Inaccurate Cuts Finally Solved!

[Frank Pratt]

Years ago I bought a no-name tape measure that caused me the same kind of grief. I went back to the store with a known good tape & checked the others. They were all the same; 1/32" off over about 3' I told store staff about it & they just shrugged. It was a large tools store chain, but they went out of business a couple of years later.

[Bill Space]

If I need to make accurate measurements I don’t use a tape measure at all. I use two “sticks” (actually thin strips of wood) held together by a spring clamp. They can be extended to fit between points, or the ends can be aligned with two edges by feel.

I will also cut strips of wood to specific lengths for repeated cuts to be made at different times. These strips become my standards for resetting (and checking) cutting distances. My Unifence scale seems extremely accurate. I use it to cut standards when that makes sense.

Of course I do use tape measures all the time like everyone else here.

But it when I want repeatability time after time, or accuracy to fit something perfectly, I rely on the very exact physical measurement two sticks can give. No numbers involved.

I think I became a believer in using sticks after marking things to length, too many times, on the wrong side of my target. How can 37&3/4” become 36&1/4” ??? (which is 37 minus 3/4”)

Bill

[Mark Bolton]

[QUOTE=Nick Shattuck;2872059]If you work in a shop with adjustable tape measures and DROs, your budget also probably includes spending mucho-$$$ to have them calibrated. I'm a hobbyist, so the Wixey DRO will have to suffice.

The Wixey readout is way more precise than what I could ever hope to see on a tape measure, and as long it's zeroed to whatever blade I'm using, I have 100x the confidence in it's measurement compared to tape.

BTW, my day job is working in a primary standards lab and one day someone thought it would be funny to send in a harbor freight freebie tape measure for calibration. And it was, because (at the time) it costs around $200 per measured point. The "customer" wanted every foot marking error measured on a 16' tape. So $3.2k for a calibrated Harbor Freight tape measure. We sent it to a lower level lab... way lower.[/QUOTE

There is nothing more remote than me associating any part of my shop with a "lab". My tapes and DRO's are calibrated regularly by me and thats a relative term. While it matters a litte, it matters very little if my tapes and DROs actually read dead on an inch or a millimeter. What does matter is that every scale in my shop measure the same thing relative to each other. That fairly simple level of "calibration" is easily done in-house on an as-needed basis. Sometimes daily, sometimes weekly, sometimes multiple times a day if we are fighting some gremlins. Its most often as simple as the method I outlined, make a cut on a hinge-pin tool, and set all the other measuring devices to that "standard".

While you may feel your wixey measuring to +/- .005 is accurate enough because you cant see the variation on your tape measure, you will find over time that simple things like cope and stick doors, going back and planing more material because you undershot or mis-cut some parts, and a multitude of other factors, make a DRO that reads in ten thou increments fine for a coarse measurement but when your setting up a shaper or router table, or needing to go back and plane a bit more material to an exact thickness because your cope and stick is all setup in the shaper and your out of the waste cushion you ran for gnarly grain and need two more pieces.

I have long railed against the notion of setting up woodworking tools to "NASA Level" standards. Now they are running to .0001 and higher but I will tell you that being able to hit sub .005" very quickly makes all the difference in the world as it relates to speed. Just a few years ago that was a fairly expensive goal to reach but now with IGaging level DROs out there you can be reading at .0055 all day long for $40 a head (three machines for 130 bucks).

I have no idea what an adjustable tape measure is other than grabbing a pair of pliers and bending the hook until everyones tapes in the shop read the same and that mutual measurement matches the DRO's lol.

[Mark Bolton]

I catch the tape return with my finger, so it doesn't slam home. It's been done for so many thousands of times, that it's automatic without a conscious thought.

Any time we start a new job, all tapes are compared, and changed out as needed. If one gets dropped, the hook is checked immediately, and tossed if bent.

I think that starts happening natively for most who begin paying for their own tapes lol. It happens especially fast for the dingalings buying the fat max style wide blade tapes that are paying over a buck a foot for a tape lol.

[Mark Bolton]

I have a great solution to the problem of inaccurate tape measures. I don't use them for fine woodworking unless I absolutely have to. Instead, I have a 39.37 inch (1 meter) stainless steel ruler and several shorter ones and all of them read the same. That is what I use to measure things.

One of my most favorite solutions to deadly accurate measurement is to not use a rule at all and just take the part to the work and mark it with a knife. Of course doesnt work if the part is not easily handleable but I agree. There are a lot of work arounds to get away from the shortcomings of a tape measure.

[Mark Bolton]

Another potential problem with tape measures: these are typically printed with something resembling a bandsaw wheel, with a tire on the wheel imprinting the marks on the blank tape. If the tire is not evenly stretched around the wheel, the spacing of marks can vary. A tape might line up with a standard for the first few inches, but then go off for a few inches, only to return to accuracy later. Bending the hook alone will not fix this sort of problem - you have to check the entire length you are going to use.

I may be wrong and I guess it all depends on the brand/manufacturer but Im pretty sure that all tape blades and adhesive scales from any reasonably reputable manufacturer now are optically scanned along their entire length in manufacturing for an accuracy tolerance and are either acceptable or rejected. My guess is the unacceptable range is far smaller than we can read.

I have had issue with adhesive backed tapes getting stretched when applied and I have most definitely gotten some import scales on machines that were noticeably off (by 1/32 or even getting progressively worse over an 80" range). But I have yet to find a half way decent name brand tape that wasnt dead on the money aside from the tip problem.

[Rod Sheridan]

Install a wixey saw fence digital readout and you'll never have to worry about this sort of thing happening again. I think I bought mine on sale for $60 and it is probably the best $60 I've ever spent on an accessory. If something happened to it, I would immediately buy a new one at full price.

How would converting to a digital scale on a saw solve an accuracy problem on a tape measure?

Regards, Rod.

[Mike Kreinhop]

I had a self-inflicted problem with measuring for the part required using one tape measure, then marking the piece to be cut with a different tape measure. I foolishly thought a standard was a standard. Then I discovered none of my tape measures or folding rulers measured the same at two meters. My three big box store 8-meter tape measures started diverging from each other at about 70cm, and by three meters, the difference was about 4mm. I could have bent the tab on two of them to make them consistent with with the third, but they would be the same only at the target distance. The problem was not only with the variance in the tab, but with the printing of the scale along the tape. For carpentry, this is not a problem, but for cutting $130 sheets of 3/4-inch finished plywood, it was an expensive problem.

I replaced my shop tape measures with Class I Hultafors tape measures (accurate to +/- 0.3mm at 2 meters). I also replaced my folding rulers with BMI Class II folding rulers (accurate to +/- 0.7mm at 2 meters). While I appreciated the accuracy, the realized gain was consistency with the measurements. I still keep a big box 8-meter tape and 2-meter folding ruler in my truck.

[Joe Hendershott]

And alternate experience. I’ve use the Wixie table saw DRO On my last couple of tablesaws. The batteries last me nearly a year and I trusted implicitly. It is become an integral and how I work at the table saw.

I've had the same experience with one I've had for 3 years. It stays accurate and the batteries do last forever. Use it at least 4 days a week or more.

[Grant Wilkinson]

Like others here, I simply use one tape to do all the measurements on a project. If the parts are out by 1/16", at least they are all out by the same measurement.

I must admit that I don't completely understand the urge to get wood measurements as precise as metal measurements. I would hazard a guess that, between the time I cut all the pieces for a project and the time that I have the time to glue them all up, the humidity in my shop, the changes in stresses on the cut pieces, and for all I know, the cycles of the moon have all contributed to change the final dimensions of the component pieces. It is wood, after all.

[Mark Bolton]

I must admit that I don't completely understand the urge to get wood measurements as precise as metal measurements.

I completely agree. It often times does become more important in a business/production environment and is very helpful so I could easily see wanting to get fairly accurate in a home shop too. Ive always felt the same way though, its wood for goodness sake (hence NASA). But the repeatability and speed of operations and setups are hard to beat. If I were doing a completely different type of work I could see myself hardly measuring much at all very accurately.

As with anything, it all depends on the type of work you do and what your workflow is, and of course what floats your boat. I would find it very frustrating to take a measure off a piece in the shop (tape measure) and then set my saw fence and have the part be too short/long because the scales dont match. I'd also find it frustrating to have to set my saw fence and all my other tools with a tape measure every time because Im forced to use a single measuring device throughout an entire job. You'd hope you could take a measure with your tape and then use the on-board scales on any stationary tool in the the shop.

[Rich Engelhardt]

f I need to make accurate measurements I don’t use a tape measure at all. I use two “sticks” (actually thin strips of wood) held together by a spring clamp.

+1.
One of the first tips I got here at SMC when I joined up was that tape measures are inaccurate & a pinch rod does a much better job - and it's pretty mindless too - no trying to figure out what that little hash mark on the tape/ruler is..r 32

[Kris Cook]

Another potential problem with tape measures: these are typically printed with something resembling a bandsaw wheel, with a tire on the wheel imprinting the marks on the blank tape. If the tire is not evenly stretched around the wheel, the spacing of marks can vary. A tape might line up with a standard for the first few inches, but then go off for a few inches, only to return to accuracy later. Bending the hook alone will not fix this sort of problem - you have to check the entire length you are going to use.

I bought a brand new Stanley 25' tape when I started my recent shop construction. I was laying out my mud sills with a steel 50' tape which was fine but I was chasing some measurements down the length of the building with the 25' tape and kept coming up off. After some head-scratching I figured out my new Stanley tape was off two inches in forty-four feet. Needless to say it went in the trash. I have always used Stanley tapes and keep a 16' tape in my woodworking apron for rough measurements. This definitely made me apprehensive about buying another tape. I ended up buying another Stanley and checking it against the 50 footer, and it checked out fine. Been using it for the entire project.

I may be wrong and I guess it all depends on the brand/manufacturer but Im pretty sure that all tape blades and adhesive scales from any reasonably reputable manufacturer now are optically scanned along their entire length in manufacturing for an accuracy tolerance and are either acceptable or rejected. My guess is the unacceptable range is far smaller than we can read.[/COLOR]

[Chris Parks]

I got sick of random cuts on my saws and for clarity in the workshop I use either a Quicky tape which is certified to a standard or steel rules, tape measures are used in the yard for landscaping. To overcome the problem I had a length of aluminium tube threaded and a head made that threaded into the rod. I then had that adjusted to a set measure using a large set of verniers and adjusted all my fences to that one standard. The rule and tapes I use are so close to that standard it does not matter.

[Sam Blasco]

And some tapes I have found will give you different readings from the top and bottom scale on the same tape!! A consistent tape is hard to find, and when you do, treat them gingerly. If I accidentally drop a tape... no matter what it is automatically replaced. I take a Starrett 12" rule with me when I want to buy a new tape for a base measure, both in push and pull with the end. It is the same ruler I use to set the base measure on my power tools too.