burnishing? with a angle grinder

[coppercone2]

I found this interesting video which appears to be a burnishing like process that uses an angle grinder. I am not sure a human can exert enough force to burnish something, but it is none the less interesting.

Have you seen stuff like this before? Not sure if the sphere is offset by design in the first part either, which almost makes it a peening process. Also not sure how safe that tool is, I think I would want a deep bore that is silver brazed if I were to try that. Or is this a purely thermal process?

[Gregg]

Shrinking disks are basically burnishers for flatter metal surfaces.
https://www.proshaper.com/product-category/shrinking-disc/
The link above shows some and has links to videos explaining how they work.

[coppercone2]

I heard about shrinking disks but this design is a little different.. do you think its 100% heat based as the shrinking disk? If you look at the offset sphere, it seems that the material is getting a knocking of sorts, the shrinking disk is way more easy to imagine as being heat based. Also, the contact area between the sphere and the plate is way different and smaller.. I imagine it making ripples in the material. The other tool also seems a little different, its made so you can apply higher pressure then with a flat flexible disk, being pretty much a dome. "thermal peening" comes to mind. I kind of want to build one and see what it does to different materials, but it looks like it might be total hell for the grinder.

[Gregg]

The ball on the grinder has served its purpose as click bait; that is about its best use.  It isn’t burnishing the metal as much as it is planishing.  Planishing is more of an impact process.  To fasten a ready made sphere to a cheap angle grinder so that it runs true is very difficult; therefore it wobbles and impacts the work piece.  Notice how in all of the examples the metal sheets are backed up.  A reasonably contoured body hammer would do a much better job of planishing.
The smaller diameter cylinder is basically using the same principle as a shrinking disk; it needs to be a really small diameter to keep the surface speed to a reasonable level.
The creator has tapped into the youtube money using some of the same tactics that the “be amazed” and the “genius ideas” type creators have been using for some time.  I can’t blame the creator for finding a way to make his life a little better; but some of the real creators with real content just don’t seem to hit the view counts as some of the lame content.

[coppercone2]

Do you think you can weld a domed? disk to a masonry bit and use a impact hammer drill to planish metal? It might actually be useful for simple shields and chassis that use thinner metal without having to use all the sheet metal equipment to make it more robust (I think they typically use some kind of wheel to make a groove that strengthens the material with a bend).

[Gregg]

An impact hammer drill will quickly make a mess of whatever you are trying to smooth.  The operator has very little control over how hard it hits.  Instead buy a reasonable quality .401 shank pneumatic chisel that features a feathering throttle and hook it up to an air regulator.  Hammer bits for these are dirt cheap but need to be modified by crowning and polishing the end that does the planishing. https://www.amazon.com/hammer-pneumatic-chisel-Extended-Spring/dp/B0859737XK
Many C frame planishing hammer kits use these same pneumatic chisel parts; they are dead simple and only have two main moving parts other than the valving.

Welding something on to a rotohammer bit and expecting it to stay together is a true test of welding skills and  heat treating abilities. 

[coppercone2]

Yeah I figured, I don't know if I need this tool, it just seemed convenient to turn one of the old worn concrete drills into something new.