Originally Posted by Mark Hennebury
I think wood moves more with temperature than your Starrett.
Enough beer will either make you not see the error or not care about the error.
Member
I think wood moves more with temperature than your Starrett.
Enough beer will either make you not see the error or not care about the error.
Contributor
I assume you have all your measuring equipment recertified at least once a year? You do use a pull scale for your measuring tape don't you? How do you calculate for sag when using a measuring tool in the horizontal position? I know there are published tables for wire sag for measurements at various temperatures.
Story is the survey party that early on surveyed the us canada border made some mistakes. The us crew stayed sober and gave as much alcohol as possible to the canadians. It paid off in a little extra land here and there.
Bill D.
https://en.wikipedia.org/wiki/Tape_c...on_(surveying)
Better then invar?
https://www.compositesworld.com/arti...ar-alternative
Last edited by Bill Dufour; 07-15-2021 at 12:30 PM.
Member
I know this is a thing for metal work. Working with wood once my initial layout is done via tape rule everything after that is relative to another part or story stick. It is consistent because I just let the air conditioning run 24/7, keeps the beer cold longer too.
Contributor
Precision always matters, accuracy sometimes matters and sometimes accuracy and precision matter.
Bumbling forward into the unknown.
Contributor
For me repeatability is far more important then accuracy. I do not care if the piece is 36" long or 36.05. as long as they are all the same. Do they still balance pistons at the factory by grouping them together in similar weight classes?
Bill D
Contributor
Bill, repeatability otherwise known as precision.
Bumbling forward into the unknown.
Contributor
When I am drinking beer, ( my preference is a locally brewed Scotch ale) I never worry about or handle tools or do any measurements. Typically this deaf guy prefers to put on some cordless headphones, put on some late 60's or early 70's rock and ROCK ON!
Ken
So much to learn, so little time.....
Contributor
For clarification,
as I see it, you need both accuracy and precision. Maybe in different pars of a job, but you need both to make it work.
In woodworking you don't have to worry about high tolerance specifications. But you do have to do high tolerance fit of components.
In woodworking you may not care if your dado is 0.750" or 0.755" but you have to have accuracy when you dress your panels to have them fit, and you have to have precision if you want all of them to fit.
If you want to cut all of your mortises 0.500" ( your target measurement)
and they end up being 0.510" you don't have "accuracy" in that you have missed your target measurement. But you have precision because they are all the same size.
So now your need both accuracy and precision to complete the joint.
When you cut your tenons. Your tenons need to be accurate in that they need to be, for example 0.510" ( or whatever fit you decide)
plus you need precision for them all to be consistent.
And of course no one cares if you make a table 60" long and it ends up 59.95" So you may not need accuracy in this part.
But for the overall job you need both accuracy and precision, and to know when and where to apply them.
Contributor
I can't imagine even the most skilled machinist or tool maker using a steel scale (rule) in a situation where 0.0008" deviation would come into play.
These type measurements would more likely be done with a micrometer or height master. I personally use the Mitutoyo Height Master on a Starrett granite surface plate for critical measurements. My Height Master has a resolution of 0.000010".
David
Contributor
moldmaking, HotRunners specifically - Where I work at my day job we regularly machine and hold +- tolerances of 5microns (a little less than 0.0002in) I believe we have some components that are even 1/2 of that…
Last edited by Mark e Kessler; 07-16-2021 at 7:54 AM.
Contributor
A simple no tool method to check fence and blade setups for high precision crosscuts.
Take a couple of pieces long straight square stock and mark the face and edge on each one.
Trim the ends off of two sticks.
Stand them up on a flat surface. slide them together, with the faces facing the same direction see if they fit. Rotate one 180° check again. That's it!
Repeat the process to check the edges.
This will tell you if they are square to a much higher degree; much easier to see and measure error, then checking the end with a square. And it tells you square in both planes.
This is the most accurate way to check your miter-saw fence, table-saw fence, sliding table saw etc. It tells you if the fence is square to the direction of cut, and if the blade is square to the table.
The longer the sticks the more you will magnify your error. For instance if you use 2"x2"x 50"long you will magnify your error approximately 48 times.
one quarter of a degree off of square on a 2x2 measure about 0.009" but at 50" it measures 0.218 and this method will double that error to 0.436 gap at the top of your two sticks. So it is easy to see minute error in your fence or blade setup-up.
By doing a few test cuts and adjusting your fence until the gap disappears you can obtain a very high degree of accuracy with no tools.
This is similar to a high precision reference cylinder square method.
You could also use round plastic tube if you want.
square-cut sticks.jpg
Contributor
To build the pyramids they needed a good level. So they built a wooden trough around the job site for reference. Had a boy or two keep it filled with water to a mark at all times. Worked very well. Definitely better then in Piza, Italy using more modern tools.
Contributor
But the Piza logo has been much more successful than the Camel cigarette logo
Contributor
I can hold 2/10ths (0.0002") or better as well with both my Nakamura Tome and Matsuura cnc machines. But I'm not using a steel rule/scale to verify this.
David
Contributor
The tower in Piza was built straight in the first effort (about half way) then the project stalled for some time, during which the ground settled and the tower tilted. When someone continued the work they built straight from there. It continued to tilt until recently when it was straightened up. Now it is the crooked tower of Pisa.
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