Tool for reaming out and expanding the inner central bore of a cylinder?
February 23, 2021 4:39 PM   Subscribe

I am looking for a hand tool to cut an enlargened chamber into the central portion of a piece of material that is cylindrical.

It already has a central bore, but I would like to create a section of larger bore starting about 5-6 centimeters or so in from the edge of the cylinder, going about 1-2 centimeters along the cylinders length (and obviously ending before reaching the far edge). The enlargened bore diameter would ideally be about a millimeter or two larger than the existing bore.

In my head I would call this an expandable reamer, something you insert to a desired depth, expand the cutting edge to engage the inner diameter surface, ream desired length and repeat until inner dimension/diameter is achieved. But it seems that an 'expandable reamer' is something different.

Can you tell me this tool if it exists? Obviously I would probably need to buy a set, but for reference the diameters involved would be about 2-4 centimeters. The material is hard rubber - a fairly soft and easily cut material. I'm not terribly worried about exact precision.

Hand tool is fine as I don't have a lathe or any real machinist's tools.
posted by alhadro to Home & Garden (6 answers total)
Best answer: It sounds like you might be able to use an adjustable hone to take off a couple mm off. A small engine cylinder hone might be an ideal size and should work on hard rubber. Usually I think people use a drill to turn them but IDK.
posted by glip at 4:52 PM on February 23 [2 favorites]

On a lathe this would probably be done with a boring bar if you could fit it into the existing center-hole. By hand you're probably stuck improvising. There are linoleum carving tools that kinda sorta have the profile you need, same with some clay working tools, but if you need a smooth parallel bearing surface in there you may have some trouble without a lathe.
posted by range at 5:23 PM on February 23

You should be able to use adjustable expansion reamers. Amazon or any industrial supply house has them.
posted by Raybun at 6:36 PM on February 23

Would a spade bit or a forstner bit work, or a holesaw? You'd probably want one of those little pseudo drill presses and good workholding to keep everything in place.
posted by Jobst at 5:35 AM on February 24

Best answer: What you are looking for is a bottle boring tool. (Ignore the stuff at the top of the page and skip down to the videos and links below.)
posted by ZenMasterThis at 2:41 PM on February 24

There's some good advice above, but as an experienced machinist, this gives me pause - rubber doesn't like to 'machine' by the textbook definition of the word. Abrasive cutting tends to load up with gummy crud, and cutting tools designed to cut metal usually aren't sharp enough and don't have the correct relief. Work-holding is a challenge too.

If you've got a lathe, I could think of a way forward, clamping it with a plug in the center and using hand-ground boring tools and some trial and error until the cutting looks good.

If not, a flapper sander of very aggressive cut on a power drill might work. You'd need to keep things cool which might mean a spray-bottle of water or taking a lot of breaks. It depends on what is going on with the abraded rubber-you want to see the rubber swarf(machined-off bits) dropping out of the way, you don't want to see it hanging around the cutting action and gumming things up.

Good luck!
posted by Dmenet at 10:13 AM on February 25

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