Found this link in a search for Schrader Bellows piston cups for an air power feed couple months ago and thought I'd put in my 2c worth. Breakout is a non-existent issue (unlike how manual feed can be) with their hydrocheck system. Nor is advancement or retraction speed. I reconditioned one on an old drill press about 25 years ago and still use it today regularly.
The hydraulic check is infinitely adjustable to both regulate feed speed and where it kicks in, and the against whatever pressure you have the air cylinder pressure valve set for. The feed I use is an older unit that has manual, rather than micro-switched valving, and trip dogs to advance and retract the drill spindle and set where the hydro-check is engaged.
Amazingly, despite the fact that Shrader Bellows was acquired by Parker Hannifin, the piston cups I needed are still available, but it took a long time to get them, so I tore apart a couple backup units I had and one set wasn't too dried out, but did leak air by it into the exhaust port, though not too badly. It actually works out well, because I rout the air cylinder exhaust port to a tube on the drill quill to blow the swarf off of the drill, and the continuous air flow helps cool the drill. The sudden burst of exhaust blows it off into the shop vac.
Here's a short video my daughter took of her mom on her first cam drilling session. Her speed picked up enormously after drilling a few hundred. You will notice there is no waiting time nor is there a hint of chatter or squeeking on break through. The material is Delrin 150. Like any material, Delrin wants to climb the drill on breakthrough, so it has to be held down firmly. Also, the cutting edge where the flute meets it may need to be honed on a bit more obtuse angle so you don't get a burr on the breakout side. It seems counter intuitive, but it works.
That aluminum spacer riding on the reduced shank of the drill is there so I can pound a Morse #2 to straight shank adapter into the spindle nose tight enough to prevent the reduced shank drill from slipping in the adapter. I bore out a bar of aluminum on the lathe with the same drill used in the machine , and part off an inch beyond the drill depth. Then I put in a ½” drill and drill the bar (still in the lathe) and part off for the spacer. The spacer then goes onto the drill shank before putting it and the adapter into the spindle nose, and the long bar goes over the drill and shoves the spacer up to the adapter without touching the end of the drill.
It can then be pounded up however much is required to really tighten up the cheap adapter without damage to the drill. It also works out handily for getting a good angle for the air nozzle blowing down the drill flutes.
Incidentally, for those of you who micky mouse things the way I do, that blue painter’s tape is not affected by oil the way other tape is.
As others have said, unless you need a production machine, this type would require too much setup time for general shop use.
http://www.miterclamp.com/videos/Marjie_Drilling_11mb.mp4
Cheers,
Jim