As you drag any of the editing handles, the dimension may be rotated. If the datum dimension object is totally non-referenced i. If attempting to graphically modify an object that has its Locked property enabled, a dialog will appear asking for confirmation to proceed with the edit.
If the Protect Locked Objects option is enabled on the PCB Editor — General page of the Preferences dialog, and the Locked option for that design object is enabled as well, then that object cannot be selected or graphically edited.
Double click on the locked object directly and disable the Locked property or disable the Protect Locked Objects option, to graphically edit the object. Dialog page: Datum Dimension. This method of editing uses the following dialog to modify the properties of a datum dimension object.
The Datum Dimension dialog. This allows the default properties for the datum dimension object to be changed, which will be applied when placing subsequent datum dimensions. This affects the dialog only and does not change the actual measurement unit employed for the board, as determined by the Measurement Unit setting in the Board Options dialog Design » Board Options.
The PCB Inspector panel enables the designer to interrogate and edit the properties of one or more design objects in the active document. Used in conjunction with appropriate filtering - by using the PCB Filter panel, or the Find Similar Objects dialog - the panel can be used to make changes to multiple objects of the same kind, from one convenient location.
The PCB List panel allows the designer to display design objects from one or more documents in tabular format, enabling quick inspection and modification of object attributes. NOTE — WR1 corresponds to the assertion that each datum that is used in a datum system shall be established from one or more datum features.
NOTE — WR1 corresponds to the assertion that the datum feature shall be used to establish a datum that is used in the datum system. NOTE — Datum target numbers are described in 7. NOTE — UR1 corresponds to the assertion that each datum target shall not be used in any one datum target set more than once.
NOTE — UR2 corresponds to the assertion that within a datum target set each datum target shall be identified by a unique datum target number. NOTE — WR1 corresponds to the assertion that each datum system specification shall only specify the precedence of datums used in the datum system that the specification characterizes. NOTE — WR2 corresponds to the assertion that each datum system specification that specifies a tertiary datum shall also specify a secondary datum.
NOTE — WR3 corresponds to the assertion that each datum system specification that specifies a secondary datum shall also specify a primary datum.
NOTE — WR4 corresponds to the assertion that each datum system specification shall be referenced by at least one geometric tolerance or dimension. NOTE — WR1 corresponds to the assertion that each datum system specification shall only specifymaterial condition properties for datum features used to establish the datum system that the specification characterizes.
Technical drawing that illustrates the usage of dimensions that reference a datum system specification. The technical drawing is a partial reproduction of Figure 6 — 46 of Design Dimensioning and Tolerancing [13]. NOTE — On technical drawings, the precedence of a datum within a datum system is typically specifiedin a feature control frame. The location of the compartment containing the letter s corresponding to the datum feature s from which the datum is established indicates the assigned precedence.
The compartment for the primary datum if it exists is immediately to the right of the compartment containing the tolerance value.
The compartment for the secondary datum if it exists is immediately to the right of the compartment for the primary datum. Lastly, the compartment for the tertiary datum if it exists is immediately to the right of the compartment for the secondary datum. NOTE — A datum within the context of one datum system may be assigned one precedence, e. NOTE — UR1 corresponds to the assertion that no two datums of a datum system shall have the same precedence. Technical drawing of a hydraulic valve.
This technical drawing is a partial reproduction of a drawing presented on page in Geometric Dimensioning and Tolerancing [14]. NOTE — A datum feature within the context of one datum system may have one material condition property applied, e.
Table 1. Table 2. Table 3. Table 5. Table 6. However, deficiencies in entities of the type mentioned above will only be passed on to the STEP application protocols that incorporate them. This figure shows that datum feature A the outer most cylindrical surface is used to establish the primary datum a center axis of the datum system specified by three concentricity tolerances e. Also, Fig.
Furthermore, both datum features Aand B are used once again to establish the primary datum yet another center axis of the datum system specified by the position tolerance i. As the Part 47 model limits the number of datums that may be established from a datum feature to one, this situation cannot be represented with the Part 47 model.
As the Part 47 model limits the number of datums that may be established from a datum target to one, this situation cannot be represented with the Part 47 model. Technical drawing illustrating multiple use of datum targets.
This technical drawing is a reproduction of a drawing presented on page in Geo-metrics IIIm [8]. NOTE — On technical drawings, datum target frames are used to group datum targets into datum target sets.
Multiple Datum Target Numbers The Part 47 model fails to account for the fact that multiple datum target numbers may be associated with a datum target, whereas the DSCDM does account for this fact. Additionally, datum target frames specify datum target numbers by which the datum targets are identified within the datum target sets. Composite Datum Features A composite datum feature is a datum feature that is composed of other features.
Depiction of a composite datum feature that is composed of two opposing planar features. Depiction of a composite datum feature that is composed of four cylindrical features holes. Also, note the wording in clause 2. NOTE — The term datum reference letter is somewhat of a misnomer, as a datum reference letter actually refers to a datum feature.
Therefore, it is believed that occurrences of this case are probably extremely limited. Technical drawing illustrating the application of modifiers to both datum features that establish a common datum. This technical drawing is a reproduction of FIG. Datums Without Datum Features or Datum Targets The Part 47 model cannot be used to represent datums that are not directly established from datum features or datum targets.
As there are four datums and only two datum features, the situation shown in Fig. Example of datums not directly established from datum features. Conclusions This paper has presented a data model the DSCDM that covers the concepts of datum systems, datums, datum features, and datum targets. As it is an optional attribute, the gender of a person need not be specified. Therefore, it may take on a string value.
Underlying Data Model Structure. Table B. Table B2. NOTE — All the specializations included in this appendix have been incorporated into the data model that is presented in Appendix E. Specialization of Datum The Datum entity could be further refined to account for the different types of datum i.
Diagram illustrating a constituent datum feature. However, for brevity, Fig. Datum Reference Frame vs Datum System.
NOTE — There is no requirement that the datum planes of a datum system be mutually perpendicular. Illustration of a datum reference frame. A sentence in clause 4. However, he believes this is because of the different datum systems. Therefore, only one datum reference frame is needed to specify these interrelational positional requirements.
Data Populations. Table E. Data population that corresponds to the technical drawing presented in Fig. References S. Feng, and Y. ISO International Standard , Industrial automation systems and integration — Product datarepresentation andexchange — Part Integrated generic resources: Shape variation tolerances, International Organization for Standardization, Geneva, Switzerland ISO International Standard , Technical drawings — Geometrical tolerancing — Tolerancing of form, orientation, location and run-out — Generalities, definitions, symbols, indications on drawings, International Organization for Standardization, Geneva, Switzerland ISO Draft International Standard — Industrial automation systems and integration — Product data representation and exchange — Part Application Protocol: Electronic assembly, interconnect and packaging design to be published.
Foster, Geo-metrics IIIm, the metric application of geometric dimensioning and tolerancing techniques, as based uponharmonization of national and international standards practices, Addison-Wesley Publishing Company, Inc. ISO International Standard , Industrial automation systems and integration — Product data representation andexchange — Part Integrated generic resources: Fundamentals of product description and support, International Organization for Standardization, Geneva, Switzerland ISO International Standard , Industrial automation systems and integration — Product data representation andexchange — Part Integrated generic resources: Materials, International Organization for Standardization, Geneva, Switzerland ISO Draft International Standard , Industrial automation systems and integration — Product data representation and exchange — Part Integrated generic resources: Shape variation tolerances,International Organization for Standardization, Geneva, Switzerland ISO International Standard , Industrial automation systems and integration — Product data representation andexchange — Part Implementation methods: Clear text encoding of the exchange structure, International Organization forStandardization, Geneva, Switzerland The truth is that we want to provide the loosest tolerances possible while still allowing for the functionality of the part.
Tolerances any tighter than required result in more expensive parts that are difficult to make. They go hand in hand with engineering. Should basic dimensions for a position tolerance always originate from the datums referenced in the feature control frame? Yes, a positional tolerance requires that basic dimensions be used to locate the feature back to your datum reference structure. Recall that basic dimensions have no tolerance, all of the tolerance is coming from your feature control frame.
If your basic dimensions lead back to something other than the datum structure in the feature control frame it has no meaning, right? The application of a form control to a surface is completely independent of your datum targets.
Datum targets are merely points, lines or areas defined on a part contour that is frequently too complex to lend itself to the standard datums like planes and axes. Your datum targets are best spread as widely as possible to provide for the greatest stability of the part during inspection and should be located with basic dimensions. Also, remember that a secondary and tertiary datum are required when a primary datum is established with datum targets.
Is there any standard procedure for how plane A should be defined, as you mentioned you can use a granite slab, 3 datum points taken by a measurment machine or Gauge pins. But in my opinion the placement of the theoretical plane A can differ quit abit between these three options.
If nothing is stated, is it free to use any of the options? Yes, you are correct. Unfortunately you are talking about the application through the science know as metrology. Unfortunately, this is out of the realm of our experience. Our expertise is application of the standard to create a product drawing to define it for engineering purposes.
I would welcome and encourage you to research this on your own and report back for the communities benefit. Thank you for quick respons, you did understand the question correctly. If anyone else know the answer I would appreciate an reply. I have an simulare question regarding Datum B, which is defined by two points making a axis. When you do not defined were this points should be on the drawing, is it up to the measurment opperator to just take two random points?
Or do they take alot of points along the line making a line between those points. Or can they even use an granite slab even in this case?
It truly is up to the inspection technologist. You can work with the quality dept to develop an inspection plan that calls out what you want. If you are looking to specify exactly how the datum setup is to occur you might consider using datum targets.
You can determine what type point, line or area as well as the shape if you use area square, circle etc. That being said, if you have a parallel requirement for example, there is no requirement for the number of points to be sampled and technically, 3 pts make a plane. Hi, Thanks for a great site! I have a question about use of datum planes: I am designing a cuboid shaped part with a circular feature at the centre on one surface which is the functional interface so important, and it is tempting to create 2 perpendicular planes through what are the hole centre lines, to then dimension and tolerance everything to these central planes.
If so what would be the correct method? What would you propose? This is a printed part much like a casting. The Tolerance of the printed part is Profile. Using a CMM the roundness of the boss shows. I believe the callout on the DWG is incorrect for several reasons. My customer is a very well known aerospace company. I would like to give them several examples of why their DWG callout is incorrect.
I would very much appreciate any input from you. Based on what you are describing your customer wants you to locate the tolerance zone for the hole at the precise center of your boss datum.
I am being instructed to put a MMC modifier on a datum drilled hole feature. They are stand alone, not connected to any other feature. My thought is that they should not be boxed. Tolerance the datums to what? What are you trying to do with them? Knowing whether the datums are planes or features of size impacts the controls that can be applied to them. How to tell the difference? Datum surfaces have the datum leader line attached either directly to the surface or as part of an extension line NOT inline with with a dimension.
Datums that are features of size in this case will be directly in line with the dimension associated with two parallel opposed elements. Knowing in advance that your part has holes in it that are toleranced with position, your part has to have basic dimensions from A, B and C to these holes.
The datums are essentially determining the start of the world, not the end of it. These statements assume that your datums are 3 mutually orthogonal planes and that no other datums exist. I have a square part 3. Datum -A- is the 1. The only feature control frames are for the bolt patterns. A point of clarification, are your datums to the features of size or are they to individual surfaces?
We typically recommend for stability purposes that for a mutually orthogonal datum reference frame you have a flatness control on your primary and perpendicularity controls on your secondary and tertiary datums. With regard to your holes that have an associated feature control frame. Basic dimensions do NOT have any tolerance directly associated with them. All of the tolerance for your feature the holes is coming from the feature control frame.
The value in the FCF is your tolerance zone. It is defining a cylindrical zone that the axis of your holes must lie within. Because you have A B and C referenced in the feature control frame the cylinder must be oriented perpendicular to A and basically located from B and C hence the basic dimensions. Remember that your datum structure is really telling how to set up and inspect the part.
First datum A must come into contact with the inspection equipment, then datum B and finally C. It is from the intersection from these 3 planes that features using geometric controls are basically dimensioned. I hope this helps. I had to make an assumption or two based on your description of your part. We have 29 individual lessons on the topics you need to know.
Each lesson varies between 10 and 30 minutes long and comes with an skill evaluation quiz to assess your progress. I am trying to make a checking fixture for a flange. In my situation I have a surface which is datum A. Datum C is one of the eight holes located on surface A. I want to make a fixture where I can measure the position of the eight holes which depends on the datums A B and C. The diameter of the flange is only 4. Does anybody have suggestions for the design. I know I have to clamp datum B by means of a chuck but I want to gauge the position of holes at the same time.
Depending on your particular design you could specify Datums B and C at MMC which would allow you to determine the virtual condition of each datum to use in your gage. A Datum Indicator placed on the surface of the tube specifies that the OD of the tube is the datum. What differentiates the 2? Why call out an axis as a datum vs.
This is where my confusion lies, when to use 1 vs. OD of the part as the datum. Can someone explain the differences so I can understand it better?
With regard to calling out datums it makes no difference where you have your datum in line with the dimension of size and connected to the diametral leader line or touching the surface. This will also always result in a simulated datum of an axis.
Where it does matter is in regards to the straightness control. If the feature control frame is associated with the diametral size tolerance then the straigthness of the axis is being controlled and rule 1 is overridden i.
If you happen to have a copy of the standard flipping between Section 5. Thanks for this blog, I have a question regarding critical dimensions, can we have 3 critical dimension at the same time? OD, Wall thickness and ID? Can you explain further? For datums, a cylindrical feature is referencing the theoretical axis of the cylinder as the datum axis both when placed on the feature and the diameter while using the physical feature of the cylinder as your physical datum.
When we measure the distance from a datum line- 6 dia hole to the axis of a hole A practical issue with the manufacturer in checking method. Please advice. Is there a position requirement on the holes? What is the basic dimension between holes, is it the 80? Where Delta X and Delta Y are the differences between the drawing and the produced part e.
No, think back to geometry. At a minimum you need 3 points, ideally spaced apart as far as practical to define a planar datum. Hope this helps. Hi, Does placing a datum on a dimension represents the datum is the centerline of that datum? Even if not a diameter. Dimension 10 is distance from one side to the other. Datum A is places on the dimension, just like now, but referred to a length not a diameter.
Placing the datum symbol on the opposite side of a dimension arrow indicates that the datum is the centerplane or axis for cylindrical parts of the associated dimension. You got it right. Hello, Can someone please let me know what does it mean when measuring inside diameter of piece of metal there is hole dimension followed by symbols GG? Thanks Abe. The resulting diameter of that averaged circle is the gaussian value of your diameter. The fact that the end of the duct is trimmed is irrelevant.
The datum reference frame with the referenced datums is telling you in what order to set up the part on the inspection table and to measure everything that calls out those datums in that particular order with respect to that framework. The only way you would then be measuring from the trimmed end is if that surface was given a datum, lets say D, and then have D called out for the position of the holes.
I am having some problems with our Q. Now, one way or another all dimensions have to have a tolerance, either thru traditional dimensioning or geometrically. This is of course assuming that both the right side of the bracket and the hole are based off of the same datum structure.
The easiest way to solve this argument is to examine the drawing and determine where datums A, B and C or whatever intersect and make a pen mark. All dimensions that define the size, location, orientation or form of part features that use these datums in the feature control frame that make up this reference frame must be basic and must tie back to it somehow.
The only scenario that would result in what your QA is saying is if the right side had a datum attached D, L, whatever and the feature control frame for the hole called out that new datum. Otherwise, your interpretation is entirely correct. All measurements must be made relative to the defined datum reference frame. For example, a metal box with one side open as the A datum, due to the part having holes where it will obviously be anchored to the mating part.
What is the best way to make the box as well as the best way to inspect it? We have differing views and an objective view would be some help. So this is something that comes up a fair amount in my industry with our avionics thermal covers and raceway covers.
Your part is a simple box shape, like a UPS box with the flaps opened deg from the closed position. Cut two of the flaps opposite one another off with a box cutter. The remaining flaps are your mounting surface and have your mounting holes in them. However, in a front view of the box flaps extending left and right you need to connect the two surfaces with a broken line and specify that datum A is comprised of 2 surfaces [ A ] 2 surfaces. Now, normally you would add a flatness tolerance to improve stability of the part during inspection.
This can only be done with a surface profile control see Fig. From here, you can start grabbing edges, surfaces and holes to further define your datum structure and complete your part. Holes can still be controlled using basic dimensions, surfaces can still be controlled using orientation and profile controls etc. This mimics the actual application of your part where your required tolerances would actually apply.
All we care about is that the part works and fits into the assembly. Lastly, keep in mind that the tolerances you are calling out apply to the finished part. So, excessively tight tolerances could potentially cause issues due to warping from the welding processes.
Unfortunately, this is one of the drawbacks of using welded sheet metal assemblies. If anyone else on the forum has a metal fabricating background feel free to join in the conversation. Keep those questions and comments coming. As a product Engineer , whenever i go through drawings castings or machined and after reviewing various call out Tolerance.
My first thought is how to machine it , what should be the set up process, Do i need to machine in same set up— in order to maintain XYZ dimension. You seem to be thinking along the same lines as I am. Based on what the part is and the geometric constraints placed on it I could make some educated inferences as to the machining sequences.
Again, your best bet is to consult with your company machinist, or if you have serious concerns contact a machine shop in your area that is likely to get the work. Here are some things I would consider when setting up the G code for milling or turning.
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