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Power Vs Accuracy

Discussion in 'MACHINE BUILD LOGS' started by cohokidd, Dec 25, 2016.

  1. cohokidd

    cohokidd United States Iron Registered Member

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    I am looking at and researching a new CNC router. As a journeyman mold maker I know the components of what I use at work, a Mikino VMC. Which like most big mills runs on servo drives and ball screws. When I started researching CNC routers I became aware of the other choices available. First the stepper motors that can replace the servo's and 2nd the rack transmission systems that are used instead of the ballscrews. I am looking for any knowledge and advice about these 2 subjects. So far I think I would rather go with the stepper motors. They seem to be very close in accuracy and require less maintenance. So the cost of upgrading to servos doesn't seem worth it. Am I missing anything major on this topic? I am certain I want to go with ballscrew and square guide rails on the Z axis and was fairly certain I would go with that same setup on the XandY axis. Then I read in a few places that when going with a large router spindle (larger then 2.2KW) that a rack and gear system is required/strongly suggested on the XandY travel. How true is this? How much loss of accuracy is there by not using the ballscrew? Is the extra power worth the loss of accuracy? Thank you to anyone who can give me any advice on these topics. Please don't hesitate to add in any other information you feel is critical when choosing a CNC router.
     
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  2. brino

    brino Active User H-M Supporter-Premium

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    Hello cohokidd,

    I am sorry I have no experience to add, but I wanted to say I appreciate the topic/question and have "watched" the thread so I don't miss anything.
    Welcome to the group!

    -brino
     
  3. cohokidd

    cohokidd United States Iron Registered Member

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    Thanks for the interest. I have pretty much picked the router I want to go with, at least the frame and manufacturer. There are just a few customizable components, like these I need to choose before placing the order.
     
  4. JimDawson

    JimDawson Global Moderator Staff Member Director

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    Welcome Aboard!

    I have worked with just about every configuration of router out there. So far, I haven't seen a lot of difference in accuracy between the rack & pinion vs. ball screws. There are also some that have a timing belt drive, but I have no experience with those.

    For the tabletop type routers the most common is ball screws and stepper motors. I have never seen one that didn't have a ball screw on the Z axis. On some of the wider routers, I have seen ball screws on both sides of the gantry. My 4 x 8 is all ball screw.

    If this is for home hobby use then open loop steppers are a good choice. Accuracy is not as good as with closed loop servos because it is possible to lose steps and then the controller has no idea where the tool bit is at. For hobby work this is not normally a problem. It is possible to close the loop on steppers, and operate them like servos. This is what I'm doing on my machines, but it is relatively expensive to do so.

    If your router is going to be used for commercial work or you need high accuracy and higher speeds, then I would recommend going with hybrid steppers or servos for increased accuracy and higher performance. I just did an upgrade on a 5 x 10 Multicam router for a customer and installed Teknic Clearpath SD servos. I found those the be a nice little unit. Direct bolt in for a NEMA 34 motor, and they take a step & direction input just like a stepper, and have the drive built in. I think they also have a NEMA 23 motor size. They close the loop internally.

    Looking forward to seeing you new toy...er, tool:) We love pictures.
     
    Last edited: Dec 25, 2016
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  5. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    When we were researching the build for the high school I spoke with many manufacturers of commercial routers. What I found is that on the rack & pinion systems they would claim 0.001" positioning accuracy but when pressed about operational accuracy it was 0.005" to 0.007".

    R&P is better for rapids than ball screws. For the high school accuracy out weighed speed so we went with ball screws plus we primarily only cut aluminum sheet up to 3/8".

    We use servos at the school. I have steppers on my mill and small router at home. If sized properly the chance of missing steps is very low.

    Sent from my SAMSUNG-SM-G900A using Tapatalk
     
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  6. cohokidd

    cohokidd United States Iron Registered Member

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    http://uploads.tapatalk-cdn.com/20161225/a24f806e2008f75e7d2eb4d1628e98c4.png

    This is the machine I think I am going with. The current configuration I'm thinking about. This base and gantry wish 400w Japan Panasonic servo drives and motors 3.0kw spindle 3.7 Fuling inverter. And the rack and pinion and square guide rail. I was nervous about buying a China built machine but I can't spend double or triple the price to buy one made here. I have spoken to a customer of theirs here in the states. They had nothing but good things to say. I will be using the machine for a level of work somewhere between hobby and commercial. I do have a day job but have a small I make a customer part for local boat owners out of 3/8-1/2" plate aluminum. Then I would be doing more woodworking. Please let me know what you think


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  7. JimDawson

    JimDawson Global Moderator Staff Member Director

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    I know nothing about the company nor have I seen their products. In the pictures it looks nice, professional. You can't beat owner testimony, so that is a plus. You might ask the US customer if they have worked with aluminum on that machine. As you know, there is no substitute for mass when it comes to machining.

    The Panasonic servos should work fine, top of the line equipment.

    A few questions come to mind. What control software are you planning on using, and is it being supplied with the machine? Is this supposed to be turn-key out of the box? Do you know anything about what CAM post processor is needed?
     
  8. brino

    brino Active User H-M Supporter-Premium

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  9. cohokidd

    cohokidd United States Iron Registered Member

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    It is the heaviest gantry I could find on any router of similar size. Both Mach 3 and DSP are offered. Not sure which to choose lots of reading available out there on that subject!!! Sounds like personal preference to me. They both work. The post processor has crossed my mind but a guy at work that wrote ours for Gibbs Cam said he'd write one for me.


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  10. cohokidd

    cohokidd United States Iron Registered Member

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    Thank you. I have talk to multiple sales people and even used my wife's email to switch things up. I pretty much always got the same info from them. So either they are fairly honest or they have theirs story very straight between all sales people


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  11. cohokidd

    cohokidd United States Iron Registered Member

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    It says it comes with A11 DSP but in emails they say Mach 3 is available at no extra charge. I'm guessing that's up front. DSP Is free and Mach 3 is not correct?


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  12. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    You should ask if it is a full version of Mach3. It might just be the trial version of Mach3 which is restricted to 500 lines of code or a bootleg version that seems to come with so many things from China. I have a couple of those where the screens are all in Chinese. The full licensed version is $175
     
  13. cohokidd

    cohokidd United States Iron Registered Member

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    Thanks for sharing your sharing your experience. Have you had any maintenance with your servo system? I read that there is more maintenance with them then servos but the Fanuc servos on the Makino mills I use at work seem maintenance free. I don't know just a lot to choose from. Another person on here posted below that he looked up the machine I'm probably purchasing at Blue Elephant's website. He say they are good top of the line components.


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  14. cohokidd

    cohokidd United States Iron Registered Member

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    So do you prefer Mach 3 over DSP? If so why? As a Mold maker as my day job I have a strong CNC background. So feel free to spell out the differences I think I'll understand. From what I've read it sounds like they both do the same stuff but Mach 3 looks nicer/more professional but capabilities are about the same


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  15. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    At the school we are using cheap Chinese DC servo motors which we added US digital differential encoders to and are being driven by Advanced Motion Controls servo drives. We have had no issues with the servo system in the two years it has been in service. We did have some initial issues with the custom motor drives which were later abandoned for an off the shelf solution. Here is a video one of the parents put together about its creation.
     
  16. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    I am not familiar with DSP. I use Mach3 on my mill and router at home and the school router uses Linux CNC.
     
  17. cohokidd

    cohokidd United States Iron Registered Member

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    Jim thank you for letting me know you can run steppers in a closed loop. I didn't know that. Like I originally said I really don't know anything about steppers. So I've been reading up on them. I think I understand the drivers but the motors still confuse me. Mainly the model numbers. So if I go with steppers they use open loop driver and FL118 motors. I found a driver model made by Yako that is closed loop. It runs both analog and digital. So when they return from their long New Years celebration I am going to ask them what the extra charge is for that set up. I read somewhere that Mach 3 won't recognize the Communication from the motors but the drivers will do corrections anyways. Does this sound correct? Do you use Mach? Thanks for the information


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  18. cohokidd

    cohokidd United States Iron Registered Member

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    Here is a link to the drivers. If you have time to check them out and give me your opinion that would be great.
    http://www.yankong.com/EN/index.php/proview-54-25.html


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  19. JimDawson

    JimDawson Global Moderator Staff Member Director

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    I'm not able to find the specs on the FL118 motor, so I can't help much there.

    In order to use the closed loop function on the Yako drives you would have to have an encoder on each axis. I can't tell whether or not the FL118 motors have a built in encoder. As far as I know, Mach3 does not receive or use any feedback from the motors. Once you get pricing on the Yako drives, do some price comparison with other systems. The may be a better motor/drive combination for the same money. Ordering the machine with no motors/drives might be an option, that is exactly what I would do.

    I have used Mach3 in a couple of low performance systems with good results, but IMHO it is not up to the task for higher speeds and accuracy. Because of the limitations of Mach3, I wrote my own CNC software and designed the control system. It is competitive with most commercial CNC control systems available today.
     

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