Technically, centerless grinders are “OD grinders” as well, but they are two very different machines. They’re designed for grinding metal, someone who knows what they’re doing can grind more exotic materials as well. They have to have the right skill sets and even possibly different types of grinding wheels as well.
I’m just curious. I’ve never heard of anyone grinding rubber before. I don’t doubt that it can be done.
This company grinds rubber all the time, their main business is grinding rollers for printing presses, printers, and other precision type roller work.
The grinder was just an old Cincinnati centerless grinder and they had a way of feeding the rubber through it. They can hold tight tolerances on it too, I didn’t stick around to watch them run extruded cord stock through one but it is a main part of their business. Since I build their molds and urethane centrifugal tools the grinding part only effects my work in the amount of excess material they want to be removed during the grinding operation.
Parker Seals couldn’t extrude anywhere close enough to the tolerances they needed evidently, which I found of interest simply because I’ve built extrusion dies that can hold pretty damn close sizes, especially if the material is exactly consistent batch after batch like that would have to be.
I think what the issue is that they have to post-cure them in an over or autoclave and that is where the biggest shrink variation can happen on really tight parts.
Parker must have had a very good QC department on them, but they would have cheerfully chucked my customer under the bus if it could have been shown they were negligible in any way.
Also, the o-rings were spliced by Parker Seal, they weren’t molded as a ring but as cord stock then cut to length and spliced after. The splice is usually done on a very acute angle to give a larger cross section for the adhesive or vulcanizing to bond securely. Properly bonded by either method will result in a bond at least as strong as the o-ring in its natural shape anywhere else.