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Pressure Roller Spring Tension And other Trouble Shooting

Discussion in 'Troubleshooting and Build Support' started by Gefahren, Jan 16, 2012.

  1. Gefahren

    Gefahren Member

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    Hey Y'all,
    I've been away from my phlatprinter for awhile because of a few things. First I had trouble getting good consistant cuts from it and became frustrated with it. Then alot of other stuff piled up, but that's another story.

    Anyways what was happening was the material would skew one way then the other while traveling in the X direction. This had the effect of making the material 'Walk' along the Y axis. I fixed this for small parts by putting some guides on one side of the machine so it would 'walk' against these guides and not be able to travel. On larger or more complex cuts it would still end up skewing the material most of the time.

    I had this idea some time ago but never had a chance to check it. I used my fish scale/thrust meter to see how much pull it took to pick up the pressure roller 1/2" on either end. I found that they were very different 16lbs 11oz on the end the material would 'walk' from and 13lbs 14oz on the other. I was wondering if anyone else had seen this or not?

    I plan to remove the springs and add a weight in place of each one hanging below the machine. A couple of bricks should do it and I can get them fairly close to each other to even out the pressure. Then I'll dust off my machine and see if that fixed the skewing/walking problem.

    Nice to be back hopefully!
     
  2. 3DMON

    3DMON Moderator Staff Member

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    I'm curious of your results. Welcome back.
     
  3. rcav8r

    rcav8r Moderator Staff Member

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    Welcome back...
    Did you get the updated drive rollers? I had skewing issues with some issues materials until I replaced the rollers. I never checked the spring tension, but my left side does "feel" a bit softer.
     
  4. Gefahren

    Gefahren Member

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    I did get the updated rollers unless there has been some other change to them since the first one. I hopefully will be able to test this out tonight.
     
  5. Gefahren

    Gefahren Member

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    Ok, I've been able to get back to this (Got sick) finnaly. I disconnected the main springs and just let the wieght of the rollers hold the foam down. I ran a test "air" cut and it appeared to be right on spot so I had it cut out that old bridge design of mine. That cut file has alot of long "x" axis cuts so it's good for finding skew or shift in the material. When it got done, It looked like I'd lost some "x" steps by about 1/8". Before I let my machine sit around for so long, it wansn't losing any steps AFAIK, So I'll go back and check all the pulleys and stuff. When examining the cuts at the far ends of the foam I can tell it was skewing also. So now I'll hang some bricks off the handle on each side to see if the extra pressure keeps it from skewing. So far with just removing the springs it doesn't seem to be walking anymore at least.
     
  6. Gefahren

    Gefahren Member

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    When it rains it pours... but I finaly got back to this.

    Ok, I made a cut file that has two cuts in the 'y' axis 21" long at either end of a 40" cutting square. Then it has 43 cuts on the 'X' axis spaced at 0.5" accross that same cutting area. I tried this test with both no springs/no wieght and no springs/2bricks per side (see pictures). My machine has apparently gone all wonky and I have no Idea what it could be(checked all the tensions and set screws).

    Here's how I have the external pressure roller wieghts(bricks) set up


    Here is the cut without the extra wieght and no pressure roller springs.

    As you can see the cuts alongs the 'x' axis are not spaced out right, they are crowded together and are not as wide as the 21" 'y' axis cut. So I can see the material shifted in the +Y direction. Also it's harder to see but the ends of the 'x' cuts do not all line up either. They seem to stairstep alittle as opposed to each one being off alittle.

    and here it is with the wieghts

    Here the material shifted in the -Y direction since all the 'x' cuts are spaced out farther than they are supposed to be. They still have that slight stairstep in their endpoints. It seems like I'm losing 'x' steps at regular intervals.


    With both of these I can also see that the 'x' axis cuts spacing is narrower at one end of the material than the other so I'm still getting skew too. 1/2" to 3/4" shift in the material is pretty significant and I don't know what to do to stop it. I've got to hook the pressure roller springs back up and see how it fairs in this same test.

    I have an idea about how I'm losing steps in the 'x' axis. Along time ago when the plastic pully split I replaced it with a metal one I had laying around. Now that I'm trying to remember, I don't know if it was actually the same pitch as the original, I just remember that it seemed to fit well. I know some of the metric and standard pitches are really close to each other.

    I'm open to all suggestions on how to eliminate this skewing/shifting problem that I'm having, I'll run any other tests you guys can think of. I've been away from this for several months and I feel like I don't remember anything on how to diagnose or fix this.

    Thanks. Attached files [​IMG] [​IMG] [​IMG]
     
  7. TigerPilot

    TigerPilot Well-Known Member

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    Gefahren, I don't think that you are loosing steps. If you were you would have seen the lines stepped on the x axis. Yours look strait in the pictures. Since the lines with the bricks are further spaced than the ones without it means you had slip without the bricks, which is to be expected, of course. I have skew too on the thicker stuff I'm using and I made a guidance for it. I think that I've posted some pictures of it.
     
  8. Gefahren

    Gefahren Member

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    Thanks for the reply Yoram. Sometimes all I need is for someone to point things out before I can see it.

    I might not be losing steps on the x axis. It's hard to see without putting a ruler on it, but if you do then you can see 4 or 5 of the x cuts line up at the end and all the other x cuts to one side are longer and to the other side are shorter. That's why I was thinking something like the belt jumping a tooth. But looking at it more the amount of skip would be alot more if the belt actually did that. My current hypothesis for this is that it's an effect of the material skewing back and forth as it cuts.

    So I'm still up for any suggestions on how to stop the skewing/shifting. I've seen Marks machine cut and plenty of other peoples machines cut near perfect every time it seems. So I know it's something I've got off on my end of things, I just can't figure out what.

    One other thing about my machine that I've forgotten to mention is the Y gantry isn't exactly parallel with the bed. I say this because on any piece of foam if I get the bit just touching the surface at 'Y' zero it is in the material 1/16" at most at 'Y' Twenty. I don't know if this can have anything to do with it, I did level the machine side to side and front to back at each end.
     
  9. kram242

    kram242 Administrator Staff Member

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    This is a tough one to try and figure out with out being there to see it in action. But all the key points can be looked at like the pulley slipping, as you know they can slip just a little in one direction and not the other. If your using the plastic pulley with the aluminum hub on the stepper, the plastic part can slip on the aluminum hub over time of heating. If you have one of these on your x axis let us know.
    If this is the case we can send one of the c16 guides kit and you could give that a try. It will at least keep the material from moving side to side.
    Hope this is a help
    Mark and Trish
     
  10. Gefahren

    Gefahren Member

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    I didn't know there were guide kits. I've missed alot.

    I don't have the original plastic pulley with the aluminum hub. The Plastic and aluminum separated along time ago. I had an all aluminum pully laying around from another project and I used it. I don't know if it was the same pitch as the original, it looked like it fit. But I don't remember if it was metric or standard. I'll have to try looking up what pitch it was. I think when I first replaced it I posted about it, let me look that up.

    I checked my old posts and found it. The one I have on the machine is a 40dp.
     
  11. kram242

    kram242 Administrator Staff Member

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    Good deal Gary! :good:
     
  12. jonquinn

    jonquinn Member

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    I don't see the C16 guides kit in the store. can someone post a picture of what they are?
     
  13. Gefahren

    Gefahren Member

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    I didn't see the C16 guide kit in the store either, but I did a search on the forums and found where they were discussed (apparently I made several posts in that topic... Age is catching up to me!)

    My drive rollers are spiral wrapped in opposite directions from each other. Has anyone shown that spiral wrapping effects the machine in anyway vs. straight wrapping? I'm willing to order some more grip tape if you all think it might help. If no one has an opinion I guess I'll leave it on, since it's a real pain to pull off.

    I'm also going through and measureing everything I can on the machine to see if something is off. like are the rollers higher on one end (or just one roller) is the gantry square to the bed, are rollers (pressure or drive) parrallel, ect.. It all 'looks' perfect and the design of the machine doens't really leave room for missalignment, but I've got to figure out why this one skews and shifts and others don't.

    BTW, at one time I thought I had it running near perfectly, so I also want to know what changed.
     
  14. Gefahren

    Gefahren Member

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    Well, I think I can safely say that spiral wrapping the drive rollers vs. straight wrapping doesn't make a difference. My new grip tape is arriving today but I went ahead and took the old stuff off. Then I put two wraps around it just to try. (this also allowed me to triple check the tension and screws and stuff)



    Then I loaded a piece of foam and plunged the bit at zero then had it travel to X 40 and back 14 times @ 200 ipm and this is how far it was off.



    Thats about 1/2" on the Y axis and 1/4" on the X. Still don't know why the X is losing, but what I really want to figure out now is the shift on the Y. Trying to fix one problem at a time. Attached files [​IMG] [​IMG]
     
  15. kram242

    kram242 Administrator Staff Member

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    Is it possible that you are losing steps? maybe you can try running the same test at a slow speed?
    Mark and Trish
     
  16. rcav8r

    rcav8r Moderator Staff Member

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    A head scratcher for sure. Can you see it wondering over time? That is, is it SLOWLY wondering, or did you set and forget then come back and saw it was out? If it is wondering, you still may have a mis aligned roller ( which would explain the Y shift, but not the X.
    Have you tried with a different material?, i.e. a sheet of balsa?

    How about the wiring.. is it tight in those little white blocks? I ditched mine in favor of a soldered plug. I have had experience of those loosening in the past, and the motion of the machine may be enough. Also I think some folks here had issues with that. I used 0.1" pins/sockets for the plugs.

    FWIW, I cut about 16 sheets of 3/32 balsa and a sheet or two of 1/16" this weekend... The 3/32" used 2 passes. EVERYTHING came out perfect :) Even my small (1/4") circles were round.
     
  17. TigerPilot

    TigerPilot Well-Known Member

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    It's amazing how some machines do everything perfect and some don't even so they all come from the same 'mold'. I can't get, for the life of me, perfectly round circles. It's better now than when I started but still not really really round. :girl_cray2:
     
  18. rcav8r

    rcav8r Moderator Staff Member

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    Yoram; I read about the backlash issues and such (and I understand how it is ALWAYS there), but for some odd reason all my tolerances must be canceling each other out. (knock on balsa ;) )

    Also I have been using another program (DevCAM) to generate my G-Code, and it seems to do a better job on circles (machine doesn't "sing" when cutting them), but I even got round ones with the PhlatCode.
     
  19. Gefahren

    Gefahren Member

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    Well Mark, I must be losing steps because I re-ran that same test (X +40 then back to zero 15 times) at 40ipm and its as dead on as I can tell for the X axis. Also it only drifted/shifted 5/32" this time, but I had removed the material from the machine between the last test and this one, so it might not be exactly where it was last time.

    So, any ideas why I'd be losing steps at only 200ipm? I don't cut that fast but I seem to remember you doing 400ipm rapids with no problems on one of the live shows.

    I've not tried anything but the blue foam since I fired the machine back up so I don't know if any other material behaves better/different.

    It is slowly wandering with each pass. The first pass or so looked good but with every one it became more apparent that it was shifting. 5/32" over 15 passes is only 1/96" drift with each pass. Although it was higher with the higher speed.

    I don't know about it not 'singing' when cutting circles(i've not tried this time around) but before I wrote g-code to use the Arc commands instead of the line segments like the phlatcode does and didn't notice a sound difference really, but I didn't do full circles in the phlatscript.

    I'm gonna get a water level after my machine and see if there is any twist in the machine or the rollers. My bubblelevel is to big to fit on the bed because of hte pressure rollers so I've not leveled front to back on the bed directly but at the top of the machine instead.

    It's got to be something...

    I'll also try swapping the pressure roller springs left to right and see if that makes a difference. Like I started this topic with, one of them measures stronger than the other(not that I'm very accurate with a hand held fish scale, but that one side was consistantly more than the other).
     
  20. Gefahren

    Gefahren Member

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    Ok, I have the C16 guide kit installed (I'll make a topic on that later) and the foam stays centered very well without draggin on one guide or the other.

    Now after having replaced my driver chip I got to some testing last night.
    First problem was that with the normal X drive pulley the belt skips no matter what speed it's going. I've tried all sorts of belt tensions from very light to extreame and it always skips. I put my slightly oversized spare pulley back on and the belt skipping is gone, but I'm still losing steps.
    This makes me think that something is loading up the X axis, but I don't know what (that could also explain the whole Skewing/shifting problem that started this)

    So does anyone have a suggestion about how things should be, or what could be wrong that I can check??
    :questions:
     
  21. rcav8r

    rcav8r Moderator Staff Member

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    Without the stepper connected, do the rollers roll freely?
    Without the stepper connected, can you push a sheet of foam through the machine? I have never done this but in theory it SHOULD work. Is there skewing there?
     
  22. thunder hawk

    thunder hawk Member

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    I had the same problem when cutting acrylic on my pp.
    You may want to check and see if your x-axis drive rollers are parallel
    to each other and the Y-axis guide rods of your pp.
    I added a small piece of shim tape to the slot that the roller sat in.
    That cured the problem of stock walking along the y-axis on my pp.

    Another thing to check is the height of your drive rollers.
    If the drive rollers are not parallel to each other and the y-axis guide rods in
    height, that can also cause problems with skewing and cut depth accuracy from
    side to side. Shim tape will help with this problem as well.

    Not all springs have the same tension. Take the tension springs off the machine and
    check each spring with your fish scale. If the numbers don't match when the springs
    are stretched to the same length then go to the hardware store and get some
    springs that match. Take your fish scale with you. I replaced my springs with springs
    that matched. That helped.

    There is one thing we all have to live with, and that's the fact that foam is not
    consistent in density or thickness from side to side or end to end, and that
    can cause inaccuracies in cut parts to. If you look at the surface of fan fold foam,
    it's wavy and that makes the sheet slightly longer in length along the surface.
    This can cause your parts to be slightly off along the length of the sheet.

    Hope this bit of information is helpful to you.

    Cheers.
    George H. Boyd
     
  23. Gefahren

    Gefahren Member

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    Sorry I'm slow to reply, my mother in law passed away Thursday morning sortly after my last post. She was at the end of a lenghty 8 year battle with cancer.

    I will check those things on my machine when i get a chance.
     
  24. kram242

    kram242 Administrator Staff Member

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    Sorry to hear about your loss Gefahren, its always a tough road to travel after losing someone close. You family will be in our prayers my friend.

    Let us know how it goes with your new testing and also be sure to check that the drive roller pulleys are not off center.
    Thanks
    Mark and Trish
     
  25. Gefahren

    Gefahren Member

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    Thankyou for the kind words Mark, they always help at times like this.
     

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