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    Default building large format machine

    Monday I received my K40 machine and have established that 40w will do all my work. Now I need to work with much larger material so I'm looking at a) building a machine up to 1600x800mm using the laser tube system less power supply from the K40 b)converting the laser less K40 box to a CNC light duty router.

    My first question involves larger steppers- I'm seeing double and triple minimum angle specs vs the K40. K40 seems to be 0.6 deg and NEMA 23 2 phase seem to be 1.8 deg and 3 phase 1.2 deg. Add in larger drive cogs and I'm concerned about getting any where near the 0.001" resolution claimed for the K40 system.
    So what resolution can be achieved?I don't really understand micro steps maybe thats involved.

    Next I'm considering these mechanical setups, the dual head units are not what I need but the prices seem like a better value and who knows it might get put to use in the future-
    https://www.aliexpress.com/item/Best...08.4.36.aj56EJ

    https://www.aliexpress.com/store/pro...612.0.0.qSiwZ8

    Any one have experience with these or recommendations in this general size ?

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    Default Re: building large format machine

    Quote Originally Posted by crossup125 View Post
    the 0.001" resolution claimed for the K40 system.
    Never heard about marketing?

    CNC lasers, constructions, service


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    Default Re: building large format machine

    Keep in mind that the beam expands with distance so you don't have quite as much cutting power at the far corners of the cutting area.

    If you don't plan to do any engraving then steppers can be quite small. 1.8 degree steppers are the most common and half stepping should suffice I would think. This is a good article about drive modes:

    Microstepping, Full Step & Half Step | NMBTC.com



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    Default Re: building large format machine

    Thanks for the link Michael. It was helpful because I've read on the subject but most of it was negative on using microstepping,without explaining how or why. Why would it be implimented if it wasnt useful?No such implication in the provided link.

    I still have a lot of homework to do but at this point I'm scaling back to 1300mm and of course being that I'm doing model planes my wood will never be more than a fraction of the width of the work area but occasionally full length. That should minimize the beam spreading some by avoiding the far corner. Of course it would be nice to put several pieces of wood in and utilize the entire work space hence my hedge of a oversized C02 Power supply to support a future(hopefully from use) replacement tube of greater power. Where I need more info is deciding if using 3 phase steppers will give me more potential resolution or perhaps my Smoothie controller wont use it. I'm in daily contact with the manufacturer of the board so that info is forth coming. Additionally I see in photos of the mechanical systems I'm considering what appears to be differing reduction on the stepper to belt drive. AFAIK, the less expensive setup uses less reduction and larger steppers. So the larger the reduction, the less travel per step. Then it becomes a question if the software can be configured to provide the proper number of steps per distance. I'd guess these are likely non issues but as a newbie, Im not going to guess on spending a total of $1500 on this mod.



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    Default Re: building large format machine

    Although stepper accuracy is desirable keep in mind that the optics are working against you. Since everything is never perfectly straight or square you can't guarantee the beam exits the lens at the same angle over the table. Also I found coolant temperature to have an affect on where the beam hits the first mirror.
    A test is cut a circle and then try to rotate it in the piece it was cut from.


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    Default Re: building large format machine

    Larger format machines usually have larger mirrors and sometimes larger cutting heads/lens. I had a 100w small format Bodor with a small laser head and it was a ***** to get the laser head aligned compared to my 1300x900 machine. Gene

    4x4 shopbot with chicom water cooled spindle
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    Default building large format machine

    If you have a recent k40 with the M2 nano board, the controller uses a variant of the a4988 stepper driver used in many 3d printers. It is microstepped. The stepper motors are .9 degree per step and not 1.8.

    Microstepping greatly helps with making the motor run smoother and decreases resonance. Two big advantages. Almost everyone uses microstepping drives these days to control stepper motors.

    Smoothieboard will not run 3phase stepper motors, only two phase. You can always hook up external 3phase drivers and motors via step and direction output terminals.

    A lot of the higher end laser cutters use servo motors and high resolution encoders to get the speed and resolution required i.e. epilog.

    I have a k40 but it died in a lightening strike that hit my house last Friday.



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    Default Re: building large format machine

    I was told by the supplier of the mechanical setup that they recommend a NEMA 23 stepper, 3 phase 1.2deg. That was for a setup which I believe is using a 1:2 reduction. I'm hoping to get a better one with I believe 1:3 reduction. That should increase the resolution of each step by either 2 or 3, right?
    While researching sources, I ran across closed loop steppers and given the modest price penalty I thought it would be worth the protection against missed steps. AFAIK the sensing is on the motor so its not like some systems that use a sensor to report actual positioning but still any sort of unusual load might have less inpact if it always know if it executed the proper number of steps.

    Jfong, I actually thought the K40 was 0.6deg and it IS the NANO. I guessed that it was typical for steppers to do multiples of 0.6deg , hence 1.2 and 1.8. However, my memory isnt the best and its a moot point. I do intend to use external drivers so I presume 3 phase wont be an issue with the Smoothie then.As above, likely to be closed loop too, which again should be only an issue to the external driver which must support closed loop.
    Thanks for the help, quite useful and reassuring.

    As to mirrors and the head, all are being supplied by the mechanical sysem suppler as an integrated system, I had no hand in picking the components but indeed everything is larger than the K40.



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    Default building large format machine

    I have a smoothie, you can use any external driver with it as long as it supports step/direction inputs.

    Before spending any money on closed loop three phase stepper drivers, I'd look into getting true servo system instead. I use ones from Geckodrives, Applied Motion, Parker , Copley etc.

    Teknic Clearpath seems the popular now but haven't tried it yet. Not much more than a close loop stepper system. I have several Teknic brushless motors (not ones with the clearpath integrated drivers). They are well made.

    I was making a bigger laser using the k40, smoothie corexy with Parker brushless servo system. Now that I lost a bunch of equipment, I don't know anymore.



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    Default Re: building large format machine

    Servo motors are total overkill unless you plan to do a lot of high speed engraving.



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    Default Re: building large format machine

    I think servos would be a real budget buster. Right now I'm almost decided on a MJUnit custom size-1220x610, very competitive price and its just plain beautiful. Almost too pretty to use and built like a brick poop house. People are responsive as can be and how can you beat $145 shipping? Decision is waiting on another company that has a great bundle with steppers/drivers included but $400 shipping -which I've asked for alternatives.

    Price from MJUnit is for single head

    Attached Thumbnails Attached Thumbnails building large format machine-htb1ccowgxxxxxaoxxxxq6xxfxxxb-jpg  


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    Default Re: building large format machine

    So this morning after a productive message exchange with the MJUnit people I thought I'd beat the bushes one more time to make sure my decision include all available suppliers as searching for this stuff is a bit hit or miss given the way the Chinese use key words....like stereo music as the first words in the title.

    Anyway that effort found a previous thread here on a large format project, it looked interesting so I looked it over and found the OP had changed directions and replaced his mechanicals with.... MJUnit. It is actually the first pictures I've found of a non example minimum dimension unit. That helps as you can see from the pic I posted the short rail example unit looks monstrously beefy when in reality its pretty normal as far as rail size

    . One of my big concern was it appears to be the "outer Guide" style design which typically seems to use rollers on the actually guide track. The MJUnit claims to use a dual row(top and bottom, on each side) linear bearing. So not Hiwins but at least not external rollers like most outer guide designs

    http://www.cnczone.com/forums/genera...er-cutter.html



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