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Thread: Nico's PM-25 CNC Build

  1. #21

    Default Re: Nico's PM-25 CNC Build

    Thank you for the compliment!

    I currently do not have my machine set up for rigid tapping. At some point, I may add an encoder to the spindle to make that work, but I have read that the servo encoder isn't sufficient for rigid tapping. I don't know how much truth there is to that, but I don't tap enough to invest the time to figuring that out. However, I am very pleased with the motor I have on the spindle. The difference between a real industrial servo motor and the hobby components I am used to is incredible. The motor and drive come with hundreds of pages of documentation (not exaggerating at all, literally several hundred pages) and the build quality is day and night. While I certainly couldn't justify purchasing one new for full price, if you can find one on the used market, I wouldn't hesitate to get it. The vibration problems I had were in the spindle, not the motor, but they have mostly been sorted out. I regularly run the spindle at 10,000 RPMs now and haven't had trouble with excessive heat. The vibration could be better, but it is completely usable at that speed.

    LinuxCNC has a wizard to walk you through the configuration. I don't have a motion controller separate from the computer. I use an inexpensive parallel port breakout board to interface the PC and the machine. The set up was just telling the computer which pins were going to what, what step rate, microstepping, ballscrew pitch, max speeds, etc I was using. Next time I am using the machine, I will try to remember to make copies of the ini and hal files, though they are going to be pretty standard and the same as what you will get when go through the configuration wizard.

    I am happy to answer any more questions if you have them!



  2. #22

    Default Re: Nico's PM-25 CNC Build

    I finished putting the way covers together and I am hopeful. They stay together well look to fit pretty well too. A few of the sheets aren't completely straight, so the spacing between each segment isn't uniform on top. I may have to go with a more sturdy material if that turns out to be a problem. There is always the option of remaking the sheets out of steel instead of aluminum. The sliding action is good. They index off each other correctly and as long as I slide them out and in straight, I had no trouble with them binding up. Occasionally, one of the segments did pop out of the slot, so I am thinking the .025" shims will be needed on the sides to keep them centered up and prevent the parts from separating.

    One other thing I had not considered was the noise they would make when you open and close them. It sounded a lot like those heavy wood blinds on windows that go *ClackClackClackClackClackClack" when you open them. I have a feeling when I have the Y axis going at 500 IPM, that could get obnoxious. If it does, I may stick a small rubber bumper or something in the slot to keep that noise to a minimum.

    Here they are in all their assembled glory.




    You can see the slight clearance between the segments here. Once I put the .025" adhesive rubber strips along the left side, that will be filled and should be kept uniform.


    Here they are collapsed. You can see the sheets bowing slightly downward on a few of them. This creates the slightly larger gap between a few sheets. You might also notice the topmost ones have a slightly larger gap than the rest of the sheets. That would be because someone wasn't careful enough when he modeled it and made that gap too large...




    I am thinking I will sand the sheets to a brushed finish, maybe around 800 grit sandpaper. I don't want to make them shiny and then have them look rough as soon as a chip scratches them, but I also think they will wear better with a surface that slides easier.

    One step closer to getting this machine the way I want it! It will soon be time to wrestle with the new electronics set up. I am looking into building a new PC to control it. I want to get rid of the big ol computer that has to sit next to the machine. Hopefully something with slightly better performance that I can fit in a smaller package. I was thinking of putting the control PC in the same box as the electronics, but the fear of noise interfering is pushing me to give it its own box



  3. #23
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    Default Re: Nico's PM-25 CNC Build

    Very nice kit parts ...



  4. #24

    Default Re: Nico's PM-25 CNC Build

    New ballscrews arrived!!! I have to say, the difference between this set of screws and the first one I got is like carbon black and the surface of the sun. Ok that might be a bit of an exaggeration, but this time I am happy with what I got while last time I was disappointed.

    The company I ordered from delivered everything as promised and everything was correct. I was quoted a 15 day lead time from the time of payment, and I received my screws 16 days from payment (close enough for me). All 3 screws were the correct length, correct pitch, correct nuts, and correct end machining. I measured all 3 screws bearing and coupler diameters, and checked runout on the Y axis. I got the following numbers: (all measured using a 1" micrometer that in theory measures to .0001")

    X Axis:
    Bearing Journal Diameter - .4718" (.0006" undersize)
    Coupler Diameter - .3935" (.0002" undersize)

    Y Axis:
    Bearing Journal Diameter - .4718" (.0006" undersize)
    Coupler Diameter - .3934" (.0003" undersize)
    Bearing Journal Runout - Barely above .0005"
    Coupler Runout - Slightly above .0015"
    Front Nut Runout - Slightly below .001"
    Rear Nut Runout - .0015"

    Z Axis
    Bearing Journal Diameter = .5890" (.0015" undersize)
    Coupler Diameter - .4709" (.0015" undersize)

    I really can't find anything to complain about there. Screws seem straight as far as I can measure, end machining is well centered, fit with the ballnuts is excellent, finish is shiny, rotation is smooth and silent, what more could I ask for?

    Have a few pictures!

    They were shipped in a sturdy cardboard box and suspended using foam inserts. They were well supported and seemed like they could take a solid beating without any damage to the screws. Much better than the flimsy box and bubble wrap the first ones were sent in. The screws were nicely oiled, had protectors covering the threads, and were wrapped in plastic bags that were taped at the ends.


    Those ground threads are just pretty to look at. And they look thicker than my rolled screws of the same diameter.


    In case you were wondering how I measured the runout, here is how. I used v blocks to hold the screw while using a dial test indicator to measure the movement as I rotated the screw. The v blocks are sitting on my surface plate. The indicator base is sitting on the counter top, which I know isn't ideal, but I think it is good enough.



    Comparison between the new and old screws. You can see the nut on the ground screw is longer than the rolled screw. I also like the look of the ground screw much more.


    The only thing I don't like is that the screws have no preload. Initially I thought the manufacturer messed up, but I think this one was my fault. The invoice had "P0" in the product number for each screw which I should have clarified before purchasing. I am pretty sure I specified no preload because of this. As you can see, the spacer is only touching one of the nuts, and this is the case for all 3 of them.


    All in all, I am happy. Total cost was $531.60. I thought there would be an import tax, but as it turns out, you don't need to pay an import tax on goods for personal use worth less than $2500. So no tariff! I am going to need to add some shims to preload the screws, but at this point I see no reason these won't be a huge improvement.



  5. #25
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    Default Re: Nico's PM-25 CNC Build

    shooter123456 what type of grease do you use?



  6. #26
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    Default Re: Nico's PM-25 CNC Build

    Can you share the seller of the ground screws?



  7. #27

    Default Re: Nico's PM-25 CNC Build

    Quote Originally Posted by pippin88 View Post
    Can you share the seller of the ground screws?
    Changsha Terry Machinery Co, from his thread on Hobby Machinist



  8. #28

    Default Re: Nico's PM-25 CNC Build

    Quote Originally Posted by rmachinist View Post
    shooter123456 what type of grease do you use?
    Nothing special. For the ballscrews I use a general purpose automotive grease and for the spindle bearings, I use a "high performance" automotive grease. No issues or complaints, but I can't say whether some of the fancy spindle bearing greases would perform better.


    Quote Originally Posted by pippin88 View Post
    Can you share the seller of the ground screws?
    footpetaljones is correct. Contact Sophia for a quote. sophia@ntl-bearing.com



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