I have a bunch of small rubber rings that I need to conduct testing on. The rings start at about 15mm ID, and need to expand to 65mm and be held there for months. Right now, my solution for expanding the rings is using a tapered beam which increases from slightly smaller than 15mm to 65mm, and I am manually sliding the ring down until it reaches the constant cross section area of 65mm. This; however, is very tiring on the hands, and I am sliding about 30 of these rings on different tapered beams a day, I was wondering if anyone had any better suggestions. I can't think of any easy cheap way in which I could expand and hold these rings at a certain diameter. I started thinking of a complex mechanism with linear actuators inside and realized it would be too much work. Is there something I can do with air pressure? These rings are also then heated, so I would need something that could expand/hold at temps between 60 and 80 °C as well.

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    $\begingroup$ Make a tool similar to what vets or farmers use to put rings on calves balls. Just make sure you keep your fingers out the way. $\endgroup$
    – Solar Mike
    Feb 2, 2022 at 20:41
  • $\begingroup$ If the ID of the ring starts out at 15 mm, then you only need to transfer it to a 65 mm diameter rod, unless the ring's ID starts smaller than 15 mm, then you would need a two-stage transfer. $\endgroup$
    – r13
    Feb 3, 2022 at 2:01
  • $\begingroup$ @r13 - ah yes!! lots of stages with smaller expansion ratios would be easier! i.e. modify OP's mandrel into alternating conical and cylindrical sections. Then have multiple "tools" (each an "expandable hole") sized to overcome one of the conical sections. "Expandable hole" can be a hole in a baseplate, with a plastic cylindrical tube pressed in or glued into a c'bore, standing up an inch or so. Cut slits into the tube (axially) to let it expand. Mount an outer elastic o-ring on the tool tube to keep it closed up... have a row of these and stick your mandrel into each one ... $\endgroup$
    – Pete W
    Feb 3, 2022 at 10:01
  • $\begingroup$ First suggestion is to get a tube of KY. Get rid of the friction losses first. $\endgroup$
    – Phil Sweet
    Oct 31, 2022 at 23:09

1 Answer 1


Here is a suggestion. You'll need to make some calculations and necessary modifications though - Add a few more expanding bars and an extendable ring plate at the open mouth to ensure the circular shape.

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