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Unusual sine bar - advice on gage blocks

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  • Unusual sine bar - advice on gage blocks

    I bought an interesting sine bar on eBay a few weeks ago:


    http://www.ebay.com/itm/281493093966

    And I also got a set of adjustable parallels that I figured I could use with this instead of gage blocks for moderate accuracy:


    http://www.ebay.com/itm/191417723992

    I probably don't really need these, but they seemed like a good acquisition at the time, and inspired by the class lessons on sine bars. Now I am considering a set of gage blocks, and I will also need to get a granite block to complete my inspection and set-up system. I might also need a height gage and other things, but I may actually have some old tools that will work for that:



    For the gage blocks, we were introduced to the standard 81 block set, but I have also found a couple of inexpensive sets with smaller numbers of blocks, and wonder if they would be good enough:

    http://www.ebay.com/itm/Precision-Ga...g/400379652753

    and

    http://www.ebay.com/itm/281511180931

    The first link includes a block that is a half-tenth:

    2 blocks: 1.000" & 0.1005"
    9 blocks: 0.1001" to 0.1009" in step of 0.0001"
    9 blocks: 0.101" to 0.109" in step of 0.001"
    9 blocks: 0.110" to 0.190" in step of 0.01"
    3 blocks: 0.200", 0.300" & 0.500"
    3 blocks: 1.000", 2.000" & 4.000"
    1 block: 0.10005"


    I'm not sure of the advantages of the 81 block set over these with smaller numbers of blocks. It seems that either would be capable of the same range of measurements, but perhaps the set with less blocks would take more than four to obtain certain values.

    This seems to help answer the question:
    http://www.mansontool.com/merchant2/...de=Gage_Blocks


    Last edited by PStechPaul; 12-14-2014, 06:17 PM.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

  • #2
    You want to use the minimum number of blocks to get to the stack size you need. The larger sets make that easier because they have more intermediate sizes, at higher cost.

    Comment


    • #3
      Here's a random number 3.845"

      With 9 blocks it takes 6,with 81 blocks you can do it in 3.

      Comment


      • #4
        Here is some useful advise regarding the accuracy and sizes of slip gauge sets:

        http://en.wikipedia.org/wiki/Gauge_block

        https://www.google.com.au/search?sou....0.Q8wPlShnyyo

        An "81" Grade "B" set will cover most requirements as will a Grade "B" surface plate.

        If you are looking at real consistent accuracy you will need to consider tool calibration as well as ambient conditions in the "Inspectorate" area.

        Comment


        • #5
          For most purposes, especially with a sine bar, I doubt that I would need anything more precise than 0.002", and I can use the adjustable parallels and a digital caliper or micrometer to get close enough for most angles I would ever need to make. For instance the sine of a 33 degree angle is 0.544639 and for a 6 inch sine bar that would be 3.2678". Suppose I used a caliper and set an adjustable parallel to 3.266". That would be an angle of 32.979 degrees. If it were 3.269", the angle would be 33.013 degrees. So an error of 0.003" in height or 0.003/3.2678=0.019% produces an angular error of 0.034 degrees out of 360 or 0.0094%. So I doubt I would need the high precision gage blocks, although I could use them to calibrate my micrometer and calipers and be pretty sure of 0.001" accuracy. I don't have a good environment either, and the variations in temperature would be significant, and the high humidity would probably cause the blocks to rust. I think I'm talking myself out of buying them.

          Now I'd like to learn more about how I might be able to use the sine bar other than just for measurement. It would probably be more useful to me to use it as a part of a tilting vise for milling angles. It has a single T-slot that I could use with clamps, and maybe I can use the tapped holes to attach it to the milling table at an angle as needed.
          http://pauleschoen.com/pix/PM08_P76_P54.png
          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030

          Comment


          • #7
            Good information. I think I would be able to make a base for this sine bar to make something like the sine vise you show in the last image.



            Here are some better images of what I have:



            Last edited by PStechPaul; 12-14-2014, 11:21 PM.
            http://pauleschoen.com/pix/PM08_P76_P54.png
            Paul , P S Technology, Inc. and MrTibbs
            USA Maryland 21030

            Comment


            • #8
              Originally posted by PStechPaul View Post
              For most purposes, especially with a sine bar, I doubt that I would need anything more precise than 0.002", and I can use the adjustable parallels and a digital caliper or micrometer to get close enough for most angles I would ever need to make. For instance the sine of a 33 degree angle is 0.544639 and for a 6 inch sine bar that would be 3.2678". Suppose I used a caliper and set an adjustable parallel to 3.266". That would be an angle of 32.979 degrees. If it were 3.269", the angle would be 33.013 degrees. So an error of 0.003" in height or 0.003/3.2678=0.019% produces an angular error of 0.034 degrees out of 360 or 0.0094%. So I doubt I would need the high precision gage blocks, although I could use them to calibrate my micrometer and calipers and be pretty sure of 0.001" accuracy. I don't have a good environment either, and the variations in temperature would be significant, and the high humidity would probably cause the blocks to rust. I think I'm talking myself out of buying them.

              Now I'd like to learn more about how I might be able to use the sine bar other than just for measurement. It would probably be more useful to me to use it as a part of a tilting vise for milling angles. It has a single T-slot that I could use with clamps, and maybe I can use the tapped holes to attach it to the milling table at an angle as needed.
              You have got a very grip of reality and common sense here as many or most real everyday tolerances are quite wide and achievable on most machines - and that applies to a lot of stuff that can be done by hand or flame cut and/or off-hand ground if needs be.

              The trick is to analyse the job or requirements and find the best tolerance range and class of finish to get the job done. Once you have that you can work through your range of methods of achieving the end result required in the most practical, effective way and with the least effort and time needed.

              If I wind up with a method or requirement that seems a bit demanding, it is a signal to go back and re-think it all again - from "square one".

              If it suits, it is quite in order to fabricate a job - or part of it if needs be - to get a satisfactory result - there may be no need to "machine" it at all.

              Some times a New machine" may not be needed as an exiting "lesser??" machine may be quite adequate if the operator/user/HSM-er were to improve his skill-sets to the level required.

              Comment


              • #9
                I have a sine bar and no blocks. I typically use the sine bar for angles <10°, and for that, a piece of round turned to the required diameter works just fine.

                Comment


                • #10
                  Anyhow, that's NOT a sine bar.... it's a "sine plate", and the t-slot is useful for actually attaching a part to be machined to the plate. A sine "bar" is more of a reference tool.

                  While it is fashionable to state that you don't need accuracy better than "X", it is important to make a distinction between dimension accuracy and angular accuracy. Angles may need very good accuracy, for instance a taper for a morse, B&S, etc socket. Whatever your degree of "NASA" tolerances, you still need the parts to fit together, and you can't have the taper shanks wobbling loosely.

                  Plus, the use of at least some gage blocks for tool calibration is very helpful and necessary if you ever make parts that must be 'to print" without having the other part to fit to. That can be simply for your own purposes, it need not be for pay.
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #11
                    Originally posted by PStechPaul View Post
                    For most purposes, especially with a sine bar, I doubt that I would need anything more precise than 0.002", and I can use the adjustable parallels and a digital caliper or micrometer to get close enough for most angles I would ever need to make. For instance the sine of a 33 degree angle is 0.544639 and for a 6 inch sine bar that would be 3.2678". Suppose I used a caliper and set an adjustable parallel to 3.266". That would be an angle of 32.979 degrees.
                    It's easy to generalize the error analysis of a sine bar.

                    The equation of a sine bar is:

                    h = L * sin(A)

                    where:

                    A = desired angle
                    L = length of sine bar (between roll centers)
                    H = stack height

                    Taking the derivative wrt 'h' we have:

                    1 = L * cos(A) * dA/dh

                    so the angle error (dA) in terms of the stack height error (dh) is:

                    dA = dh/(L*cos(A))

                    Using your numbers, we have

                    A = 33 deg
                    L = 6 in
                    dh = 0.0018 in = (3.2678 - 3.266)

                    so dA = .0003577 rad = 0.0205 deg

                    which agrees favorably with your error of 33 - 32.979 = 0.021 deg
                    Regards, Marv

                    Home Shop Freeware - Tools for People Who Build Things
                    http://www.myvirtualnetwork.com/mklotz

                    Location: LA, CA, USA

                    Comment


                    • #12
                      You can use the sine bar or plate in the mill vise by setting the angle on the bed of the vise and either clamping the material in the vise (if wider than the sine bar) or clamp the sine plate in the vise and clamp the part to the plate.

                      Comment


                      • #13
                        Angle plates are very handy and will measure very accurately (to just south of a slip gauge - in a good set) in increments/multiples of 0.25 degrees (~ 1 in 230 or 0.0044 per inch) and they can be visually interpolated to quite an accurate degree.

                        http://i200.photobucket.com/albums/a...gleplates1.jpg

                        These digital protractors are calibrated to the same accuracy as that of a digital protractor (0.1 degree ie = 1/10 degree = 1 in 573 or 0.002" per inch). And they are easier on the eyes when you are trying to read them then trying it on a vernier caliper.

                        So, considering the angular accuracy required, a sine bar may not be needed or justified as there are perhaps better suited alternatives for your job.

                        http://i200.photobucket.com/albums/a...gleplates3.jpg

                        http://i200.photobucket.com/albums/a...gleplates3.jpg

                        Comment


                        • #14
                          Just remember that for a taper fit, an angle difference giving an error of a thou or two at one end is the same as a mile.... the taper will rattle, and will only hold if forced in very hard, which is not a good idea.

                          If you need only ordinary accuracy, why bother? Just get an angle fixture with a degree scale and get on with life. Or set that thing as accurately as you care to, using adjustable parallels, a protractor, gage blocks, etc, and proceed.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #15
                            Another reason for using the minimum number of blocks that the larger sets allow is that the error accumulates with each additional block used. If each block is +/-20 uMeters, then a stack of three blocks will be +/- 60 uMeters while a stack of 6 would be twice that or /- 120 uMeters.

                            Since the idea of using blocks is to get the maximum accuracy, it is best to use as few blocks as possible. Thus the larger sets are more desirable.

                            Looked at another way, a larger set can be of a lesser grade and still meet a desired level of accuracy. Thus, a larger set may be more economical.


                            Originally posted by Optics Curmudgeon View Post
                            You want to use the minimum number of blocks to get to the stack size you need. The larger sets make that easier because they have more intermediate sizes, at higher cost.
                            Paul A.
                            SE Texas

                            Make it fit.
                            You can't win and there IS a penalty for trying!

                            Comment

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