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Thread: new cnc not running as fast as advertised.

  1. #31
    Where are you at with all this Eugene?

  2. #32
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    I got some good results other day with 3d but could only run z axis at 150 due to size of motoron z axis and no air balance to help with weight of spindle. In talking to the company that made cnc told me if put in double stack motor same as the y axis and the motor I replaced in x axis could go faster. i ordered the double stack motor and am going to test at 200 with 3d file. if get good results will do same 3d file at 250 to see how fast can go before start losing steps. the silver tube on the side of cnc pretty much is set up at present just to keep spindle from dropping down when power off now based on them limiting speed of z axis to 150 because of weight of motor ya would of though that if person had air installed on the cnc would of set up as air balance but that will be project for next year i guess. My air system basically wright now has a regulator set at 2 psi with tube running into bottom of the air cyclender and the top is vented. anyone have good drawing on what parts needed to make work as air balance? the process was, is of frustrating but now i am seeing light at end of tunnel.

  3. #33
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    Eugene, what happens when you increase the psi to the air cylinder? I don't know if they're the same but the cylinder on my Z is set at 33psi. I can't imagine what possible benefit 2psi could provide you.
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    "It's paradoxical that the idea of living a long life appeals to everyone, but the idea of getting old doesn't appeal to anyone."
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  4. #34
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    It is enough to keep cyclender from droping when turn off power. If my old cnc was still in shop would be lot easier to see what needs to be done to get wright.

  5. #35
    If you can unbolt the Ball nut from the Z axis, you want to adjust the pressure in the air cylinder so that with the weight of the spindle, dust collection hose and anything else hanging on the spindle, it will counterbalance, not float up or down. That way you have essentially zero weight to work against, just the mass of the thing when the stepper tries to move it.

    I was helping a friend with a little CNC mill retrofit, Dynamyte table top unit. We added gas struts to the Z axis headstock and were able to use direct drive steppers (they had been gear reduced) and went from 60 ipm maximum to over 300 ipm and we were able to 3D contour at a much better speed.
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

  6. #36
    Youve got something confused I believe. The cylinder is not there to hold up the spindle on shutdown. When we shut down we shut everything down, air and all, and still use a block on the spindle because it will drop when air bleeds off. I will almost guarantee you that youve got something confused in the air balance end of it as well as possibly other areas. As Brad said, you'd not want the Z motor to haul the entire payload. Bigger spindle and machine but we are running 50 or 58 psi on the balance cant remember off hand.

  7. #37
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    Quote Originally Posted by Mark Bolton View Post
    Youve got something confused I believe. The cylinder is not there to hold up the spindle on shutdown. When we shut down we shut everything down, air and all, and still use a block on the spindle because it will drop when air bleeds off. I will almost guarantee you that youve got something confused in the air balance end of it as well as possibly other areas. As Brad said, you'd not want the Z motor to haul the entire payload. Bigger spindle and machine but we are running 50 or 58 psi on the balance cant remember off hand.
    My thought as well.
    As I asked above, what happens when you increase the psi to the air cylinder?
    Please help support the Creek.


    "It's paradoxical that the idea of living a long life appeals to everyone, but the idea of getting old doesn't appeal to anyone."
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  8. #38
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    I deleted my last comment Mark. I felt there was too much rambling off topic.

    Why do you think the air cylinder is not intended to counter the weight of the spindle? That is what it is for. My spindle weighs around 25lb, and you would be hard pressed to find a stepper that could lift that efficiently for 3D cutting without an air counter balance. The air regulator on mine is set at 38psi, but mine will be different. Did you discuss this with Ben? It is an easy calculation if you find the tech specs for your spindle that show its weight.

    I have the same machine and am puzzled by your comment about the air cylinder. If you are leaving the air on, then I get it, but otherwise it will drop to the table. I always turn off the air when not in use so my air compressor stops cycling (my spindle uses 3cfm air for cooling). I believe you have to get into the production machines before they build a mechanism to hold the spindle off the table when not in use. There is very little friction in the ball screw and linear guides in the Z axis for obvious reasons, so the only way to lock the spindle without air is with a locking mechanism that engages when the air drops too low (kind of like air brakes on a big truck).

    Did your machine come with the double stack (SH2681-5144) stepper on the X axis? Mine has the double stack on the Z and Y, but a single stack (SH2681-5142) on the X. I believe my 10hp HSD spindle is heavier, so it might be by design; however, my X axis will require more power to move and I have never had any stalling in that direction with the single stack. I have cut sheet goods up to 400ipm with a 3/8" cutter (melamine). The Z axis and Y axis require the most power due to the weight they must move while cutting. The gear ratio on the Z axis is also quite a bit different and that changes the RPM the stepper operates at when cutting a max speed. I never found the exact power curves for the steppers on this machine, but a sample one with a similar part number is shown below. You can see how the power drops off as the RPM increases. Servo curves are much different.

    stepper-curve.PNG
    I would be cautious how much you spend on new steppers. I have a quote from DMM for $1800 (CAN$) to swap out all the steppers and drives to use 0.8kW servos. They have assured me they can make it all work with WINCNC.

    Did you look at the z axis accel setting with Ben? I had to reduce mine to stop a random stall I was experiencing, but that is probably more to do with my spindle.

  9. #39
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    Well, I was talking to tech when got cnc and told me air should be set at the low psi number. Last night was still having the issues with 3d while cutting at 2ooipm cranked air regulstor up to 35psi and the 3d problem went away. Cranked ipm up to 300 in all access and still looked good. I am thinking the air balancer will stay set higher but am going to check spindel will dial indicator to see if getting movement. Maybe need to shim bearings.

  10. #40
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    I leave air on to cnc all the time. Did same with last cnc and no iaaues.

  11. #41
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    Ok, I see.

    I have never had to adjust the air regulators on the machine. I set the regulator on my AC to 100psi, and all of that has worked fine.

    I was not suggesting leaving the air on is a problem at all. I have a tool changer so my spindle leaks air continuously when the air is on. My shop is next to the house so I prefer that the AC does not cycle frequently.

    Sounds like you pretty much have it working. Good for you.

  12. #42
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    When we shut down our 2 Bessie's the air shuts off.

  13. #43
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    No ATC so I leave the air on 24/7.
    Please help support the Creek.


    "It's paradoxical that the idea of living a long life appeals to everyone, but the idea of getting old doesn't appeal to anyone."
    Andy Rooney



  14. #44
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    I would be a little leery of leaving the compressor on to keep air to the cnc The printing company I cut for let the air on for their big printer and a line blew over the weekend and the compressor over heated and started a fire.

  15. #45
    Im in the Jerome camp. We shut down the air, drier, etc. nightly. I had a head gasket let go between the hi/lo stages on an almost brand new Quincy at one point that caused the poppet relief on the head to open at about 125psi (175 cutout) and it would never let the compressor reach cutout so it would have just run non-stop. Not sure if it would've burned the place down but if it'd have happened on a Friday night and no weekend work who knows. Additionally we have timed drains on the main tank as well as the drier so they are bleeding all night long and all weekend long causing the compressor to cycle. But Id guess if I had a home shop, garage or basement, I might leave the air on if I had nice tight system with no leaks. Too much pipe and leaky coupler bodies in the shop for that.

    Brad, as an aside, assuming your WinCNC but incase you didt know, M12C1 may likely be the command to close the jaws on your spindle when you have no tool in. I always find that rushing air when no tool on the ATC annoying.

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