card thing won’t work that well due to not supplying enough power thus causing the stepper motors to lose steps.

    I came across this cheap add on. Will this work?






    I’ve noticed the last one is a PCI-E slot with less pins. Is that a problem? I know pci-e is faster, but would less pins cause compatibility problems?


    Aside from that I have seen very CHEAP refurbished desktops on Ebay with free shipping and their specs are pretty good for their price. For ex for $200 you can get a dual core 3 ghz processor with 2gb-4gb ram and 500 gb of space in hard drive and they have a parallel port PLUS it came with monitor and other hardware such as keyboard and mouse.

    Should I get a laptop or a desktop for a CNC with parallel port built in? I would choose a laptop over a desktop (because of 1 advantage: portability) if power supply to the CNC is not a problem (But I read on this forum that it is sometimes a problem thus causing the stepper motors to lose steps, correct me if I am wrong and tell me many different ways it will or will not work such as will it be fine if power was plugged it? What if it ran straight from the battery?).

    Because of that possible problem I decided to go with a desktop over a laptop to avoid the slight power supply problem to the CNC stepper motors. I haven’t ordered a computer yet, but planning on a desktop (portability shouldn’t be too much of a problem, but it is still nice to have which a desktop lacks). Also 3D modeling on a desktop for price would be faster due to better specs.

    I know I will use a separate power supply to power the motors, but there is still supposed to be power from the computer to transfer the code to the stepper motors.



    @gera229, the DB25/Parallel Port cards work in my experience; these are definitely the cheapest option. Assuming you’re using Linux/EMC2, you may need to do a bit of additional work to get the software talking to the card. Whether it’s PCI-e or not would depend on what motherboard you have in your existing PC.

    The refurbished desktop seems like a good way to go if you find that price point affordable. All the sources I’ve read recommend against laptops as supposedly their power management settings can interfere with the real-time signalling that’s needed over the parallel port. I have not personally tried with any laptops, though.

    You are right about the roles the power supply/computer play in the system: the computer supplies precisely-timed low-power signals to the power supply/driver, which provides high power to the motors.



    I would like to know the specs on your PC.

    Reason is because I will be cutting 3D things to make plastic moldings, but wouldn’t too slow of a PC be too slow to render and transfer code for 3D objects?

    I know PCI-E vs PCI depends on your motherboard, but in parallel port for these stepper motors which would be more compatible to convert to parallel port? (For example USB isn’t compatible although it converts to parallel port). I know PCI-E is faster, but the fact that it has less pins, does that make it less compatible?

    What did you try a Parallel card on? PCI or PCI-E?



    @gera229, here is the PC that I use (it has a built-in parallel port).

    The EMC2 wiki also has lots of great info on hardware specs for your controller PC.



    In your guys build guide, are there limit switches? Or is that a plan for V2?

    Will limit switches work with the hobby cnc board? I may need 7 limit switches. 1 for home and the other 6 for the max distance to travel in x,y,z with 2 limit switches for each axis.

    There is also this barebone with a dual core cpu:


    But I’m picky about the reviews. Grr power supply issue…

    And this:


    But idk if it comes with a CPU because it does not list the exact CPU type.



    Hey, I ordered the HobbyCNC Pro package. Aside from that, I was wondering how you guys adjust the height of the Z-axis for the starting point? Manually? I mean you cannot disable the individual drivers on this board if you need to (without having to power the the entire unit down) right?

    Also does this board have step and direction signal filtering and buffering?




    @gera229, 7 limit switches might be a little overzealous, imho. I’d use at most 5:

    -2 for X (home & far end)

    -2 for Y (home & far end)

    -1 for Z (high travel only)

    A simpler way to do it is to use three switches:

    -one for the X axis home (whichever corner of the bed you designate as zero)

    -one for the Y axis home (whichever corner of the bed you designate as zero)

    -one for the Z axis home (the highest travel the Z axis can go)

    This will let you set up a homing routine, so that when you start up the machine it will find its home location. If you use EMC2 (and some other software packages), you can set software limits relative to your home positions. So if you have 12″ of travel in X, for instance, the machine will only go that distance away from the home position.

    To set the Z position, we do it manually. You can jog each axis independently, and set an offset home position in software which essentially ‘zeroes out’ each axis.

    Also does this board have step and direction signal filtering and buffering?

    afaik it does not, but with this setup you shouldn’t need it. The HobbyCNC board uses a DB25 parallel port connection which allows the PC to provide essentially real-time signalling to the board/motors. I believe buffering would apply to boards using USB, since their serial connections can’t do the same real-time signalling & thus need a buffer to correct signal timing.



    Ok I was just wondering because I was comparing it to this board: http://www.xylotex.com/4axBoard.htm

    Which does indeed have filtered and buffered STEP and DIR signals signals and uses a Parallel port to connect to the computer.

    Also from this forum: http://diylilcnc.org/forum/topic/v2-electronicsdriver-board

    I came across this link: http://www.buildlog.net/blog/2011/08/open-source-4-axis-stepper-driver/

    In that page I read this:


    All step and direction signals are filtered with a RC filter and a schmitt trigger. This is ideal for a noisy environment like a laser cutter or CNC machine. The RC filter frequency is high enough to allow 1uS pulse control of the drivers.”

    Looks like noise can cause the machine to distort or something??? I looked up schmitt trigger and it had an application that has something to do with noise and frequencies.

    Is it like the noise we hear or something like from motors? Or what is the definition of noise in technological terms?

    So, are you sure filtering is not necessary? Lol.

    Also do you guys have drawings for your Driver Board Case?



    Hey guys from the instruction manual I read this and finding it difficult to understand:

    Those looking to really cut costs could use threaded rod and a coupling nut instead of the acme rod/nut in the Z-cart, as per oomlout’s original plans3. This can save close to $60 off the total cost;

    I can’t understand this:

    however the trade-off is the need for more rotations on the Z-motor to keep the same speeds on the Z-axis, which may require you to lower overall feed speeds when milling to prevent losing steps.

    Explain it better. Why lower overall feed speeds?

    Does the Z-Axis speed have to be consistent with the x and y axis speed or something? Doesn’t it adjust automatically and slow down to have the z-axis catch up or something?



    I guess it depends on the software: Either you can just configure the overall speed (meaning you would need to set this to the speed of the slowest axis) or you can set the speeds for the individual axes (I would expect that from good software) and it will go as fast as it is allowed to in x/y axis respectively z axis and will automatically wait in x/y if it is necessary for z to catch up.

    So I guess you should look at the CAM software you are going to use and find the settings for this things to see what it can do.

    (but again, I haven’t got a clue, I’m just writing what seems logical to me)



    I got all my electronics parts and would like to cut out the case for all of it. Do you guys have drawings for it? I want to use a CNC to cut it.



    There are plans for it included with the plans for the rest of the panel parts, if that’s what you mean. You will need to adjust it for cutting it with a CNC mill if you don’t have access to a CNC laser.



    @gera229, you can also find CAD files that have been adjusted for CNC routing on the downloads page (titled v1.0.2 CNC Cut Pattern).

    To your question re the threaded rod vs acme rod: the acme rod we spec for the Z axis is precisely-machined threaded rod that’s made for machine axes. You can also use threaded rod, which is rod with threads like you’d see on a regular steel bolt (just longer). The threaded rod is not made for use in machine axes, so it’s not as precise & will wear out more quickly. You’ll also need to adjust the settings in your driver software to allow for different threading ratios.

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