Machining tips needed - making a manifold

MHD

Making a dil manifold for my breather project. Any one got a fool proof way of machining the tapered recess for the O-ring in a manifold to mate to a standard 3/8 UNF scuba fitting? A idea on the correct tool if one exists would be highly appreciated

Matt

wizbang

Hi Matty, I made up a couple of manifolds. all of them square and blocky but are holding up just fine without leaks. (touch wood). The recess was the trickiest bit without a lathe or milling machine.

I did mine with a counter sinking bit and then smoothed it out with the dremel but if I had to do it again I would just make the recess with a ball bit on the dremel.
If you have a pedestal drill you can buy the square faced drill bits that would do a good job.
Once again I got help from Jason and Damon. Thanks guys.

Skipbreather

Hello Matt-

It’s not that hard, but the correct simple tools and order of operations are very important. I’ve done many 3/8-24, 7/16, and even a few ½ inch O ring ports up to and including custom machined first stage regulator HP gauge ports. All of them worked just fine. The only machine tool that is ABSOLUTELY necessary is a decent drill press.
1st: Lay out your pattern on your metal stock.
2nd: Center punch the port locations.
3rd: Drill a first small hole at the center punch point.
Now you need the first special tool: a piloted counter sink the same approximate diameter (+/- a few thousandths) as the O ring for you particular port size. (Don’t know the port/ O ring diameter? Try measuring an existing port on a regulator or similar.) These small tool bits are very common in the machine tool and aerospace world.
4th: Increase the size of your first small hole to the size of you counter sink’s pilot. Common pilot sizes are 1/8, 3/16, ¼, and even 5/16 inches. (Yes, I know there are others ;-) )
5th: The “fun” part- Use your counter sink to cut your port. Depth is very important. Too deep, it WILL leak. Too shallow, the O ring does not have enough volume to squish into and it oozes out from under the fitting going into the port, and will eventually blow out. A small amount of O ring protruding above the cut port is what you want- say 5 to 10% of the O ring’s total thickness. A good eyeball helps here.
6th: Now increase the pilot hole size to the proper size for the tap drill for your chosen thread.
7th: Tap the hole’s threads. Tip: To get very precise threads, don’t take the manifold out of the drill press vise after you drill the tap drill hole. Mount your tap into the drill press chuck and start tapping the threads by turning the drill chuck BY HAND. And DON’T be stingy w/ the cutting oil if you expect clean threads.

Hope this helps-
Ken

Drmike

Our standard is to ensure final assembly sees the o-ring compressed by 25%.


So our o-ring grooves are at a depth 75% of the o-ring cross sectional area (for face seals)

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