Randall Young wrote:
>>>>
>>>>
>>Could someone elaborate on how to check for flatness? And what kind of
>>tolerance is allowable?
>>
>>I'm pretty sure an experienced (machinist, mechanic, ...) , with a good
>>straightedge could do this by eye. But I'm imagining myself in this
>>position and being a novice, I suspect I'd screw it up. Without the
>>experienced eye, what tool(s) would be used to measure this?
>>
>>
>
>I'm strictly a shade-tree mechanic, I'm sure there are better methods. What
>I use is a straight edge and a feeler gage. For an overall check, Hold the
>straight edge firmly against the surface to be checked, and try to slide a
>.002" feeler gage between it and the surface all along the edge. On a 4-cyl
>head, I'd do this in 7 or 8 places, boxing in each combustion chamber and
>then once again outside the pushrod holes (if present). For a local check,
>like where the gasket blew before, hold the straight edge firmly against the
>surface, and shine a light through from the other side. If you can see a
>local deviation, it's too big, IMO.
>
>My straight edge is a carpenter's square that I know now is straight from
>having compared it to freshly-milled heads. But I didn't know that to begin
>with, so I just double-checked as much as I could (making the same
>measurement using a different section of straightedge and getting the same
>result); plus if I thought I had a problem I got the surface milled. The
>machine shop agreed that my first warped head really was warped, so I guess
>I got it right. A tool and die type machine shop would likely have a
>surface plate they could check it against for you (for a price), but I
>didn't do that.
>
Thanks.....
I was trolling for answers. The interesting part was the .002
specification. I'm taking an
introduction to precision machining as a hobbiest. The instructor mixes
the program students with
the amateurs. As a hobbiest I get to build the paper punch with a .015
tolerance.
Like this....http://www.grubinski.com/grubinski/fabrication.html
The program students are hacksawing and filing a piece of sheet steel to
a tolerance of .002.!
The purpose of the exercise was to hold that tolerance with hand tools.
When I learned that
I went out and started shopping for magnifiers.
Steve Shipley
Seattle, WA
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