Page 3 of 6 FirstFirst 12345 ... LastLast
  1. #21
    Quote Originally Posted by GrahamWhite View Post
    I spoke to cnc4you today and they suggested for rack and pinion instead of running nema23's 4Nm with 3:1 reduction I could have just gone with 34's at 8.7Nm and run them direct or fit a larger pinion for slower speed??? would that be the same?
    Bad advise for several reasons and just shows how little experience CNC4YOU have.!
    #1 The resonance directly on the motors will play havoc with the drives causing rough running. It will also Kill the motor bearings quick time.
    #2 Bigger pinion will make go faster not slower.
    #3 Bigger pinion will reduce resolution.

    The reason for the ratio is two-fold.
    #1 To increase resolution. Even a small pinion of say 15T (Mod1) will have a pitch of 47mm which is too high and will give a low resolution. It will go like the clappers but resolution or in simpler terms Smoothness will be rubbish and this shows in the cut. You want to aim for pitch between 10mm-20mm Max.
    The CnC-router parts pinion I believe is 1" or if Mod 1 will be 25T which will give pitch of roughly 78.5mm with 3:1 ratio this brings down to 26mm which is still little high for me if want to do very detailed work.

    #2 It increases the motor torque which is required to overcome the inefficiency of R&P.

    Also, the belts help lower Resonance which affects motor/drive performance. DONT under estimate Resonance because it will and DOES cripple machines performance. This is why you'll often see recommend Digital drives because they handle Res so much better, but still they have limits and Direct driving R&P off the motor would challenge them and your abilty to tune the resonance out.

    Edit: Just to go little further on why direct drive is bad idea and pinion sizes etc.
    When using a machine it's important that you spec your components so that you have best performance while cutting. One important consideration with stepper based machine is that you aim to be cutting in the motors RPM range which gives best performace while cutting.

    So if you have direct drive with big pinion and say your feed is low becasue say doing 3D work, then your problems start to multiply because now your motors are hardly turning. This scenario puts the motors/drives in place which isn't always good.!
    Yes torque will be higher but do really need it while going slow.? However motor smoothness will suffer and this will often show in the finished cut which very much matters on say 3D work. OR affect the drives thru resonance causing rough running and others problems.

    Hope this helps.
    Last edited by JAZZCNC; 24-04-2018 at 06:02 PM.

  2. #22
    Ok Thanks ,so I have gone the sort of correct ish route!

  3. #23
    I'm finally looking at the motors and drivers and found this place -omc-stepperonline.com
    in particular this driver
    https://www.omc-stepperonline.com/st...or-dm860t.html
    is that pretty much the same as the cnc4you one?
    https://www.cnc4you.co.uk/Stepper-Mo...r-60VAC-CWD872
    The stepperonline place don't do the 4Nm stepper though but they do have a 3Nm that pulls 4.2a as well as a 3Nm pulling 3.2a
    They have nema 24 @4Nm would they fit my pinion plates ?
    ---
    read more so the 24's will fit ,they have the same mount hole spacing within .1mm
    Agghhh - I know I need a Bob as well-one full of connectors or just a basic one, I have ordered a UC300eth for connecting to my pc so need 5v to power that- it that then an extra psu I need or can I pickup 5v from somewhere!
    Last edited by GrahamWhite; 25-04-2018 at 02:42 PM.

  4. #24
    Quote Originally Posted by GrahamWhite View Post
    I'm finally looking at the motors and drivers and found this place -omc-stepperonline.com
    in particular this driver
    https://www.omc-stepperonline.com/st...or-dm860t.html
    is that pretty much the same as the cnc4you one?
    Yep pretty much and will work fine for your needs.


    Quote Originally Posted by GrahamWhite View Post
    The stepperonline place don't do the 4Nm stepper though but they do have a 3Nm that pulls 4.2a as well as a 3Nm pulling 3.2a
    They have nema 24 @4Nm would they fit my pinion plates ?

    read more so the 24's will fit ,they have the same mount hole spacing within .1mm
    When comes to motors whats more important is the inductance which is rated in mH. Lower the better and when wired Bi-polar parallel you want to be looking for around 2.5-3.5mH for best performance.

    Be careful when comes to Nema sizes because some companys state Nema 23 which should = 56mm but the frame size is actually Nema 24 which =60mm. Prime example is that exact Cnc4you motor you linked to. The data sheet gives Dims of 60mm but they sell it as Nema 23.!!



    Quote Originally Posted by GrahamWhite View Post
    Agghhh - I know I need a Bob as well-one full of connectors or just a basic one, I have ordered a UC300eth for connecting to my pc so need 5v to power that- it that then an extra psu I need or can I pickup 5v from somewhere!
    Don't try to pick up 5V from else where like PC or USB. You need a stable 5V supply and ideally to lower risk of noise affecting controller you want it separate to any other devices.

    Ideally you want to be getting away from 5V for things like E-stop, Limits etc because it's very susceptible to electrical noise which gives all sorts of weird and wonderful hair pulling mysterys.

    Re- Bob's then you won't want to go the route I'd recommend because of price. Which would be UB1.
    So in which case I'd say go with cheap Bob and just make sure it uses isolated Inputs. Most Simple Bob's don't have isolation so stay clear of those.

    Highly recommend you draw up schematic and use 24Vdc safety circuit using relays. This will allow you to use 24Vdc to run thru E-stop and limit wires on the machine lowering any chance of false e-stops etc thru noise. The 5V signals you need for the Controller/BOB can then be kept to short wire runs and inside the control box which lowers chance of noise affecting machine.

    Machine just relying on 5V for everything is very open to electrical Noise. Crazy things can occur.? ie: Mr's turns on hairdrier machine E-stops, Boiler fires up machine E-stops, Kettle on, Door bell etc etc.!!. . . think you get the picture. Anyone who's been affected by noise will tell you it's pain in the arse and only beat by resonance to which pulls the most hair.!

  5. #25
    Wow, thanks :)... Can I ask just one more question? The nema 24s should be fine, although 60mm size the hole mounting is the same but they have 8 wires! Is that 4 more than usual! Or is 8 OK (they only have 8 wired ones in UK warehouse)

  6. #26
    Quote Originally Posted by GrahamWhite View Post
    Wow, thanks :)... Can I ask just one more question? The nema 24s should be fine, although 60mm size the hole mounting is the same but they have 8 wires! Is that 4 more than usual! Or is 8 OK (they only have 8 wired ones in UK warehouse)
    Ok let me explain the difference between 4, 6 & 8 wire motors. Steppers can be wired in several configurations with each making a difference to how they operate. There are 2 commonly used methods #1,#2 and one not so common #3.
    #1 Bi-polar parallel (8 wire)
    #2 Bi-polar Series (4 wire)
    #3 Uni-polar (6 wire)

    8 Wire motor is known as Hybrid Motor and can be wired in any of the 3 configurations. Each Config will affect the current used and how the motor performs. (8 & 6 give roughly same performance but unipolar require drives that allow it, hence why not often used on modern machines)

    So if using 8 wire motor this would be wired Bi-polar parallel and requires roughly 2x the amps of Bi-polar series to give rated torque. However In performance terms it holds the Torque much higher up the RPM range than does a Series wired motor for the same given voltage.
    But like all good things this comes at a cost. You have less torque lower down the RPM range.

    What this means to YOU and US is that for Router where your cutting at higher feed rates and higher up the RPM range then Bi-polar parallel is best way to go.

    If you was building say a Milling machine then you'd wire in Bi-polar Series because require more Torque lower down the RPM range. Still uses 8 wires just wired differently. Also requires less current than parallel so lower amp drives can be used. However for the same voltage the RPM will be lower because inductance is higher due to how it's wired.! . . . Again back to can't have something for nothing.

    Now 4 Wire motors are Fixed by the manufacturer and you buy them either Bi-polar Series or Parallel wound. Often they are Series wound.
    The difference being that Series wound will require roughly twice the voltage to reach the same RPM as Parallel wound motor.

    Won't get into 6 wire unipolar because it's a throwback to old tech and drives so not really relevant here.

    So for best performance with a router, you want 8 wire motors and wire them Bi-polar parallel.

    If you look at the Datasheet on the Cnc4you it will show you how the wires are connected for each method. All 8 wires are used but joined in different ways.
    Last edited by JAZZCNC; 25-04-2018 at 07:16 PM.

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


  8. #27
    Many thanks again, most of the basics ordered now, steppers, drivers and 24v psu.
    Will look a bit more into Bob's.... Yes ub1 does look the bees knees but will take more kidneys than I can afford to sell! Lol
    I'll have a look at some others that have opto isolation:)

  9. #28
    So with the ball screw it needs space for the mounts top and bottom- so doesn't work with the Vee bearing rails :(
    I went for SBR16 - supported rail bearings- would have liked square profile but the cost was too much.
    This is the state of the Z axis at the moment -getting there :) waiting on the long bearings for the rails- will be going for MDF front plate at the minute and changing to aluminium later I hope :)
    The clearance on the X axis bolts is tight but clear is clear :)
    Click image for larger version. 

Name:	20180427_170454.jpg 
Views:	85 
Size:	325.2 KB 
ID:	24145

    I will have to manually adjust the Vee bearings on the X but hopefully that's not too much of a pain(instead of cam adjusters).
    I hope this is an upgrade to the Z and not a downgrade!!
    The bottom of the X has approx. 7" clearance from the bed after I add a whole base board and then a spoil board on top- gives me a usable Z height of 7"!! providing it doesn't have too much play.
    Steppers, drivers , psu's etc all ordered- gone with a UC300eth - 5lpt for the control box
    Water cooled spindle has arrived ,wow its got some weight to it!

  10. #29
    Ok so it's time to start looking at the control box- I have a large 700mmx500mmx 200 steel enclosure which I will have to wall mount as it wont fit under the router base!
    How does someone with absolutely no knowledge of electrics design or layout the insides!??
    I've had a search on the forum and to be honest it looks a tad daunting(this is the bit I wasn't looking forward to!)
    A basic wiring diagram I can just about follow but throw in relays or anything else then I'm lost :(

  11. #30
    Hi Graham
    Think there is a diagram in one of the build threads, Dean/Jazz posted it a while back. as he is watching you he will probably be able to help.
    Regards
    Mike

Page 3 of 6 FirstFirst 12345 ... LastLast

Similar Threads

  1. NEW MEMBER: New Build of a Joe's CNC Hybrid R&P 8x4
    By GrahamWhite in forum New Member Introductions
    Replies: 7
    Last Post: 20-03-2018, 07:16 PM
  2. BUILD LOG: Plans for new build
    By jas46 in forum DIY Router Build Logs
    Replies: 0
    Last Post: 21-09-2015, 02:17 PM
  3. MDF CNC Router plans / parts for home build beginners
    By HiltonSteve in forum Gantry/Router Machines & Building
    Replies: 81
    Last Post: 10-06-2012, 02:33 PM
  4. Trying to find a kit or plans to build.
    By don_jarr in forum Gantry/Router Machines & Building
    Replies: 2
    Last Post: 16-06-2011, 04:28 PM
  5. NEW MEMBER: Hi from rainy York - build plans/questions
    By bikepete in forum New Member Introductions
    Replies: 13
    Last Post: 11-10-2009, 07:43 AM

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
  •