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    Default Lathe CNC Conversion, Questions before I start

    I'm getting ready to convert my Chinese 9x20 lathe to CNC, and had some questions. 99.9% of the work will be on aluminum, but I do have plans for a project next year that would require making some small titanium parts (K baffles for a firearm silencer). Steel will work in place of the titanium, but weight is an issue so if the lathe can handle the titanium, that would be fantastic.


    1. What length ball screws do I need? I'm planning to use C7 screws off eBay for both axes, but most of the screws are much too short (300mm) or much too long (1150mm). Would this 650mm screw work?
    2. Are NEMA 23 motors beefy enough? Concerned they'll be a handicap on anything tougher than aluminum.
    3. I'm planning to use a pair of Geckodrive 251Xs to control the steppers via a BeagleBone Black. Any pitfalls here, aside from the BBB not being especially well supported for CNC?
    4. I don't own a mill, so I need to buy mounting hardware. Any recommendations on where to buy? Or maybe somebody around here who would make the brackets and such for a fee?


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    Default Re: Lathe CNC Conversion, Questions before I start

    hi if you use an reduction drove nema 23 might be enough but slow i use 3nm nanotec motor on my mill and lathe reduction 3:1
    if you look at bbb have a look into machine kit based on linuxcnc but i for instance run my cnc lathe on an mini itx board and we love gmoccapy and the touchscreen ,..thomas


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    Default Re: Lathe CNC Conversion, Questions before I start

    Thanks for the advice. Rather than reducing the NEMA 23s, I think I'll just go with the NEMA 34s. Simpler, and more torque is more better.

    As far as the BBB goes, MachineKit is indeed what I was looking at. Primary reason I'm looking at using it over a normal computer is cost and size. My shop is very limited on space, so anything I can do to cut down on the footprint is a positive. Plus, I like screwing around with mini computers, and I've never had a reason to use the BBB before.



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    Default Re: Lathe CNC Conversion, Questions before I start

    Hi,
    i am not sure if the bbb is sufficient but if you don't need an touchscreen then have a look at RoBoard NCBox-189 CNC Machine Controller - RobotShop
    i have that one running on one of my machines only problem is the cards are verry picky ,..



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    Default Re: Lathe CNC Conversion, Questions before I start

    The ball screws from China are available machined to your measurements for a very reasonable price,
    The seller you linked to provides that service.

    Anyone who says "It only goes together one way" has no imagination.


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    Default Re: Lathe CNC Conversion, Questions before I start

    Thanks for all the advice. I think I'm still going to try the BBB route, since it costs much less than any other option I've seen. I'm a software engineer, so I'm not too concerned about iffy software or hardware that I may have to modify myself. Plus, I'm a big fan of open source, and could commit any changes I make back to MachineKit.

    Since nobody has told me I'm dumb for picking the cheap Geckodrives, that just leaves sourcing/making the mounting hardware. I've seen a few guys online that sell mounting kits for attaching NEMA 34 motors to the Chinese 9x20, price seems to come in at right around $200. Seems reasonable, but for that much, I'm tempted to spend a bit more and get a milling attachment to make it myself. But a mini mill is on the short list of tools to buy (probably with my tax refund in a couple months), so that feels like a waste.

    Any recommendations?



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    Default Re: Lathe CNC Conversion, Questions before I start

    hi mill depends on material and size what you try to achieve i have an router type of mill (german quality ) so i can do pcb everything up to alu but then it gets realy slow i also have an proxxon mf 70 cnc which can do alu but ,... verry time consuming and erratic. i then did factory conversion of steel able vertical mill ( bf 20 soze ) but made in austria
    remark this one i now made as an product which i sell so my advise make a list what you want to achieve like travel speed weight etc and how important it is for you then get the offers and compare the prices otherwise i guess everyone gives you hints from his point of view and loves his setup so much to recommend it -


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    Default Re: Lathe CNC Conversion, Questions before I start

    This may be late, but..

    Nema 34 are the wrong choice.
    They will accelerate slower than the nema 23.
    Their top speed will be much lower.

    The geckodrives have these issues:
    1. They activate from back emf. Major issue.
    Manual usage will be a pain.
    2. Noisy. Hiss.
    3. They dont have soft start.Major issue.
    Huge inrush current on multiple motor setups.
    4. Single ended. Modern drives can use differential wiring (much less noise sensitive).
    Not really important, imo, ime.

    The cheap 2M542 drives are technically much better, in categories 1-4.

    Direct driving the lathe ballscrews is a bad idea, with a lathe. Most especially with steppers.

    Reasons.
    You dont need speed.
    You want more resolution.
    You want more accuracy.
    You want more rigidity.
    You want more acceleration.

    Best sweet spot /$$ is belt drive, at 1:2, with nema 23 steppers.

    Use HTD 5/15 mm wide pulleys (ot M5, T5, gates 5 mm profile etc).
    HTD is cheaper and works just as well, imo, ime.

    Torque, acceleration, accuracy and resolution will all be about 4x better than direct-driven size 34 motors.

    I even gear down brushless servos, that are already 5-10x more accurate for more resolution, and other benefits.
    There is definitely a good reason for this.

    Example: .. My step size is 0.2 microns on brushless servos, or 20.000 steps/mm. 512 kHz speed.

    Motion control engine will be critical for threading.
    On mach3, css does not work.
    On mach4, yes, on some engines only.

    Good threading needs servos.
    This is my firm opinion after 2000 hours work, and 3 motion control engines, and 8000€.

    Good as in something you can measure, and it will pass std thread go/no go gages.
    The index pulse quality at varying rpm is critical, and only servos / hardware cards can do it really well.

    Std optical switches have varying responses, the edge is not crisp, and the delay varies with speed.
    Thus, you may get ok threads at some speed, but then not, at another.
    Or cold/hot machine, eg 390 rpm cold vs 450 warm.

    If you dont need to do industrial-quality threads, all this may not matter to you.
    A nut will thread on almost anything.

    --
    You may or may not be able to do titanium.
    The steppers wont affect this at all.

    Rather, the lathe rigidity (very low for titanium) and your tools will be the limiting factor.

    You need large cuts, and low rpm (low surface speed), for titanium. Lots of torque at low speed.
    Exactly the hardest part on a 9x.

    Otoh, I have seen a small ti. part machined with tiny tools, on a 5 axis machine.
    The forces were very low.

    Thus, its doable, if you know how or get the right tools/feeds.
    So, imo, without having done it, I think its possible, but may take some tooling and experimentation.
    With cnc anything in steel is quite easy, ime, imo, on a lathe.

    E.g.
    Deep drilling 304 stainless, 8 mm D, 140 mm deep, is really hard to do.
    (Heats, material grabs, forces are/get huge when drill heats and rubs).
    4 pieces take == 1.5 hours in total, after 6 hours experimentation and 6 extra industrial drillbits.
    Note its 17:1 diameter/length.



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    Default Re: Lathe CNC Conversion, Questions before I start

    Further to post # 8- I referred to mach3/mach4 as I am quite familiar with them, and industrial machines/hardware.

    You will find anything complex on anything non-standard will, basically, not work at all, realistically.

    Ie getting threading working on low-end hw and non-std sw is simply too much work.
    Same applies to css, multiple toolposts, leadins leadouts etc.

    Using linuxcnc on std hardware and proper hw (mesa cards) will work perfectly, imo.

    Fwiw..
    I used to do a lot of linux stuff on servers, in the past (we built/managed 70+ servers for major companies, in mission-critical operative use, for years, so..).
    Just not on cnc (various valid reasons, imho).

    You need excellent tracking, and very low latency, for end of thread pullouts to occur, perfectly reliably, and at the exact same point.
    And with extremely fast acceleration, as fast as possible.

    Any small deviation, and the tooltip digs in, forces go up 100x in less than 1 ms, or 0.001 secs, and the tooltip snaps or the work is ruined.
    You really want to thread at 600 rpm, or more, for good surface speed.
    Now the problem is that you only have 600/10 or 0.1 secs/rev.
    You need to hit at approx 1 degree accuracy, or better.
    0.1 secs/360 = 2.7 ms.


    All above is basically ONLY related to threading, especially high quality, and at moderate rpm as needed for cosmetic reasons (so the threads look good).
    Std lathe code will run fine.

    Any steppers/drives etc. will make great pieces, cones, tapers, corners etc with no problems, imo, ime.



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    Default Re: Lathe CNC Conversion, Questions before I start

    Quote Originally Posted by hanermo View Post
    This may be late, but..
    Not at all. I won't be buying most of the components for a while, just trying to collect information first.

    Nema 34 are the wrong choice.
    They will accelerate slower than the nema 23.
    Their top speed will be much lower.
    Hadn't considered speed. And cheaper is always better. Anybody have a differing opinion here?

    Also, how much torque do I really need, here? And do the motors with more torque have a correspondingly lower acceleration? If so, it would seem that the ~180 oz. in. motors would be preferred over the ~270?

    The geckodrives have these issues:
    1. They activate from back emf. Major issue.
    Manual usage will be a pain.
    2. Noisy. Hiss.
    3. They dont have soft start.Major issue.
    Huge inrush current on multiple motor setups.
    4. Single ended. Modern drives can use differential wiring (much less noise sensitive).
    Not really important, imo, ime.

    The cheap 2M542 drives are technically much better, in categories 1-4.
    Thanks, this is exactly the kind of information I was looking for. And hey, cheaper is better! I think we're going to be good friends.

    Direct driving the lathe ballscrews is a bad idea, with a lathe. Most especially with steppers.

    Reasons.
    You dont need speed.
    You want more resolution.
    You want more accuracy.
    You want more rigidity.
    You want more acceleration.
    Again, fantastic information. I'm a total novice here, so the only thing I'd considered here was the resolution.

    Motion control engine will be critical for threading.
    On mach3, css does not work.
    On mach4, yes, on some engines only.
    Can you elaborate a little here? I know what CSS is, but what is motion control engine? A quick googling didn't shed a lot of light.

    Good threading needs servos.
    This is my firm opinion after 2000 hours work, and 3 motion control engines, and 8000€.

    Good as in something you can measure, and it will pass std thread go/no go gages.
    The index pulse quality at varying rpm is critical, and only servos / hardware cards can do it really well.
    I actually am planning to do some fairly sensitive threading, for a firearm silencer. It needs to thread in nice and tight, and be perfectly straight. Any deviation off the barrel's axis and you get baffle strikes. Is this going to be a problem with steppers?

    Std optical switches have varying responses, the edge is not crisp, and the delay varies with speed.
    Thus, you may get ok threads at some speed, but then not, at another.
    Or cold/hot machine, eg 390 rpm cold vs 450 warm.
    Planning to build my own tachometer, will use components with a nice, fast, consistent response time. I've got leftovers from a project where I was measuring the speed of a bullet in flight.

    You may or may not be able to do titanium.
    The steppers wont affect this at all.

    Rather, the lathe rigidity (very low for titanium) and your tools will be the limiting factor.

    You need large cuts, and low rpm (low surface speed), for titanium. Lots of torque at low speed.
    Exactly the hardest part on a 9x.
    Yeah, I'm noticing my lathe really prefers to be toward the upper end on speed. If I have to use steel, no big deal, I'd just prefer a lighter suppressor.

    Further to post # 8- I referred to mach3/mach4 as I am quite familiar with them, and industrial machines/hardware.

    You will find anything complex on anything non-standard will, basically, not work at all, realistically.

    Ie getting threading working on low-end hw and non-std sw is simply too much work.
    Same applies to css, multiple toolposts, leadins leadouts etc.
    MachineKit claims support for CSS, threading, etc. on the BBB. I'm willing to deal with the extra effort to make it work to get a cheaper, more compact system. And if it's terrible, I can always replace it and use the BBB for something else. I've always got uses for a mini computer.

    Last edited by OutputCoupler; 12-11-2015 at 05:06 PM.


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    Default Re: Lathe CNC Conversion, Questions before I start

    Speed is not completely unimportant for a CNC lathe. The coarsest thread that you can machine is a funciton of how slow you can turn the spindle (with enough torque left to make a cut) and how fast your z axis will traverse. You need to be aware of that and what kind of threads you want to cut, as a slow z speed an an inability to slow the spindle down will limit your threading options. Also, you will need a lot of torque on the Z axis, as you will be drilling with that axis, which requires a lot of power.



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    Default Re: Lathe CNC Conversion, Questions before I start

    Good threading can be obtained with steppers too.

    Nothing wrong with geckos or Nema 23's.

    A lazy man does it twice.


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    Default Re: Lathe CNC Conversion, Questions before I start

    i just finished my 7x10 build and am ready to start turning but cant get my nema23's to turn. mach 3 shows it moving on the screen but my lathe doesnt budge. i have a simple plug and play setup with a gecko drive. it came all labled and i just plugged everything in and my motors hum but dont move. the gecko drive is green with no fault. ive configured my axises in the ports and pins etc... any help would be appreciated. thanks!



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    Default Re: Lathe CNC Conversion, Questions before I start

    output,
    Do you have any pics of your machine? Also your cnc kits ?



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    Default Re: Lathe CNC Conversion, Questions before I start

    my setup



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    Default Re: Lathe CNC Conversion, Questions before I start


    made a new video covering every detail of my setup. can anyone spot the issue?



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    Default Re: Lathe CNC Conversion, Questions before I start

    Quote Originally Posted by ENEEL View Post

    made a new video covering every detail of my setup. can anyone spot the issue?
    I believe the issue has been solved. I am using windows 7 with a parallel plug on mach 3. mach 3 only supports windows xp and vista via parallel. so I have ordered a us100 device that will go from usb to parallel and be compatible with my setup.



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    Default Re: Lathe CNC Conversion, Questions before I start

    Strange as Win 7 32 bit has support for Parallel ports so I assume you have 64 bit Win 7 - there are plenty of people using Win 7 with Mach 3 either via onboard port or via PCI parallel port cards.



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    Default Re: Lathe CNC Conversion, Questions before I start

    Quote Originally Posted by Fastest1 View Post
    Good threading can be obtained with steppers too.

    Nothing wrong with geckos or Nema 23's.
    I do threading on my mini lathe using a Nema23, 2 Nm, stepper on the spindle. Until now i run them at 1/8 step to reduce noise. This works great on most of my threading jobs. Recently i have problems threading a Cr42Mo4 M40 (ER32 collet). I had no problems on Steel or aluminum. I decided to change the 2Nm Nema23 stepper to a 4Nm Nema24 stepper. It has the same mounting flange. I could also change the gear ratio, but that would require a full redesign.
    So if you like me have a small lathe, are not in a hurry and doesn't do much large threading sizes in though steel, a stepper will do the job.
    By the way, the stepper is activated by a leaver only for threading, broaching, knurling and grinding. All other task use the original 500 Watt motor.



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Lathe CNC Conversion, Questions before I start

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