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Thread: KMB1 Conversion

  1. #301

    Default Re: KMB1 Conversion

    Well I ran across a reference that said to adjust the gibs based on current draw of the servos. I wanted to try it and see if it made sense. The post where I found it said to adjust he gibs so the motors (different Hurco mill) so the motor draw between 3 and 5 amps. Ok. I can atleast see what the current draw is.

    I have done the X-Axis so far. It started out drawing about 2.65 - 2.8 amps across the range of travel with the ends being closer to 2.8. That makes sense since the middle of the ways and gib will see the most wear. I started tightening down the gib and it took a bit of adjustment before I started seeing much change. Almost a full turn. At first I thought that meant there was a lot of wear, but the change was pretty linear until I started getting really tight. With a peak of a hair over 4 amps at the ends of travel its at about 3.7 amps in the middle of travel.
    Now remember, this machine originally ran on 90VDC and I have it running on 78VDC, so I would expect higher current at the same rapid speed.

    The fellow who described this process (I don't recall the location, but I think it was on Practical Machinist) said his machine had near two amps in current draw from the tight ends of the travel to the loose middle. I'm seeing less than half an amp difference. That tells me my machine is probably not as worn as his. I figured bracketing the 4 amp mark was as good of a place to start as any. Its dead middle of the suggested range, and well within the 35 amp capability of my servo controllers. It will take some significant cutting loads to cause any issues.
    I don't know if all of that was a good idea, but I have this machine way detuned from the speeds and acceleration I originally tested it at. It ran at over 450 IPM in testing and I currently have it set for 30iss with a 100 count following error, but the diganstic software only shows less than 50 on a hard reversal. With a larger following error I tested at over 100iss. with peaks of error on screen of 150-200ish. Still better than the best setting I had on my old Geckos.

    I think somebody must have actually loosened the X-Axis gib at some point, or maybe it had never been adjusted in its previous service life.

    Anyway, I think it will be a good place to run for a while. Now to see if I can find the Y axis gib adjustment.

    Bob La Londe
    http://www.YumaBassMan.com


  2. #302

    Default Re: KMB1 Conversion - CHATTER

    Adjusted loose (I loosened it to make sure) the Y-axis drew almost 3 amps. Across the range of travel with less variance from ends to middle. Both of those were expected since the Y likely sees less travel than the X its likely to wear less. Since its heavier its loose gib current should be higher. I adjusted it to bracket 4 amps as well, although due to the heavier weight it might have needed to be a little higher. Its 4 amps median current across the range of travel its got less than a 1/4 amp of variation.


    I don't know if this really is the correct way to adjust the gibs on a CNC Mill, but it sure makes sense. Obviously a lighter machine would require less current and a much heavier machine would require much more, but the principle makes sense.
    Now to see if the chatter has improved. Well, after I make a new rear Y-Axis way cover. I still think its likely a problem in the X -axis lead screw assembly, but I have my fingers crossed. Especially since I have a few more 4140HT parts to machine for the current job.

    One thing seems odd. I see less dither on the servos. I think the looser gibbs might have been causing it to over shoot from the mass of the table and saddle. Dither was never really bad (even on the scope it seemed acceptable), but sometimes I'd hear it for a for tiny fraction of a second on a stop with the spindle off. During testing right now I didn't hear it even once.

    Bob La Londe
    http://www.YumaBassMan.com


  3. #303

    Default Re: KMB1 Conversion

    Rewinding the transformer.

    Since I have servo drives that can handle the voltage now I am thinking about putting a few wraps back on the power supply transformer to bring the voltage back up. Any tricks? I was thinking about soldering on a length of THHN, and shrink tubing the joint.

    Bob La Londe
    http://www.YumaBassMan.com


  4. #304

    Default Re: KMB1 Conversion

    The latest... I replaced the thrust bearings on both the X&Y ballscrews this week. X went ok except it could not handle speed or acceleration afterwards. I torqued the retaining nut down with the kind of force it took to break it loose. I am pretty sure that was a mistake. Y didn't move at all at first, and then very clunky. I started wondering if torquing those retaining nuts down to hard was an issue. As near as I can tell they just have to be tight and no more. The tab washer is what keeps them from backing off. Of course the shaft tab was sheared off on both tab washers so I hunted every where for a replacement. One private party vendor has them on Amazon and Motion Industries has them available for order, but not in stock. I finally found three of them just laying there in my shop. They were hiding in this piece of metal, and all I had to do was cut them out of it.

    I still have no idea what is a good torque setting for the retaining nuts, so I am going to try 20lbs and see what happens.

    Attached Thumbnails Attached Thumbnails KMB1 Conversion-pw-04-washers-jpg  
    Bob La Londe
    http://www.YumaBassMan.com


  5. #305
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    Default

    I recently did a tear down and rebuild of the x and y of a hawk 5m. After replacing the screws, balls and thrust I had a simular issue with machine faulting under high feeds. The x and y axis had to be adjusted at the gibs to reduce drag. And machine cylcled through warm up to break the new components in. After a few hundred cycles i am back to normal. It may be the same for your machine as well IDK just my 2 pennys. [QU=Bob La Londe;2138806]The latest... I replaced the thrust bearings on both the X&Y ballscrews this week. X went ok except it could not handle speed or acceleration afterwards. I torqued the retaining nut down with the kind of force it took to break it loose. I am pretty sure that was a mistake. Y didn't move at all at first, and then very clunky. I started wondering if torquing those retaining nuts down to hard was an issue. As near as I can tell they just have to be tight and no more. The tab washer is what keeps them from backing off. Of course the shaft tab was sheared off on both tab washers so I hunted every where for a replacement. One private party vendor has them on Amazon and Motion Industries has them available for order, but not in stock. I finally found three of them just laying there in my shop. They were hiding in this piece of metal, and all I had to do was cut them out of it.

    I still have no idea what is a good torque setting for the retaining nuts, so I am going to try 20lbs and see what happens.[/QUOTE]



  6. #306

    Default Re: KMB1 Conversion

    Well, I have a different problem.

    I'm learning a lot... like you hardly need any torque on the thrust bearing retaining nut on this KMB1. I learned how to make new tab lock washers too since nobody stocks them, but several say they can get them... eventually. I even learned what the X axis is supposed to sound like with good thrust bearings. It never really had any problems, but its sure sounds a lot smoother now. Obviously the bearings were bad.

    With new thrust bearings on the Y-Axis its pretty smooth now too, but only for about 7/10 of a turn. Then it pulses. Its actually a lot worse than it was before. Before I could see a little flutter about every 1000 steps or so on the scope, but the machine appeared to move smoothly. I guess the Y-axis thrust bearings were so wore out that it allowed it to move smoother. With new fresh bearings it pulses badly. And no its not a matter of tuning. As near as I can tell the ballscrew is bent and its binding as it turns. That would sure explain the chatter I saw before. Now its unusable.

    The bad part is I don't know how to remove the new bearings and save them. The obvious way to pull the bearings pulls the rear bearing apart when you take the housing and bearings off the shaft. So... even if I find a good replacement ballscrew I'll wind up having to chase down another set of bearings too.

    Of course I have one piece to make to finish a job that is just a little too big for the little mills.

    DANG-IT!

    Bob La Londe
    http://www.YumaBassMan.com


  7. #307
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    Default Re: KMB1 Conversion

    You should be able to see the effect of tension on the bearings with a couple indicators. Put one on the casting touching the table and one on the table touching the end of the screw. When you move the table you should be able to see when actual motion starts and if the screw deflects axially in that process or on reversing motion. Either loosen the nut till you see deflection or tighten till you don't. You don't have to eliminate all deflection. .0001-.0002 inches deflection Max is perfectly acceptable for almost anything.

    Ben

    Sent from my HTC6525LVW using Tapatalk



  8. #308

    Default Re: KMB1 Conversion

    Quote Originally Posted by bhurts View Post
    You should be able to see the effect of tension on the bearings with a couple indicators. Put one on the casting touching the table and one on the table touching the end of the screw. When you move the table you should be able to see when actual motion starts and if the screw deflects axially in that process or on reversing motion. Either loosen the nut till you see deflection or tighten till you don't. You don't have to eliminate all deflection. .0001-.0002 inches deflection Max is perfectly acceptable for almost anything.

    Ben

    Sent from my HTC6525LVW using Tapatalk
    I wish it were ten times that even. Its visible now that I realize it. I think at some time in the past somebody beat on the end of the shaft with a hammer. Probably trying to drive the shaft out of the bearings to replace them. LOL. I have several ways to go I am thinking about. One is to simply turn the shaft to a different more concentric dimension. Then I could probably use a snug slip fit bushing. The trick is still getting the shaft out of the bearings without destroying the rear bearing. I might be able to do it on the press with a custom two piece press bushing if I can get the screw and bearing housing out as a unit. Might as well try since I have to pull the ballscrew anyway.

    I'd probably have to rethread it and use a different nut, but it might be worth it. Dimensions have always been good on parts so I expect the balls in the ball nut are not completely worn out. I guess I could mic a few while its out of the machine.

    Another way, and probably faster would be to just use a totally different ballscrew and make my own bearing mount to replace the front cover where the bearings are mounted now. Making a flange to adapt any other ball nut wouldn't be that hard. It might reduce Y travel a little, but I could live with that.

    I've also considered rolling the ballscrew on my surface plate, and trying to straighten it in the press. I doubt I could get it as good as you say, but I bet I could get it out of the visible range. That would be the hardest solution as I'd have to make up some special holding to try and limit bending and deflection to the areas I wanted.

    Bob La Londe
    http://www.YumaBassMan.com


  9. #309

    Default Thinking About Scrapping It Out: KMB1 Conversion

    I retrofit it, and I rebuilt it, and I repaired it many times. It still functions, but its in desperate need of repairs again. Both the X & Y have excessive backlash. The Y is just old and worn out, but the X probably needs a whole new ball screw assembly. In the middle of a job it went from about .001 backlash to about .035 backlash. I'm sure could sell the servo motors and the quill easily enough. The rest, who knows.

    I had been still using it for roughing blanks for use on the smaller machines. Basically entering code one line at a time to do functional manual milling using conventional only to take up backlash and measuring the parts. Its usable that way. I'd been using it that way for quite a while. Here is the thing though. I can slightly more easily do that same job on the new (last year) South Bend knee mill and it will make cuts the Hurco will balk at, choke, chip weld, and break an end mill trying. The South Bend has a modern 3 phase 5hp motor being powered with a 7.5HP VFD proper power and current program for the motor. It gives me pretty darn close to a real usable 5HP based on some of the crazy cuts I've made with it. Trust me when I say I do more work with the manual knee mill than with the CNC knee mill now... because its just faster.

    Basically every time I fix its more than a minor little thing, and it works great for a couple months until something else craps out, and I just don't use it. I've got two smallish lathes I could put there and get more use of the space and take up less space. I do use the lathes, although the smaller one may also be on its way out if I don't decide to CNC it. On top of that I am working on a bridge mill that will do more of the type of work I do on a daily basis, and at the moment I do not have a place to put it. Of course power in my shop is an issue as well. When I built the shop it was just supposed to be a warehouse. I figured the 100 amp sub panel I put on it was way overkill. Well, now I am constantly bearing in mind that electrical capacity budget in my head while running machines. What the peak "could" be and what the real load "probably" is. If I eliminate the Hurco I can use its electrical budget allocation for the new bridge mill I am building.

    I don't know. Just thinking. Just another one of the thoughts that probably kept me out of the good schools.

    Bob La Londe
    http://www.YumaBassMan.com


  10. #310
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    Default Re: Forgot the picture

    Bob La Londe,
    I know this is an older thread but, In this picture you have the cover off around the motor to you happen to know how much taking the covers off reduces the height of the machine, I am looking at a machine that I can get for next to nothing but will not fit in garage door unless I can reduce the height a little bit. Really don't want to try removing whole head.

    Quote Originally Posted by Bob La Londe View Post
    I forgot the picture...




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