Need Help! Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.


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Thread: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

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    Default Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Hi All,

    Sooo, I am ordering parts for my CNC machine that I am building. A very heavy ATC spindle, 2nd hand to me from a Biesse Rover, 95lb weight, I figure the Z axis up and down weight at 192 lbs, ouch! Using a big steel tube for the Z as the spindle uses a flange mount.

    Counterbalancing this monster, originally I was going to use gas struts. But, they have dampening, and the pressure is not adjustable. The dampening is the big thing. I actually contacted a supplier on aliexpress and asked about getting springs without dampening. Of course, they don't have any.

    Right now, I am looking at two 32mm bore 300mm stroke pneumatic cylinders. By my calculations (P1V1 = P2V2) and PSI x bore area in sq in = spring force, that gives me about 77 PSI required mid stroke for each cylinder. My compressor will do 90 PSI, so I can fill the reservoir. I'm looking at a reservoir of half a gallon to one gallon. Half a gallon or about 115 cubic inches would work for me. That would give me perfect balance mid stroke, and 11lbs at the top and 11 lbs the other way at the bottom of the stroke.

    I'm thinking about attaching a bottle to the gantry, perhaps a fire extinguisher, or two 1LB propane tanks. Ideally, a square reservoir perhaps 3" x 1.5" three feet long more or less would be nice. I have thought about trying to make one from 1/8" wall square steel tube and half inch plate, but I'm not certain that this is a good idea. I sure as heck will not be trying to pressurize pvc or anything suicidal like that.

    Any ideas out there on what to use for a reservoir?

    For the cylinders I am thinking about these:

    https://www.aliexpress.com/store/pro...706226382.html

    I contacted the supplier and asked for some info. As far as I can tell, it’s 3/8” BSP Thread to connect to the pneumatic cylinder.

    I was thinking of two of these to connect to the two cylinders using 3/8” ID standard compressor hose.

    https://www.aliexpress.com/item/Pack...794683816.html

    I don’t have any experience with these cylinders. I hope they don’t leak, as I don’t plan on having them continuously hooked up to an air source, I figure I can top it up once a week if I need to, if it’s more than that, then I need to rethink.

    I'll have a QD fitting to top up the pressure (at the reservoir) and two additional fittings to connect to the two hoses at the reservoir.

    Also, does anyone have any experience with the fittings that you simply push a hose into?

    Also, the pneumatic cylinder has a 1/8" hole for air to go in and out. I'm wondering if that might be a bit restrictive for my purposes. All of the 32mm bore pneumatic cylinders I have seen have 1/8" air inlet holes.

    Any advice on what to use for a reservoir, or fittings, or cylinders, appreciated.

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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Use your entire shop air system as the reservoir. 1 1/8 bore is a 1.25 multiplier (roughly.) So 90 psi in a 1 1/8 cylinder gives about 112 pounds of force.

    Unless you have some crazy fast up-down moves, the 1/8" hole will be fine.

    Those push in hose fittings work great with poly-flo hose. Just make sure the end is cut square and there are no abrasions.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    I use an air spring on my mill Z axis. I bought a 5 gallon portable air tank from Harbor Freight, Princess Auto has them also. https://www.princessauto.com/en/deta...nk/A-p8474868e

    I have mine connected to shop air through a regulator and Tee'd off to the air tank. I'm running it at about 35 PSI. 1 1/16 bore cylinder, ~50 lbs of pull in my case. All air systems leak somewhat, some more than others.

    I'm not sure how you calculated the force, air springs are linear, it will push (or pull) with the same force throughout the operating range.

    I would use nylon or polyurethane tubing and push-to-connect type fittings like these https://www.automationdirect.com/adc...Thermoplastic). The push on fittings that you linked to require a hose clamp to secure, they work fine on regular air hose.

    For cylinders and other stuff, I buy most of my pneumatic components from Automation Direct, and they ship to Canada. They offer free 2 day shipping in the US for orders over $49, not sure if that applies to Canada also.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Thanks very much to everyone who has already responded!

    Quote Originally Posted by vegipete View Post
    Use your entire shop air system as the reservoir.
    I don't have a shop air system. LOL. I have a small room in the basement. When everything is running, I won't have enough power to run the compressor at the same time. Really, can't have a compressor turning off and on whenever it wants to, it will trip a breaker with the machine running. I can top up the reservoir tank every week or something like that, but I can't have it loosing too much air while doing a job of several hours.[/QUOTE]

    Quote Originally Posted by vegipete View Post

    Those push in hose fittings work great with poly-flo hose. Just make sure the end is cut square and there are no abrasions.
    Thanks for the input. What is your experience with them running at around 100 PSI? Ever had one come loose or leak? If I get a sudden loss of pressure, during a job there is alot of weight on that Z. That has me concerned, and is why I am being cautious. Of course, I may just be being paranoid. I've never used these fittings.

    Quote Originally Posted by Jim Dawson View Post
    I use an air spring on my mill Z axis. I bought a 5 gallon portable air tank from Harbor Freight, Princess Auto has them also. https://www.princessauto.com/en/deta...nk/A-p8474868e

    I have mine connected to shop air through a regulator and Tee'd off to the air tank. I'm running it at about 35 PSI. 1 1/16 bore cylinder, ~50 lbs of pull in my case. All air systems leak somewhat, some more than others.
    I have a moving gantry and would need to route pneumatic lines through the entire length of the cable chain to use a 5 gallon. I haven't seen anyone do it this way, but then again, I haven't seen much detail on how to do this........A couple fantastic builds diy builds have balancing, but not alot of info on the choices and parts involved.

    Do you think it would be better to use a smaller reservoir that is attached to the gantry with shorter lines, or to have a larger reservoir with lines routed through the entire length of the daisy chain and down to the floor? Perhaps 15' long in total?

    You mention that all systems leak, but with yours connected to shop air, do you have any idea how much? I asked Linux Fan about it in his thread, and I believe he mentioned that a weekly top up should be OK. Perhaps that also depends on the size of the reservoir. Gas struts never need to be topped up, and can last for years, but also they aren't designed to be used in systems that have a continuous supply of compressed air, whereas pneumatic cylinders just might be.

    Quote Originally Posted by Jim Dawson View Post

    I'm not sure how you calculated the force, air springs are linear, it will push (or pull) with the same force throughout the operating range.
    The force from a pneumatic cylinder is only linear with a large reservoir. When you increase the working pressure (and therefore decrease the cylinder bore that is used), a smaller reservoir is needed when considering the difference in force at the top and bottom of the stroke. As far as I understand, that's how traditional gas struts work, with a small reservoir built into the cylinder and operating at a much higher pressure with a smaller effective bore.

    I used Boyle's law. P1V1 = P2V2 = P3V3

    So 192 lbs / 2 (2 cylinders) = 96 lbs

    32mm bore = 1.25 square inches area

    300mm stroke = 11.81"

    Cylinder volume = 11.81 x 1.25 x 2 (2 cylinders) = 29.53"

    So with a 115 cubic inch reservoir, neglecting tube volume, V1 being top stroke, and V3 being bottom stroke,

    V1 = 29.53 + 115 = 144.53, V2 = 115 + 29.53/2 = 129.77, V3 = 115

    96/1.25 = 77 PSI at mid stroke (V2)

    P1 x 144.53 = 129.77 x 77 = P3 x 115, Solving gives us P1 = 69 PSI, P3 = 87 PSI

    69 x 1.25 = 86.25, 86.25 - 96 = -9.75 lbs top stroke
    87 x 1.25 = 108.75, 108.75 - 96 = 12.75 lbs bottom stroke

    Quote Originally Posted by Jim Dawson View Post
    I would use nylon or polyurethane tubing and push-to-connect type fittings like these https://www.automationdirect.com/adc...Thermoplastic). The push on fittings that you linked to require a hose clamp to secure, they work fine on regular air hose.

    For cylinders and other stuff, I buy most of my pneumatic components from Automation Direct, and they ship to Canada. They offer free 2 day shipping in the US for orders over $49, not sure if that applies to Canada also.
    Those are the exact same kinds of fittings that are all over aliexpress. I've never used them. Always traditional quick disconnect and hose clamp or crimp connectors on a brass barb.

    Is that what you are using for your counterbalance, fittings like those? I've never used them, and perhaps I'm being overly cautious. They would probably be the easiest to set up if I buy some appropriate tubing to go along with instead of using standard compressor hose.

    Any ideas for a small half gallon or 1 gallon reservoir, that is long and narrow, preferably with three ports and easy to attach?



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by NIC 77 View Post
    Thanks very much to everyone who has already responded!

    I don't have a shop air system. LOL. I have a small room in the basement. When everything is running, I won't have enough power to run the compressor at the same time. Really, can't have a compressor turning off and on whenever it wants to, it will trip a breaker with the machine running. I can top up the reservoir tank every week or something like that, but I can't have it loosing too much air while doing a job of several hours.


    Thanks for the input. What is your experience with them running at around 100 PSI? Ever had one come loose or leak? If I get a sudden loss of pressure, during a job there is alot of weight on that Z. That has me concerned, and is why I am being cautious. Of course, I may just be being paranoid. I've never used these fittings.
    I have only used barb fittings on rubber air hose. Never tried them on poly hoses.

    I have a moving gantry and would need to route pneumatic lines through the entire length of the cable chain to use a 5 gallon. I haven't seen anyone do it this way, but then again, I haven't seen much detail on how to do this........A couple fantastic builds diy builds have balancing, but not alot of info on the choices and parts involved.

    Do you think it would be better to use a smaller reservoir that is attached to the gantry with shorter lines, or to have a larger reservoir with lines routed through the entire length of the daisy chain and down to the floor? Perhaps 15' long in total?
    I have poly airline plumbed through the cable chains on my router. Runs auxiliary hardware on the gantry. This is very common on commercial routers for ATC spindles for instance, and the push-on fittings are the norm. The long line runs won't make any difference in this application. The only time long runs do make a difference is if you need a quick full blast of air for some operation, then normally you have an appropriately sized receiver near where you need the blast of air. Would be very uncommon in a home shop. Some tire machines are one common application for this, but they have a built in receiver.

    You mention that all systems leak, but with yours connected to shop air, do you have any idea how much? I asked Linux Fan about it in his thread, and I believe he mentioned that a weekly top up should be OK. Perhaps that also depends on the size of the reservoir. Gas struts never need to be topped up, and can last for years, but also they aren't designed to be used in systems that have a continuous supply of compressed air, whereas pneumatic cylinders just might be.
    You should get away with a top up before a run as long if your reservoir is large enough. I don't know where my leaks are at, I'm old and and too many years around noisy machinery so can't hear them. But in my shop, there are 50 or more places that leaks could occur. I have never tried to isolate them. My 80 gallon receiver drains from 150 to zero in about 4 days of the compressor not running.

    The force from a pneumatic cylinder is only linear with a large reservoir. When you increase the working pressure (and therefore decrease the cylinder bore that is used), a smaller reservoir is needed when considering the difference in force at the top and bottom of the stroke. As far as I understand, that's how traditional gas struts work, with a small reservoir built into the cylinder and operating at a much higher pressure with a smaller effective bore.
    Your math is correct, I was assuming a larger reservoir. Gas struts are charged to 750 - 1500 PSI or so, and have much better seals than pneumatic cylinders. They also don't have a piston attached to the rod in a conventional sense, the pressure just acts on the area of the rod. In other words, both sides of the piston is charged and the gas (and oil) is free to circulate to either side of the piston unlike an air cylinder where the two sides of the piston are separate chambers.

    Those are the exact same kinds of fittings that are all over aliexpress. I've never used them. Always traditional quick disconnect and hose clamp or crimp connectors on a brass barb.

    Is that what you are using for your counterbalance, fittings like those? I've never used them, and perhaps I'm being overly cautious. They would probably be the easiest to set up if I buy some appropriate tubing to go along with instead of using standard compressor hose.
    I use those push-on fittings for many industrial purposes and have been for about 30 years, including having them all over my machines. My entire mill and router are plumbed with those, and I also use them on customer equipment. The were marketed by a company named Legris (sp?) about 40 years ago. They are reliable. Normally when I order from Automation Direct, I infill the order with those fittings to get to the $49 free shipping minimum if my order isn't large enough. I keep a good stock on the shelf in all sizes.

    Any ideas for a small half gallon or 1 gallon reservoir, that is long and narrow, preferably with three ports and easy to attach?
    A piece of threaded 2 inch steel pipe with screw on ends would work. An old large bore air cylinder would work also, just pull the rod out and plug the hole. But I'm not sure why you would want to add that much mass to your gantry. It would be less expensive and easier just to run some 1/4 or 3/8 air line through the cable chains.

    Last edited by Jim Dawson; 09-04-2017 at 12:17 AM.


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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by Jim Dawson View Post
    A piece of threaded 2 inch steel pipe with screw on ends would work.
    I was looking for something like that. The stuff I found was more expensive than a tank. LOL. I don't have a lathe to make them.
    Quote Originally Posted by Jim Dawson View Post
    But I'm not sure why you would want to add that much mass to your gantry. It would be less expensive and easier just to run some 1/4 or 3/8 air line through the cable chains.
    For a small reservoir it's not much mass. That being said, I'm beginning to see the light. Still not entirely there. But close.

    Thanks for all the great info by the way.

    I'm thinking perhaps a T joint mounted at the top of the Z axis. Two ends of the T go to the pneumatic cylinders and one end gets routed through the cable chain. If that is the way others are doing it and it works, why reinvent the wheel. If 15 feet of hose is OK, perhaps that's best. I could then use whatever reserve tank I can find, cheap off an old compressor or something.

    It sounds like this type of tubing is flexible enough to be routed through the chain when pressurized?

    What inner diameter of tubing are you using for your counterbalance? Your cylinder bore is a little smaller than what I am considering, and I will have two of them. So I need to pick an appropriate diameter to ensure I'm not getting a large pressure loss over the long hose.

    Thanks again for the info you've already provided!

    Also, does anyone know which is the best material for a cylinder, they have stainless steel and aluminum versions of exactly the same thing. I was thinking of stainless. That is the link I previously posted.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    It sounds like this type of tubing is flexible enough to be routed through the chain when pressurized?
    As long as the bend radius in your chain isn't too tight. 2-1/2"-3" radius should be fine.
    1/4" or 6mm tubing should be fine. If you see pressure drop over distance, just increase the pressure at the source.

    Also, does anyone know which is the best material for a cylinder, they have stainless steel and aluminum versions of exactly the same thing.
    Whichever ones are cheaper.

    Gerry

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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    I'm using 1/4 OD tubing, maybe 3/16 ID? The only time you would get a pressure drop is if you have air movement. If nothing is moving then the pressure is the same in all parts of the system. At the possible speeds that you will be operating at, any pressure drop is not going to be an issue.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Nic;
    I'm interested in the pneumatic counterbalance concept but know very little about it. I've rebuilding an old lathemaster rf45 and installing linear rails. I'm thinking that head travel (falling) will be a problem when powered down. I really don't want to use gas struts if there is a better option! By chance, do you have a design you can share or point me to?
    Thanks for sharing! There is a lot of helpful info in this thread especially about using push on couplings. I never had much luck with them but it appears that it's about time to revisit the subject!
    Bill

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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Thanks for your additional comments, Ger21, and JimDawson!

    You've converted me. I'll be running the tubing through the cable chain to a reservoir that sits outside of the machine frame. Right now I'm thinking about using 10mm OD, 6.5mm ID PU tubing, and 10mm push in fittings.

    You guys are right about the pressure drop.

    32mm diameter is approx 1.25 square inches

    Let's say I run the Z at 400 IPM max

    400 IPM x 1.25 in^2 x 2 (2 cylinders) = 1000 in^3/min = 0.58 cubic feet per min

    I looked at a few online calculators, and over a 15 foot length, the pressure drop is negligible (way less than one PSI). Someone please correct me if I made a mistake there. Also, I could use 8mm OD, 5mm ID, but the price is about the same, so I figure 10mm OD will be fine.

    The fittings I'm looking at on aliexpress are "G" fittings which I assume is the same as BSP? If I use an old air compressor tank, I will need to find a 3/8 BSP (female) to 1/4 NPT (male) adaptor, but I assume those are available on EBay.

    Actually what I plan on doing at this point is to use an old fire extinguisher as the air reservoir.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by bill south View Post
    Nic;
    I'm interested in the pneumatic counterbalance concept but know very little about it. I've rebuilding an old lathemaster rf45 and installing linear rails. I'm thinking that head travel (falling) will be a problem when powered down. I really don't want to use gas struts if there is a better option! By chance, do you have a design you can share or point me to?
    Thanks for sharing! There is a lot of helpful info in this thread especially about using push on couplings. I never had much luck with them but it appears that it's about time to revisit the subject!
    Bill
    Thanks for your encouragement Bill. I'm not familiar with the lathemaster, although I did just google it. Looks like a mini mill. I am also learning that there is a better option than gas struts. I would say for a design, one 32mm bore gas strut on either side of the mill (but you could probably get away with just one) connected to a small air reservoir. You'll probably have to have your strut(s) mounted at an angle with a mini mill configuration, so that will need to be factored into the calculations to find the component of force that is upwards and how much that changes at the top and bottom of the stroke. Definitely you'll want swivel connectors or ball joints at the ends of the pneumatic cylinders.

    Are you going to mount a more powerful motor on your mill? Well, the beauty of using pneumatic cylinders is that you can adjust the pressure later on.

    I can certainly let you know how it goes with my progress, but it will be a long time I think before this is all up and running. Probably a month to ship things to me, I just want to get these parts ordered so I can focus on building and have them when I am ready for them.

    If you can make a list of all the parts you need, you can ask for a custom order on aliexpress, probably the least expensive but it will take a long time to get to you, or you could get parts from somewhere like automation direct, as you are in the states, this might be easiest.

    The first step is to figure out how much Z axis movement you have, and to determine an approximate weight of the Z. I don't mind in the least if you piggyback on this thread with questions or comments about your own similar project, in fact I encourage it. If you'd like to make this thread a shared thread on the subject, no problems.

    Yes, there is alot of helpful info here, thanks again to vegipete, JimDawson, and Ger21, and thanks again for the encouragement.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by NIC 77 View Post
    Thanks for your additional comments, Ger21, and JimDawson!

    You've converted me. I'll be running the tubing through the cable chain to a reservoir that sits outside of the machine frame. Right now I'm thinking about using 10mm OD, 6.5mm ID PU tubing, and 10mm push in fittings.

    You guys are right about the pressure drop.

    32mm diameter is approx 1.25 square inches

    Let's say I run the Z at 400 IPM max

    400 IPM x 1.25 in^2 x 2 (2 cylinders) = 1000 in^3/min = 0.58 cubic feet per min

    I looked at a few online calculators, and over a 15 foot length, the pressure drop is negligible (way less than one PSI). Someone please correct me if I made a mistake there. Also, I could use 8mm OD, 5mm ID, but the price is about the same, so I figure 10mm OD will be fine.

    The fittings I'm looking at on aliexpress are "G" fittings which I assume is the same as BSP? If I use an old air compressor tank, I will need to find a 3/8 BSP (female) to 1/4 NPT (male) adaptor, but I assume those are available on EBay.

    Actually what I plan on doing at this point is to use an old fire extinguisher as the air reservoir.
    Using an old fire extinguisher is a great idea for an air reservoir. Though I highly suggest you don't use something too old. I've heard some bad cases of leaks. Safety first my friend



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by NIC 77 View Post
    Thanks for your additional comments, Ger21, and JimDawson!
    My pleasure

    You've converted me. I'll be running the tubing through the cable chain to a reservoir that sits outside of the machine frame. Right now I'm thinking about using 10mm OD, 6.5mm ID PU tubing, and 10mm push in fittings.
    I knew we would bring you around

    You guys are right about the pressure drop.

    32mm diameter is approx 1.25 square inches

    Let's say I run the Z at 400 IPM max

    400 IPM x 1.25 in^2 x 2 (2 cylinders) = 1000 in^3/min = 0.58 cubic feet per min

    I looked at a few online calculators, and over a 15 foot length, the pressure drop is negligible (way less than one PSI). Someone please correct me if I made a mistake there. Also, I could use 8mm OD, 5mm ID, but the price is about the same, so I figure 10mm OD will be fine.
    Your math is correct. The pressure drop will be negligible.

    The fittings I'm looking at on aliexpress are "G" fittings which I assume is the same as BSP? If I use an old air compressor tank, I will need to find a 3/8 BSP (female) to 1/4 NPT (male) adaptor, but I assume those are available on EBay.
    G fittings are a straight Whitworth thread with an O-ring for a seal
    R fittings I think have a tapered BSP thread
    F fittings have a US style NPT thread.

    Actually what I plan on doing at this point is to use an old fire extinguisher as the air reservoir.
    Just make sure the tank is not rusted out or something bad.

    Last edited by Jim Dawson; 09-05-2017 at 10:56 PM.


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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    The G fittings are not metric as far as I can tell. For example G 3/8 is the fitting to the gas cylinder.

    Yes, I will check out the fire extinguisher before I buy it. Looks great in the pics. Chromed, I believe, and tested to 500 PSI.

    Thanks again for the great advice so far.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by NIC 77 View Post
    The G fittings are not metric as far as I can tell. For example G 3/8 is the fitting to the gas cylinder.
    I stand corrected, they are a straight Whitworth form pipe thread.

    http://www.taitaja2014.fi/se/images/..._EN_ISO228.pdf



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    So I'm getting a couple quotes on my parts.

    The fire extinguisher I want to buy is a refillable water type. It already has a pressure gauge and a schrader valve, making filling up or emptying the tank of pressure easy using a standard tire inflation connector attached with a quick disconnect to my compressor hose. And I really don't want a 5 gallon tank as I don't need that much volume. Half a gallon will work for me, 2.5 gallons is ideal, 5 gallons is more than what I need. I would remove the nozzle fitting, see what the thread is, and buy an appropriate connector for the 10mm PU tubing. Voila, easy. Too bad the guy who's selling it won't respond to my emails. Looks like I may end up with a tank from an old compressor.

    So for the push in fittings, I realize now that they will work fine, but I am also considering compression fittings. Perhaps only a few dollars more for the 4 fittings I need. Two elbows, one tee, and one tank connection.

    Also considering two silencer fittings to act as filters on the other port of the pneumatic cylinder. I don't want any debris to get into the unpressurized ports (one for each cylinder) as these are double acting cylinders, but those won't be push in or compression fittings as there won't be a hose going to them obviously.

    It looks like all the fittings on Aliexpress are the G, or PT type, so BSP / BSPT / Whitworth, NOT NPT.

    But if I get a standard air tank, I can get a compression fitting for 10mm tube in NPT from EBay for the one tank fitting, so it's not a big deal.

    In compression fitting:

    NPT Male 1/4"-1/2" Compression Pipe Fitting Tube Connector Double Ferrule SS 304 | eBay

    Or push in fitting:

    1/4" NPT Shanghai male to 10mm Straight Push in to Fitting, Pneumatic Connector | eBay

    I'm guessing the compression fittings are a little more robust? It's not something I would have to take apart very often. My understanding with the push in fittings, is that you can't keep taking the tube out and putting it back in without having to trim it now and then anyways?

    I absolutely do not want any accidental tube disconnections. Are the compression fittings also be a good choice?



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    NIC - You will be sorry if you go with the compression fittings over the push lock. The compression fittings have to be perfect or they will leak and getting them perfect is not easy. They do OK in stationary applications but any flexing, over tightening, under tightening or stress can cause a leak. Push lock fittings are better. Cut the tube square and push it in the fitting. Done. They are easy to get right and handle flex and movement much better and they last for years. You can connect and disconnect the tube a few dozen times before trimming the end would be advisable. Of all the decisions you will have to make as you build, this one is easy. Pushlock.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by 1Jumper10 View Post
    NIC - You will be sorry if you go with the compression fittings over the push lock. The compression fittings have to be perfect or they will leak and getting them perfect is not easy. They do OK in stationary applications but any flexing, over tightening, under tightening or stress can cause a leak. Push lock fittings are better. Cut the tube square and push it in the fitting. Done. They are easy to get right and handle flex and movement much better and they last for years. You can connect and disconnect the tube a few dozen times before trimming the end would be advisable. Of all the decisions you will have to make as you build, this one is easy. Pushlock.
    Thank you my friend! That is exactly the kind of thing I need to know.

    The 3 BSP compression fittings (two elbows and one T), when added to my order through aliexpress cost just over 4 USD including shipping. The three push lock fittings cost about 2 USD. For a couple bucks, I now have two options. 6 bucks for 6 fittings isn't bad. The total for the cylinders, 10 meters of PU tubing, 2 fish eye swivel connectors, 6 tube fittings, and 2 silencer fittings will run about 77 USD including shipping.

    Perhaps I will have wasted $4 on the compression fittings, but it's only $4.

    I'll go ahead and order the 1/4 NPT push lock from EBay.

    Thanks Again!



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by NIC 77 View Post
    Hi All,

    Sooo, I am ordering parts for my CNC machine that I am building. A very heavy ATC spindle, 2nd hand to me from a Biesse Rover, 95lb weight, I figure the Z axis up and down weight at 192 lbs, ouch! Using a big steel tube for the Z as the spindle uses a flange mount.

    Counterbalancing this monster, originally I was going to use gas struts. But, they have dampening, and the pressure is not adjustable. The dampening is the big thing. I actually contacted a supplier on aliexpress and asked about getting springs without dampening. Of course, they don't have any.
    NIC, I was thinking about your gas strut problem. You could use a single acting spring return cylinder (SMC sells them on Amazon) with 2 air ports. You could connect the ports together maybe add a flow controller, and there you have a gas strut with no damping. With the flow controller in-line you could adjust how fast it responds. I'd post pics and links but I cant on this network.



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    Default Re: Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

    Quote Originally Posted by 1Jumper10 View Post
    NIC, I was thinking about your gas strut problem. You could use a single acting spring return cylinder (SMC sells them on Amazon) with 2 air ports. You could connect the ports together maybe add a flow controller, and there you have a gas strut with no damping. With the flow controller in-line you could adjust how fast it responds. I'd post pics and links but I cant on this network.
    Interesting thoughts.

    So if I take a normal double acting air cylinder, and I pressurize it and connect both ports together, the amount of force the cylinder would exert would be the area of the rod x the PSI, because that is the difference in area between the two sides.

    One side has the full area of the bore. The other side has the full area of the bore minus the area of the rod. So the difference is the area of the rod.

    The area of a 10mm rod is about 0.122 in^2. To get 96 lbs of force from it, 96 / 0.122 = 787PSI. That is way beyond what my compressor can do or what the cylinder or tubing can handle.

    I'd need a pneumatic cylinder with a rod of approximately one inch in diameter and a bore that is slightly larger than that.

    So for the single acting cylinder with return spring, how is it different inside? If it has two ports is it not simply a double acting cylinder with return spring (ie: one that is capable of double acting, but also will return the rod to the starting position if pressure is removed if used in single acting mode)?

    I'm not understanding the physical differences that could make this work. If there is a way, please let me know. I'm about to pay for my parts.



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Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.

Z axis counterbalance, pneumatic cylinders, air reservor, fittings, etc.