Polishing Inside of Hydraulic Cylinder

[sparkycuda]

Working on my Payhauler dump cylinders and have not found any references on polishing the inside of cylinder tube. What grit should I use and does anyone have suggestions/helpful hints for performing this operation? Using seamless stainless for inner three stages and thick-wall brass for the outer can. These are single-acting, so the rod outer surface is not as critical.
Thanks, in advance.

Ken

[Papy]

You can try to use a honing tool with a hand drill....not perfect, but probably the best and cheapest solution (link given for reference only....search "honing" on eb**)

[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)

[Zabco]

Interesting, I did not know that about cylinders in real world. I had always been under assumption (I know) they were polished. Next time I have to make one I won't put as much finish into it and see how it works. Would save a lot of time.

[Cooper]

I also use a wooden dowel with slit in end, wrap whatever sandpaper I’m using. I usually have cylinder chucked up in the lathe and just run wooden rod with sandpaper in and out by hand. I also leave a cross-hatched pattern like talked about above. Realistically for our purposes it’s no big deal how the finish is. (Still want to have it somewhat smooth) I think I use 600-800 grit hones for my final “polish”. And also keep in mind brass can sand down quick, so if tight tollarances are in need check often. I also do a quick polish with whatever metal polish compound I have around. (Any left over polish will turn your oil black quick. -I usually run the system for a bit then change oil. ).

[sparkycuda]

Thanks for all the responses. I worked on/taught 1:1 heavy equipment, but don't have experience with how the RC world is different for fit and finish of hydraulic pieces.

My Payhauler requires four stages to get retracted pin-to-pin centers at 3.9" and extended at 9", like the real one. Did learn about the differences between SAE hyd numbered o-rings and plumbing numbered o-rings: there are not the same dimensions. Plumbing #008 are 3/32" CS while hyd #008 are .070" CS. Makes a huge difference for groove and barrel fit.
Aw, the things you pick up while building stuff!

Ken

[Zabco]

What I love about this hobby, a constant supply of educational opportunities.

[skeeter]

Learn something every day. I always thought the real life cylinders were polished. After reading the explanation why they aren't, it makes sense.