Polishing inside of 0.25" cylinder?

[DianneB]

I am converting the crosshead pumps on my 1-1/2" scale American from "displacement" type with a packing glad (which always leaked and were nearly impossible to tighten up) to O-rings set in the plunger to act as piston rings.

I have done O-Rings for piston rings but in cast iron cylinders that I could hone but I am not sure how to polish the inside of a brass cylinder that was drilled but is only 0.272" diameter???

Would emery paper on a wooden dowel be best?

[Steggy]

I am converting the crosshead pumps on my 1-1/2" scale American from "displacement" type with a packing glad (which always leaked and were nearly impossible to tighten up) to O-rings set in the plunger to act as piston rings.

I have done O-Rings for piston rings but in cast iron cylinders that I could hone but I am not sure how to polish the inside of a brass cylinder that was drilled but is only 0.272" diameter???

Would emery paper on a wooden dowel be best?

I would consider using body rubbing compound as the abrasive.

[jkimberln]

I've used flex hones for this type of polishing.

[DianneB]

I've used flex hones for this type of polishing.

Flex hones come that small??

[10 Wheeler Rob]

I cut a slot with band saw in small diameter wood dowel and slip a small piece of rag in it. Put some brass polish on it and spin it with an electric drill as I push it and out of the hole.

Rob

[NP317]

I cut a slot with band saw in small diameter wood dowel and slip a small piece of rag in it. Put some brass polish on it and spin it with an electric drill as I push it and out of the hole.
Rob

I've used that same technique with brass rod and emory cloth in a slot.
You can create whatever configuration (diameter/slot length) required to get the cylinder interior polished.
If some rigidity is required during polishing, I've setup the part in the drill press vice (even in the milling machine)
and used the quill motion as needed.
~RN

[jkimberln]

I've used flex hones for this type of polishing.

Flex hones come that small??

Flex hones start about 3/16" or 4mm. Cute little things.

[rkcarguy]

The slot in a small piece of rod with a chunk of cloth works well. You can use various compounds on the cloth depending on how much polishing is needed. Fine turtle wax polishing compound followed my mothers mag and aluminum polish worked really well for me, but only have used this process one time for something so little.

[pete]

Industry does this all the time Dianne. Some high tech methods are used today. Ball sizing, electro polishing etc. But the old school way is an expanding lap or if the hole is really small then user adjusted pin hones and both are used with that Time Saver compound. Check page 1061 on the MSC website. Or you could make your own. There pretty cheap for what they will do. I'm not sure starting with just a drilled hole would work but I haven't done it yet. I think I'd ream to make the hole round with a bit better surface finish first then lap it to the size you want to then get the best surface finish. A drilled hole might take a whole lot of time to lap it round and fully cleaned up it's full length.