I'm putting together some lab equipment, and I need a rubber stopper to fill the gap between a 1/2 OD tube and a 7/8 ID opening.
I've looked into lab supply houses and they seem to have stoppers in lots of different exterior sizes, but very few (and small) interior dimentions. Finally someone told me to just drill the thing out.
Drilling the stopper out works decently, but using my normal 118^ HSS drill bit, I get a surface finishing that is pretty crappy. I worry that the seal that I'm getting is poor.
Is there a better way?
Buy some dry ice. Freeze the stoppers, machine it quickly before it defrosts. We use to do this for machining lots of soft rubber or polyurethene. Wear gloves or you will burn your fingers. Good luck. RJT
a hole punch may work , ie like you punch leather with. A paper drill uses a hollow tubular drill, maybe try a piece of 1/2 tubing as a drill
Make a "cork borer":
Use a piece of steel tube 1/2" OD and a thin wall. Grind a sharp edge on one end of the tube. Mount the tube (sharp end down) in the drill press chuck. Place rubber stopper on piece of wood. Center under tube. Press down.
The stopper will swell out a bit from the pressure and then return. This should form a snug seal on the half inch tube for the experiment.
For an easier cut try some liquid soap slathered on the tube.
Or you can just buy a whole set.
We always made our own tube drills from the hardware store brass tubing. We cut the tubing to 3" or so lengths, put in lathe and sharpened from the inside of the tube with a fine file, tube placed in drill press, stopper placed on small piece of wood - hand held with small end up, and lubed with glycerine or diswashing liquid. Slow speed and relube often.
BTW - lube any tubing being put through the rubber stopper. I have seem many folk who tried to push glass tubing through the stoppers without lube. They ended up breaking the tubing and core drilling their hand.
Go to a lab supply house and buy a set of
cork (stopper) borers. They come in a neat
telescoping set and while you're at it, buy
the sharpener gizmo as well.
The tubing trick works like a dream! Thanks guys.
Those cork boring sets are a really nice thing to have. I have used hundreds of gaskets in my time and bought very few of them unless they are laminated head gaskets. Cork, leather, cardboard and gasket paper of various thicknesses is cheap and a set of those stopper boring tubes makes quick work of the bolt holes.
Believe it or not, ArmorAll works well when coring rubber.
have a 20 pc set
found it in a pallet of junk came in from an auction
had no clue what they were but they were shiney and nested so cutley together i kept them for 20 years
thumbing through mcmaster carr one day
use them all the time now