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  • About Those Carpenters' Levels

    Good Evening, All --

    An earlier thread dealing with level instruments compares the sensitivity of a premium carpenter's level, which the maker claims is "0.5 mm PER 1 METER", to the 0.005 inch per foot sensitivity of a standard millright / machinist level such as the Starrett Model 98 in its 6-inch-or-longer versions. The difference between them seems small -- 1 part in 2,000 in the first case, 1 part in 2,400 in the latter -- but the numbers alone are misleading.

    The typical carpenter's level maker cites "attainable accuracy" assuming that the residual decentering of the bubble within the vial is not discernable, whereas the millwright level maker cites the tilt needed to displace the bubble 1 increment of vial graduation . . . typically 2 millimeters for European, Asian, and newer British vials, 1/10 inch for U.S. and older British vials.

    So how well can the bubble actually be centered?

    Well, one of the premier makers of carpenters' levels, Stabila, says on their website "The eye readily detects differences of one ten thousandth of an inch, so the reading of the difference in proximity to a reading ring from one end of the bubble to another is the least of anyone’s problem." (I'll editorialize: I'm skeptical.)

    In contrast, Princeton University's Dr. Philip Kissam concluded in the early 1950s that the uncertainty in "reading" the position of the bubble in a vial graudated in 1/10 inch increments is, under good conditions, 1/5 of a division. This agrees well with a similar study performed by Kern Instruments of Aarau, Switzerland in the early 1980s that determined a skilled operator could reliably read the position of the bubble in a vial graduated in 2 millimeter increments to 1/4 division. (1/5 of a 1/10 inch graduation is 0.020 inch, as is 1/4 of a 2 millimeter graduation after rounding to the nearest 0.001 inch.)

    What is probably the best way to state the sensitivity of level vials is to declare the vial's radius of curvature, which is unfortunately uncommon. Radius of curvature can be calculated from the second-best data format, tilt over bubble displacement -- a simple example being the 0.005 inch per foot per 1/10 inch graduation of the Starrett Model 98-12 vial . . . 0.1 inch divided by 0.005 inch per foot = 0.1 inch times 200 feet per inch = 20 feet.

    I didn't find a radius-of-curvature value on Stabila's website, but the 1970 Interim Amendment to the U.S. Federal Specification GGG-L-211C requires a carpenter's level vial " . . . a radius of 7.645 inches, minimum, equivalent to a vial sensitivity of 45 minutes maximum . . . ". One major U.S manufacturer of carpenters' levels, Empire Level, hints at the sensitivity of their carpenters' levels by offering unmounted vials for sale that range in sensitivity from 38 arcminutes per 1/10 inch to 45 arcminutes per 1/10 inch of bubble displacement.

    If a generally-recognized-as-superior Stabila carpenter's level is twice as sensitive as the competitive Empire level, the Stabila vial's radius of curvature would be in the 18 inch range. A full order-of-magnitude less than the radius of curvature of a millwright level vial.

    Bottom line: If a high-grade carpenter's level is the best you have, use it. But don't try to fool yourself into thinking it's almost as good as a millwright's level.

    John

  • #2
    I'm the one who directly compared them.....

    And I agree it is all in the definitions. I assumed, perhaps incorrectly, that the 0.5mm/m was sufficient to deflect the bubble over a "significant measurable distance". That would be something like a line division, etc.

    The typical 0.005 per 10" type level is readable to better than that.

    I have not used a carpenter's level of the type describes, and it may be impossible to read one as accurately as is implied by the "spec".

    1/10,000? easily visible? NOT!
    2730

    Keep eye on ball.
    Hashim Khan

    Everything not impossible is compulsory

    Birds are NOT real, they are spying on you

    Comment


    • #3
      According to the Moyers Company their better acrylic level vials are calibrated for 30 arc minutes per 2mm along the vial; that's a 1/114 slope.

      http://www.wamoyer.com/tubular_vials.html

      You can find level vials for practically any application. Carpenter (actually "framing") levels are made to several vial resolutions but the most common is the two line vial representing 1/8" per foot (center bubble to bubble tanget with line) so that it can be used for plumbing drains but that is not cast in concrete. The level can be eyeballed much closer than that; 1/64" per foot is readilly attainable if you use reversal technique.

      A carpenter will get inensely annoyed if forced to use a machinist level for structural carpentry. It's too damn accurate. He'll be chasing the bubble all over the place. He wants a level for carpentry not machine tool leveling.

      1/8" per foot (1/96 slope) equals 36 minutes about. 1/64" (0.015") per foot (or 1/750 slope roughtly) equals about 4 1/2 minutes. That's a long way from 0.005" (1/2000 slope) per 10 inches for the Starrett #98 style machinist's level and ten times a long way for a 10 arc second master precision level (1/20,000 slope).

      A good framing level is all but useless for the final leveling and alignment verifications for machine tool accuracy but handy for lots of other stuff around the shop. Better have one in the roolroom near your shop grade machinist levels and your boxed and babied master precision levels.
      Forrest Addy
      Senior Member
      Last edited by Forrest Addy; 04-10-2008, 12:50 AM.

      Comment


      • #4
        So,why would a person in a HS setting need a precison level?


        A carpenter's level is for a carpenter and a machinist's level is for a machinist.

        That said what are you using it for?If you just want to set your shortbed lathe level so the coolant doesn't run all to one end then a good carpenter's level is fine.
        If you want to do the same with your bridgeport mill,then a carpenter's level is fine.

        A level is practically useless for setup unless ballpark is all you want,so forget that.


        The cheapest carpenter's levels aren't even good for carpentry so they are out.Most have curved vials set willy nilly into a plastic or screendoor aluminum extrusion and are no better than a sardine can filled to a line with water.The better levels,glass filled resin,aluminum or bound wood are better,but the older cast iron milled edge levels are tops.A good CI level when you can find one will run $80-100,about what a good 98 will cost,but it will be more useful.

        I have at least two 98's,I seldom ever use them.I have an old Stanley 16" CI level with a 3" vial that I use for most things and it works fine since the 98's can't find a visable error.It's as close as a level is capable of getting so what more would one expect?

        Sure you can get master levels,I have one at work for checking over the lathe beds every so often,but how many HSMer's can split with $500+?
        wierdscience
        Senior Member
        Last edited by wierdscience; 04-10-2008, 01:55 AM.
        I just need one more tool,just one!

        Comment


        • #5
          I use the 98 every so often to check (now that it was set once) the lathe for twists. Usually all is well, sometimes not

          I saw a significant improvement when I used it the first time to set the bed up w/o twisting. Decreased chatter, decreased the "shift" when reversing the carriage, generally better.

          Anyone is free to do whatever. Apparently the P.O. of mine did nothing at all, and didn't even know how to set up the back gear lever, OR the countershaft...... And it didn't make his nose fall off.
          2730

          Keep eye on ball.
          Hashim Khan

          Everything not impossible is compulsory

          Birds are NOT real, they are spying on you

          Comment


          • #6
            Two messages

            There are two messages here - different but not necessarily inter-dependent:
            - using a level; and
            - getting something/anything, a lathe, a mill - level.

            Put all the references, theory, quotes/cites etc. aside and try the damned level for your-self. Set it level - on an adjusted level surface. Now progressively pack one end with shims until the bubble just moves to one graticule/"mark" and record the shimming. Now leave the shims under that first end and start shimming the other end until the vial moves one graticule/"mark" "back". Work out the difference between the height of the two packs of shim and you have the sensitivity per graduation of the level. The sensitivity per unit length of the level is easy from that point

            If you have access to a a "dressed and true" magnetic chuck from a surface grinder - a 5" x 10" or a 6" x 12" will do (the bottom and top faces must be flat and parallel to a very high order of accuracy - say less than 1/2 a thou between highest an lowest (or better if possible). Put the "fences" up around the periphery of the chuck. Set the chuck on parallels or "same size" packer/s as required. Put several new say 1/2" steel balls on the magnetic chuck - switch magnets "off" - of course. Now see where the balls run to. It might just surprise you how accurate this is.

            The sensitivity of both methods can be considerable enhanced by starting the lathe or mill motor and drive but with the spindle in "neutral" (ie "between gears") - put a bowl of water on the machine (lathe/mill) and see that the surface of the water "shimmering" slightly. Now try the "level" and the "ball" methods and you should find that their accuracy and resolution are considerably improved as the "stiction" between the vial fluid and the vial in the case of the "level" and the balls and the chuck in the other is reduced or eliminated.

            I know, I know, I know its not in accordance with "the old sacred texts as done since time immemorial etc. etc. ........." but those texts are just references and guides and they are not the "Dead Sea Scrolls" or holy-writ. All that they describe is a method - not a ritual. Same applies to "Machinery's Hand-book" and the like.

            Sure, what I've said is a bit "agricultural" but as with a lot of "agricultural stuff" it works quite often - not always but often enough to be worth trying.

            Comment


            • #7
              hold on there...

              they dont mean you can see a 1/10,000 difference in bubble position!

              they mean that a 1/10,000 difference in level will result in a bubble position move you can see.

              which for a vial gradutaed in 1 part in 2,000 this means "seeing" 1/5 of a division.

              Comment


              • #8
                Maybe

                Originally posted by dsergison
                hold on there...

                they dont mean you can see a 1/10,000 difference in bubble position!

                they mean that a 1/10,000 difference in level will result in a bubble position move you can see.

                which for a vial gradutaed in 1 part in 2,000 this means "seeing" 1/5 of a division.
                Maybe its different "down here" in up-side-down OZ, but my 0.02mm per 1 meter (ie 1 in 50,000) machine level is the calibration of the vial graduations ie 1 graduation movement = 0.02mm per meter. My "Precision Machinists Level" is the same.





                http://www.machineryhouse.com.au/Pro...stockCode=Q208

                http://www.machineryhouse.com.au/Pro...stockCode=Q205

                As J Tiers has rightly said on a couple of occasions recently, the base of the level must be "flat" else the level and its vial/s are of no practical use for the intended purpose.

                The machine square is at least to Grade 1 standard so far as I am aware but even Grade 2 2 is quite adequate for my purposes as regards being flat and square in addition to the 0.02mm per metre accuracy and calibration.

                Comment


                • #9
                  Originally posted by oldtiffie
                  I know, I know, I know its not in accordance with "the old sacred texts as done since time immemorial etc. etc. ........." but those texts are just references and guides and they are not the "Dead Sea Scrolls" or holy-writ. All that they describe is a method - not a ritual.
                  Thanks Tiffie. You're probably right -- the level/two collar method described in all the machinery texts is just theoretical pedantry. Just fire up the lathe and Get 'R Done.
                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                  Comment


                  • #10
                    "Texts"

                    Originally posted by oldtiffie
                    I know, I know, I know its not in accordance with "the old sacred texts as done since time immemorial etc. etc. ........." but those texts are just references and guides and they are not the "Dead Sea Scrolls" or holy-writ. All that they describe is a method - not a ritual.

                    Originally posted by lazlo
                    Thanks Tiffie. You're probably right -- the level/two collar method described in all the machinery texts is just theoretical pedantry. Just fire up the lathe and Get 'R Done.
                    Thanks lazlo.

                    I didn't say that at all.

                    What I did say is that whilst these "texts" are valid there are or may be other methods that will - as you say "Get 'R Done" - as well.

                    Too much is made of the text and not enough of the reason or substance.

                    The way that some would have it, they are cast in stone and start off with "Thou shalt/shalt not ......................... " and inevitably the self appointed custodians, High Priests and "Holy Rollers" want to "take charge" to the extent that no doubt nor question/ing is allowed under pain of eternal damnation etc.

                    Some of the performances are not much short of an Evangelical "voices and messages" effort.

                    I'm probably well beyond damnation and salvation - nothing new there - but I'm used to it and I'm staying put.

                    Perhaps it all started in Haiti - and that Voodoo doll with all the big needles in it is me - no risk!!

                    Oops - I can hear François Duvalier ("Papa Doc") and his "Tonton Macoutes".

                    I'd best be off - quickly!!

                    Comment


                    • #11
                      Just fire up the lathe and Get 'R Done.
                      Yeah...round is a relative term and highly overrated in my book Sounds like Tiffie may find a wood lathe more to his liking

                      Seriously, however, I have used a really long (24"?) number 98 (.005/foot) as well as their master precision level (.0005/foot). I now own one of the import .0005/foot levels and it seems to work well too but it arrived slightly off calibration and that's an annoying process...I digress.

                      Working with the .005/foot #98 is handier when starting the levelling process. The master precision levels are quite sensitive and take a while to allow to settle as each change is made. Handling has to be kept to a minimum as warm hands will change the reading. Its this extra sensitivity that is actually useful when finalizing adjustment...even moreso than its precision.

                      In the discussion of all of this its important to separate the precision of the instrument from the desired degree of precison of the levelling job. If you use a measuring instrument with precision exceeding the desired precision of the operation then you can emphatically know what you ended up with--even if you are satisfied with some twist. If you use one less precise, then you can only guess at the real end result as the instrument is not capable of showing you what you actually settled for.

                      Paul
                      Paul Carpenter
                      Mapleton, IL

                      Comment


                      • #12
                        Get a "woodie"

                        Originally posted by pcarpenter
                        Yeah...round is a relative term and highly overrated in my book Sounds like Tiffie may find a wood lathe more to his liking

                        Seriously, however, I have used a really long (24"?) number 98 (.005/foot) as well as their master precision level (.0005/foot). I now own one of the import .0005/foot levels and it seems to work well too but it arrived slightly off calibration and that's an annoying process...I digress.

                        Working with the .005/foot #98 is handier when starting the levelling process. The master precision levels are quite sensitive and take a while to allow to settle as each change is made. Handling has to be kept to a minimum as warm hands will change the reading. Its this extra sensitivity that is actually useful when finalizing adjustment...even moreso than its precision.

                        In the discussion of all of this its important to separate the precision of the instrument from the desired degree of precison of the levelling job. If you use a measuring instrument with precision exceeding the desired precision of the operation then you can emphatically know what you ended up with--even if you are satisfied with some twist. If you use one less precise, then you can only guess at the real end result as the instrument is not capable of showing you what you actually settled for.

                        Paul
                        Thanks Paul.

                        Its not the Carpenters Levels that I'm having problems with - or the Carpenters' (yours??) rules either that I'm having trouble with. (I agree with your post).

                        Sounds like Tiffie may find a wood lathe more to his liking
                        Finding a wood lathe is not a problem for me either, as "going against the grain" is second nature to me - though I suspect that finding a lathe that "would" is a problem for some others. Perhaps they need to "wood(en)" it.

                        Comment


                        • #13
                          I have one of the Empire carpenter levels-
                          http://www.empirelevel.com/true_blue/default.asp
                          they say it's accurate to .0005" per inch. So does this put it at .005" per 10" ?
                          Anyhow it seems to be a decent level for 30$.

                          Steve

                          Comment


                          • #14
                            Originally posted by S_J_H
                            I have one of the Empire carpenter levels-

                            they say it's accurate to .0005" per inch. So does this put it at .005" per 10" ?
                            It's got an extruded "Aircraft Aluminum " body -- how flat could that possibly be?
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                            Comment


                            • #15
                              That's 6061 Heavy Duty Aircraft Aluminum. It's got to be good. Just don't leave it in the sun.
                              Jim H.

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