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Measuring.... yeah, just measuring

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Forum topic by Charlie posted 06-06-2012 05:40 PM 954 views 0 times favorited 9 replies Add to Favorites Watch
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Charlie

1067 posts in 1040 days


06-06-2012 05:40 PM

Topic tags/keywords: tip

My kitchen remodel involves installation of Blum Tandembox drawers. While they do provide some SAE equivalents, they are primarily a metric system. The conversions don’t work out exactly. I was cutting a piece of 1/2 inch plywood on my table saw and checking to see if everything was square, making little adjustments, etc. I had ONE tape measure that was marked in both SAE and metric.

I checked my crosscut sled. Good
Checked fence-to-blade. REALLY toed out at the trailing end. Adjusted all nicey nice. Just a tiny bit of toe out (about 1/64 to 1/32). Didn’t put a gauge on it. I don’t think I need to be .001 accurate. Just nice and square.

How does it cut? Smoooooth. OK so I start measuring the piece I’m cutting. Using the metric side of the tape. Keeps showing me a 3mm taper in about 14 inches. Huh?

Recheck this and that. Adjust this and that. Try the crosscut sled again.
3mm taper.
WHAT?
HOW CAN THIS BE? I JUST CHECKED IT!

Long story short, it was the way I was holding the tape! The hook measures differently if you tilt the tape over to one side. The piece is square as it can be. I was using the TAPE wrong! Or expecting too much.

So I measure out 120mm from fence to blade. Make a cut. Measure piece. It’s 123mm.

Aw….. c’mon….

Tape measures are made to measure OUTSIDE, not INSIDE, and the hook on the end was adding 3mm.

OK, I’ve had enough. I went to Lowes and bought a “yardstick” marked in mm and cm, and a digital caliper that does both metric and SAE.

My reasoning is that this drawer system is metric. They make reference to SAE equivalents in the instructions, but when you start adding things up in SAE, they get farther and farther off from the metric measurements. I’m not going to be crazy obsessed (I do that easily), but I know these drawer systems expect pretty tight tolerances and the closer I can get to being right on, the better time I’ll have installing everything.

So I bought a couple of more accurate measuring tools for the work. I don’t think that’s crazy. :)

Moral of the story: Don’t take something as simple as measuring for granted. Tapes measure outside. Rules measure inside.

The upside of this little adventure is that my saw is now off my about 1/2 of a mm in 12 feet! :)


9 replies so far

View Bill White's profile

Bill White

3589 posts in 2715 days


#1 posted 06-06-2012 06:20 PM

1/2mm in 12’? Nah! Ya gotta get closer than that. :)
That’s the reason I use a plain old wood folding rule when cutting close tolerance stuff.
May not be the most sophisticated tool in the chest, but it works today just as it did 50 yrs. ago.
I have also found that tapes will vary so, when working with a helper, we ALWAYS compare tapes before we start a job.
Good catch on your part. Doesn’t it feel god to know that ya haven’t lost your mind over measurements?
Bill

-- bill@magraphics.us

View patron's profile

patron

13185 posts in 2095 days


#2 posted 06-06-2012 06:34 PM

just about every tape and angle (on machines)
are different it seems

when i work i try to use the same one throughout

but as bill says always check them against the rule
(that what we do in cab shops)
every week monday morning
check all our tapes
so we are all on the same numbers

sometimes with pliers bending the hook in or out
they do fall sometimes and get banged around

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View DS's profile

DS

2132 posts in 1175 days


#3 posted 06-06-2012 06:47 PM

I use a Stanley Fat Max tape. (Freebie plug) It measures inside and outside to nice precision.

I always calibrate my tape measures when I get them and I was pleased that I didn’t have to fuss with the Fat Max at all. The oblong rivet slot was the thickness of the tab so that inside and outside measuring was accurate from the start.

If you drop your tape, it is a good idea to recheck it.
I trust my tape more than I trust the fence on my table saw. (Inside or outside measurement)

3mm seems like an awful lot. Throw that tape in the trash and start over.

And no, I don’t work for Stanley. But I use some of thier tools.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Charlie's profile

Charlie

1067 posts in 1040 days


#4 posted 06-06-2012 06:56 PM

I looked for a wood folding rule that had metric markings. Nothing local. The 3 ft steel rule I bought was the only rule I could find with metric markings. I also bought a new metric tape measure and I did compare them against each other. Right on for now. Next time I’m in Canada (we’re only about 10 minutes from the bridge) I think I’ll stop in a hardware store or something and see if there’s a folding rule.

I gotta say, I really like the metric measuring. No fractions to deal with. I think it would equate to fewer mistakes. :)

We Americans just don’t think in metric terms though. If someone says they’re 183cm tall, we have no concept if they are average, tall or short. :)

View Dan Krager's profile

Dan Krager

1742 posts in 988 days


#5 posted 06-07-2012 12:48 AM

yah, and can you imagine a woman being proud of 90-60-90?

My first impression of Charlies description was that he had, like me, dropped the tape and bent the hook.

I started to convert to metric, but ran into SO much stuff that isn’t I couldn’t use it enough to get a real feel for it, you know where it becomes automatic to think metric.

I like the really old method of story sticks where numbers are mostly irrelevant after the initial layout where they might be relevant.
Dan

-- Dan Krager, Olney IL http://www.kragerwoodworking.weebly.com

View Charlie's profile

Charlie

1067 posts in 1040 days


#6 posted 06-07-2012 09:59 AM

I like story sticks. They Eliminate a lot of errors. Started using them when I was learning brick laying from a friend of mine many many (almost TOO many) years ago.

View groland's profile

groland

129 posts in 2166 days


#7 posted 06-07-2012 06:15 PM

If memory serves, most tapes have a sliding “hook” on the end. When measuring the outside length of something the slide moves away from the coiled tape so as to exclude the width of the hook. When measuring, say, the inside of a drawer, the hook moves a bit towards the coiled rule to compensate for the width of the hook.

But, like a lot of people here said, I like rigid measuring tools for furniture making. I have 48”, 36” and 18” rules and one of those big T-square-like things made for drywall contractors plus a large “rafter” square for obtaining right angles. I think tapes are great for house framing and other less critical measuring tasks, but I’ll take a rigid rule for fine work.

I can’t help sharing my dad’s opinion that a “ruler” is a person who leads others and a thing with which you measure is a ”rule”.

View Carl Webster's profile

Carl Webster

82 posts in 1552 days


#8 posted 06-07-2012 06:59 PM

I worked in the aerospace industry for about 40 years and they even had a place in the calibration lab for calibrating tape measures. The calibration labs were controlled at a certain temperature and relative humidity to assure repeatability of measurements. If the equipment (including tape measures) couldn’t pass the calibration test, it was discarded and replaced with new equipment. I’m sure that the aerospace standards were stricter than the average wood shop requirements, but metal tape measuring equipment does wear over a period of time with use.

-- Carl in SC

View None999's profile

None999

24 posts in 940 days


#9 posted 06-07-2012 07:11 PM

Good thread to remind me to check my tape hooks. I don’t remember where I picked up the habit (long ago) but when I need to make a more precise measurement, I’ll place an inch mark on one end of the workpiece and subtract that from the reading on the other. Of course that’s really only convenient for shorter measurements where you can overlap the end of the tape.

-- None

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