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<TITLE>Re: Measuring Surface Flatness (was "Cabinet Grade Particle Board")</TITLE>
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<FONT FACE="Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12.0px'>On 11/19/04 7:57 PM, "John Pavlick" <jpavlick@idseng.com> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><SPAN STYLE='font-size:12.0px'><FONT COLOR="#0000FF"><FONT FACE="Arial">Mark,<BR>
A good way to measure flatness / trueness (is that a word?) is the "winding stick" method:<BR>
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</FONT><FONT COLOR="#0000FF"><FONT FACE="Arial">Take two perfectly straight bars or rods, each painted lightly on one edge - one white, one black. Lay them on your bench with the colored edges facing you and sight from a distance. You should see one color only at first, then the other color should appear evenly as you stand up slowly. If you see it more on one end, that is the "high" side. This will show you any twist. To check overall "flatness" you can use a long straight edge or the string method. My bench is 8' x 27" and this method works for me. <BR>
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</FONT><FONT COLOR="#0000FF"><FONT FACE="Arial">As far as 2x4's being "overkill" for the bench frame - well yes, maybe they are but it's kind of like having too much money or too much horsepower...<BR>
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</FONT><FONT COLOR="#0000FF"><FONT FACE="Arial">John Pavlick<BR>
<a href="http://www.idseng.com">http://www.idseng.com</a> <a href="http://www.idseng.com/"><http://www.idseng.com/></a> <BR>
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</FONT><FONT FACE="Tahoma">-----Original Message-----<BR>
<B>From:</B> discussion-request@nsrca.org [<a href="mailto:discussion-request@nsrca.org]">mailto:discussion-request@nsrca.org]</a><B>On Behalf Of </B>Mark Grabowski<BR>
<B>Sent:</B> Friday, November 19, 2004 11:21 AM<BR>
<B>To:</B> 'discussion@nsrca.org'<BR>
<B>Subject:</B> Measuring Surface Flatness (was "Cabinet Grade Particle Board")<BR>
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We've seen some great ideas from several folks. However, a common element to this discussion is that you need to measure how flat the surface winds up. What tricks are you guys using to actually measure how flat the surface is of the bench you just built?<BR>
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There is only one way measure true surface flatness and that is with a surface place and a precision height meter. This is a great method if you 1) have a large enough surface plate and the space to use. (This could double as a dining room table, tell the wife it is solid granite and will match the counter tops). 2) you have the money to buy a calibrated height (plus or minus 0.0001 inch accuracy).<BR>
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Strings are foolish, how do you account for gravitational pull on the strings? There is an arc you have to account for. Boards will warp with temperature and humidity changes.<BR>
Maybe your best bet is to go find a billiards' supply house. Buy the slate table is built from. ( I saw this at Scott Anderson’s house) It is very flat and true. This will be your reference plane, next buy a true strait edge and a good set of feeler gages. You can measure the any deviations of the surface with the flat edge and the feeler gages. The slate can be used to verify the flatness of the strait edge.<BR>
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Now you have had your first lesson in metrology 101, there will be a test tomorrow. (LOL)<BR>
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Randall Bearden<BR>
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