4x8ft CNC router - steppers, drives and sanity check


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Thread: 4x8ft CNC router - steppers, drives and sanity check

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    Default 4x8ft CNC router - steppers, drives and sanity check

    I have designed in Autodesk Inventor and am in the process of building a CNC router, 4x8ft, steel frame, MIC-6 plates. I'll be using steppers driving a pinion on a rack for the X&Y axis, a screw for the Z. Pretty typical stuff.

    Power available is 220V 1-ph @30A, maybe 50A depending but enough either way.
    The table is 2x4x3/16" tube, 2x3x1/8" cross supports
    The gantry is MIC-6 risers, welded steel cross tubes.
    Total gantry Mass to be moved by the two X steppers is 225#
    Hiwin 20 series rail and bearings throughout, medium preload, 12" bearing spacing
    20 pitch, 20 degree racks, driven by a 1" P.D. spur from a timing pulley / belt reduction of undecided ratio.

    I plan to cut:
    Wood: 1" MDF, 3/4" oak solid and plywood, 3/4" solid pine and plywood, maybe some exotics
    Plastic: 1/4" polycarbonate, 1/4" acrylic and several lighter plastics, maybe PE
    Metal: 6061 / MIC-6 aluminum, brass
    Other: 3mm / 6mm foam for the RC airplane hobby (possibly cut with a hot knife/pin)

    All materials I expect will be cut at 60ipm max, the foam maybe 100ipm. I'm estimating 75# max cutter force.
    I'd be nice to traverse the table in 30 seconds or 180ipm no load.

    I'll start with a 3/4hp router motor later upgrading to a spindle, which means cutting metal will come later.

    I have an older 800MHz PC running WinXP dedicated to the job with USB, serial and a parallel port. I can build another computer if needed.
    I also have a 48VDC 40A power supply I could use.


    OK. I calculate with orientalmotor.com the X axis will require 625oz-in at 59rpm, 2.0 safety factor to make the cutting specs at 75% efficiency. Therefore each X axis stepper theoretically will need to make 312oz-in torque.
    I'd use the same stepper for the Y and Z which should work nicely.

    Yes the frame is heavy, it is also ridiculous rigid and once complete should be a workhorse. I have work lined up for it now and for the foreseeable future.



    Now for the most asked question which I have spent a great deal of time trying to figure out.
    Which steppers and drives?

    I'd like to use KL34H295-43-8B, NEMA 34 MOTOR 906 oz-in. Torque falls fairly propertional with the speed. The chart doesn't mention voltage.
    142oz-in per motor @ 3000ppm half step which is 470ipm using a 1:3 ratio.
    460oz-in per motor @ 400ppm half step is 60ipm max cut speed per motor.

    That's a huge amount of torque

    I'm in love with the NEMA 34 motors and that above is way too much torque so:
    KL34H280-45-8B might be a better choice at 640oz-in. Unfortunately I can't find a torque curve.


    If you're still reading. Any suggestions? Do you see any obvious errors in my logic? I'm looking for stepper torque curves now. Any suggestions will be welcome.
    What is a reasonable maximum pps at 48V with motors in this range?

    I'm considering the KL-9082 driver here: http://www.kelinginc.net/KL-9082.pdf

    The long story short, I have some money to build this finally so I don't want to cheap out on parts to regret it later. The motors and drives are the last things to figure out.

    Thank you,

    Similar Threads:
    Last edited by spiral72; 07-23-2014 at 09:40 PM. Reason: Error in my pps - rpm formula


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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Ok, no opinions? That's discouraging



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Size and weight aren't the most important factors in choosing motors. How fast you want to accelerate, and your max velocity are what's most important.

    Do you see any obvious errors in my logic?
    Yes.


    All materials I expect will be cut at 60ipm max
    I'd be nice to traverse the table in 30 seconds or 180ipm no load.
    The speeds you're looking at are way too low.
    You really want to be cutting MDF and hardwoods at 200+ipm. Any slower and your tools will wear out very quickly, due to the heat generated at such low chiploads.
    Cutting forces at 60ipm would probably not exceed 5-10 lbs. To achieve 75lbns of cutting force, you'd probably need to be cutting full depth through the 1" MDF, at 500+ipm, and would probably require a 5hp spindle to keep it from stalling.


    You're going to want much more than a 3/4 hp router. That's the equivalent of putting a lawnmower engine in a corvette.

    The 800Mhz PC isn't going to cut it. I'd look for a 2Ghz Pentium 4 or newer if you plan on using the parallel port. If using an external motion controller, than I'd go with a much more modern PC.


    The motors you're looking at should easily give you 500+ipm rapid rates.
    Torque curves are helpful, but don't tell the whole story. Unless you are using the same drives, at the same voltage, with the same exact settings, the torque curve may be very different in your application.

    For a Nema 34, my recommendation would probably be to find something in the 640oz range, with the lowest inductance you can find.

    I'd also avoid the 9082 drives. Go with either the KL-8070D Digital drives, or Gecko G201X or G203V drives. They'll be much smoother and faster than the 9082's and are only a little more money.

    Sounds like you're building a very heavy duty machine frame, and trying to go really cheap on everything else.

    Gerry

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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Aside from all Ger's good advice, I'd add that if you're using those large motors, you'll get better performance out of them with a higher-voltage power supply. The Gecko drives recommended above will take an 80v PS; not sure about the KL drives.

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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    ger21:
    Thank you for your advice. I will recalculate everything at 200ipm cut speed. I used to run a cnc router at work a long time ago, but I don't remember cutting MDF that fast.... my memory is flawed obviously.
    Yessir, a spindle is on the list, but it will be a bit. I'll be making 1/8" deep passes until I can afford the upgrade.
    Cheap!? Hmmm, you mean the computer and router I hope? I thought the steppers and drives, linear components etc were all fairly high end stuff.

    Regardless I will look for the 640ozin steppers you suggest.

    Thank you very much. I will follow your advice

    Awerby,
    The KL units accept 72V, 80V absolute max.... which means 72V. I will look for a higher voltage supply. Thank you for the advice.

    edit: The power supply I intended to use seems to be dead. Looks like I'll be buying a new supply after all.

    Last edited by spiral72; 07-26-2014 at 11:00 AM.


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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    I use KL8070D on my x-axis motors. My machine is a 48x96 and I get rapids of 600ipm and cut at 200+. My Z plunges at 30 (I could do 60 but most bits can't) and rapids at 150. My Y and Z are using hybrid nema34 steppers with 1128oz-in torque. My x uses 2-980oz-in steppers. You have a HUGE amount of mass to accelerate with a steel gantry. Unless you can get enough power to accelerate rapidly your cut speeds will be greatly reduced in all but the longest straight cuts.

    I have been down the road you are traveling. The frustration factor of too-small steppers is amazing. If I had a nickel for every dime I wasted on under-sized motors I would have a lot more nickels.

    I started with a DeWalt 1 3/4 router as well. After ruining 2 and setting one on fire I bought a proper 2.2kw spindle. Routers are not made to run continuously, they have terrible runout, they are air cooled so they blow dust all over the shop, and they are noisy. Mach3 can control a spindle. If my spindle is running at 24000 not in material I can have a conversation next to the machine in normal tones. It is water cooled with a radiator that is remote mounted out of the dust stream.

    Electronics: If you have not purchased your BOB yet I would recommend an Ethernet smooth stepper and c32 BOB sold by cnc4pc.com. The smooth stepper eliminates the need for a parallel cable and plugs directly into the c32 board. Most of the connections on the c32 are RJ45 so you can use Cat5 cables. Also the smooth stepper gives you 34 i/o's.

    The highest voltage your drivers can stand is recommended. Higher voltage means that your wire will experience less voltage drop and can be sized smaller making it more flexible. Be careful. 80 volts DC can bite just as hard as AC. It just doesn't cause as much resonant hum in your ears.



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    rbraeking:

    That is a lot of good information. I run the numbers again with 200ipm cut speed, 0.5s acceleration time still with 75lb cutting force and I get 650ozin of torque required on the X..... which should be something like 1/4 the torque available with 640ozin steppers and a 3:1 pulley ratio. I will look at this again.

    I do not have the BOB yet, or any electronics other than the apparently broken 48V power supply and an old PC. I will look at the boards you recommend by cnc4pc. The ethernet version would be nice to relieve all duty from the PC which means I can be doing other things on the computer without worry..

    Thank you for the information and recommendations. I will consider every bit of it.



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    rbraeking:

    I've all but decided on the Ethernet smooove stepper. Thank you, I think that is a device with no negatives especially since it relieves the computer from the burden of diddling the parallel port pins. I have some more reading to do, but I'd like to go with a C10 BOB. I don't need a charge pump with the Ethernet, the ESS output spindle speed when I get one and I don't need two ports worth of IO. They're features I'd be paying for but never use. If that's stupid tell me and if you don't mind tell me why.

    I really think I like the KL8070D over the Gecko drives mentioned above. I'm considering sticking with that.

    I haven't yet decided on 640ozin, 906ozin or another. Calculations say either one is fine, but the 906ozin motors have lower inductance.



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    I think that you will regret the C10 decision.

    Negatives: No spindle control. Need ribbon cable to interface with the Ethernet card. No relays for accessories i.e. coolant pumps, dust collector, vacuum pump, etc., Need to share limit switch inputs. (All your limit switches can be wired in series.) It works. No led feedback (if your motor is not turning you can't look at the card and see if it is sending the signal), individual wiring connections. (My fat fingers and bad eyesight make this a negative. You may be an exception to this line of thinking)

    I agree that the charge pump is redundantly repetitive, however, the advantages far outweigh the additional cost of the C32. The charge pump feature can be disabled by flipping a switch on the card. Mach3 has a lot of power that you will not be able to use with the C10. You have a Hemi engine and you are contemplating installing a Model T transmission behind it.

    I don't think that you have considered all the mass you are trying to accelerate/decelerate in your motor calculations. Your z and y with its motors, router/spindle, cooling system,dust collection, and linear bearings must be moved by the x-axis. It also has to drag all the motor cables and limit switch cables back and forth. Normal stepper motors have no feedback so in order to avoid missed steps it is essential to over-size the motors. 0.5 in/sec/sec is awfully slow acceleration. Mach won't even allow less than 0.5 unless you reduce max speed to below 120. At 600 ipm rapids it would take 20 seconds to get up to speed. Yawn. And Mach will start decelerating 20 seconds before it gets to the end of its move. If you are jogging, when you release the jog key the axis will decelerate to a stop. Hopefully you can anticipate when this happens so you can release the button soon enough. Re-enter your calculator using 60 in/sec/sec acceleration/deceleration and see what it returns for a motor size. You should shoot for 600ipm as a rapids speed. A lot of time is wasted in running a job if the router cannot re-position rapidly. Commercial machines rapid at 1800. (Camaster Cobra) That is an exaggeration on their part because it will never get up to that speed unless the acceleration is nearly instantaneous.

    Good luck on your build.
    Bob



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Spiral72

    Another thing that you possibly have not considered is the rapid loss of torque in stepper motors as speed increases. Your calculations are finding initial torque necessary to start the load in motion. if your motor makes 2 revolutions per inch of travel then at 600ipm the motor will be rotating at 1200rpm. The available torque will be 1/3 to 1/4 the initial torque of the motor. If you get your desired resolution through microstepping then you have already reduced the motor torque. I am a tinker, not an engineer but I know what I know from trial and error.......mostly error. After posting my last I fired up my machine and increased the max speed to 1800 just to see what would happen. (testing Cobra's 1800 claim) The motor stalled after about 20 inches of travel. I attribute that to loss of torque due to increase in rpm. I just hate to see you go through what I did in not sizing my motors strong enough to begin with.



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Not discounting your own experiences.

    But there are countless threads here from members who purchased motors that were too large for their machines, and who got much better performance going with smaller motors. Bigger is often not better.
    A steppers torque rating is not the whole story. You can buy two different motors with identical torque ratings that will perform very differently. A 6 amp 640oz motor will give you much higher speeds than a 3 amp 640oz motor.

    If you go to the MechMate forum, you'll see a similar size machine where I think almost everyone uses motors in the 640oz range, and they typically have rapids in the 600-1000ipm range.
    Gearing and voltage play an important role in top speed, as does the choice of drives. Good quality drives can provide 50% or more performance.

    CNC Router Parts used to offer both 640 and 960 oz motors, but it looks like now they only offer the 960 oz motors. Maybe they've found that those are the best choice with their 3.2:1 rack and pinion systems.

    Choosing stepper motors can be difficult and confusing. If you can't find other users with similar systems that work well, make some calls to reputable companies that work with these systems on a daily basis. Preferable someone that actually sells machines, and not just motor kits.

    - - - Updated - - -

    Not discounting your own experiences.

    But there are countless threads here from members who purchased motors that were too large for their machines, and who got much better performance going with smaller motors. Bigger is often not better.
    A steppers torque rating is not the whole story. You can buy two different motors with identical torque ratings that will perform very differently. A 6 amp 640oz motor will give you much higher speeds than a 3 amp 640oz motor.

    If you go to the MechMate forum, you'll see a similar size machine where I think almost everyone uses motors in the 640oz range, and they typically have rapids in the 600-1000ipm range.
    Gearing and voltage play an important role in top speed, as does the choice of drives. Good quality drives can provide 50% or more performance.

    CNC Router Parts used to offer both 640 and 960 oz motors, but it looks like now they only offer the 960 oz motors. Maybe they've found that those are the best choice with their 3.2:1 rack and pinion systems.

    Choosing stepper motors can be difficult and confusing. If you can't find other users with similar systems that work well, make some calls to reputable companies that work with these systems on a daily basis. Preferable someone that actually sells machines, and not just motor kits.

    Gerry

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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Gerry,

    Obviously higher amperage translates into more power with a given voltage. What we really need is watts of power. 6 amps at 24 volts will yield about half the power of 6 amps at 48 volts. The torque ratings advertised for steppers is holding torque. Of course, once in motion less power is needed to maintain a given speed unless there is also resistance ie when cutting.

    Spiral,
    I think that Keiling products are made for Keiling by Leadshine®. I have attached a pdf of their spec sheet which includes torque curves. (I think. If it doesn't get attached go here: http://leadshineusa.com/UploadFile/Down/86HSxxd.pdf)



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Gentlemen, thank you for the time you've put into the replies!

    I'm still undecided on 640 or 906ozin motors. 600ipm I feel would be plenty fast. That's traveling the table in under ten seconds with 460ozin X2 of torque which should be considerably more than required.
    I calculated 60ins2 acceleration which should require 660ozin torque on the X axis which is nearing a 906ozin stepper requirement as long as I want the 2X safety factor.

    Thank you for the Leadshine link. I'd seen that before but didn't make the connection. I'm studying that now.

    Ger21: CNCrouterparts still offers the 640ozin motors. They have the "PRO" series stuff which is 906ozin and related parts and the "Standard" stuff which is 640ozin.

    I'm still comparing specs, calculating and shopping around. I feel like I've chosen a good drive and motor controller. The frame is jam-up as are the mechanicals so far. I just received the screw ball bearings and thrust bearings today which are good for an absurd amount of force. The first shipment of Hiwin should be here this week. I'm checking everything for the Nth time and sending 75% aluminum plates off to be cut tomorrow. At least I know it'll be NEMA 34 so that will be done.

    I typically shy away from all-in-one devices (C32). I'll make my decision at a later time. I still have a bunch of mechanical money to spend I wouldn't mind building the controllers myself actually, but time costs a lot more than the savings of a ready made board.

    I'm likely going with the 906ozin steppers simply because I have a torque curve (however valid it is in my application) and even in the worst case, I have enough torque.



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Another thing to consider is Leadshine® Hybrid Steppers. They are like regular stepper motors but with an encoder that feeds back to the matching driver. In NEMA 34 you have your choice of 566 or 1133 Oz-in. The nice thing about them is that you do not have to oversize to protect against missed steps. The driver will catch it up if it does miss a step. They are available at AMT-Source of affordable quality servo/stepper motor controls. They are also made for Automation Technology Inc under the Keiling® brand name. You can buy them direct from either but I have found Arturo Duncan at cnc4pc to be a good supplier who is DIY friendly.



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    I calculated 60ins2 acceleration which should require 660ozin torque on the X axis which is nearing a 906ozin stepper requirement as long as I want the 2X safety factor.
    Remember that acceleration will be linear, and will require the same torque at your top speed as it does when it starts accelerating. So if you need 660oz of torque, you'll need that at your maximum rpm you're accelerating to.



    The nice thing about them is that you do not have to oversize to protect against missed steps. The driver will catch it up if it does miss a step
    The problem with that, though, is that the other axis will continue to move along at their normal rate while the one axis is catching up. Not a problem if it only loses a few steps, but if it stalls for a second, your parts may still be ruined.

    Gerry

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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Gerry wrote: "The problem with that, though, is that the other axis will continue to move along at their normal rate while the one axis is catching up. Not a problem if it only loses a few steps, but if it stalls for a second, your parts may still be ruined."

    That would be the case only if you did not have a margin of speed available. Since the heavy torque requirements are when actually cutting there is beau coup extra speed available for catching up. If you clock your motors to run at 700 and make your rapid moves at 600 you will have some catch up room. Realistically, if you are missing more than a few steps there is another problem that the drivers can't solve. You would have the same problem with true servo drives as well. The "hunting" problem of servos is avoided using hybrid steppers. I am especially happy with the hybrid on my Z axis. Since there is the difference in torque required to pull out verses to plunge. The mass of the spindle is either working for you or against you. Other axes are unaffected by gravity. I had been having step loss problems with my Z prior to installing the hybrid. It was always plunging deeper and deeper throughout the jobs. Now, after hundreds of plunges, the axis remains true. It is especially evident in drilling operations and 2.5d carving.

    Bob



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    I tested my machine this morning using the new ethernet smooth stepper/C32 combination on the x-axis. (96 inch axis) The single 650 did the job. Evidently I was not losing steps in the motor but in the parallel port. I am much happier with the ethernet connection. It buffers the packets rather than running in real time depending on the computer's not being compromised by the Windows® OS robbing utilities.

    If Spiral72 needs a BOB, I have a C1 on hand. It has never been used as I got my C11 while waiting for the C1 to ship from a local reseller. It retails for $73. Make me an offer.

    Bob



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    That would be the case only if you did not have a margin of speed available. Since the heavy torque requirements are when actually cutting there is beau coup extra speed available for catching up.
    In most cases, you lose steps because you don't have enough torque. So if you already don't have enough to prevent lost steps, then you certainly won't have enough to catch back up right away.

    If you have an overabundance of torque, then you shouldn't be losing steps.

    Gerry

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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    Quote Originally Posted by ger21 View Post
    Remember that acceleration will be linear, and will require the same torque at your top speed as it does when it starts accelerating. So if you need 660oz of torque, you'll need that at your maximum rpm you're accelerating to.
    Yessir, I'm still calculating the X axis though which has two motors for a theoretical 330ozin torque per. The 640ozin should do it but not at a 2X safety factor I was looking for. I'm pretty well sold on the 960/906 etc ozin steppers thanks to y'all. Heck it's an $80 or so cost increase which isn't a whole lot considering the overall cost.

    Quote Originally Posted by rbraeking View Post
    Another thing to consider is Leadshine® Hybrid Steppers
    ............I am much happier with the ethernet connection.
    ............I have a C1 on hand.
    Oh man you have no idea! I saw those but it'll have to go on my wish list for now. It's outta budget. I am looking pretty much exclusively looking for dual shaft steppers though for just such an upgrade

    Yessir, I'm glad you twisted my arm on that. There is no way I'm driving this thing off the parallel port now. I have a CNC hot wire foam cutter running on the parallel port. It's kind of pathetic.

    C1: That is very kind. I will research the C1. Give me a couple days. I do like all the optoisolation, not for the computer 'cause the ethernet handles isolation, but it'll protect the Smoove Stepper.


    What happened to Enco!?? I thought they had great prices from what I remember. McMaster is less expensive for the screws! Good grief.
    I'm waiting for my Hiwin products still. It's like waiting for Christmas man! The riser plates should be out of the machine shop this week. I'm planning to cut blanks out of the rest of the plate tomorrow, punch some holes in my cross tube weldments and worry about calculations some more. I should just quit beating the numbers and spend some money already. I hope to order the remaining Mic-6 plate next week.

    I was hoping to powdercoat the steel, but at $400..... Nope, it'll have to be automotive primer / paint which should be slightly less durable.
    I'm shooting for mid-September first cut!



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    Default Re: 4x8ft CNC router - steppers, drives and sanity check

    General industry practice is to oversize stepper motors by about 50% over your needed torque values. If your application requires 300oz-in of torque at a certain RPM, then you will want to size and power the motor for 450oz-in of torque at that RPM. This is recommended by all manufacturers unless you have done a wonderful job of understanding the mechanics in your application, and even then you'll want to design in error corrections and fault tolerances.

    If you size your motor too big you run into weird resonance problems, and inefficient power consumption. In a same series of motor it is possible to have a higher torque at a higher RPM with single or double stack over a triple stack motor.


    Those motors on automationtechnologies aren't even provided with a torque curve. I wouldn't even bother with them honestly. It doesn't even say what is 640oz-in for that nema34 motor, it's probably the holding torque, but they don't specify that. Without a torque curve over the RPM band you haven't even a clue of the motor's capability. It might fall off like a rock after 100RPM. This lack of information is how motors get sized so poorly.

    Quote Originally Posted by spiral72 View Post
    That is a lot of good information. I run the numbers again with 200ipm cut speed, 0.5s acceleration time still with 75lb cutting force and I get 650ozin of torque required on the X..... which should be something like 1/4 the torque available with 640ozin steppers and a 3:1 pulley ratio. I will look at this again.

    640/4 = 160oz-in * 1.5 = 240oz-in is a 50% oversize. What RPM will you running the steppers at here? I'm interested in seeing the calcs.

    I like automationdirect - they have settings on each driver for the motor. Components seem to be of high quality. I'm testing a C35S breakout with a USB Smooth stepper driving the STP-DRV-6575 with matching nema23 motors and I really am happy with them (benchtop testing).
    Stepper Systems | AutomationDirect.com
    they provide torque curves for their motors as well



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4x8ft CNC router - steppers, drives and sanity check

4x8ft CNC router - steppers, drives and sanity check