It can be used almost anywhere to represent any feature of size. When you have a hole in a part such as a bolt pattern, true position is usually called out. However, this can also be applied to any feature of size in need of a location tolerance, such as a pin, a boss, or even a keyway. In the image below you can see how a hole is called out using the position tolerance symbol. Position can be used with Max Material Condition ( MMC), Least Material Condition ( LMC), projected tolerances, and tangent planes. Locating surfaces is to be controlled via Profile. See the above central elements of a hole, slot and sphere. Position may be applied to any feature of size (Feature with physical dimensions like a hole, slot, boss, tab, or sphere) and control the central elements of these size features. For clarity on these two terms check out our article and video here. However, it is correctly termed in the ASME Y14.5 standard as simply “Position”. Application:Īlthough incorrect, we title this page and sometimes refer to the symbol as “True Position” since this is typically the term people are referencing when they are looking for the position tolerance. However, since this is such a useful symbol, we will continue to add content and examples for other uses of this nifty little symbol in the coming months. The two methods of using Position discussed on this page will be RFS or Regardless of Feature Size and under a material condition ( Maximum Material Condition or Least Material Condition). Position is one of the most useful and most complex of all the symbols in GD&T. In other words, the Geometric Dimensioning and Tolerancing “Position” tolerance is how far your feature’s location can vary from its “True Position”. The “ True Position” is the exact coordinate, or location defined by basic dimensions or other means that represents the nominal value. Of course, lengths are customized for each job.True Position, or just Position as the ASME Y14.5 standard calls it, is defined as the total permissible variation that a feature can have from its “true” position. A wide range of depths are available, far too many to list here, so please contact your local manufacturer for more information on their offerings - in general depths start at 6" and go up to 30" and beyond. Standard widths are specified in the above publication, but can be customized as needed. The following table comes from the American Institute of Timber Construction's Standard Specification for Structural Glued Laminated Timber of Hardwood Species publication.ĪNSI/AITC A190.1-1992 allows for any width and depth of glue laminated timber. It is advisable to check with your contractor or lumber supplier before finalizing design details so you aren't surprised by what you receive. However, in some cases, like the big-box hardware stores, the boards come in dimensional widths similar to softwood widths. In most cases, hardwood boards come in random widths to be ripped to size by the woodworker. For instance, hardwood trim that ends up being just over 1" thick (surfaced on 2 sides) is called a five-quarter (5/4) board. In North America, hardwood lumber is usually specified using the quarter system, where a board is identified by its thickness in quarters of an inch. Surfaced refers to a finishing process that smooths the lumber to remove all saw marks. Hardwood lumber is sized based on how many sides are surfaced. According to NIST Publication P20, actual lengths must be at least equal to the nominal length, but can be up to 3" longer than the nominal length. Softwood lumber comes in a number of standard lengths as listed in the table below. North American Standard 8-by Timber (Surfaced 4 Sides, S4S) NOMINAL SIZE (INCHES) North American Standard 6-by Timber (Surfaced 4 Sides, S4S) NOMINAL SIZE (INCHES) a nominal 8x8 timber has a minimum finished size of 7.25" x 7.25"), most timbers over 7" are finished with 1/2" removed. While NIST Publication PS20 indicates that nominal 7" to 15" thick timbers should have 3/4" removed for a finished dimension (e.g. Softwood lumber that has a thickness over 5" is called timber. North American Standard 4-by Lumber NOMINAL SIZE (INCHES) North American Standard 2-by Lumber NOMINAL SIZE (INCHES) North American Standard 1-by Lumber NOMINAL SIZE (INCHES) In the United States, softwood lumber is governed by the National Institute of Standards American Softwood Lumber Standard (PS 20). Softwood lumber is generally used for framing walls and floors.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |