1. What is circumscribing circle size? The circumscribing circle size is defined as the smallest diameter circle that will completely enclose the entire cross-section of the extruded shape.
2. How may we determine the circle size that our profile will fit into? When determining circle size, the profile should be treated as a triangle. The length of the hypotenuse is the determining factor. Whatever dimension is achieved should always be rounded up to the nearest whole number.
3. How "unique" can my designs be using aluminum extrusions? Aluminum extrusions offer designers a freedom from "standard" shape restrictions that is unrivaled among other materials. The major advantage of "putting the metal exactly where you want it" provides an unlimited variety of opportunities for imaginative new designs including: simple or complex shapes; parts that self assemble, hinge or interlock; solid, semi-hollow and hollow shapes; and high-finish, high-strength precision parts.
4. What's the difference between a solid, semi-hollow and hollow shape? Hollow, semi-hollow and solid are the three general categories of extruded shapes. A shape is described as hollow if a completely enclosed void exists anywhere in its cross-section. In a semi-hollow shape, a void is only partially enclosed. (Your extruder can give you guidance, but by definition, for a shape to be semi-hollow, the area of the partially enclosed void must be substantially greater than the square of the gap's width.) A solid shape is one which is neither hollow nor semi-hollow.
5. What, specifically, is a semi-hollow shape? By definition a shape, any part of whose cross-section is a partially enclosed void in which the area is substantially greater than the square of the gap's width. In calculated terms, it is a shape whose wall-section partially forms a hollow, where the ratio of the hollow's area to the square of the gap's width is as follows:
   GAP WIDTH RATIO
   Less than .062" Over 2
   .062" to .124" Over 3
   .125" to .249" Over 4
   .250" to .499" Over 5
   Greater than .500" Over 6
6. The cost of running my semi-hollow extrusion is almost cost prohibitive. Do you have any suggestions to reduce the cost? To reduce the cost of your extrusion, reduce the ratio between the void area and the gap. Any improvements in reducing the size of the void will reduce pressure on the die tongue and provide easier extrusion. Another way to reduce the void is to increase the wall thickness. While the weight per foot will be greater, it is possible that the price per foot will be less. Also consider widening the gap. If the gap can be enlarged enough, it may classify the extrusion as a solid shape.
7. Is there an alternative that would save the cost of drilling and tapping holes that are in the ends of my extrusion? Most extrusions can be re-designed to include what's commonly known as a "screw boss." A hole size can be specified by your extruder to accommodate either subsequent tapping when required or a self-tapping screw.
8. What factors most influence tooling service charges and lead times? Initial costs and lead times for extruded aluminum are usually a good deal lower than those required for die casting, forming, roll forming, stamping, pultrusion, impact, or vinyl extrusion. The shape of the extruded profile (solid, semi-hollow or hollow) is an important factor. Other factors are: product surface finish requirements; special dimensional tolerances; and special alloy, design or production requirements which could affect die life.
9. We manufacture a large four-piece bracket. How much can we save on assembly costs with aluminum extrusions? Aluminum extrusions can be designed for easy, quick assembly with other parts. These designs, coupled with aluminum's light weight, allow for cost-saving packaging, delivery and on-site assembly of larger products. The labor and skill required to handle and assemble products by manufacturers, dealers or end-users are significantly reduced. Exact savings differ with each application, and your Shapemaker extrusion specialist should be consulted.
10. When would I want to use a two-piece extrusion? Sometimes a two-piece extrusion may dramatically reduce the cost of secondary fabrication. Also, the smaller of the two extrusion pieces may be less costly to produce, both in terms of metal cost and tooling costs.
11. How can I best assure that my extrusions will snap-fit together? The best way to design extrusions that snap-fit together is to allow for long appendages that can "flex" easily during the snap-fit assembly. A recommended approach is to purchase all parts that are expected to snap together from the same manufacturer.
12. Can different joint designs be used on a single extrusion assembly? Nesting, interlocking and snap-fit joints can be combined in the same extruded assembly. For example, snap-fit elements can easily be combined with rotating elements in the same design.
13. We have a vinyl extrusion that we want to make into an aluminum extrusion. Should we be concerned about the tolerances of the aluminum extrusions? Typically, the tolerances of the aluminum extrusions are much tighter than those of vinyl. It is better to fit the vinyl extrusion to the aluminum extrusion, since it remains constant.
14. How can we determine what are standard length and width tolerances for aluminum extrusions? There are so many variables in determining tolerances that the best solution would be to consult with a reputable extrusion company.
15. Can standard and customized tolerances be routinely produced? Aluminum extrusions are manufactured routinely to the close dimensional tolerances required for parts that must fit snug with other parts. Cost is minimized when an extruded product is designed to function well at standardized production tolerances. However, tighter, custom tolerances can be specified when necessary.
16. What does the term "metal dimensions" refer to in relationship to tolerances? "Metal dimensions" refers to dimensions measured across solid metal, which are easier to produce to tight tolerances than those measured across a gap or angle. Rely on "metal dimensions" as much as possible when designing close-fitted mating parts or other shapes requiring precise tolerances.
17. What can I incorporate in my design to minimize the potential of extrusions with twist and bow in them? Shapes with near uniform wall thicknesses tend to be less affected by thermal distortions than do shapes with heavy and light areas in them.
18. How do I determine the flatness tolerance for a shape I am proposing to extrude? Begin by checking the standard flatness tolerance chart. Then check with your extruder to see if the particular shape corresponds to the standard chart. Quite possibly, the shape is one that would allow the extruder to do better than the chart. On the other hand, the shape may have a detail which makes it "other than an average shape." In this case, additional tolerance may be required. Discussion with your extruder should result in a satisfactory tolerance.
19. I usually work with machine tolerances. Why are aluminum extrusion tolerances so large? Machining generally controls dimensions on small areas. The extrusion process controls those cross-section dimensions on lengths as long as 150 and 200 feet. Other reasons for tolerance difference include extruding temperature, pressure variations, die wear, angularity, and type of alloy used. Even though these tolerances may be larger than machine tolerances, the extrusion process is much more cost-effective than machining when the application allows. Many times tolerances closer than those published are available from the extruder. Designers should consult with their extruder on what tolerances are available.
20. What is the significance of marking "exposed surfaces" on the extrusion design drawing? Marking exposed surfaces provides thoughtful design techniques for producing a superior extrusion. The extruder knows to give these surfaces special attention and protection during the extrusion process for either functional or cosmetic reasons. The narrower an exposed surface, the more uniform the finish will be. Webs, flanges and abrupt changes in metal thickness may show up as marks on the extrusion's opposite surface, particularly on thin sections. Additional precautions can be taken in the extrusion tool design and extrusion run-out to minimize surface blemishes. If the exposed surface is highly critical, your extruder may be able to suggest a secondary finishing operation such as buffing, brushing or polishing.
21. What are I.D. marks and why does my extruder need them? I.D. marks are either a small depression or raised area (usually .015 by .015) placed on a non-exposed area of your extrusion cross-section. It is an identification for both you and your extruder to verify the source of your extrusion. This is very important and helpful if you have multiple sources for the same part.
22. Is it true I should use a uniform wall thickness on extrusions? Not necessarily. Uniform walls may make it "easy," but more importantly, a big advantage of an extrusion is the ability to put the metal exactly where you want it. Discuss your design needs with a Shapemaker extruder, and design the shape that best fits your needs.
    

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