Tweet
Rex!
The scraper comes into play when the fresh bushing has been produced slightly undersized.
Commercially available bushings often come out of the package a perfect fit to a fresh journal. But when the bushing is pressed into a hole that has ~.0015" interference, the bore of the bushing collapses slightly as well, usually about a half a thou, depending upon the thickness of the bushing wall.
The journal will stick in the bore of course. Forcing it in and out will make marks (or you can use a felt tip pen and look for the exposed metal).
Merely scraping the highspots in a cross-hatch fashion will allow the journal to be inserted slightly further.
As the operation is repeated, the area of contact will widen.
The amount of material removed is in the order of tenths of a thou, so it is a long process.
But if the other end of the journal is properly located within its bushing, it will actually show any misalignment in the new bushing as you gently force the cover on and off of the dowels.
You will only be removing metal from where it is needed. It also must be noted that often the interference signature can often be opposite of the true highspot, so some careful observation and a little intuition go a long way: Such as if you realize the signature is opposite a bulge from where the bushing has been pinned.
Even a piloted reamer or hone will 'walk' slightly to the side of a pinning bulge, so a scraper is the only way to accurately remove only the bulge.
I also spin an abrasive nylon brush within the hole to smooth any burr, and further illuminate the highspots with the next trial assembly.
It is harder to describe the process than it is to perform, but it does take much more patience than most modern metal butchers can muster.
I'm certain a better tutorial can be found at http://www.lindsaybks.com/
....Cotten
PS: I mentioned "supply" of scrapers in my previous post. You want them very sharp on their hollow-ground edges.
The scraper comes into play when the fresh bushing has been produced slightly undersized.
Commercially available bushings often come out of the package a perfect fit to a fresh journal. But when the bushing is pressed into a hole that has ~.0015" interference, the bore of the bushing collapses slightly as well, usually about a half a thou, depending upon the thickness of the bushing wall.
The journal will stick in the bore of course. Forcing it in and out will make marks (or you can use a felt tip pen and look for the exposed metal).
Merely scraping the highspots in a cross-hatch fashion will allow the journal to be inserted slightly further.
As the operation is repeated, the area of contact will widen.
The amount of material removed is in the order of tenths of a thou, so it is a long process.
But if the other end of the journal is properly located within its bushing, it will actually show any misalignment in the new bushing as you gently force the cover on and off of the dowels.
You will only be removing metal from where it is needed. It also must be noted that often the interference signature can often be opposite of the true highspot, so some careful observation and a little intuition go a long way: Such as if you realize the signature is opposite a bulge from where the bushing has been pinned.
Even a piloted reamer or hone will 'walk' slightly to the side of a pinning bulge, so a scraper is the only way to accurately remove only the bulge.
I also spin an abrasive nylon brush within the hole to smooth any burr, and further illuminate the highspots with the next trial assembly.
It is harder to describe the process than it is to perform, but it does take much more patience than most modern metal butchers can muster.
I'm certain a better tutorial can be found at http://www.lindsaybks.com/
....Cotten
PS: I mentioned "supply" of scrapers in my previous post. You want them very sharp on their hollow-ground edges.
Comment