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  1. #337
    Registered Need TECH Help!'s Avatar
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    Default Re: Hurco BMC20 Dynomotion Retrofit

    Quote Originally Posted by m_c View Post

    ......The 1uM option isn't actually any more accurate than 5uM, as they use the same optical scales, however they're still more accurate than magnetic tape systems. (I just rechecked that, and the Renishaw tape system only has positional accuracy of +/-20 to 40uM, and even the standard M-DRO optical scale only varies from +/-5 to 10 uM depending on length).
    I wondered about that. What is the point of close resolution if the accuracy is so much larger? I did use glass scales one time from SINO that had an accuarcy of 5uM. But was on a small RongFu mill. They worked really well, but feed was only 100IPM.

    http://www.homecncstuff.elementfx.com/


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    Default Re: Hurco BMC20 Dynomotion Retrofit

    Quote Originally Posted by Jim Dawson View Post
    I have Renishaw LM-10 1um on my mill & router, but I put Ditron MR200 1um on my lathe. Same form factor and specs as Renishaw. I have tested them side by side and found them to be functionally equivalent. About $120/axis including the mag tape and shipping.
    Where did you get them? Alibaba is the only place i have found so far.
    Thanks,
    Troy

    http://www.homecncstuff.elementfx.com/


  3. #339
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    Default Re: Linear Magnetic Scales (Hurco Mill)

    Quote Originally Posted by Need TECH Help! View Post
    Looking for scales for my mill now. Looking at the magnetic scales. Renishaw scales and reader heads are a bit pricey. Dont want to got that route unless i have to. Has anyone used or heard of these scales ? https://www.machine-dro.co.uk/indust...-encoders.html
    They have some on ebay sold in the states.
    Attached is data sheet of the 5uM. I have emailed them about getting a 1uM or 2 uM.

    Tom or anyone see any issues with using these scales with my Kflop/Kanalog/Konnect combo? Obviously want to use them to close the loop at table and head of mill. My max Rapids are 800IPM.
    Also is the encoder reading speed of Kflop 1Mhz total for 8 axis or 1 Mhz per encoder?

    Thanks,
    Troy
    Im surprised to see all you guys using scales. Seems like a headache to setup and potential things to break with adding scales IMO. Especially Chinese ones. If you have some accuracy problems now why not spend the money on new thrust bearings and rebuilding ballscrews? Just seems so much simpler to me. And a machine without scales can still be very accurate as long as theres no slop in the axis and you have decent encoders. Your hurco should be very accurate with those dmm servos if there are no mechanical problems.

    Each axis can take 1Mhz input. The previous owner of my machine actually set my Z axis speed set at 1.25mhz and it works perfectly, still running it this way. So theres a little headroom there. Probably safer to stay below 1mhz, im sure Tom set that maximum for a reason.



  4. #340
    Gold Member Jim Dawson's Avatar
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    Default Re: Linear Magnetic Scales (Hurco Mill)

    Quote Originally Posted by Need TECH Help! View Post
    Where did you get them? Alibaba is the only place i have found so far.
    Thanks,
    Troy
    I purchased directly from Ditron. I have attached a pdf that is not available on the web.
    Contact Info:
    Jaeger Hou
    E-mail: sales@dcoee.com


    Quote Originally Posted by mmurray70 View Post
    Im surprised to see all you guys using scales. Seems like a headache to setup and potential things to break with adding scales IMO. Especially Chinese ones. If you have some accuracy problems now why not spend the money on new thrust bearings and rebuilding ballscrews? Just seems so much simpler to me. And a machine without scales can still be very accurate as long as theres no slop in the axis and you have decent encoders. Your hurco should be very accurate with those dmm servos if there are no mechanical problems.
    You are absolutely correct, the machine should be as mechanically perfect as possible. You should not rely on electronics to overcome mechanical problems, but it is possible.

    The reason I went with the mag scales originally was because I needed to replace my encoders during an upgrade and thought I would try the mag scales to see how they worked out. In the case of my mill I have had Renishaw LM-10, 1um units installed for about 4 years, they have been trouble free and are extremely accurate. I bought them cheap on Ebay when there were hundreds of them available. All of those are gone now. Shortly after I did the mill upgrade, I installed them on my 4x8 router also, and they work fine at up to the 600 IPM rapid speed of my router. I have no way to test them at higher speeds. Since then I have installed mag scales on 3 other machines with great success.

    I have some other projects the I am going to CNC (is that actually a verb?) and want to install mag scales also. With the used Renishaw units no longer available, a bit over a year ago I asked Ditron if they could duplicate the Renishaw units, and about 4 months later they had them in production. I have tested the Ditron units against the Renishaw units and have found them to be functionally equivalent. I have found both to be very accurate and with a tight machine actually able to machine parts to single digit micron accuracy. Close enough for me

    Attached Thumbnails Attached Thumbnails Hurco BMC20 Dynomotion Retrofit-dm-pdf  
    Jim Dawson
    Sandy, Oregon, USA


  5. #341
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    Default Re: Linear Magnetic Scales (Hurco Mill)

    Quote Originally Posted by mmurray70 View Post
    Im surprised to see all you guys using scales. Seems like a headache to setup and potential things to break with adding scales IMO. Especially Chinese ones. If you have some accuracy problems now why not spend the money on new thrust bearings and rebuilding ballscrews? Just seems so much simpler to me. And a machine without scales can still be very accurate as long as theres no slop in the axis and you have decent encoders. Your hurco should be very accurate with those dmm servos if there are no mechanical problems.
    ......
    The machine X&Y is within .0003" mechanically. The Z axis is boxed with a counter weight and is within .0005".
    Having feedback from actual slides and not just encoder on servo, will make up for the small amount of mechanical friction/stiction issues. First done this on a bridgeport clone that had steppers ,several years ago. Closing the loop at the table made a big difference for that dovetail machine. Went from machining a 1.0" hole with about .0015" hole roundness to .0005-.0007 roundness, sometimes better, very consistently.

    Also i have a old Magnaturn South Bend Lathe that i am retrofitting now, little at a time and would like to find a good linear scale for it also.And after it a Router/Plasma table. To many projects, especially now that i have my own shop that needs to make me money.

    Troy

    http://www.homecncstuff.elementfx.com/


  6. #342
    Gold Member Jim Dawson's Avatar
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    Default Re: Hurco BMC20 Dynomotion Retrofit

    Quote Originally Posted by m_c View Post
    I built a small digitiser/probing machine, using a 3040 as a base, a KFlop + KStep for control/drive, and closed the loop using 1uM scales from Machine-DRO.

    They are pretty generic Chinese scales, so if you're across the pond, I'd look at buying direct from china. The same scales can be found on aliexpress. Although Machin-DRO at the time happened to not cost much more than buying direct from China, and had what I wanted ready to ship.

    To get 1uM, they need different reader heads, and if you're wanting to use them with the Kanalog, I'd be asking to get the differential output option as well.
    The 1uM option isn't actually any more accurate than 5uM, as they use the same optical scales, however they're still more accurate than magnetic tape systems. (I just rechecked that, and the Renishaw tape system only has positional accuracy of +/-20 to 40uM, and even the standard M-DRO optical scale only varies from +/-5 to 10 uM depending on length).
    You are missing one term in the specification, that is +/- 20 to 40um per Meter. And depends on the resolution of the read head. I have no way of checking the actual accuracy over that distance so am not able to verify the specification. I have found that over shorter distances, (120mm) they are accurate to 1um, verified on a high end CMM.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Linear Magnetic Scales (Hurco Mill)

    Quote Originally Posted by Need TECH Help! View Post
    The machine X&Y is within .0003" mechanically. The Z axis is boxed with a counter weight and is within .0005".
    Having feedback from actual slides and not just encoder on servo, will make up for the small amount of mechanical friction/stiction issues. First done this on a bridgeport clone that had steppers ,several years ago. Closing the loop at the table made a big difference for that dovetail machine. Went from machining a 1.0" hole with about .0015" hole roundness to .0005-.0007 roundness, sometimes better, very consistently.

    Also i have a old Magnaturn South Bend Lathe that i am retrofitting now, little at a time and would like to find a good linear scale for it also.And after it a Router/Plasma table. To many projects, especially now that i have my own shop that needs to make me money.

    Troy
    I bet your hurco would interpolate a hole much better then 0.0015 if its in good shape and you run a reasonable speeds. If you need it better then that you could always use a boring head.

    So when you guys use linear scales, are the encoders still used at all or are they completely replaced by the linear scale?



  8. #344
    Gold Member Jim Dawson's Avatar
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    Default Re: Linear Magnetic Scales (Hurco Mill)

    Quote Originally Posted by mmurray70 View Post
    I bet your hurco would interpolate a hole much better then 0.0015 if its in good shape and you run a reasonable speeds. If you need it better then that you could always use a boring head.

    So when you guys use linear scales, are the encoders still used at all or are they completely replaced by the linear scale?

    I completely replaced my encoders with the linear scales.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Linear Magnetic Scales (Hurco Mill)

    Ya the hurco will mill a hole within .0003". A hole is just a good test.
    Still use encoders at the drive .The scales go to KFLOP for a dual closed loop system. Something the "big industrial boys" make you take out another loan to achieve on there machines

    Troy

    http://www.homecncstuff.elementfx.com/


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    Default Re: Hurco BMC20 Dynomotion Retrofit

    Quote Originally Posted by Jim Dawson View Post
    You are missing one term in the specification, that is +/- 20 to 40um per Meter. And depends on the resolution of the read head. I have no way of checking the actual accuracy over that distance so am not able to verify the specification. I have found that over shorter distances, (120mm) they are accurate to 1um, verified on a high end CMM.
    I did check a couple different read heads, and that figure remained the same, so I'm assuming it's because that's the spec of the grating (or whatever it officially gets called..) on the magnetic tape, and not related the head.
    And the 10uM figure for the scales was for up to a metre, so they are still technically more accurate. I know that on my probing machine, which is based on a generic 3040Z, repeatability is only around 10-20uM, however I suspect a combination of frame flex/wobble and the cheap probe is a major factor in that.


    However, what we've not discussed is suitability. Optical scales generally don't like coolant or contamination, so unless you can manage to mount them where they'll be well away from coolant/swarf/dirt, magnetic tape is likely to be a far better option.



  11. #347
    Gold Member TomKerekes's Avatar
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    Default Re: Hurco BMC20 Dynomotion Retrofit

    I think one important thing to understand is that optical glass scales typically use a 20um printed scale on glass where magnetic encoders typically use 2000um magnets on tape. So the magnetic scales need to rely on about 100X more interpolation to obtain the same resolution. Optical scales typically have precision, repeatability, and jitter far better than their specified resolution, where magnetic scales typically have precision, repeatability, and jitter worse than their resolution. Magnetic scales can sometimes have hysteresis (essentially backlash) and also nonlinearities that repeat over the 2000um pitch.

    Magnetic scales have the advantage of being more robust than glass scales, and less susceptible to contamination, and lower cost.

    So it depends on the requirements which is the best choice.

    Unlike with glass scale where the resolution pretty much tells the whole story, with magnetic scales I think it is important to dig a little deeper to make sure they will meet your requirements.

    Regards

    TK
    http://dynomotion.com


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