Precision Measurements, Do They Matter?

dusty · Post by **dusty** » Thu Jun 04, 2009 4:20 pm

Certainly they matter but when doing general wood working it is still debatable, in my mind, whether measurements to the hundredths and thousands really matter.

In another thread I participated in a discussion on a fixture for setting the quill in a repeatable manner. As a result of that thread I got involved in making a fixture to do the same thing. That inevitably led to creating miter track runners (miter bars).

I looked around the shop for a piece of hardwood that could be used. I finally found a piece of white oak that in a previous life had been a miter fence of sorts. I decided to sacrifice that since I could not remember the last time I used it.

The first step was to thickness plane it to a thickness equal to the width of the miter track on the Mark V table. A couple passes to clean up one side and then a couple more to get to the right thickness. The right thickness was determined by checking to see if I could insert one side of the board into the miter track. I got there by making 1/8 revolution turns (1/128") on the rank of the ProPlaner.

Once there, I determined how deep the miter track was and I then proceeded to rip that board down into 3/8" thick strips (miter bars). I ended up with eight pieces. All reasonably close to the same, at least by previous standards.

I knew they were a little too thick but the plan, going in, was to run them thru the planer all together. This would result in all the strips being exactly the same thickness and I already knew they were the same width because they had been cut from the same board that had also been thickness planed.

Once done, I inserted each one into the miter track on top of the 520 rip fence. They all fit real nice. Good thickness and good and snug laterally (no wiggle room).

I could have quit right then. I should have quit right then. Instead, I decided to measure them with my new digital caliper (early Father's Day gift).

Measuring the widths at three locations on each piece I got widths that vary from .720" to .731" and I got thicknesses that vary from .300" to .322". This variation sort of surprised me. Remember, I've already tested them by insertion into the miter track and they are all excellent fits.

The thickness variation really surprised me because they all were passed through the same planer at the same time - I mean side by side simultaneously.

BOTTOM LINE: They all work perfectly well for their intended purpose, even though they vary by as much as .022" in thickness and .011" in width.

tdubnik · Post by **tdubnik** » Thu Jun 04, 2009 4:33 pm

My attitude towards all of this is to get as accurate as possible. As you say our woodworking equipment is not precise but does a pretty good job. There are a lot of variations in blades, tables, fences and on and on. Our material of choice the wood itself is not consistant. Grain changes, the density is different often even within the same board. Working with wood is never going to be perfect.

My reason for trying to get as accurate as possible is because I don't want to compound the problem. The way I see it, there are enough issues with precision in the first paragraph. Anything that I can to to not introduce more leads to a better end result in my opinion. If I can bet my blade aligned to the miter slot within .001 instead of .005 I have improved my precision. This same concept applies to measuring, marking, any other alignments. I'll use whatever I have or can purchase within reason to achieve that.

Not only that but it's fun to have some of the latest gadgets to absolutely let you know that your last cut was "not quite perfect". I bet these folks love to drive us woodworkers crazy.

robinson46176 · Post by **robinson46176** » Thu Jun 04, 2009 5:08 pm

dusty wrote:Certainly they matter but when doing general wood working it is still debatable, in my mind, whether measurements to the hundredths and thousands really matter.

In another thread I participated in a discussion on a fixture for setting the quill in a repeatable manner. As a result of that thread I got involved in making a fixture to do the same thing. That inevitably led to creating miter track runners (miter bars).

I looked around the shop for a piece of hardwood that could be used. I finally found a piece of white oak that in a previous life had been a miter fence of sorts. I decided to sacrifice that since I could not remember the last time I used it.

The first step was to thickness plane it to a thickness equal to the width of the miter track on the Mark V table. A couple passes to clean up one side and then a couple more to get to the right thickness. The right thickness was determined by checking to see if I could insert one side of the board into the miter track. I got there by making 1/8 revolution turns (1/128") on the rank of the ProPlaner.

Once there, I determined how deep the miter track was and I then proceeded to rip that board down into 3/8" thick strips (miter bars). I ended up with eight pieces. All reasonably close to the same, at least by previous standards.

I knew they were a little too thick but the plan, going in, was to run them thru the planer all together. This would result in all the strips being exactly the same thickness and I already knew they were the same width because they had been cut from the same board that had also been thickness planed.

Once done, I inserted each one into the miter track on top of the 520 rip fence. They all fit real nice. Good thickness and good and snug laterally (no wiggle room).

I could have quit right then. I should have quit right then. Instead, I decided to measure them with my new digital caliper (early Father's Day gift).

Measuring the widths at three locations on each piece I got widths that vary from .720" to .731" and I got thicknesses that vary from .300" to .322". This variation sort of surprised me. Remember, I've already tested them by insertion into the miter track and they are all excellent fits.

The thickness variation really surprised me because they all were passed through the same time planer at the same time - I mean side by side simultaneously.

BOTTOM LINE: They all work perfectly well for their intended purpose, even though they vary by as much as .022" in thickness and .011" in width.

YES !!!!! I have been trying to convince people of that for years... Its Wood !!! Work it like wood... "Work" wood (hence, "woodworking"), don't machine it. Be an artist not a technician. A guy teaching a class once told a BIL of mine that he (the guy) could never work with a Shopsmith because his work had to be with-in .001 on everything he did. I told my BIL it was hogwash... Wood can change that much while you eat lunch...

That is the reason we make all of those slotted holes and slip fit panels etc. so the wood can expand and contract with out ripping itself apart.
I have an old unused house down the road that was sat on wood beams that were hand-hewn around 1840. In places they were a little rough by sawn standards but they were exactly as accurate as they needed to be for the job they were doing.
Accuracy is important especially in the machine but if you take a micrometer to every entry hole you cut into a birdhouse you need help...

Now if you look at about half of these new houses when the sun is shining down the side and you see all manner of variation then those guys could use a dose of improved accuracy.

navycop · Post by **navycop** » Thu Jun 04, 2009 5:42 pm

I think this comes into play if you are building a kitchen cabinet. Say you want to put a glass front on it. Of course the miters and rabbets have to be percious. If you are building a dog house, I'm sure Fido won't mind if the miters and angles are knot exact. That's what wood filler is for...

dusty · Post by **dusty** » Thu Jun 04, 2009 5:53 pm

navycop wrote:I think this comes into play if you are building a kitchen cabinet. Say you want to put a glass front on it. Of course the miters and rabbets have to be percious. If you are building a dog house, I'm sure Fido won't mind if the miters and angles are knot exact. That's what wood filler is for...

I guess you are right. I have wood filler in the shop in a big squeeze tube.

charlese · Post by **charlese** » Thu Jun 04, 2009 9:55 pm

Hi Dusty! I'm surprised that you were surprised by the measurements of your sized miter board. We all have been discussing this Thousandths thing since 2006 on the Forum.

At first, I came out totally against setting up a woodworking machine to the nearest thousandths of an inch (pet peeves). Later, after being convinced that repeatability was the major issue, I agreed that to set up the machines as square as you can and to a thousandths of an inch was not bad, but still question the benefit of the time spent doing this.

For a woodworker that really enjoys messing with the machinery, I say - Have fun, and enjoy your setting up methods. My thinking relative to jigs is similar.

In the final analysis - I MOST CERTAINLY COME IN ON THE SIDE WITH FRANCIS. After talking about this issue ad infinitum on the Forum - my conclusion is..."Folks will do what folks will do!" For those that believe they can cut, shape, plane, joint, etc. a piece of wood to the nearest thousandths of an inch - let them believe it!
Although no saw, no machine, not even a laser can accomplish this, they will continue striving to achieve this impossible goal.
But guys - - IT'S THE WOOD, NOT THE MACHINE that won't allow this.

However I do wish more woodworkers would try to understand the physical features of wood! This knowledge will make their woodworking be a lot more satisfying than trying to mill it to the nearest .001". I'm pretty sure their projects will come out a bit better also.

The very worst scenario I can think up:- -The woodworker who will measure his freshly cut wood with a micrometer (newer digital calipers) , find it to be .002" off - then stop to set up his machine again.

dusty · Post by **dusty** » Thu Jun 04, 2009 11:32 pm

charlese wrote:Hi Dusty! I'm surprised that you were surprised by the measurements of your sized miter board. We all have been discussing this Thousandths thing since 2006 on the Forum.

I was surprised, Charlese, because this was a piece of seasoned hardwood that had been in my shop for years, it was a piece of recycled furniture, I had just passed it through the surface planer and then ripped in into as many pieces as I could safely and then measured them.

I measured first by inserting them into the miter track, where they all fit well, and then with the micrometer. In a span of twenty minutes max I got those deviations.

I created a chart on six of them. I'll recheck the measurements tomorrow just for curiosity.

Yup, we will do what we will do. I'll blame my own oddities on being an Engineer with back ground in Performance Testing.

a1gutterman · Post by **a1gutterman** » Fri Jun 05, 2009 12:03 am

navycop wrote:I think this comes into play if you are building a kitchen cabinet. Say you want to put a glass front on it. Of course the miters and rabbets have to be percious. If you are building a dog house, I'm sure Fido won't mind if the miters and angles are knot exact. That's what wood filler is for...

Wood filler on a dog house? Must be a pretty special dog!

Ed in Tampa · Post by **Ed in Tampa** » Fri Jun 05, 2009 12:43 am

dusty wrote:I was surprised, Charlese, because this was a piece of seasoned hardwood that had been in my shop for years, it was a piece of recycled furniture, I had just passed it through the surface planer and then ripped in into as many pieces as I could safely and then measured them.

I measured first by inserting them into the miter track, where they all fit well, and then with the micrometer. In a span of twenty minutes max I got those deviations.

I created a chart on six of them. I'll recheck the measurements tomorrow just for curiosity.

Yup, we will do what we will do. I'll blame my own oddities on being an Engineer with back ground in Performance Testing.

Dusty
I don't doubt the differences for a minute. If you remember in jointer discussion Nick talked about how wood compressed slightly as the knifes cut into it and then immediately decompressed. Wood is not uniform and one part will compress more than another, also wood that has been compressed will decompress differently also. This can happen within an fraction of an inch over the entire lenght of the board.

Running a board through a planner exposes the wood to many different pressures, from the feed rolls, from the knifes, from chips that fall onto the board or planner table. Any these all effect the wood differently along the entire length of the wood.

I toss in with Farmer and Charlese on the trying to get wood to the thousandths.

Frankly I get excited when my projects come together and joints are tight enough to prevent me from having to use all my wood filler.

charlese · Post by **charlese** » Fri Jun 05, 2009 3:00 am

dusty wrote:I was surprised, Charlese, because this was a piece of seasoned hardwood that had been in my shop for years, it was a piece of recycled furniture, I had just passed it through the surface planer and then ripped in into as many pieces as I could safely and then measured them....

I'll blame my own oddities on being an Engineer with back ground in Performance Testing.

I really don't care to go on and on and..... about this subject, but wood was my schooling and my job for over 30 years. Now that's a lot of blah..blah, but WE REALLY HAVE TO TRY TO UNDERSTAND WOOD as a commodity that can be used in many types of construction.

Nick has tried to emphasize that same understanding in his books and in his site "Workshop Companion". Look under the main heading of "Woodworking Know How" In the Workshop Companion he speaks of a CORE KNOWLEDGE . The part of that core knowledge he has already put into the Companion is "The Nature of Wood" This understanding is so BASIC and so CRUCIAL to woodworking.

That section of the "Workshop Companion" should be actually studied and understood in order to avoid many surprises when working with wood.

Now let's go to the fact that Dusty's piece of wood was once a piece of furniture and was in his shop for years. Then that piece was sliced and planed. That's a whole lot better than if the wood was cut green and not allowed to season, but it does NOT make that wood become perfectly stable.

Should we be surprised that some internal stresses in that wood may have changed? No! Should we be surprised that maybe some slight compression of cells occurred during machining? No! Should we be surprised that perhaps a series of cells closer to the summer wood of an annual ring have a different expansion rate than cells in the spring wood of the same annual ring? No!

If someone would do the same cuts on a piece of UHMW Plastic. The results may come out with closer tolerances.