what to do with a free scrap dumpster find ?

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..

that's the same set up i will use for the draw bar air cylinder which is common when you use both sides. the long stroke air cylinder for the head is only using one side of the cylinder and an accumulator tank. it's about as basic of a use as you can get. you don't need the force of the return stroke for this. i would think of it as a way to cut the weight of the head in half and have the same force needed to lower the head.
Haas automation did an air over oil system that works the same way. they have far more weight to deal with so the air over oil is a Hydraulic Counterbalance. what i am trying is a pure air spin from this concept. some of the bigger machines are dealing with heads 1500lbs plus. here is a link that shows more details.

www.haascnc.com/service/troubleshooting-...e---replacement.html

i had a chance to play around with this type of set up and it works like i thought it would. it seems like about 40 to 45 psi is about neutral with just the force in the upward direction on the cylinder. the only snag i hit was the press fit on the bearing for the gear drive. i have to make that connection better the first stab at it was a bust but i think i have it figured out. down side was once the ball screw is attached the head has to come up off the machine just about all the way to get the screw out of the machine.

one other thing i over looked was the need for two lead in lines to tie into the hard lines. i had a temporary attachment just to play around with and half the lines had leaks. the ones i was sure i could seal got sealed and all those were fine so things should be pretty air tight when finished.

once i get the screw back into the machine i can play around more and test it more but it looks like a winner so far a counter balance.

one other thing i noticed was the placement of the air cylinder has it's place for consideration. the closer you can get it to the center of the lift point the better off you will be in the end. but in my case i am pretty limited to where i can fit one so it takes a little more force to make up the difference as result. just food for thought if anyone should try this. i did not want to have to build framework just to mount one. especially with the price of material the way it is now.

went back and reworked the drive gear connection on my ball screw and got that sorted out, i had to drill and tap the end of the ball screw and add a second bearing to the block that connects to the head of the machine. i ended up boring the back side so i had a ledge to keep things from pulling out of a press fit, so i turned a plug that got pressed into the second bore and bored out for the second bearing and used the taped hole to lock that side in and pull the shoulder of the screw against the other bearing, had everything i needed so at least it did not cost anything extra

once i got all that back together i started running lines and mounted the portable air tank to the back of the machine. i have 2 regulators one is for the counterbalance and the other is for the power drawbar since they operate at different pressure. i ended up putting the oiler regulator combo on the draw bar air cylinder. after thinking about it more. it seemed like it would not do much for the counter balance since there is not very much air flow to circulate the oil..

did some figuring and somewhere around 200lbs for force lifting seems like the sweet spot to even out the  force for lifting and lowering the head. i don't have an exact weight but it's around 275lbs to 300lbs so things seem about right since you have the weight and gravity working with you going down i would expect better than 50 percent gain on the force needed in the lifting direction. 

good news is my power draw bar works. but i can only get 90 psi at he machine so my force is not as high as i want as a result of this. i have 100psi at the compressor but by the time it gets over to the machine i can not get over 90psi. the long hose might have something to do with the drop taking a guess? so at 90psi i think i am getting around 650lbs the way it sits now. i was looking to get 900lbs at least but unless i can boost the pressure i'm stuck where it is.

i found some information before on this but there are some other factors that play into it i think. i noticed the pull force on high speed spindles are far less than say a 10,000 rpm spindle. i would think HP factors into it as well but i have not seen anything on that part. Haas has some info on the topic and a 10k spindle falls somewhere between 925lbs to 1300lbs on a 30 taper but the smallest spindle i have seen on those machines is a 7.5 HP spindle. mine is only 3HP

if i remember right the high speed spindles only require 400lbs to 600lbs of pull force. less cutting force on high speed machining so that makes sense.

well anyways @90psi that limits the air cylinder 1095lbs so i need to get more force at the holder by getting more air pressure to the machine, the air cylinder i have is rated to to 145psi so it should be ok. an extra 10 psi at the machine would probably get me to my 900lbs at the holder i just have to wait and see what i can do for now. it works though

On the compressor pressure switch, there is usually an adjustment. You might be able to just adjust it a bit to get say 110-120 psi. My compressors do about 120 psi.

i was not sure if the pressure switch had an adjustment or not? i never had a need to push the upper limit until now. i have a 50ft hose that has been on it forever and to be honest the hose has seen better days. so maybe between the adjustment and getting some new hardware on the compressor side will get me where i need to be.

i needed to add some air drying anyways so i will come back to this when i get that far. i was just happy to see things work since i never built a power drawbar with the finger clamp and using holders with pull studs. i started a different one a few years ago but never got air cylinder or spindle mounted to anything to test it out.

if i can get 110 psi that would put me in the 1200lbs force range at the holder and that would be picture perfect for a 30 taper.

i picked up an programable oiler so running oil lines is next before i get to far. 5/32 line or 4mm are what i need but i was looking for compression fittings and they are hard to find in that size? i honestly think i spend more time looking for the right stuff than actually being able to work  on the machine.

Maybe I'm lucky as I get custom brake lines made by my local specialist hose shop and they have never let me down. He carries 4mm fittings.

CPVC piping which is suitable for hot and cold water distribution has a 400 psi pressure rating at room temperature, and a 100 psi pressure rating at 180°F.
It is cheap and will actually increase your storage by going to a 1" or larger header. Air hose is always a bottleneck.