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View Full Version : Lapping a knee that's out of square



Neil Jones
02-25-2009, 10:28 PM
I purchased a 6" cast iron knee made in China. Its ground but it's out .004 in squareness. If I can grind it to be within .0005 of square using a magnetic squaring block and a surface grinder how difficult would it be to lap it to within .0001 of square? What tools would I need?

Forrest Addy
02-26-2009, 01:23 AM
Back when I was a brawny male I'd tune up your Chinese cast iron knee in a couple hours with a square file and a scraper. I'd get it flat and square within 0.000`" (maybe closer).and all I wound need is a small surface plate, a surface gage, a a couple of of parallel camp and two good parallels, and a dial test indicator. Now it would probably take most of a day if my legs held up.

Find a Ford "Trade Theory" Book and look up how to move metal with hand tools. Goes quicker than you might think.

http://www.alibris.com/search/books/author/Henry%20Ford%20Trade%20School.%20Shop%20theory%20D epartment

This book should be in every home shop.

You ON'T want to lap it it would take forever and you have to guard against rounding the edge, squaring one direct as it drifts out in the other, loose abrasive, etc.

Neil Jones
02-27-2009, 02:41 PM
"all I wound need is a small surface plate, a surface gage, a a couple of of parallel camp and two good parallels, and a dial test indicator.

What size parallels?

Granite or cast iron?

Starrett sells granite ones with cases. I don't know where to get cast iron ones and the cases for them.

When is your next class on scrapping?