tag:blogger.com,1999:blog-6261993076995357307.post4717960631929181611..comments2023-11-05T06:16:56.961-05:00Comments on the Carpentry Way: A Ming-Inspired Cabinet (84)Anonymoushttp://www.blogger.com/profile/14328401081765407624noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-6261993076995357307.post-28429189152155155652017-01-29T06:44:31.634-05:002017-01-29T06:44:31.634-05:00Roland,
thanks for the comment. 'Hello' t...Roland,<br /><br />thanks for the comment. 'Hello' to a fellow geek I suppose?<br /><br />Properly dried wood is unlike steel in that changes in temperature do not affect the material dimensionally. Rather, changes in relative humidity - which can certainly be shifted by variances in temperature - cause changes in wood's physical dimensions. It's the humidity level which is important, not the temperature. I'm sure you know this, however many people labor under misapprehensions concerning the effect of temperature change upon wood, so I thought I would mention it all the same with the intention of clarifying the matter given that others will read this entry.<br /><br />Having read Moore's Fundamentals of Mechanical Precision, I'm at least dimly aware of the issues revolving around temperature and metal movement, and understand that precision metal working applications require careful control of temperature. I'm hardly in that league with my work, and for sure it is beyond the level of accuracy which I think is necessary to achieve close fitting parts. And besides, I have no control of ambient conditions in my shop (having no heating) beyond opening and closing a window or two. <br /><br />While a couple of thousandths of an inch can manifest as an obvious gap to my eye, a couple of ten-thousandths of an inch are not -- and are not clarities of cut I can achieve with my equipment anyhow.<br /><br />Having now had the chance to use a DRO on my mill, I much prefer it, like my Digimatic calipers, to rulers and tapes. My eyes are getting old and, for one thing, these more modern technologies are a boon as compared to squinting at the graduations on the rule and trying to interpolate. As it is, I find I keep the Optivisor on my head a lot more than initially anticipated...<br /><br />Anonymoushttps://www.blogger.com/profile/14328401081765407624noreply@blogger.comtag:blogger.com,1999:blog-6261993076995357307.post-64374479227144536502017-01-28T13:01:02.379-05:002017-01-28T13:01:02.379-05:00Is this the newest wood machining website? ;-)
In...Is this the newest wood machining website? ;-)<br /><br />In 2008 I measured a Stanley steel tape measure on our Stiefelmayer 3D CMM at work because I also had some doubts about its accuracy. I put one precision ground steel block on the 100 mm mark, and another one on the 2500 mm mark. The distance should be 2400 mm (94.4881 in). I measured 2399.91 mm (94.4846 in). I thought that was pretty darn accurate, given that it has 1 mm increments.<br /><br />On a long build the deviations between wooden parts and steel vernier calipers and tape measures due to temperature swings in your shop could have a significant influence.<br /><br />Steel has a CTE in the order of 12×10⁻⁶ K⁻¹. Woods seem to be around 3×10⁻⁶ K⁻¹ in the length direction and around a factor of 10 higher in radial and tangential direction. A 10 K (or °C) difference in temperature will make a 1000 mm (39.37 in) steel ruler expand or contract around 0.12 mm (0.0047 in). This is why the rooms for measurement machines are generally temperature controlled and why you have to leave parts there for 24 hours before measuring them.<br /><br />DRO's often use special glass rulers with a low CTE. So they can be very accurate, especially with temperature compensation.Roland Smithhttp://rsmith.home.xs4all.nl/noreply@blogger.com