50 Replies Latest reply on Jan 13, 2017 1:36 PM by John Stoltzfus

    Drawings with Inadequate Dimensions

    Maha Nadarasa

      There are drawings in YouTube with Inadequate Dimensions. By means of searching the sketch only you can find this dimensions. Is this acceptable in the real world?

        

        • Re: Drawings with Inadequate Dimensions
          Dan Pihlaja

          Not really.  Although you find it more often than not.

          We have customers that have dimensions missing on some of their prints for parts that we have to make, but since some of those drawings are 30 to 60 years old, they don't want to make a revision to the print to fix the issue (because they would end up having to remake the drawing from scratch).

           

          Either we were the first one to notice, or it has been that way ever since day one and no one cared enough to make the change.   If it were me, I would fix the drawing, but since its not me, we have to deal with it.

          • Re: Drawings with Inadequate Dimensions
            Mike Pogue

            I thought I knew something about this, but decided to consult the Bible before I posted. Turned out I was wrong.

            ASME Y14.5 2009 is explicit. Scaling drawings is not allowed. If a vendor guesses at a dimension, they are out of line. How rigorously you can enforce this in practice probably depends on how good your drawing is other than the missing dimension. Your sheet format should have the note DO NOT SCALE DRAWING to reinforce the point. The caveat is that drawings made in 1921 are unlikely to call out ASME Y14.5 2009. So you'd have to dig up whatever spec is called out on those drawings to gather the interpretation of missing dimensions.

             

            Legal document is the right attitude. And your drawing is bootstrapped from the interpretation specification listed on it. Without that, you are just kind of floating around in a world of opinion.

             

             

            • Re: Drawings with Inadequate Dimensions
              Paul Risley

              Maha,

               

              You are seeing real word examples of piss poor design and detailing.I have seen from the posts you have been posting about missing dimensions. Although this is frustrating in the 3D world of cad, imagine a toolmaker at a lathe or mill planning a part and he starts to realize he can't make this part or that part because of missing definitions.

              It is becoming more common place to rely on the model as the bible and the print as a "guide". The industry standards are shifting and MBD(Model based definition) is becoming more popular. However before that comes about fully expect to see more and more prints with the note as follows:"Print is reference only, use cad model for all critical features".

              From a drafting standpoint fine makes the job easier, I guess. The real problem lies in understanding how things are made. A computer is a tool. Solidworks is a tool. Neither of which works like a mill, lathe, EDM, waterjet or other machining tools work. When designing a part, assembly or whatever one of the fundamental things to consider is "How is this going to be made?".

              I went a little off topic, but the core is there. Anyone can pick up how to use the software the value of that person becomes do they understand how to apply the software to work in concert with all of the other post operations to actually make a part?

              I do not begrudge anyone who wants to learn or be self taught. I have worked with designers with no formal training who could outshine graduates easily enough. What makes any designer I interview standout is their understanding of how things work, technical information can be taught, terminology can be taught. Geometrical awareness and how things go together can be taught to a certain extent, however it is up to the individual to make the effort to learn how things are made in their respective fields.

               

              Not really an answer to your question, but this has been a hot button topic in our shop for the last couple of years/ designers.

                • Re: Drawings with Inadequate Dimensions
                  Marty Laury

                  Paul,

                   

                  I have run across engineers that assume that the drawings of no consequence and only need a few dimensions because the vendor will always use the model to make the parts. This may be true for some of our vendors. My argument is that our own incoming inspection does not use the model to inspect parts, only the drawings. Also, I have never seen a tolerance entered in the model/sketch dimensions. I find this to be a dangerous practice. I haven't been able to convince anyone. It's frustrating.

                   

                  Marty

                  • Re: Drawings with Inadequate Dimensions
                    John Stoltzfus

                    Paul Risley

                     

                    Well said....

                     

                    I do want to add in the fact that we can make all our drawings black with dimension lines, but does the shop have the where withal to inspect those dimensions, no doubt in my mind that models need to be dimensioned properly, however I also feel that the consensus is to get manufacturing what they need to produce quality components.  We manufacture components that would be very hard to dimension and even if I would add dimensions, there is no way our shop would be able to check it, we tweak the CNC program till the component meets the the Marketing Department aesthetics, parts with sweeping curves into infinity.

                    Here we have 2 CNC machines and the parts going to those machines only get dimensioned for overall and hole locations etc, then the model is loaded in the CNC program and the programmer is well versed on the process that it takes to produce the final product, they are the guys that add extra material etc....

                     

                    My conclusion is - not every shop is the same and the Engineer/Designer and Drafts Person need to adapt to the industry and business they're working for...

                    • Re: Drawings with Inadequate Dimensions
                      Rick McDonald

                      In my company, if the machinists find a missing dimension or problem, or even something that is not 100% clear, they are REQUIRED to go to the engineer and get the document corrected or made clear.  This can be a penciled in update (we are a small shop without ECO structure) temporarily.  If needed the Engineer will go out to the shop and identify and watch the process to be sure the Engineer understands the machinist and the tool operations. When the part is completed and verified, the Engineer must update and finalize the drawings.

                      Also, if the machinist has a better way or option to do something that they think is more efficient or easier they are again to go to the engineer and ask for approval or clarification (just had this happen this morning with a drawing from another designer who is on vacation, and the machinists said the end mill is too short to easily make the cut - can it be shorter or from a different side - the result was the depth was not critical and could be done as the machinists suggested - saves time, effort, material and cost).

                      Every designer / Engineer that is hired here must have a working knowledge (minimum) of basic machine shop tool operation - minimum of manual lathe and mill.

                        • Re: Drawings with Inadequate Dimensions
                          Marty Laury

                          Rick,

                          You work in a complete system.  No dead ends.  Sounds like heaven.  It is the goal here but it's a step or two away.  It will take practice.

                          I spent a lot of time on the board with a pencil.  If you don't have all the dimensions, you can't even draw the part, let alone make it.

                            • Re: Drawings with Inadequate Dimensions
                              Rick McDonald

                              Marty,

                              It has it good and bad like anyplace but more good than bad

                              This year is looking like it will be a tough one.

                              One problem is, with a new president = unknown economy and companies waiting to see so they are holding back on orders.

                              We do products mostly for wafer fabs and Solar Cell manufactures and they are all trying to cut costs.

                              On the plus side many of our systems are for improving quality or wafer handling which = cost savings to the customers process.

                              Hopefully it will pick up soon.

                          • Re: Drawings with Inadequate Dimensions
                            Maha Nadarasa

                            Will Model based definition make 2D drawing redundant?

                              • Re: Drawings with Inadequate Dimensions
                                Paul Risley

                                The short answer is yes in the fields where it can be used that is it's purpose to keep all data for that part/ assembly contained in the model.

                                 

                                Every designer, engineer and shop will have various opinions of the validity of MBD. I know for our shop it would never make it into the workflow. One area of our shop is dedicated to profile grinding which requires massive amounts of prints for 1 piece, typically 10-20 sheets per part.

                                 

                                On the flip side of that we have a manual machining center for doing 1 offs that require prints, to expect a computer at every Bridgeport, lathe, grinder, gun drill, welder, etc... would be ineffective and costly.

                                 

                                What it will really come down to is demand and level of expertise, the drawings details have slowly been getting less and less, so this inherently will affect MBD, If a person cannot detail a part properly to get the yielded results how will they define a model to generate better ones?

                            • Re: Drawings with Inadequate Dimensions
                              Chris Champions

                              Maha,

                              Anyone can post a video clip on Youtube and it's not represented for any standard practice. Just wondering why it's your concern?

                              • Re: Drawings with Inadequate Dimensions
                                Gary Lucas

                                I have my own standard that I apply to dimensions. If the shop has to get out the pencil, paper, and maybe the calculator then your drawing is WRONG! The shop is part of our team, challanging them to figure out the needed dimensions is not team work. If they are misinterpreting what you drew then maybe you should learn how to do their job too. 

                                 

                                By the way, I am the guy doing most of the drawing not the guy making the parts.

                                  • Re: Drawings with Inadequate Dimensions
                                    Jim Steinmeyer

                                    Gary,

                                    This can go two ways. While I agree with you for the most part, I feel that people on the floor should be treated as people that have a brain and can think. Some don't but the good ones want to use their minds to keep from being bored. Yes the dimensions should be provided to make the job clear but quality people don't like being treated like a robot.

                                             On another issue raised here, there are designs where full dimensions are impossible to give. Many  surfacing projects come to mind. A few years ago I had a project where I designed a windshield that both bowed around the cab but also bowed from top to bottom. I had to ask how to dimension it for our vendor and Matt Lombard responded saying that the vendor needed to use the model to determine the dimensions. This type of modeling is more of a specialized case but there are times when complete dimensions just aren't possible. I have no idea how windshields were designed before CAD systems.

                                    • Re: Drawings with Inadequate Dimensions
                                      Daniel Schulz

                                      "If the shop has to get out the pencil, paper, and maybe the calculator then your drawing is WRONG!"

                                       

                                      This is the old 'dimension for mfg' vs. 'dimension for function' argument.  I could just as easily say that if the part is not dimensioned for function, the drawing is wrong.  Dimensioning for function results in less cost.  Our job is to make money. We are a team - we are not slaves to mfg.

                                    • Re: Drawings with Inadequate Dimensions
                                      Eric Blankinship

                                      I know this is kind of a side-bar to the topic being discussed here but I agree that missing dimensions are not acceptable.  Every time I make a new drawing I do a 3D check.  Kinda a fake thing that I've made up for myself to be absoloutely sure that I haven't forgotten to detail everything and that I have no duplicate dimensioning on my print.

                                       

                                      I put the model to the side not even looking at it and I take my drawing and try to produce my model using nothing but the dimensions on the print. Also when making the model I check off each dimension as I use it so that I know when I am done if any of the dimensions on my print were unnecessary to making the model.  After I am done I take my model based on the drawing and I lay it on top of the actual model and do the good ol' combine subtract going both ways.  If both give me the error message of (the resultant model is empty) I know I have added every dimension that is needed to make this part.  This entire process may sound tedious but I find it saves me time long run over having a drawing with mistakes.

                                        • Re: Drawings with Inadequate Dimensions
                                          Rick McDonald

                                          I like that.

                                          I do that part way where I look at each view and see that every edge or feature is defined.

                                          If not, I verify it is defined in another view or way.

                                          I also look at my tolerances and precision (number of decimal places) to insure they are both accurate and not unnecessarily too tight - no reason to machine to .0005 when .02 would do fine - just increases cost and time.

                                          Usually we use "our" standard tolerances wherever possible:

                                          When I started here there was no standard and no tolerance table - I got that defined and implemented on each drawing.

                                            • Re: Drawings with Inadequate Dimensions
                                              Gary Lucas

                                              One thing about tolerances that often gets overlooked.  The idea that a dimension shouldn't have more decimal places than the tolerance needed is not strictly true if the part will done on a CNC machine where they are programming from your drawing not a model. Often the CNC will choke because internally it may work to many more decimal places and won't accept points that are not actually coincident.  I worked for about a year programming for a pair of milling machines from drawings that had holes spaced 1/8" apart but the dimension said 0.12" typical for thirty holes in a row.  Program it as written and the last hole is 0.150" from where it ought to be.  I actually preferred higher decimal places for the basic dimension and then a bilateral tolerance that told me how close it really had to be.  Way easier to program that way.  When I see 0.5625 I don't think its over dimensioned, I think okay it's fractional dimensions shown as decimals and thank you very much for saving me the time of looking up the fractional equivalent of 9/16"

                                                • Re: Drawings with Inadequate Dimensions
                                                  Rick McDonald

                                                  Gary,

                                                  You make some very good points.

                                                  What we do here if we have a hole that is truly .125 the engineer will specify it as .125 even if we could be looser so that the arrayed placement would be correct - we also will show a reference dimension across a larger group (usually first to last) to show the total length expected:

                                                  If we make a 9/16 hole with will typically mark it with the full (up to 4) decimal places needed to correctly define it as "0.5625 (9/16)".

                                                  But again - that is our method.

                                                    • Re: Drawings with Inadequate Dimensions
                                                      S. Casale

                                                      These are just my thoughts:

                                                       

                                                      I like the way you annotate the dimension. Although, the concept of shrinking a fractional dimension from 9/16 of .5625 to some less precision makes sense and doesn't. Keep in mind GD&T is not about how the part is made. GD&T is specific to its form fit and function.

                                                       

                                                      So if I have a hole that I want 9/16 apart, inherently we know it be .5625. If we call out the dim .5625 and don't change the tol block (you had shown), we end up with a far more expensive part. If we want the same dimension, .5625 it is better we control it with an additional tol call-out such as .025 or whatever real tol desired.

                                                        • Re: Drawings with Inadequate Dimensions
                                                          Rick McDonald

                                                          Scott,

                                                          I agree with your comments.

                                                          I probably wasn't clear enough on my use of the shrinking of a dimension.

                                                          If we have a series of holes and the distance between them can be ±.005 from each other, I could show the dimension as a 3 decimal. However I want the accumulated distance to be a certain distance that would actually require x number of holes at a 4 decimal precision to accomplish this.

                                                          In my example above I dimensioned 2 neighboring holes, specifying 4 digit precision (.3750 - 24 equal spaces - non accumulating).

                                                          I also have specified a reference dimension across the 2 end holes with a total distance of 9.0000 inches,

                                                          I could have also specified the hole spacing with 3 decimals as (.375 - 24 equal spaces - non accumulating) and got the same ultimate space to the end (9.000") but the hole to hole spacing could vary ±.005" instead of ±.0005" - as long as the final distance was 9.000"

                                                          this is what I meant.

                                                          The .5625 (9/16) designation example was for drilled holes - since 9/16 is truly .5625" if we mark the drawing only with the decimal .5625 the machinist will try to produce a final hole that is between .5620" and .5630". By also adding the (9/16) reference, the machinist knows to use a 9/16 drill instead (even though a 9/16 drill will produce a larger hole than .5625 depending on the quality of the drill since the drill tip is not always dead on center and produces wobble - making a larger hole than the diameter of the drill.