Thread: Thk kr

  1. #1
    Hi,

    I've been reading this forum for a while now. Lots of knowledge people here. I was wondering if any of you had used or had any views on the KR actuators from THK?

    I can get a used THK KR55 with 680 travel (2 blocks) or 800 (if I remove 1 blocks) for a fair price. I was thinking of using it for the X axis, on a machine that will occasional use pretty large router bits, primarily on hardwood. The lead is 20, so it's going to need some torque to shift it I guess.

    My main reservation is not knowing how to compare the permissible loads on one KR block vs two rails and four blocks (well spaced).

    Any advice appreciated.

  2. #2
    I can't see a problem but would need 2 blocks.
    Regards the lead then depends on the work your doing and the micro stepping your using on the drives.
    For Mainly wood use then 20mm lead will be ok and with average 800 micro-steps then you'll have theoretical resolution of approx 0.02mm which is plenty for wood.!! . . . . You'll also have massive OTT speed for cutting so you may want to think about gearing it 2:1 and increase torque and resolution.?

  3. #3
    Quote Originally Posted by JAZZCNC View Post
    I can't see a problem but would need 2 blocks.
    Thanks for your reply. The blocks are each 128mm wide (including the wipers etc), which is why I thought I might be able to get away with one block.

    Quote Originally Posted by JAZZCNC View Post
    You'll also have massive OTT speed for cutting so you may want to think about gearing it 2:1 and increase torque and resolution.?
    Yes, good point. It's not ideal. I'd rather chuck the most powerful stepper motor I can find on there, instead of gearing it down. I'd like to keep it simple and uncomplicated if possible!

  4. #4
    Quote Originally Posted by ~andy View Post
    Thanks for your reply. The blocks are each 128mm wide (including the wipers etc), which is why I thought I might be able to get away with one block.
    You Could try it but I wouldn't 128mm just isn't enough IME..!!


    Quote Originally Posted by ~andy View Post
    Yes, good point. It's not ideal. I'd rather chuck the most powerful stepper motor I can find on there, instead of gearing it down. I'd like to keep it simple and uncomplicated if possible!
    Yes Know what you mean regards KIS but going bigger on the stepper isn't always the best and it's a common mistake for people to think bigger is better, which really isn't the case with steppers.

    If you go with larger Nema 34 motors then just be mindful you'll need drives capable of handling large voltage, minimum 80Vdc or better still 240Vac high power drives. If large DC drives then you'll need Large PSU to match which are very expensive to buy so then you'll be looking at building your own so KIS is not so KIS anymore or cheap.? . . . That said I'd recommend you build your own in any case has Unregulated PSU are just better for steppers full stop.

    Because you have such a high lead in your case you'll get away with Nema34 regards speed but you'll still need the correct drives/psu or you'll be underwhelmed with the performance.!!
    Last edited by JAZZCNC; 25-08-2013 at 06:27 PM.

  5. #5
    I don't need massive speeds out of the machine. I'm happy with the 2m/m jog speed I have set on my current machine. That would be 100RPM at this pitch.

    At this speed I'm guessing voltage isn't a huge issue. I do have a 24v/20A industrial switch mode supply that I can use for this project. Equally, if it's required I can throw a toroidal and some fat caps in a box.

    I just need to figure out how much grunt I'm going to need to move the Z axis now! Sure I'll find a Nema 23 that can do the job.

  6. Read http://www.mycncuk.com/forums/faqs-p...do-i-need.html

    Quote Originally Posted by ~andy View Post
    I don't need massive speeds out of the machine. I'm happy with the 2m/m jog speed I have set on my current machine. That would be 100RPM at this pitch.

    At this speed I'm guessing voltage isn't a huge issue. I do have a 24v/20A industrial switch mode supply that I can use for this project. Equally, if it's required I can throw a toroidal and some fat caps in a box.

    I just need to figure out how much grunt I'm going to need to move the Z axis now! Sure I'll find a Nema 23 that can do the job.

  7. The Following User Says Thank You to irving2008 For This Useful Post:


  8. #7
    Quote Originally Posted by irving2008 View Post
    Thanks. That's exactly where I went after typing my reply. I seems that the 4Nm Nema 23 steppers I had my eye on at CNC4YOU should be fine.

    At 100RPM, I reckon I should be able to get away with this DIN mount power supply (IRC you can adjust it up to 28v), which would be a nice tidy solution. I'll be mindful that I may need to swap it out for something larger when I pick the drivers.

  9. #8
    Hi,
    no personal experience with these KR, but as far as i remember reading at cnczone the guys were not too happy with the KR assembly. At least for Z.

  10. #9
    I did have a quick read over at CNC zone about the KRs. I can see that people using the smaller models, single block, and large routers might have an issue with them as Zs. I've picked up a KR46, with two blocks and it's the same width as the spindle I'll use, so I'm sure it will be fine. It does look a bit tall, being so thin.

    The KR55 is a monster, beautifully constructed.

    Click image for larger version. 

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