Ron how am I going to get you to make wood patterns if you think 1/8" is close enough? ;-)
I've built patterns that were +/- .005" of the design parameters, about 6", and other that were +/- .125" over about 20 feet. That's about .0065" per foot Starret rules have a tolerance of .001" per inch, so I think I got close, when everything was measured I was off by 3/32". But that's using a tape measure and calculating the shrink at .25" per foot. So how close is close? My tape measured a 6' rule with no visible error, but according to starret ther 6' rule could be off by .072 or +/- .036".
Dave Patterson
odd_kins@yahoo.com
http://home.comcast.net/~oddkins/foundry_home.html
--- On Tue, 1/25/11, Ron Thompson <ron@ourcadguy.com> wrote:
From: Ron Thompson <ron@ourcadguy.com>
Subject: Re: [gingery_machines] Re: new article: How Accurate is Your Micrometer?
To: gingery_machines@yahoogroups.com
Date: Tuesday, January 25, 2011, 6:27 AM
On 1/25/2011 9:01 AM, Rick Sparber wrote:
>
> Shannon,
>
> You ask a very good question that has no answer. It is sort of like
> beauty.
>
> I know people that define accurate as better than 1/8" while others
> that define it as better than 0.0001". I try to talk about getting the
> best possible accuracy rather than an absolute number.
>
> Rick
>
>
>
I took a 2 year machine shop course at a local college. One of the
things I learned was to take my expectation of accuracy from 1/8" to .001".
In woodworking, 1/8" is acceptable and you can't get much more accurate
because wood changes with humidity. Metal, not so much.
I tried making wooden stuff to a higher standard, but was dismayed when
it stopped working due to swelling. Tolerance and clearance do not mean
the same thing.
--
Ron Thompson
On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA
There are two kinds of posts on newsgroups.
1. This is what I have done...
2. This is what I think...
Be aware of the difference!
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