[skyguynca]

`I have seen them on several larger router tables,my table has a heavy head assy and I would like to install a pneumatic cylinder to assist the z axis
Does any one here really know how the system works, can describe how and what parts are needed to make it work correctly?

Thanks
David
San Jose, CA

[sajurcaju]

Would spring support do it? Lots simpler.

Steve

[skyguynca]

Thank you for your reply Steve, but honestly I am asking about a pneumatic assist system, not a spring.
If you do a full search on here you will find out springs do not work well, and do not last very long,
and the assist is not linear which is important.

[Al_The_Man]

Further to the PM, you may be able to use a normal pressure regulator with a pressure release valve to operate when the compression cycle occurs.
Al.

[DonKes]

"If you do a full search on here you will find out springs do not work well, and do not last very long,
and the assist is not linear which is important."

Maybe I am confused about which system you are talking about,

but springs are linear unless you try hard to make then not linear.

Springs last a looooooong time, as in car valve springs.

Springs are not very good for this application because you need a preload equal to the weight of the z-axis with a zero spring rate.

Don

[skyguynca]

Further to the PM, you may be able to use a normal pressure regulator with a pressure release valve to operate when the compression cycle occurs.
Al.

Thanks Al, I will see if I can find one.

[skyguynca]

In this application you can not get the spring to apply the linear force to balance the head. As the spring stretches it will apply more force to pull the head down as the distance increases, that does not balance the head, as you get closer the force lessens, here again it is not linear.
If you search you will see it has been tried with very poor results. Varible gas springs like in the hood of your car or trunk lid have had promising results but can get quite expensive and you never really
know what the real pressure is when you order them, some people have had to buy several sets to get it right.

The air assist is used on commercial machines and works quite well, we have one on my machine at work.

[wizard]

There was a thread some months ago on a site related to this very question. I'm not sure which site though.

In any event in the simplest form you need to size an air cylinder to provide the amount of lift you need at a moderate air pressure. In other word sized so that you can provide the balance you need at a point below your shops airline nominal pressure, say 75 percent. The reason being to give you room for adjustability.

Adjustability implies an air regulator. You need to spec an air regulator that can "blow down" or unload the pressure side of the cylinder as axis movement tries to compress the air. This is important because some regulators will act as check valves effectively resisting axis movements. The other problem is that regulators that do unload the controlled side of the regulator do so with a limit on the CFM that they can handle. This CFM issue is why sizing the cylinder is important as you want to minimize the amount of air used by the system.

You should be able to find online engineering references to help with caculations. For relatively small machines like routers you may find that the sized cylinder is to small to do the job mechanically. That is you end up with a flimsy rod. It might help with sizing to use the rod end of the cylinder to help reduce effective piston area. On the blind side you simply install a large muffler.

Assuming you can find a suitable regulator and air cylinder this is the cheapest approach to a counter balance. There are available specialized hardware for this sort of usage commonly used on big presses. If the air volumes get out of hand you may need to resort to more complicated pneumatics.

You might want to consider something though. It is often cheaper to simply update the axis drive, a bigger motor or a better match on the gearbox ratio can often be good enough. Contrary to popular belief router Z axis aren't that heavy in most cases. Further it is often difficult on Z axis to even hit max feed rate. This all depends upon the design of the Z of course but you might want to consider what a different motor will do for you.

In this application you can not get the spring to apply the linear force to balance the head. As the spring stretches it will apply more force to pull the head down as the distance increases, that does not balance the head, as you get closer the force lessens, here again it is not linear.
If you search you will see it has been tried with very poor results. Varible gas springs like in the hood of your car or trunk lid have had promising results but can get quite expensive and you never really
know what the real pressure is when you order them, some people have had to buy several sets to get it right.

The air assist is used on commercial machines and works quite well, we have one on my machine at work.

[skyguynca]

Well I have found a suitable air actuator, a good pressure regulator and a high cfm calibrated and adjustable pressure relief valve. I plan on setting just enough pressure to be just below neutral on the head weight, and then set the relieve at the head weight so any down z movement will open the relief and let the air flow out till the head stops moving down and the pressure equalizes. The relief valve is designed for this purpose so it will hopefully work well and have a long life.

My z axis is actually quite heavy, more than you think. I am building bridge mill, truss style framework and sheeted in 3/16 sheet steel. Very heavy but very ridgid.
Will have a work table of 60 x 40 and a Z of 30 inches.

David

[DonKes]

Put a large air tank in parallel with the air cylinder and you wont have much problem letting air in or out. If your air tank is 10 times the volume of the cylinder, the variation in pressure will be only 10 percent of the initial pressure.

Don

[skyguynca]

thanks for the advice Don, I will give it a try

[UA_Iron]

You will get more force from the cylinder if it pushes up as opposed to pulling up on the loaded stage per same pressure. You should use a clevis with a spherical bearing joint in it on the rod end for maximum cylinder life.

[bodini]

http://www.cnczone.com/forums/diy-cn...-cylinder.html

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