tag:blogger.com,1999:blog-3841543812574325787.post8593609932317959452..comments2023-12-07T10:14:01.890+00:00Comments on Matthew's Blog at Workshop Heaven: Mythbusting Flatness (part 1)Workshop Heavenhttp://www.blogger.com/profile/11783322295821347851noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-3841543812574325787.post-55651685588460920592012-11-26T22:04:17.391+00:002012-11-26T22:04:17.391+00:00Thank you Richard,
Now I understand why you poin...Thank you Richard, <br /><br />Now I understand why you pointed out how immaculate the finish is on the surfaces of the new super squares!<br /><br />I guess that given the very fine tolerances that your tools are made to, properly accurate metrology tools are an absolute must in your workshop. For us humble woodworkers a good quality Engineer's B grade would indeed be considered definitive.<br /><br />My beef is with those that sell bits of ground flat stock and call them 'precision woodworkers straightedges', not understanding that dimensional consistency and straightness are far from the same thing. <br /><br />When combined with the unsuspecting purchaser's misguided faith in their accuracy, they can be even more dangerous than a fluffy slipper!Matthewhttps://www.blogger.com/profile/16318609298794308615noreply@blogger.comtag:blogger.com,1999:blog-3841543812574325787.post-61839827547572666042012-11-05T20:07:25.514+00:002012-11-05T20:07:25.514+00:00actually, for most peoples work a cheapo straight ...actually, for most peoples work a cheapo straight edge will be perfectly fine, apart from the occasional obvious piece of garbage the main point of its cheapness will be less rigour in its inspection, flimsier construction and more obviously a coarser finish to the parts that matter, its thats last point that is most pertinent. <br /><br />something that is never raised and as a toolmaker/ prod eng is foremost in my mind is that a lot of the reliability/ tolerance of the thing is imparted by the method of manufacture ie the actual machine tools involved, were they nackered pre WW1 vintage in the back streets of Delhi with a man on pricework or something a bit more capable.... therefore perhaps we could say that for general workshop use the 'B' grade type item is perfectly good from hopefully a reputable source. I suppose with the cheaper stuff its whether you can live with the coarser finish or lack of conformity to a stated British Standard grade, ie 'B', 'A', Inspection etc, I know I couldn't..... <br /><br />and of course its what you test against, metrology can get involved and demands rigour, and so we must need something a bit more than our 'gannies fluffy slipper to compare against !!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3841543812574325787.post-4182235129935554012012-10-08T07:53:12.781+01:002012-10-08T07:53:12.781+01:00Hi Johannes,
Yes, a power jointer will make a re...Hi Johannes, <br /><br />Yes, a power jointer will make a reasonably flat surface so long as pressure is applied to the workpiece in the right sequence when feeding the timber. <br /><br />Power jointers can get you within a mm or so of finished dimension and will leave a slightly scalloped surface due to the rotation of the blades. This takes care of the grunt work and a hand plane can then be used to achieve a smooth surface that is accurate to a tenth of a mm.Matthewhttps://www.blogger.com/profile/16318609298794308615noreply@blogger.comtag:blogger.com,1999:blog-3841543812574325787.post-28299711734870148722012-10-07T11:16:17.731+01:002012-10-07T11:16:17.731+01:00hi
so I think I understand the piece of wood beco...hi<br /><br />so I think I understand the piece of wood becoming convex if you take too many through shavings with a hand plane. But I was wondering if a power jointer actually makes reasonably flat surfaces (in the direction of plausible) when it's properly set up? because the fact that the outfeed table is at the same height as the cutting edge of the blade, and the infeed table is variable, always seemed logical to me in that it should produce a flat surface. Is that a resaonable expectation?<br /><br />regards JohannesAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3841543812574325787.post-45201163234460992372012-10-07T05:09:59.836+01:002012-10-07T05:09:59.836+01:00Hi Otis, You can check them by doing a flip test. ...Hi Otis, You can check them by doing a flip test. Lay the straightedge on a piece of paper and carefully mark a short line with a marking knife at either end and another one in the middle. Turn the straight edge over (i.e. you are still referencing off the same edge) and repeat the middle mark. This will double any error making it easier to see, if you see two lines - it's not straight. Repeat the exercise a few times to be sure and always have the bevel of the knife flush against the edge so that you get a true reading.<br /><br />All materials expand and contract to some degree with changes in temperature, that's just physics. Good straight edges are carefully heat treated to make them as stable and uniform as humanly possible. In other words if the whole thing gets minutely bigger in all dimensions at the same time, its straightness will be unaffected. Matthewhttps://www.blogger.com/profile/16318609298794308615noreply@blogger.comtag:blogger.com,1999:blog-3841543812574325787.post-43120155267200675372012-10-06T08:50:46.983+01:002012-10-06T08:50:46.983+01:00Very Interesting stuff - I'm always worried th...Very Interesting stuff - I'm always worried that my veritas straight edge is out when working with musical instruments - Is there any way of checking if a straight edge is flat without buying another straight edge? Do temperature / atmospheric changes affect the the accuracy of a straight edge to a considerable degree?Anonymoushttps://www.blogger.com/profile/04749074005459274454noreply@blogger.com