Originally Posted by DannoXYZ

So I take it you've never ever used the hone before and yet you pass judgement on my 10-years of using it a shop, eh? Blanket, all-or-nothing, black & white statements can't really compare to actual numbers. Here's what a brake-cylinder hone is used for:

1. master-cylinders in cars have piston pushing inside a bore with 0.0010-0.0015" clearance.
2. this gap is sealed with a rubber O-ring that's riding in a groove at the end of the piston
3. brake-fluid is anhydrous and absorbs moisture from the air.
4. over time, a year or two, the brake-fluid absorbs enough moisture that it actually starts to percipitate out of the fluid under cold-temperatures
5. these droplets of water eventually corrodes and rusts the walls of the master-cylinder
6. the corrosion and rust chews up the rubber O-ring and you end up with soft brakes, the pedal may even go all the way to the floor in extreme cases
7. So... you repair the master-cylinder by disassembling and using the brake-cylinder hone on the corrosion and rust present in the cylinder.
8. with WD40 or cutting-oil, 30-seconds with the hone typically removes 0.0002" of material (at minimal spring-tension setting). Usually a good idea to measure the cylinder and piston beforehand to ensure maximum-clearance of 0.0030" is not exceeded in the process of honing (reduce honing time if clearances are close to the limit already).
9. replace O-ring on end of piston with new one,
10. reassemble brake master-cylinder, pour in new fluid and you've got new brakes!

Note that the surface created by the hone is smooth enough to seal against 1300psi of hydraulic fluid with just a rubber O-ring!

With a seattube and cutting-oil, 10-20 seconds of the hone typically won't even remove the primer-paint that's sprayed down there! But it really does a nice job on the soft porous rust and other corrosion. It's much safer than reamers. You have to be careful with those and adjust them to the minimum since just 1/4-1/2 of a turn can take off 0.0020" of material instantly.

Next you're gonna tell me that programming the mill to take off 0.0005" from the surface of a corroded seat-post in my lathe is a dumb idea too right? After all you've probably done it a thousand times...