Polishing Inside of Hydraulic Cylinder

[Zabco]

I've had pretty good results by using Micro-Mesh or Alpha Abrasives finishing films. Come in grits from 320 through 60,000. Packs of assorted grits are commonly available in hobby stores or online. I make a mandrel slightly smaller in diameter than the inside of the bore that I want to polish. Recommend using plastic rod and not wood as the finishing process is done in water and the wood will swell and cause binding. Cut the abrasive films into strips about 1/2 to 3/4 inches wide and long enough to wrap around the mandrel a couple of times. Place film into a slit cut into end of mandrel and wrap around. Chuck other end of mandrel in battery operated drill. I do this under a faucet with a small stream of running water into the cylinder bore to keep the film lubricated and the bore flushed out so don't use a plug in drill. Start with coarsest grit and then run drill at medium speed while pushing mandrel in and out of bore. check appearance of bore surface every couple of minutes and when it appears to be uniformly "scratched" across the entire surface go the the next higher grit and repeat. I usually go up through 30,000 grit which pretty much leaves a mirror finish. Takes a little time but works well for me.

[Rimrock]

The inner of a cylinder tube is in real life not polished, for some good reason. There are some traces, crossings, from more or less course honing tools, up to like 300-400. This apply also to engine cylinders. These traces are there for getting a thin layer of oil film on the walls to lubricate the gasket / piston ring contact surface. If fully polished no oil can stay there. In the scale world it's no big deal, and one can not get it fully polished anyway so a bit oil fill always manage to stick there. Do as you like, what makes you sleep better in the night, polish or just leave as is. I sometimes use a tool called 'Flexhone' and run it through the cylinders a couple of times, other times glue a 600-800 grit paper to a rod and pull through. Most cylinders that are ready made in the scale world have not been threated. But again, no big deal as one not operate 8 hours a day)