Jim using these calipers with a rule is alive and well, in the professional and hobbiest areas. I have the 4" and 6" spring tension type and the 10" of the screw tension and the trammel points that get me to any size I need. All starrett too. Required tools in a patternshop and for turning, wood or metal. A starrett rule has a tolerance of +/-.001" per inch, that's close enough that you should not need a gage block, now you just need a good eye. When using a shink rule you have no choice, you have to use a rule, unless you want to calculate every dimension. Anything closer than .015" you should be using something that requires less "feel" than these calipers. These can be used to check clearance between parts but that too is a visual thing. I'm sure if you want to take the time you can get quite close, but that only works at home. In the work place +/- .010 to .015" is close enough for this style of caliper. to check clearance you might be able to get
to +/- .002". But these would be real world applications.
Dave Patterson
odd_kins@yahoo.com
http://home.comcast.net/~oddkins/foundry_home.html
--- On Tue, 2/1/11, Jim Barnes <uhrgerat@yahoo.com> wrote:
From: Jim Barnes <uhrgerat@yahoo.com>
Subject: [gingery_machines] Re: new article: The Intersection of Art and Precision
To: gingery_machines@yahoogroups.com
Date: Tuesday, February 1, 2011, 10:04 AM
Rick,
Thanks for posting the article. I recently picked up a set of Starrett Toolmaker inside and outside calipers--these are much smaller than the ones in your article. They are probably no more than 4" in overall length. The small size is one of the main reasons I got them. They are alot easier to use than 6" dial calipers. I also have a set of spacer blocks to practice with and to set the calipers to a specific width. For practice the drill is to put the outside calipers on the blocks, then transfer the measurement to the inside calipers, and then measure the result with a micrometer. Or, in reverse from mic to inside to outside to blocks. It is a bit of an art--getting the alignment right, just the right amount of feel, and measuring with the mic without actually compressing the calipers. And with all due respect to Dave Patterson, it's my understanding that using calipers with a ruler died out at the turn of the last century. I won't claim any
personal knowledge but I was told that they were usually used with gauge blocks, set to the desired dimension and then used to check the progress of machining. Certainly makers sense to me. Since I'm a hobbyist I don't have to work to any greater precision than .001" +/- some tolerance. When I started using dial calipers (Helios, with very sharp needle points) about 25 years ago to measure dental pathologies, I was working to hundredths of a millimeter (0.00039"). We did cross comparisons for repeatability. Once you get to a certain point, the inter- and intraobserver error starts to wash out any alleged gain in precision. So, I guess what I'm trying to say is that unless you have a CMM, you may not get all that much precision from instruments that allegedly deliver it. The person using the instrument is part of the instrument.
Again, thanks for the article and if you run across a set of the dainty, round-legged Starrett calipers, try 'em out.
Jim B.
[Non-text portions of this message have been removed]
http://groups.yahoo.com/group/gingery_machines/app/peoplemap/view/map
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