Z cutting deeper the more time goes by ??? - Page 2


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Thread: Z cutting deeper the more time goes by ???

  1. #13
    Gold Member Mr.Chips's Avatar
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    Default Re: Z cutting deeper the more time goes by ???

    For your information, here's the right side of the 3/4' ball screw Y axis drive.

    Attached Thumbnails Attached Thumbnails Z cutting deeper the more time goes by ???-right-side-y-axis-jpg  


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    Default Re: Z cutting deeper the more time goes by ???

    Had some free time and disconnected the Z axis assembly (two button head cap screws) from the acme screw and removed the router. The Z assembly moves up and down the two linear rails using four trucks connecting the assembly to the rails. The assembly moved up and down the rails by hand effortlessly, without and binding or tight spots, it is perfect.

    I ran the disconnected nut assembly to the top, middle, and bottom if its travel There wasn't any vertical looseness or free play at any position.

    I am satisfied that there is not an issue with any part of the mechanical parts of the Z axis.

    So where to now?

    I would like to eliminate the TXT file its self. Here is how the TXT file was generated and settings:
    The TXT file started out as printed pages in this case Chinese text, (my wife is Chinese, and this was to be a MDF poster for their up coming womens fellowship) I scanned the pages and saved them as .JPG files. I opened a new file in VcarvePro 8.5 (16x20") and imported the files and converted them to vectors. i then used the "curve fit to vectors" utility to smooth out the lines, i was told this enables the cutter to travel more smoothly. I used 60 degree V bit utility, with settings of: Pas depth 0.050", Feedrate 35 IPM and plunge rate of 5.0 IPM. I recall the run time was 2 hr 45 min. Roughly 2 hours into the cut the Z started cutting deeper, I then stopped the run and checked the Z Zero point and it was 0.080" lower than the surface of the material, when the file started the Zero point was set to the surface of the material.

    In years past I have ran 16x20" MDF cut posters like this without an incident.

    I can attach the file if you would like to look at it and possibly see if possibly there might be code in there that would have caused the problem

    With this information so far does anyone have any suggestions?

    Thank You all for your kind suggestions.

    Last edited by Mr.Chips; 03-22-2019 at 05:51 PM. Reason: spell corr


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    Default Re: Z cutting deeper the more time goes by ???

    I'm a late comer to the party. I had exactly the same thing happen to me. It turned out to be a slipping flex connection to the screw. I first thought it was a problem with my cut file, but it happened with different files. Rule that out. So, I started looking at the mechanical. I messed with just about everything. It all looked and felt good. I was sure everything was tight, but nothing, other than a loose connection, explained what was going on. A slipping connection to the lead screw made the most sense. I recalled that a couple of years earlier, I tried a product called Vibra-tite as a thread locker vs.the tried and true Locktite. I removed the two cap head fixing screws, cleaned out the gunky Vibra-tite from screws and connector, used blue Locktite and reinstalled the screws. I tightened the screws down so tight I ended up camming out the head on one of the screws. I know it was slippage, because tightening down the screws solved the problem.

    I zero through cuts to the spoilboard and never cut into the spoilboard. One day, I noticed a very shallow cut into the spoilboard, but since I was only a couple of thousands, I didn't think too much about it. Sometimes it would make a light cut into the board, sometimes not. Then, one day I was cutting some wood brackets for my dust collection system and the bit dove deep and caused a mess. I thought it was the cut file, so created a new one and ran it. Same problem, different area on the part. That led me on my quest to track down and fix the problem.

    Gary




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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by GME View Post
    I'm a late comer to the party. I had exactly the same thing happen to me. It turned out to be a slipping flex connection to the screw. I first thought it was a problem with my cut file, but it happened with different files. Rule that out. So, I started looking at the mechanical. I messed with just about everything. It all looked and felt good. I was sure everything was tight, but nothing, other than a loose connection, explained what was going on. A slipping connection to the lead screw made the most sense. I recalled that a couple of years earlier, I tried a product called Vibra-tite as a thread locker vs.the tried and true Locktite. I removed the two cap head fixing screws, cleaned out the gunky Vibra-tite from screws and connector, used blue Locktite and reinstalled the screws. I tightened the screws down so tight I ended up camming out the head on one of the screws. I know it was slippage, because tightening down the screws solved the problem.

    I zero through cuts to the spoilboard and never cut into the spoilboard. One day, I noticed a very shallow cut into the spoilboard, but since I was only a couple of thousands, I didn't think too much about it. Sometimes it would make a light cut into the board, sometimes not. Then, one day I was cutting some wood brackets for my dust collection system and the bit dove deep and caused a mess. I thought it was the cut file, so created a new one and ran it. Same problem, different area on the part. That led me on my quest to track down and fix the problem.

    Gary
    Thanks for the suggestion Gary but I checked the vertical play of the acme screw when the Z assembly was disconnected from the screw and no vertical play, plus check the second picture I have a bearing below the flex coupling to prevent any vertical movement and both of its locking set screws were tight.
    The mystery continues.
    I’m gonna run the file again in the morning and see what happens. Thinking of rigging up a dial indicator set at the deepest cut so I can know when it happens if it goes deeper than expected.



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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by Mr.Chips View Post
    Thanks for the suggestion Gary but I checked the vertical play of the acme screw when the Z assembly was disconnected from the screw and no vertical play, plus check the second picture I have a bearing below the flex coupling to prevent any vertical movement and both of its locking set screws were tight.
    The mystery continues.
    I’m gonna run the file again in the morning and see what happens. Thinking of rigging up a dial indicator set at the deepest cut so I can know when it happens if it goes deeper than expected.

    My issue had nothing to do with vertical play. I believe my problem had to do with what happened when the Z axis went positive. The coupling was slipping in the positive direction, because the weight of the moving parts require more effort to go up than down. You've probably observed this when turning the acme screw with the stepper removed. Easy to screw it down, but much more effort required to turn it in the up direction. Anyway, because the coupling was slipping, it meant that Z wasn't going up as high as the program commanded. Then, when Z was commanded to go negative, it was already too low, so the bit cut too deep. I don't believe your bearing would prevent the same thing from happening to you. If the coupling slips, it just means the router won't go as high as it should. The weight of the router and related parts translates into less effort required to go negative, so coupling slippage has less, if any, influence on how far negative the router travels.

    If your coupling set screws are truly tight enough, I have no other suggestions to offer. I would note that when I was checking things, the coupling was not so loose that I could hold the coupling in one hand and turn the screw with the other. It seemed tight, but clearly wasn't tight enough.

    I wish you the best of luck.

    Gary




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    Default Re: Z cutting deeper the more time goes by ???

    Thanks Gary
    Your reasoning is very sound, after the run I checked, all the Z axis stepper, Coupling, the large bearing and router bit, didn’t find anything loose. I’m going to run the file again this morning and see what happens.
    I’ll post results.



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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by GME View Post
    My issue had nothing to do with vertical play. I believe my problem had to do with what happened when the Z axis went positive. The coupling was slipping in the positive direction, because the weight of the moving parts require more effort to go up than down. You've probably observed this when turning the acme screw with the stepper removed. Easy to screw it down, but much more effort required to turn it in the up direction. Anyway, because the coupling was slipping, it meant that Z wasn't going up as high as the program commanded. Then, when Z was commanded to go negative, it was already too low, so the bit cut too deep. I don't believe your bearing would prevent the same thing from happening to you. If the coupling slips, it just means the router won't go as high as it should. The weight of the router and related parts translates into less effort required to go negative, so coupling slippage has less, if any, influence on how far negative the router travels.

    If your coupling set screws are truly tight enough, I have no other suggestions to offer. I would note that when I was checking things, the coupling was not so loose that I could hold the coupling in one hand and turn the screw with the other. It seemed tight, but clearly wasn't tight enough.

    I wish you the best of luck.

    Gary

    I believe the issue is what GME said or you are losing steps. In either case there is lost motion in the up direction. If the set screw push directly on the shaft I would put flat spots on the shafts. Then clean the set screw and hole threads with acetone or some other degreaser then use blue Locktite on them. Once it slips or loses steps the machine does accurately know when the bit is in the Z axis.



  8. #20
    Gold Member Mr.Chips's Avatar
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    Default Re: Z cutting deeper the more time goes by ???

    Thank you for your suggestions, I ran the file again and the Z zero point from I originally zeroed at the surface only increased 0.010” in depth.

    What I did between the first run and the second run:
    1. Tightened all the Z axis related set screws, more than I would normally hand tighten, just enough to hear one tick of the S Screw. None of them were moved more than that single tick, none found loose.

    2. Changed the pass depth from 0.050” to 0.100”. Cutting MDF with a 60 degree V bit

    Don’t think the increase in pass depth had and depth effect, just ran the file about 35 minutes faster.

    Summary:
    At this time I’m thinking it was related to the set screws.
    The lathe turned end of the acme rod does have flats as well as the stepper motor.
    However the big flange bearing under the alignment coupler tightens down on the acme rod, no flat spots. I think I should turn the section down and make some flat spots for those set screws to secure to.

    Again thank you all for your input and keep me focused.

    HH



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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by Mr.Chips View Post
    Thanks
    Didn’t see a “rapids” figure on that screen, maybe it’s called something else there?
    Motor tuning is a mystery to me I just came up with these settings and didn’t change them for years, maybe they are not what they should
    be.
    Here are my motor tuning settings, IN PER MIN
    VELOCITY .................70.02
    ACCELERATION....... 5
    G’s ..............................0.0129509
    STEP PULSE .............5
    DIR .............................5

    Thanks
    HH
    Yes those are the 'rapids' ... basically the fastest speed the machine can run at They look reasonable, but as you say, after 10 years things may need an overhaul. Missing steps is the most likely cause of the problem, but what is causing it may not be so clear. Reducing the Velocity and Acceleration are just a quick fix to try to get a job out, but may be necessary if the stepper motor is 'struggling with old age' or it may be that there is simply a tight spot due to dirt that is the cause ...

    Lester Caine - G8HFL
    http://medw.co.uk - Home of electronics for the Model Engineer


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    Gold Member Mr.Chips's Avatar
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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by lsces View Post
    Yes those are the 'rapids' ... basically the fastest speed the machine can run at They look reasonable, but as you say, after 10 years things may need an overhaul. Missing steps is the most likely cause of the problem, but what is causing it may not be so clear. Reducing the Velocity and Acceleration are just a quick fix to try to get a job out, but may be necessary if the stepper motor is 'struggling with old age' or it may be that there is simply a tight spot due to dirt that is the cause ...
    Thanks for the suggestions Lester,
    Please see the post before this one #20 where I explain what I did between the two runs.
    No dirt, as I detailed I disconnected the Z axis from the acme rod, removed the router and moved the assembly that runs on two linear rails and four trucks up and down by hand, completely smooth travel without and hesitation at any point.
    Thanks



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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by Mr.Chips View Post
    Thanks for the suggestions Lester,
    Please see the post before this one #20 where I explain what I did between the two runs.
    No dirt, as I detailed I disconnected the Z axis from the acme rod, removed the router and moved the assembly that runs on two linear rails and four trucks up and down by hand, completely smooth travel without and hesitation at any point.
    Thanks
    New stepper motors are no expensive these days ... probably worth picking one up ... I've a stack of old Taig stepper motors and dropping the new ones in allowed increasing the speed and acceleration after they had been trimmed over the years ...

    Lester Caine - G8HFL
    http://medw.co.uk - Home of electronics for the Model Engineer


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    Default Re: Z cutting deeper the more time goes by ???

    Quote Originally Posted by Mr.Chips View Post
    Thank you for your suggestions, I ran the file again and the Z zero point from I originally zeroed at the surface only increased 0.010” in depth.

    What I did between the first run and the second run:
    1. Tightened all the Z axis related set screws, more than I would normally hand tighten, just enough to hear one tick of the S Screw. None of them were moved more than that single tick, none found loose.

    2. Changed the pass depth from 0.050” to 0.100”. Cutting MDF with a 60 degree V bit

    Don’t think the increase in pass depth had and depth effect, just ran the file about 35 minutes faster.

    Summary:
    At this time I’m thinking it was related to the set screws.
    The lathe turned end of the acme rod does have flats as well as the stepper motor.
    However the big flange bearing under the alignment coupler tightens down on the acme rod, no flat spots. I think I should turn the section down and make some flat spots for those set screws to secure to.

    Again thank you all for your input and keep me focused.

    HH

    IMO, .010" increased depth sounds like a lot. Since tightening the set screws seemed to have solved the more immediate problem, you may want to look at tuning your Z axis "Steps per" motor setting in Mach 3. Are you familiar with Mach3's "Axis Calibration" routine under the "Settings" button? The button is just below the menu bar. Just asking, because it sounds like it may have been around 10 years since you last set it. The Mach3 calibration routine makes it easy. I would also take the opportunity to measure, and adjust for, any backlash. With 10 years of use, you may find some. I'm not sure if I was just lucky, but when I ran an acme screw on Z, my backlash was only .001" and the backlash compensation worked well to adjust for it.

    Gary




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Z cutting deeper the more time goes by ???

Z cutting deeper the more time goes by ???