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Thread: Drifting Skipping Axis?

  1. #31
    Join Date
    Apr 2013
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    Kennebunkport, Maine
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    4,097

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    About minute 5.
    https://www.youtube.com/watch?v=3iwKFDER494

    Have you checked tightness of X rail bolts, and X stepper?
    Both of those loosened up on me after about 18 months.
    Scott Plaisted
    2013 Desktop/spindle/VCP 9
    Maine

  2. #32
    Join Date
    Feb 2016
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    44

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    Yup. Everything has been tightened, nothing was what I would have called loose.
    I may get in there and try and adjust those pots. But before I start messing with electrical boards I wanted to ask: if slowing/raising the feed rate at the time that it is loud and vibrate-y didn't affect it, do we still think adjusting that pot will have a positive impact?

    I wanted to throw something else out there. Could I be perhaps asking too much out of my machine? I know during the second failure I was running a 2.6ips,2ips,16k feed/speed. That's just under (.004875) the chipload range (it's a .005-.007) that my Onsrud chart says I should be for that 1/4" bit in a 2-flute. I used to run at slower feed/speed but while research these calculations I read somewhere that folks were doing all their hardwoods at 16k RPM, which makes my 2.6ips make some sense.
    This may have also been my feed/speed I was running the other time the failure happened as well, I just can't remember; but it's likely.
    I've recently been reading more about feed/speed recommendations for hardwoods and I see a lot around the 1.5/.7-1/12k (chipload or .00375... so even lower out of the Onsrud range) suggestion. This is a pretty big difference over what I was running. Granted, the second failure that I know was at the higher feeds/speeds was a finishing path through a mere .050" of wood... hardly what I would have called taxing... but I thought it was worth throwing out there.*
    Chris
    *I thought it might be worth throwing out there because when I first got the machine and Iw as just playing around with it not cutting anything I set the IPS higher than the Desktop can handle and that made it definitely lose track of where it was supposed to be!

  3. #33
    Join Date
    Apr 2013
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    Kennebunkport, Maine
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    I wanted to watch all the vids and reread everything and think about it.
    Never having cut long diagonals,or that big a 3D, I still might try 2,2 and even 1.5,1.5 for Move Speeds. 2.6,2 is faster than I've ever 3D'd.
    A friend with a Desktop in OZ cuts 2,2 all the time, and I tried it, but on small stuff it was a little too jerky for my taste.
    I wish one of the Desktop Luthiers would chime in
    Chiploads for the Desktop are usually only a very rough guideline I've found.
    No way on the finish toolpath it will ever get up to 2.6, but it will try.
    Try some scrap at 1.5,1.5 and then 2,2?
    Have you read any of Brady's VR threads or blogs?
    Here is one;
    http://www.talkshopbot.com/forum/sho...public+service
    Wish I could help more
    scott
    Scott Plaisted
    2013 Desktop/spindle/VCP 9
    Maine

  4. #34
    Join Date
    Jan 2004
    Location
    Jasper, TX
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    516

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    Thanks Scott. This was very timely as I just tried the smallest V-carve for me. Very jerky. Will try some of these settings and watch the machine for smoother cuts. Merry Christmas.

  5. #35
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    Apr 2013
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    Kennebunkport, Maine
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    Merry Christmas all
    Glad the shop is up and running David
    Yep, no sense telling the machine to go faster than the cut allows.
    Quite frequently on Teeny fonts and such, I'm down in the sub .5IPS range in dense hardwoods because of tearout.
    I'm still on Desktop default VR settings because I'm mainly one of's now....I'm chicken
    scott
    Scott Plaisted
    2013 Desktop/spindle/VCP 9
    Maine

  6. #36
    Join Date
    Feb 2016
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    I don't want to claim victory just yet... but I successfully milled out a new maple neck using 1.5,.7,12k. I still don't see how when the machine says it'll cut up to 4ips that doing a finish path through a minuscule thickness of rosewood would give it pause... but it's looking like it did.
    I'll be doing more and more tests on cheaper woods before pulling out the fancy stuff again, but hopefully this is the last of my woes?
    Best,
    Chris

  7. #37
    Join Date
    Apr 2007
    Location
    Marquette, MI
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    3,375

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    Chris...
    I will take a stab at your question: "I still don't see how when the machine says it'll cut up to 4ips that doing a finish path through a minuscule thickness of rosewood would give it pause..."

    It will. Give it a vector that is 4" long.

    The advertised speeds for most any mechanical product are the maximums. Like the speedometer in your car. You will seldom, if ever, run at the maximum attainable speed, but we as humans often make our decisions based on those maximums. What you need to realize as you go forward with this craft is that when doing 3D work you may seldom have a vector more than a few hundredths of an inch long, many just a few thousandths.

    Toolpath parameters at near max speeds cause over acceleration and deceleration, which in most cases cause a loss of position or lost steps. The machine will keep attempting to reach the speeds you set, until it fails, as you have found out.
    Gary Campbell
    GCnC Control
    GCnC411(at)gmail(dot)com
    ShopBot Controller Upgrades
    http://www.youtube.com/user/Islaww1


    "We can not solve our problems with the same level of thinking that created them"
    Albert Einstein


  8. #38
    Join Date
    Feb 2016
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    44

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    So this appears to be back... whether I just got lucky for awhile, or it was happening in smaller amounts to a point I couldn't tell as readily, or I just don't use my machine that often (probably cause I have to deal with stuff like this all the time!)... I don't know.
    But here's the newest data: It seems to ONLY happen when I'm working in 3D! It also never happens on the roughing paths, just the finishing paths! I contacted the MeshCAM guys and got this answer:

    "It's tough for me to say what's going on in the part since I don't know what it should look like or what the orientation is but I'm familiar with the skipping steps problem.
    First, when the job is done, jog the cutter back to 0,0,0 and see if the zero point moved. If it did, you're skipping steps.
    This is almost always due to:
    - ESD/Static electricity if you're in a dry environment.
    - Aggressive acceleration and speed limits set in the router itself.
    - A bad motor or drive board.
    - Mechanical binding or jamming on the linear motion hardware
    MeshCAM may show this behavior more because the toolpaths raster back and forth more than 2D CAM programs so there's more opportunity for the problem to occur."

    Apologies for anyone going back and reading it, for unexplained reasons over the last couple years there have been a bunch of words randomly repeated, etc. in the posts. Through this thread I've already addressed the static issue. We've talked about my feeds/speeds; although I still think 2.25 xy/2z IPM doesn't sound crazy. Not to mention it works MOST times just fine. I'd have also thought if this was the issue I'd see it on both the roughing and the finishing paths? Lastly, we also addressed mechanical jamming as Shopbot gave me a bunch of new bearings... sadly they were all for the Y gantry. Maybe I need to call them up and ask for the X axis bearings too?

    Please help, I'm back to being afraid of my bot
    Chris

  9. #39
    Join Date
    Apr 2013
    Location
    Kennebunkport, Maine
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    Sorry to hear Chris...I thought we were done.
    One thing if you could check, that we didn't address.
    Type UT in the command line of SB3, and read the UD instructions.
    Then type MX,4 an doing nothing else, type UD and let us know the Packet_ET number please.

    It's been almost 2 years...have you blown computer out? USB ports? Checked for any wires that may be crimped/broken? checked connections?
    I'm fishing a little here you can tell

    Does it do it on an air cut?
    For kicks and giggles try 1.5,1.5 IPM again?

    Check the Packet ET first though. That's Comms.
    scott

    Oh....Has anything been added to your computer just before this started again?
    Scott Plaisted
    2013 Desktop/spindle/VCP 9
    Maine

  10. #40
    Join Date
    Feb 2016
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    Packet_ET - 16.5 (ms;good<20)
    No idea what that means though hahaha.

    It has indeed been awhile but I've been doing mostly 2D work with my machine and therefore I guess I just wasn't seeing it happening. I was lucking out or something.
    Connections seem to be good. I have not blown my computer out, but I guess I could give that a try.

    Yes it does it with air cuts. Over the last few days I've run a long (35 minute) 3D path over and over. First round it failed after the second run of the path. I came back and the bit had lost about 1/32" in the X and lost about 1/4" in the Y.
    Next round I ran it probably half a dozen times (same path) before it failed. This time only lost in the Y, but it was closer to 3/8". I was also watching the machine this time and saw the "random slow downs" you can see in the video below. I have had this issue before but for some reason didn't think to connect the two things. Basically the machine will just random lower the feed rate to super slow. I can then stop the path and resume at which point it speeds up to normal again. I don't know if this is the CAUSE of the lost steps but seems interesting. Another thing to note is that it seems the steps are lost regardless of whether I stop/resume or just let it finish at the slower feed rate. I have seen this happen NUMEROUS times in 3D paths. I have seen it happen in a 2.5D path as well, but it's very rare.


    Same computer, nothing added. Doesn't even connect to the internet and is used for 3 things: notepad (notes on path orders for complex projects), Vectric, and SB3.
    Best,
    Chris

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