collets

Hi John

There was a tool design published in ME sometime in the 1970's for expanding copper piping into tube plates on boilers, It very basically consisted of a piece of rubber tube, a close fit to the inside dia. of the pipe to be expanded. Through the centre of the rubber tube was a fairly close fitting bolt  with washers at either end of the rubber tube and a nut to put it all under compression. The idea was slip the tool into the end of the pipe to be expanded, run the nut along the bolt to compress the rubber tube, which having no where else to go got fatter as it was forced to shorten. That loaded up the tube to be expanded and so job done. To get the tool out just release the nut and allow the rubber to go back to it's original length. I've tried this with odd bits of tube stuck through washers and it works. The origianl tool design was more complicated having handles like a pipe wrench that you could squeeze rather than fiddling with nuts and bolts, but the principle is the same. I think for your purposes this would work quite well as you would have a lot of "feel" for what was happening. The rubber tube would be kinder to the brass than a steel expander, sizes wouldn't be critical and you can always squeeze a bit harder if you haven't got quite enough increase in diameter.

I'm sorry I can't help with issue numbers, we used to get Model Engineer in our works library which is where I saw the idea and it's stuck with me ever since.

Hope this helps.

Keith

Hi John

I think if you use o rings you'll get a series of raised ridges rather than a smooth overall expansion. If all your looking for is a couple of thou, you might get that with a suitably sized dremel type sanding drum and fine abrasive paper, effectively an internal grinding/honing job, even if you have to make an extended shank to reach the bottom of the ferrule.

Martins suggestion of sanding down the male ferrule sounds a lot easier.

Keith