Precision Measurements, Do They Matter?

foxtrapper · Post by **foxtrapper** » Fri Jun 05, 2009 7:07 am

Lots of folks get lost in the accuracy of their equipment. Give them a micrometer and they're try to 2x4 framing for a house aligned within a thousands. All for no good reason.

Yes, when building an internal combustion engine those thousands matter when it comes to bearing clearances.

No, those thousands don't matter when framing a house. Nor do hundreds matter. Heck, half an inch barely matters.

Long out of use and practice is the old tick-stick. A darn usefull way of getting and using good measurements that have absolutely nothing to do with scale or units. I often use a tick-stick, or similar methods. It works well, and takes the angst out of fretting over 32 inches or 32+3/32.

paul heller · Post by **paul heller** » Fri Jun 05, 2009 8:50 am

Remember this post? Francis should have added the bit about those concerned with incredible accuracy vs. those who consider eyeball accuracy good enough.

In some parts of the country you can cut a board one day and go back the next to find it is not the same size due to humidity shifts.

Again this is another example of the beauty of our craft - to each his own. Even if no one can see it, if it is important to the craftsman who built a project that incredible accuracy be inside the work, then it must be in there for that particular craftsman to be proud of that particular project.

Paul

e.friedl · Post by **e.friedl** » Fri Jun 05, 2009 9:00 pm

I'm in agreement with what's been said. Wood isn't suitable to being held to plus or minus a thousandth. That being said, setting machinery to a thousandth of an inch means that if I want to work to a hundredth of an inch, I can be sure that the process is more than capable. And sometimes a few thousandths of an inch can be important. If I make a series of box joints and I am more than a couple of thousandths off. Ten or twenty fingers later, I will unable to get the joint together as those thousandths keep adding up. So there is a place for precise measurements, but not for every thing I do.
And beside I like using my calipers as a marking gauge, they may be more than I need but I like using them. So do what works for you and be aware than sometime high precision is needed and sometimes not.
Ed Friedl

robinson46176 · Post by **robinson46176** » Fri Jun 05, 2009 10:39 pm

Shhhh... Don't tell anybody but I did happen to buy a pair if micrometers at a yard sale today...

Not really expensive when new but they look like new and I only paid $2 for one and $3 for the other. One was a 0 to 1" and the other a 1" to 2". The quality seems more than adequate for my needs. I may use them in some rebuilding but not on wood.

I have a number "expensive" mikes in the metal shop in one of the big old tool boxes by the metal lathe. I just bought these because they were cheap and they seemed to need adopting. This was another one of those sales where there were almost no other tools and these two mikes were the only thing even close to that category. I always wonder when I encounter a sale with odd items like that why he even had them.

Then again I start looking at some of the odd stuff I own...
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I did pass on one item that I sort of hated to walk away from. It was a large heavy Craftsman 6" jointer on a stand with a motor that all looked pretty good for $50. One of the old good ones. You just can't adopt them all.

mickyd · Post by **mickyd** » Sat Jun 06, 2009 1:43 am

robinson46176 wrote:Shhhh... Don't tell anybody but I did happen to buy a pair if micrometers at a yard sale today...
Not really expensive............ I may use them in some rebuilding but not on wood..........

farmer....be honest. Have you EVER used a micrometer on a piece of wood?

charlese · Post by **charlese** » Sat Jun 06, 2009 2:07 am

e.friedl wrote:. And sometimes a few thousandths of an inch can be important. If I make a series of box joints and I am more than a couple of thousandths off. Ten or twenty fingers later, I will unable to get the joint together as those thousandths keep adding up. So there is a place for precise measurements, but not for every thing I do.
And beside I like using my calipers as a marking gauge, they may be more than I need but I like using them. So do what works for you and be aware than sometime high precision is needed and sometimes not.
Ed Friedl

Well said, Ed! And in a good concise way! I also use my caliper as a marking gauge. However it is set to 'inches and fractions, rather than thousandths.

I agree about the finger joint thing. When I made these magazine holders, a trial run was made after setting up with a set up bar. Then just a tap with a screwdriver handle set the joint jig in the right place. Probably, I would have been really frustrated trying to use a caliper (or a jig with an adjusting screw) to measure the thousandths necessary to make some 20 fingers. The accuracy is certainly needed, but a sideways tap with a tool sets it up just as well as measuring, but a little less frustrating
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robinson46176 · Post by **robinson46176** » Sat Jun 06, 2009 7:46 am

mickyd wrote:farmer....be honest. Have you EVER used a micrometer on a piece of wood?

Absolutely never...

I do however keep my hatchet calibrated to +/- .0001

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I don't know why Shopsmith didn't incorporate a hatchet function into the Mark V as a 6th mode.

mickyd · Post by **mickyd** » Sat Jun 06, 2009 12:03 pm

charlese wrote:Well said, Ed! And in a .......

I agree about the finger joint thing. When I made these magazine holders, a trial run was made after setting up............

Beautiful work Chuck. Can't wait to getting into the build phase.

With all the stuff you make, you must build and sell, correct? There is only so much wooden stuff and household can have.

charlese · Post by **charlese** » Sat Jun 06, 2009 2:21 pm

mickyd wrote:...With all the stuff you make.... There is only so much wooden stuff and household can have.

He! He! That's what my Sweetheart tells me! Now, I can't wait for a boughten piece to break, or for my Grandkids to have babies.

I love your reports and photos of restoring old Shopsmiths to better than new condition. Keep the reports coming! BEAUTIFUL WORK!! I'll bet your future wooden stuff will look as good!

Thanks for the compliment, Mike! No! Haven't made a thing for sale! Got an offer to make some quilt hangers that is tempting though!

cincinnati10 · Post by **cincinnati10** » Sat Jun 20, 2009 11:41 am

This makes as much sense as measuring with a Micrometer, Marking with Chalk, Cutting with an axe. The only way to easily work to those tolerances is to eliminate layout lines and go with a numerical control milling machine to make all the parts. Even then you have a material that can change from early day to late in the day with humidity changes.

Certain dimensions are critical. Some are not. Who gives a hoot if drawer guides & runners are identical lengths to within 0.001. The most critical cuts I can think of are in joinery or where two pieces must slide, glide, or fit together.

The most insane part of this concept is that wood moves.

It's more important to design with wood where you allow for wood movement yet don't have a finished piece that shakes rattles and rolls.

If you want to work to the 0.001" tolerance, and boast of your precision, better choose a non-hygroscopic material that also doesn't change with temperature in the normal range for your part of the country.