what to do with a free scrap dumpster find ?

         

i spent some time working on the servo motor mount and pinion shaft to drive everything. the back driving seems to have stopped with the drive gear engaged and i can actually drive the head up with a cordless drill so a 1HP servo should have not trouble. i still want to play around with the air cylinder idea plus i have one coming tomorrow anyways. it's still good to have some kind of aid for lifting a heavy axis so i will try to make something of it .

the only down side i encountered was my mount for the servo motor. i can only get 3 connection points. not the end of the world just something i don't typically do but i have seen it done quite often so it is what it is. but now i know how long to make my stand offs and i will have to buy some longer cap screws for that part as well.

i had a extra short 20mm ball screw that i bought just for the nut for another project. i figured half the work was done so i decided to find a use for it since i had the bearing block for it. it was cheaper for me to buy the whole assembly rather than just the nut so it was just extra parts on hand.

i made some new wipers for the linear shafts the old ones were in pretty sad shape and the one came off in pieces so they were ready to retire after almost 50 years

after looking at my old air compressor tank i think it is actually to big for this. more volume is good but i think it might be a 30 gallon plus tank which is to big to fit well anywhere. so i think i will just buy a portable air tank and use that instead. i found a 11 gallon tank for $60 which will fit much better behind the machine. a 5 gallon tank is about half that in cost so it's a toss up between the two.

i stared working on the mounts for the air cylinder but stopped at the base mount. i was just going to attach the threaded rod of the air cylinder to a mount attached to the head but decided to get a clevis pin so that had has a pivot point. i was worried about putting stress on the shaft if things were not perfectly straight.

fittings and everything else add up fast so it is not as cheap as i thought i figured a regulator with a oiler would not be a bad idea either. i'm not sure what kind of oil would be best for an air cylinder so will have to look into that part some more.

so how i think things will work is the portable tank will act as an accumulator and the regulator will control my set point. i can get a pressure relief vale and add that on the accumulator side to blead off any pressure if it should go above my set point. you can get those in 5 psi increments so easy enough once the set point is determined.

i'm thinking you get constant force going up and down but you probably only reduce the head weight by maybe 60 percent. the part i am curious about the the amount of air loss? the return action is not used so that part either vents to or pulls a vacuum from atmosphere.

so as of now the cost is around $275 in case anyone is curious

i'm also going to take a guess and say having some force in both directions would help in the backlash department as well on this axis. tracking down the right fittings to seal everything up has been a treat too. everything thing here in the Sates is NPT but a lot to the cheap stuff you pick up on line is not so finding fittings is a pain in that respect.

I feel your pain re air fittings. I do remember thinking the tank was so cheap but spent about 4x its value on air fittings. Its another example of where the  non-ISO US standards catch you out. You use NPT and the rest of the world uses BSP I have encountered this myself when fitting a similar air tank to my 4WD. I think you are looking at the pressure switch the wrong way. It should be there to ensure that the design pressure of the tank is not exceeded. Say its 100, 120, 150 psi whatever. Set the pressure you wish to use with a regulator. In my case, the tank was good for 180 psi so I used a 150 psi pressure switch so I had maximum air to seat a tyre and ran my air lockers from a regulator set to 90 psi.

To regulate different pressures for the up and down stroke, you can use a needle valve.
 

the tank has to be able to handle the pressure no doubt and in a compressor situation what you are saying holds true 100 percent. but with this kind of set up it's different than what you would find on a compressor. the accumulator tank is just the holding place for the working pressure of the air cylinder. air cylinders and the force they create are directly related to the bore of the air cylinder and the amount of pressure you apply to them. this particular cylinder can produce over 600lbs of force if you apply enough pressure to it. i don't need to operate at that to do what i am doing. i only need somewhere in the ball park of around 40 psi to generate the amount of force needed to offset the head weight of the machine, the basic idea is to to equalize the force going up and down so both directions of travel need the same amount of force to move.

when going up the air cylinder pushes the head up and coming down it pushes the air back into the accumulator tank. the pressure relief valve just is a safety valve to make sure the pressure build up in the tank never gets to far away from the set point being the working pressure.

the compressor supplying the air is it's own system like your thinking .the regulator and oiler will only output say 40 psi to the accumulator tank. i may need to add a check valve after the regulated 40 psi? so my quest for fittings might carry on

i stopped at the store on my way home from work this morning and looked at tanks and decided to try the 5 gallon tank over the 11 gallon tank. so i did some figuring and with the 5 gallon tank i have about 14 times the volume of the air cylinder i am using.

i did see some talk on the subject over on CNCzone and based on what i seen over there the volume was only 10 times greater on that case but someone made a comment about 20 times greater being a target figure. so i am close to the middle road based on that.

if you have a stand alone set up where it's not hooked up to a out side air source i would lean towards 20 times the volume but it would appear you can get away with as little as 10 times the volume on your accumulator tank.

the main reason i liked this sort of set up over a gas strut or gas spring you would find on a lift gate of a SUV or something like that is being able to cycle more. i was looking at gas struts and most are only rated for 5 or 6 cycles per minute. not really up to the task for this application and most of them are rated for around 25,000 cycles for the life time as well. so i can't see them lasting very long. when they go bad you need to replace the entire thing. at least with the air cylinder you have a shot at rebuilding it.

i looked for a while for what is recommended for lubrication for air cylinders but could not find anything so i think i will just try air tool oil and see how it works? i would think air tool oil would be safe on the seals in the air cylinder?

Back to the pressure and valve one post back. I am the last who should be advising you  but I suspect you are using the wrong valve for your application.
The retract stroke should vent to an exhaust port not try and return back to the air tank. That makes no sense.
I had a check valve on the inlet side of the tank to prevent any loss of air through leaks in the lines etc.
The picture I shared is actually the correct type of valve, just it is being used for a one way mist coolant application so I had to block off one port (with the needle valve that as already fitted.)

Here is the same valve firing an air ram..