Expanding Mandrels for workholding on a lathe (& other ops.)

Simple shop-made expanding mandrels can be used to hold parts on the inside when you can't hold them on the outside, either because you want to machine the outside or, as in this example, where the outside is already finished & would be damaged if held there.

[@georgeantonaros5580]

Very nice !! 🤗

[@WrenagadeWorkshop]

Good to find another UK machinist :)
I just got myself an expanding mandrel so I can turn a pair of small three step pulleys for a milling head attachment.
Subbed for support, you have some cool content and looking forward to more ;)

[@dense505crew]

They can be rough as long as you can skim them each time you use them. Everything else can be rough but the mounting surface will then be as good as your lathe.

[@joeshmoe5935]

Make mine out of hex stock. Number each side to its corresponding jaw number that way everything is always concentric when need to use it in future.

[@jackschapira7681]

I'm trying to figure out a way to expand the rim of a shelled out coin using my mini lathe and similar technique to the use of an expanding mandrel. Its used in magic tricks! Any suggestions on how to do this?

[@MidEngineering]

Like stretching a ring? Take a look at this -
czcams.com/video/VWXrqMHkjwA/video.html
Maybe you could do a similar operation in a lathe using something like a knurling tool with a plain wheel ?

[@jackschapira7681]

I was thinking this... but what would keep the coin shell in place while the knurling tool expanded the rim? To shell it out I have made a chuck that clamps in the coin under pressure so I'm not sure how knurling would work in terms of applying the opposing outer pressure

[@MidEngineering]

@@jackschapira7681 Holding a part is one thing, stretching the metal something else! Will need a lot more force - pipe expanding machines often use hydraulic power. Hence why I thought you'd have a better chance with a rolling/swaging kind of process. Not sure that would be possible though as I guess you need to stretch/expand the face of the coin as well as the rim? Are you trying to make an oversized coin? You might need to start from scratch - I have an old pantograph engraving machine that could probably do that!

[@jackschapira7681]

@@MidEngineering it must be possible, as the market is in the magic industry that use expanded coin shells in magic routines. The coin shell fits over the regular coin, so essentially doesn't need an expanded face but the rim is expanded ever so slightly thay it can cover the regular coin. Do you think this is possible using a mini lathe?

[@MidEngineering]

@@jackschapira7681 As you say, it must be possible to do - but on a mini-lathe? I really don't know!