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  1. #11
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,011. Received thanks 221 times, giving thanks to others 5 times.
    Quote Originally Posted by hanermo2 View Post
    I am perhaps the only one with experience, who has done this, so...
    Yet nobody has ever seen any prove that you have, despite being asked numerous times...
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  2. I try to provide data.
    Any data that seems incorrect, please comment on.

    I have numerous pics, data, stuff from numerous clients, and none of it may be shared without prior approval from clients, and usually client they do not want to.
    I try to help people, thats all.

    Quote Originally Posted by m_c View Post
    Yet nobody has ever seen any prove that you have, despite being asked numerous times...
    Last edited by hanermo2; 25-02-2017 at 09:26 AM.

  3. #13
    Thank you Hanermo2 for the valued information.

    I read your concentrated post at least 10x times to understand what's in there, but I think I got there in the end.

    I understand steppers driven by belts are not accurate enough, and steppers driven by gears are rigid, suitable for the application, but the problem with these is the backlash. Is that correct? It does make sense, as the belt at the end of the day is made out of flexible material, unlike gears which are made out of steel.

    When you say you'll be switching to secondary, do you mean you'll add another servo stepper for the C axis, but driven by a worm gear or a gearbox?

    In my headstock I still got there a secondary spindle with spur gears all over it. There's also a clutch mechanism on the front panel which can engage the secondary spindle with the main spindle. So I might be able to direct connect a servo stepper for the C axis to that secondary spindle. But the trouble would be the backlash between the spur gears, and probably less accurate than a belt drive.

    Today I grabbed a 2.2kW motor (that was quick!), but don't know many details about it yet. It was free of charge and it's blue :) . Next I'll need to invest in some VFD and play with it to understand the process.

    I'll keep reading here in there.

    Cheers!

    LE Have found this 'CNC Lathe Spindle Encoder' design http://ve7it.cowlug.org/spindle-encoder.html
    Last edited by Valfar; 24-02-2017 at 09:05 PM.

  4. #14
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,011. Received thanks 221 times, giving thanks to others 5 times.
    Quote Originally Posted by Valfar View Post
    I was aware of the brake system design for a 4th axis. But my thoughts were to use the 4th axis simultaneously. The brake could be added as an option though, when only one face would need machining. But it adds to the complexity, and I'm trying to keep it as simple as possible. Wouldn't a geared 12Nm Nema34 do the job without a break? I don't need high speed & feeds. I will consider a brake if it doesn't.
    You would need to run some figures using the torque your milling spindle could produce, and the diameter of your work piece, to calculate the torque required at the 4th axis.
    I.e. using some random figures, say your milling spindle can produce 1Nm, and you have a 5mm radius (10mm diameter) cutter.
    At the very edge of that cutter, you potentially have 200N of force (1Nm/(0.005m/2)).
    Now apply that 200N to the edge of a 25mm radius work piece, you get 5Nm of torque produced (200N*0.025).

    That means under perfect transfer of torque conditions (very unlikely), you need 5Nm to hold the spindle. You're not likely to get perfect transfer of torque, however the torque applied isn't constant, and that is compounded by should the cutter snag, you have the inertia of the spindle/cutter which will produce peaks far higher than 5Nm.
    However that is assuming you're using some form of side cutting cutter, cutting at a tangent to the workpiece, and at 90deg to the 4th axis axis. Things like drilling holes around the circumference, will result in minimal rotational torque being applied to the 4th axis.

    If you want to run figures, most of this can be worked out to a reasonable accuracy.

    Also, good point m_c about the low speed motor driven by the other one at extremely high RPM. Haven't thought about it. That means the lathe motor (the 2.2kW low RPM komatias has been suggested) can be permanently attached to the spindle, and a servo (hybrid) stepper would need somehow to be detached when in lathe mode.

    I see this guy nailed it. He made a lathe and a 4th axis mill run simultaneously. I'm sure you are well aware about his project.
    https://www.youtube.com/watch?v=b2-Kdud7eiA
    That is a video of the original design from that thread I posted. It's worth having a read of that thread, as Simpson explained quite a lot about how he designed and built the inturn's.
    And with a single motor attached to the spindle. What's the catch?
    Getting the required torque.
    Plenty of homework for the week-end.
    Thank you for your time. You guys are great!
    Spreadsheets are your friend for working out some ball park figures for the required torque.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  5. #15
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,011. Received thanks 221 times, giving thanks to others 5 times.
    Quote Originally Posted by hanermo2 View Post
    I try to provide data.
    Any data that seems incorrect, please comment on.

    I have numerous pics, data, stuff from numerous clients, and none of it may be shared without prior approval from clients, and usually they never do not want to.
    I am not engaged in a popularity contest, and if/when I want to show publicity stuff I will do so.

    I try to help people, thats all.
    But I thought you had built this as a personal machine?
    At least that's what you seem to claim until anybody asks you for prove.

    And just so you know Valfar, Hanu has posted about this mythical machine for many years on various forums/email lists, and although his theory is reasonable, nobody has ever seen any kind of prove that such a machine actually exists. Whenever pushed for evidence, the excuses I've seen are he has no camera, he can't because of confidentiality, or the toys simply get launched out the pram, so make up your own mind.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  6. #16
    Thank you m_c! It does make sense, and I've also found some spreadsheets for calculating stepper torque values. I also believe they are a good start before deciding to buy.

    Also, an excellent tutorial (from my point of view) can be found bellow:
    http://www.mycncuk.com/threads/1524-...otor-do-I-need

    But now Hanermo2 wrote:
    Quote Originally Posted by hanermo2 View Post
    My experiences, working at this for 10+ years.
    Steppers are no-where near accurate enough.
    Even the best belt drives are not accurate enough.
    Now from my understanding that means stepper motors driven by belts are not accurate enough (what's the exact value of this? 10 thou? 100?), and the way to go would be either a worm gear or a gear box. But the problem with these is the backlash they introduce, and a good quality one is out of the question for a DIY budget. Is that correct?

    That leads me to believe is the belt itself causing the problems, being flexible, and not the stepper. Is that correct?

    And of course, a brake system applied on the C axis would work, but that means the same issues are encountered on the other axis (XYZ) as well?

    Quote Originally Posted by m_c View Post
    Getting the required torque.
    I understand the torque value, but this contradicts with the high RPM value needed for the lathe operations?

    Cheers!

  7. #17
    This is the AC motor I have, similar to the one in the link bellow.

    http://www.brookcrompton.com/upload/...E_W_CI_IE2.pdf

    Brook Crompton
    kW: 2.2
    V: 380-415
    A: 5.0-4.8
    RPM: 1415
    Phase: 3

    I shall use it for the lathe operations.

    Is there a good VFD you would recommend, or should I just go for a reasonable one over the e-bay?

    I will have to also design a lathe spindle encoder similar to the one in the link bellow, is that right?

    http://ve7it.cowlug.org/spindle-encoder.html

    Cheers!

  8. #18
    Quote Originally Posted by Valfar View Post
    Now from my understanding that means stepper motors driven by belts are not accurate enough (what's the exact value of this? 10 thou? 100?), and the way to go would be either a worm gear or a gear box. But the problem with these is the backlash they introduce, and a good quality one is out of the question for a DIY budget. Is that correct?
    One data point based on my own recent experience. My setup might or might be applicable to your situation but it might give a little bit of insight. I've been working on a Z height setting macro on my router. I'm winding a 2.2KW watercooled spindle up and down using a 1605 ballscrew driven by a 3Nm stepper via a 1-1 HTD5 belt and pulleys. Max speed 2500mm/min but can't remember current acceleration settings off-hand - think it's about 400mm/s/s. I can touch off the setting plate, wind the Z up and down 50 times at full acceleration/rapid speed, and retouch. I get repeatability within one or two microsteps, time after time. That corresponds to 3-6 microns (0.003-0.006mm) variation. Ok, the machine is very new so the belt has hardly had time to stretch, and I don't claim that the machine has long-term accuracy of anything like this. Similarly, I can set one tool to the work surface, change tools, retouch off a fixed setting plate, and the new tool will be just touching the surface of the work. That is testing various aspects of the drive system, and I'm pretty happy with it. You will be needing very high precision gearing to get anything close to that, and/or very careful attention to fitting and adjusting and maintaining, and/or a lot of money to buy the components. Although my own experience is with a router, I would be happy to get that performance out of a vertical mill.

    Belt drive might not be perfect but it beats any gearing available at an affordable price, I suspect. And while a stepper might not have the resolution of a high-count servo encoder, how often will you need that level of resolution?

  9. #19
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,011. Received thanks 221 times, giving thanks to others 5 times.
    You need speed for turning. To give an example, I run my lathe at 2000rpm for 20mm aluminium, and that is nowhere near the recommended speed. The reason I limit to that, is to stop the stock whipping in the spindle, as it's not got any spindle liners to support material.

    Running some basic figures for 20mm bar through HSMadvisor, for 6061 series aluminium recommended speed is 10222rpm, low carbon steel is around 1900rpm, and 316SS is 724rpm.

    With stepper motors, the rated torque is holding torque. As soon as the motor starts spinning, the actual produced torque at the shaft quickly drops off.
    Also, you can only guarantee a stepper motors position to one full step (1.8 degrees for a standard 200 step motor). The main purpose of microstepping is to improve smoothness at low RPM, not to improve positioning. Microstepping may provide fractional steps in movement, however due to friction/stiction within the system, the exact distance cannot be assured.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  10. #20
    What you guys are saying makes perfect sense to me, but here's one other thing I cannot understand without actually testing a stepper.

    Say a (standard 1.8 degrees/200 steps) stepper motor is rated at 10Nm holding torque (never mind the micro stepping), and we apply a tangent force. With no rotation, just holding the spindle in place, what does this actually mean in practice?

    Will the 10Nm stepper keep the spindle dead locked until the 10Nm value is reached, and then it starts skipping in the direction of the force?

    Ok, say not until 10Nm value is reached, but will it keep the spindle dead locked until at least 5Nm is reached and than it start's vibrating within the 1.7 degrees interval, and when it reaches 1.8 degrees (10Nm torque) value, it skips in the direction of the force?

    Or will it vibrate anyway, no matter the applied force? So for 1Nm it'll vibrate 0.2 degrees, for 2Nm -> 0.4 degrees and so on (is it a linear or logarithmic graph?). If yes, I can understand why a brake is needed in this case.

    I hope it makes sense.

    Cheers!
    Last edited by Valfar; 27-02-2017 at 04:33 PM.

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