I did do one basically by hand on a really really nasty XTR chainset a while back.....just to see how bad you could buy and turn it round.
There are various tools and it can be done by machine or by hand all the way through.....or mix and match a bit.....that's what i tend to do.
https://www.retrobike.co.uk/threads/xtr-crank-resto-how-bad-can-it-be.429344
By hand is work! Its going to take a few hours....as i say this is a patience job, not ultimate skill......or though as with all thing you will get better with practice.
Basically by hand, buy yourself a mixed pack of wet and dry paper off ebay....buy klingspor or something reasonable quality. Like this.
https://www.ebay.co.uk/itm/12118529...ar=420176724272&widget_ver=artemis&media=COPY
240, 400, 600,800,1200......if its really bad you might need 120 too. Finer the grade higher the number. Oh and a few buckets of water. If you want a ultra fine finish just keep going through 1500 and 2000........2000 if getting towards what i use to cut back paint clearcoat, so you are getting pretty fine on metal!
If your worried out taking the edges off or rounding them out, try wrapping the paper round a small hard rubber block of even a bit of softwood. Really you only need to worry on the harsh grades.
Wet your paper by leaving it to soak in the bucket for 10mins before you use it.....this is especially true of finer papers. You want it floppy. Keep the item and paper well rinsed.
Change the water regularly...use warm if its a cold day!.
Sand in opposite directions for each grade if you can.....that way you know when you have sanded out the last lot of scratches you put in.
My old boss said "polishing is just getting all your scratches in the same direction " its true....
One thing to consider is that if you have serious cuts across a surface you have to take the whole surface down level or you will see it. You cant just sand out isolated areas otherwise the change in angle of the reflected light will show it up. This is where knowing when to stop comes in.....that is sadly an experience thing.
Once at 1200 or 1500 or 2000 ( depends on just how far you want to go) just use a good metal polish....Mass is
@Peachy! favourite and smells nice i just use autosol as im old skool!
Thats it really.....expect to loose a few hours on a crank, but hey, that XTR m900 crank above i use everyday on my daily driver.....£30......if you see another like that for that money......let me know.....
Machines......angle grinder and a bench polisher (never owned a polisher, i use a £12 draper 650 watt drill in a workmate btw at home)..... get you there faster, but also especially with a grinder can remove material FAST! Also holding stuff takes a bit of care....120 flap discs go through fingers like butter!
If you do decide to get a home kit for a drill, something like this will do you....
https://www.ebay.co.uk/itm/29146577...9nCWsLLSLi&var=&widget_ver=artemis&media=COPY
These are the guys I've bought from at home and at work for a decade. Its everything you need once you have any initial damage out with 120 / 240 / 400 grade. That size and kit is all i have at home.
As i said above, just have a go. Find a crappy crank and try.....
One final word.....just remember PLEASE wear safety glasses and go online and read a guide to using rotating wheels safely. Having your teeth knocked out by a flying crank arm is not fun. Also gloves as the bits will become quite hot on a wheel and ear defenders ( its loud) oh and a mask as breating in a mix of paste, alluminium and cotton fibre is not recommended!
All the best and please play safely.
Heres a few pics. All these bits were horrid when they arrived and have been turned around. In a time when cash is short and parts are expensive..........