Need Help! Pneumatic Counterbalance Z-Axis Rong FU 45


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Thread: Pneumatic Counterbalance Z-Axis Rong FU 45

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    Member bill south's Avatar
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    Default Pneumatic Counterbalance Z-Axis Rong FU 45

    Over the years I have seen many references to using a pneumatic cylinder and reservoir for counter balancing the head for a z axis. Previously I asked this question in an active thread but decided to start a new thread to prevent cluttering up someone else's posts.
    I am rebuilding my old lathemaster RF45 and adding linear rails on the z axis to eliminate the pesky problem of binding on the ways. I previously used weights and pulleys as a counter balance but didn't particularly care for all the movement taking place behind the mill. And, the weights were not covered thus could have been a safety issue.
    I would love to switch to a pneumatic system but I have no idea how to design one. I searched the web and see many different designs but I would like to keep things as simple as possible. I have an old air tank for the reservoir and don't mind sourcing the other required parts if I can figure out what to buy. And I have the head off the machine, thus can get an accurate weight for calculating size and pressure of cylinder.
    In my "perfect" system, the air circuit would be stand alone with just make up air added on occasion.
    Any help will be appreciated.
    Bill

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    Default Re: Pneumatic Counterbalance Z-Axis Rong FU 45

    Have you measured the amount of Z movement? The weight of the head and the amount of movement are the two things to figure out.

    Then, are you going to make brackets so that you can mount the pneumatic cylinder(s) in a straight line up and down, or are they going to be angled. If angled, then you should figure out what the angle is at the top and bottom of the stroke which depends on the mounting position. The upwards force will be the cosine of the mounting angle x the force from the cylinder. So at zero degrees (vertical), it's 100%. At 30 degrees, it's roughly 87%.

    Once you roughly figure out how you are going to mount them, then you can pick a stroke for the cylinders from the different models that are available, then you will know the exact dimensions to complete the design.

    I can let you know more when I finish ordering my parts. I've never done this before either. Obviously you've read my thread.



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    Default Re: Pneumatic Counterbalance Z-Axis Rong FU 45

    Thanks NIC;
    I will definitely have the sizing/design information before I order anything. Also, since I have not designed the installation yet I'm guessing that it will be a straight line installation. I will make this decision when machining the column for the new linear rails.
    Just to be clear about my needs, what I'm requesting is for a description of how the system works (simple description). Things get much clearer to me design wise if I understand the concept!
    I'll continue to follow your thread since it will probably answer many questions for me.
    Thanks for the response!!!!.
    Bill

    billyjack
    Helicopter def. = Bunch of spare parts flying in close formation! USAF 1974 ;>)


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    Default Re: Pneumatic Counterbalance Z-Axis Rong FU 45

    I am in the same boat as you guys. I have a "pneumatic counterbalance valve" that should release air when it senses the Z axis go down and give a configurable pressure going up. Still work in progress here but I will likely copy the circuit diagram from the machines at work.

    Making chips, day by day


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    Default Re: Pneumatic Counterbalance Z-Axis Rong FU 45

    Quote Originally Posted by KriegKuts View Post
    I am in the same boat as you guys. I have a "pneumatic counterbalance valve" that should release air when it senses the Z axis go down and give a configurable pressure going up. Still work in progress here but I will likely copy the circuit diagram from the machines at work.
    What kind of machines do you have at work?

    You can connect a pressure regulator valve to dump air, but then you'd have to have a constantly running air source.

    Here's an interesting pic about a Haas machine:

    https://diy.haascnc.com/procedures/v...ment#gsc.tab=0

    Looks to me like they use air over hydraulic oil running at some very high pressures and a small cylinder bore. No idea what the Z axis weighs on one of those. Also, looks like a closed system.

    I have to think dumping air isn't necessary so long as you have an adequate reservoir based on the sizes of your cylinder bore and stroke. Correct me if I'm wrong.



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    Default Re: Pneumatic Counterbalance Z-Axis Rong FU 45

    Quote Originally Posted by bill south View Post
    Thanks NIC;
    I will definitely have the sizing/design information before I order anything. Also, since I have not designed the installation yet I'm guessing that it will be a straight line installation. I will make this decision when machining the column for the new linear rails.
    Just to be clear about my needs, what I'm requesting is for a description of how the system works (simple description). Things get much clearer to me design wise if I understand the concept!
    I'll continue to follow your thread since it will probably answer many questions for me.
    Thanks for the response!!!!.
    Bill
    A simple pneumatic counterbalance would be an air cylinder that pushes (or pulls) on the Z axis to counteract gravity. The amount of force it applies can be easily adjusted by the air pressure in the system. Force = pressure x area of the cylinder piston. A cylinder with a 1" bore area pushes with a force of 15 pounds when the air pressure is 15psi. A simple system would be an air cylinder and a reservoir pressurized to the pressure necessary to provide the desired lift. There is an ideal ratio of reservoir size to cylinder bore. Basically, you want a large enough reservoir so that there isn't a large pressure increase when the Z axis moves upward and compresses the cylinder. A more complex system would incorporate a fast acting regulator and air compressor to maintain a constant pressure as the cylinder travels through its stroke.
    One thing to watch out for is the damping effect. Your cylinder has to have large enough ports and your air lines have to be large enough so that they don't restrict air flow as the cylinder is compressed and extended as the Z axis travels up and down. You don't want the cylinder acting like a shock absorber. If I were going to do this I would probably use a single acting, spring return cylinder and close off the port with a flow controller so the cylinder operates with a vacuum pulling up in conjunction with the spring. Just adjust the amount of vacuum to achieve the desired lift. The cylinder sizing would be a little more critical if used in this manner.



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