Measuring Error

[D._Frederick]

When I started to assemble components I had sawed out, I found that I had up to + or -  1/16 inch error. I went and found my Starret scale and found that the error was  from the sliding tip on my tape measures.

What do you use to get accurate saw cuts?

[Warbird]

I just compensate when using the tape measure, always making the outside cut such that the tape is pulled tight. 

[Sprucegum]

I use a ruler whenever possible. If I have to use a tape measure on a precise cut sometimes I start at the 10" mark to get away from that wiggly tab.

[Tom]

D. Frederick
Were you sawing on your tablesaw?  

I begin measuring from the 1" mark and add the inch at the other end, if I want accuracy.

We get hung up on accuracy sometimes  when we really want conformity.  There was a test done on tape measures by Wood Magazine a while back.  The looked at Stanley as well as the two for a nickel chinese tapes.  They found that very few of the tape, even some of the same brands, were accurate.  Some were off as much as a half inch in the test range.  It was either  12 or  16 foot tapes they were comparing.

It is recommended that you even use the same tape measure throughout a project rather than keeping one at convenient points around the shop.

[Ole CB]

Dr,

  What saw are you using? I assume it is a table saw. What works best for me is to set the rip fence as close to the desired rip size as I can, I always measure from the blade to the fence and then measure from the fence to the square cut 'groove' at the saw blade, then measure and align both ends of the fence to that groove. I then rip into a scrap piece and check the resulting cut and adjust as needed. Most table saw fences can be out of square with the blade up to 1/8" and some times more.

[Dave Shepard]

When laying out joinery in timber framing, I "burn" a foot. I convert all measurements to feet and inches, using 5 feet 7 inches, as opposed to 67 inches. This way I'm not adding any weird amounts to my measurements, I just start at 6' instead of 5', then count off to 7 from there. I always check a new tape against my square, and adjust the hook so I get the right numbers.

[Tom]

If it is really a concern, you should measure the entire tape.  If the test I mentioned above is accurate, the marks on the tape can be off.  Probably some because of the width of the lines , but some because the foreign companies who are manufacturing the tapes don't recognize the same  quality control that many craftsmen require.

How much difference is there between two 20' tapes?  Have you ever looked? 

[pigman]

+ or  - 1/16 " is closer than anything I build. ;D  But I do make all parts that need to be the same length exactly the same by using a stop block on my sliding sled for the tablesaw. Example, a table can vary in height by 1/2 " and no one will notice, but all the legs need to be exactly the same length. I use an aluminum ruler to set the stop block on the sled. I only use a tape measure for rough cuts.

[Tom]

I thought you had inches marked off on a pigs tail and unraveled it when you needed to measure something.
Are all of your pigs the same size.  ;D :P

[pigman]

Tom, I cut off the pig tails the day the pigs were born so that method would not work. ;D

[ely]

back in the day when i worked as a rodman on the layout crew. our company men thought we were doing a poor job and payed another survey crew to check our "work". turns out the boss was right we were off 1/8 of an inch one way and 3/16ths the other way.  not too shabby for a building that measured 865ft x 482 ft. our elev. was dead nuts though ;D.

my tape is the same each time i pull it to measure something. so the only time i get concerned with it is if i am trying to build some project to fit within constraints.

[D._Frederick]

I use my Powermatic 66 for most cutting, I bought it in the late seventies and it came with a cast iron fence. I never upgrated it with a hi tech. fence, so I always end up measuring from saw teeth to the fence. I have been using a combination square or tape to set the saw up. I ran into problems when I cut some components on the chop saw and on the PM, there found my problem. The only way to set-up the saw is to measure the cut-off pieces, the teeth change distance from still to running.

I guess that I will keep a steel scale handly and just make rough cuts with the tape measure.

I have gliding table on the 66, but have a problem keeping it cutting square.  When its working, it really is nice to cut up a sheet of plywood.

[fishpharmer]

Tom, I cut off the pig tails the day the pigs were born so that method would not work. ;D

Do you drop them straight into the pickling jar? ;)

[dutchman]

I like to flatten the hook, of the tape, on a flat surface with a small hammer.
The rivets that hold the hook can be peened with a nail set, or you can super glue.
The hook will losen over time. Can't stand mismeasured lumber.
That's why I'm a sawyer not a carpenter.
My regular job is tool & die finisher, and +- .0002 is what I have to work with.

[beenthere]

The hook on a tape is supposed to slide to adjust for inside and outside measurements. Checking this 'slide' amount is good to know when there is wear and time to replace (if the tape is used to measure both ways).

[CHARLIE]

If my board is too short, I just cut it again and keep cutting it until it fits. :'(

[woodmills1]

I cut de board tree times and it's still too short


I left my board stretcher at my old house

[Burlkraft]

Anything within a 1/4"  is good  ;D  ;D  ;D

[WDH]

For furniture, throw the tape measure out and get you several high quality steel rulers  .

[fiddle1]

They say measure twice cut once.....the more expensive
the wood you'll want to measure more than twice.


-----i suggest you get a metric ruler. Metric has advantages over standard in smaller increments
especially when you are deviding measures in half for symmetry.

when buying a ruler look for fine line increments and evidence that
the ruler was machinist made and not stamped.

Its best to use ruler in combination with a square and a very sharp pencil. I even use magnifiers to
ensure that my lines are not overly thick.

Sometimes i use a special scribing knife to make finer marks than i can get with a pencil.

[clif]

My thoughts on measuring ( I build  houses etc.) every measurement is in 1/16's or + / - (meaning a 1/32) now can you expect trim, cabinets etc. to look professional if you do not start from the foundation towards that end.  I think it was in the Patriot " Aim small miss small".  Due to the inherent nature of wood, it is often not economical to make every thing perfect, but if you do not try to get it right only luck will get it there.  How much more difficult is it to measure and mark some thing accurately than it is  to measure and mark it inaccurately.   Tapes come in all qualities, cheap is not usually good.  If someone on the crew is often off we check tapes and throw the inaccurate ones in the trash.  Occasionally a hook is bent out of square or the rivets are smashed and the hook will not move properly ( fix it).  How much do you save buying a cheap tape???   Well, that was my soap box for the day, thanks for listening.  Clif

[SwampDonkey]

If I need matching pieces, I cut them all to length at the same time. Also, if your noticing error in the width of your board, as in ripping 4" off a 6" wide board, and it sits in the heated shop for a week or two or three, you can loose that 1/16" as well. Ain't it fun? :D

[Brad_bb]

As some mentioned, instead of using the tongue of the tape measure, you "Burn and inch", or "Burn 10 inches".  In other words you start measuring at 1" or 10" and add that onto your final length respectively.  It can be a little difficult if working alone.  It's great with another person.  A pin hole in the start of the tape can be used with a pin or small nail, so long as you make sure THAT does not introduce error via play.  Most timberframers use the " Burning"method, and will mark the dimension with a tick mark from a razor knife or scribe. It takes commitment to use the knife to mark.  Once you do it, it's there for good.  If you make a mistake, any finish you use will darken the score line and make it stand out more. 
Lastly, one of my frustrations with the "Burning" method is forgetting to add onto your original measurement.  You can then end up cutting it too short.  I usually measure more than once, but I have made this mistake and it is frustrating especially when using timbers.  I am presently inquiring with a tape manufacturer to find out what it would take to make a run of special tapes with the zero location offset an inch or 10 inches and a different tongue.  There's a number of other features I'd like to see if I had my way.  A tape that is already "Burned", would save some people some measurement mistakes.

[Dave Shepard]

I've seen people use a clamp to hold the tape at the "burned" dimension. After I do my layout, I will sometimes move the hook to the line, and make sure the overall dimension is right, within the tolerances of the hook.

[dnalley]

Reading this thread reminds me of the old saying "straining at a gnat to swallow a camel".  That play in the end of a tape was made into it for compensating for inside as well as outside measuring.  Check your tape out to see how accurate it is.  If it's bent on the hook, fix it right or chunk it out.  As far as holding an inch or ten, unless you can hold it securely (after you've placed it as close as you can to the end or edge of a board....potential error) you've still got to mark your measurement, hopefully not forgetting the inch or ten you held.                                                                                                                                                                                                                                                                              I have one 48" ruler that I bought from the "box" store that won't match any tape I've ever checked it against, so I don't use it for measuring, just a good straightedge.  I believe in working as close as you're capable of--always.  Just a good work habit.  That way maybe you don't wind up compounding so many errors.  After all, it's woodwork---not a Swiss  watch!  Unless you're working with saws with digital readouts I think you're making a mountain out of a molehill.  After all, a ruler or a tape is NOT a precision measuring instrument.