Smoothing a rough hole--suggestions?

Question

I've got a passage in a die head that I need to smooth up. Looks like it was drilled and nothing further was done to it. Material is hardened P20. Hole is 18mm straight with a through length of 12-13 inches. I need to get the inside smooth/polished with no visible surface pits. scratches, drill marks etc. Estimate I'll have to open it up

10-15 thousandths to get below the worst of the grooves.

Hole goes through, but I only have 1 1/2" clearance on the back end, so everything has to be done from one end. Final diameter, concentricity, straightness and taper aren't important. I would actually like it to finish with a slight taper, smaller at the rear.

Mounted points, followed by Cratex and then polishing compound on a felt bob? Expanding carbide reamer first to get it smoothed up a bit? Flex-Hone and a brass lap?

Thanks,

Bill

Paul · Accepted Answer

Ream as smooth as you can then go at it with on of those hone brushes (looks like a bottle brush but with small abrasive balls on each bristle) powered by an air drill or equivalent. For final finish use a 'butterfly rod' which is nothing more than a 1/4 rod with a saw kerf splitting the end for an inch or so, into that slit place a length of folded length wise abrasive cloth, power the 'butterfly rod with a die grinder for higher RPM. Use progressively fine grades of abrasive cloth to desired finish.

At least that's what I'd try....

Regards Paul

William Noble · Answer

I had good luck using a suitable lap and a range of lapping compounds to do something not totally unlike what you want to do

steamer · Answer

--Google on "Flexhone".

peter divergilio · Answer

How about an old fashioned brake cylinder hone?

Smoothing a rough hole--suggestions?

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