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  • How to Design a Custom Bracket

    How to Design a Custom Bracket

    You need a bracket but can’t find it at the local hardware or superstore. Look around the room you are in. Chances are you will see a number of applications where brackets are used to hold loads that you take for granted. Desktops, shelving, countertops, even flooring are held up with bracketry of some type.

    So you decide to design your own bracket. Use the following simple guidelines to formulate and design the type of bracket you will need to successfully meet your requirements.


    Loading

    The starting point is determining what loading you are going to subject the bracket to. We will assume that the loading that you are designing to is a static load as described below.

    Static Load - A load which does not undergo a change in magnitude or direction during a measurement procedure.

    Essentially it is a load that is not moving around. Basically, like a shelf with books on it. There is a very complicated formula that determines the deflection of the bracket under load. Because you have better things to do with your time Short Run Pro has made a bracket deflection calculator for you. Click here to enter the bracket calculator.


    Material

    Next you want to determine what material you want to use. The standard types of material for metal brackets are:
    • Carbon Steel
    • Aluminum
    • Stainless Steel
    Use this link to go to an area that will describe the material for you: http://www.shortrunpro.com/genEngGuidelines.aspx?tab=1


    Shape, Dimensions and Holes

    The shape and dimension of your bracket will obviously be determined by the shape of the item it is holding up but will also be affected by the load capabilities and the ease in manufacturing (cost control). Keep in mind that strength considerations of the part are not just functions of the material thickness but of the bracket shape. As a part has added features your strength can improve dramatically. As seen below both these bracket are of the same thickness but the first one will be significantly stronger due to the gusset (small triangular piece) welded on the bracket. This is a nice feature for keeping the profile of the bracket small yet creating a strong bracket.

    Bracket with Gusset Bracket with Gusset for Added Strength



    Another method to increase strength is to add more profile to the part. As you can see below the Pan type bracket is significantly stronger than the same thickness L bracket because of the profile of the bracket

    Added Profile for strength of bracket



    By examining your application you should be able to generate basic dimensions. For example, say you need a bracket to hold a 40 lb ladder in your garage:

    A simple “L” shape should do. One leg bolted to a stud and the other where the ladder is placed. The ladder is only 4” wide so 2 pieces of a 6” x 6” x 2” wide “L” bracket would work fine.

    Deflection of this bracket under the 40 lb ladder will be .014” or essentially no deflection. This ¼” bracket is plenty strong to hold the weight of the ladder.


    Mounting Holes

    Almost all brackets have some type of mounting holes. In our case we need 2 holes on the 6” length being bolted to the stud. A ¼” lag bolt should do the trick See screw and bolts type:

    http://www.shortrunpro.com/ScrewAndHoleBoltGuide.aspx?tab=1

    It makes sense to space the bolts evenly on the 6” face and in the center. Since I am using a ¼” bolt then we need the hole size to be .26. (1/4” = .25 so we need a little larger hole to accommodate the screw.) The bracket as it was described to be designed can be seen below.



    If you want threads in a bracket this is called a tapped hole. This might be needed if you were mounting something into the bracket but did not have a nut on the opposite side. For instance you were mounting a piece of electronics onto a bracket and could not get a bolt on the opposite side.

    If you want the head of the bolt to be recessed into the bracket (not sticking out) this is called countersinking.


    Material Finish

    The standard material finish is important not only from an aesthetic viewpoint but also to help in resisting rust. If the use of the bracket is outdoors you definitely will want to have a good paint job or use stainless steel.

    Use the following link to our material analysis page to describe the types of finishes available for you bracket.

    http://www.shortrunpro.com/genEngGuidelines.aspx?tab=1


    Manufacturability

    You want to control your costs and the best way to do this is to make the bracket easy to manufacture and selecting the right material.


    Material Costs

    Stainless and Aluminum are almost 6 times the cost of steel. If you can make it from steel and paint it then do it.


    Design

    OK – this isn’t easy but worth the read.

    • Flat Blanks
      • Most fabricators these days have the ability with lasers to produce any shape you want. Flat plates of varying design are simple these days. If you can keep it flat do so. Keep in mind that you will be paying for laser time so the more intricate the part the more time to run
    • Mounting Holes
      • Again, keep it simple. If you can keep your hole pattern symmetrical and evenly spaced then do so. If you have special design then you have to have a hole pattern that matches. Special hole patterns can add cost to your part.

        If you are using wood screws then oversize you hole about .10 to .15 for clearance (if ¼” screw use .26 hole)

        If you need tapped hole (screws put into metal of bracket) then you will need to specify thread size. See Screw and Bolt Guide to help with this selection.

        http://www.shortrunpro.com/ScrewAndHoleBoltGuide.aspx?tab=1
    • Forming
      • Keep the design simple and symmetrical. L shaped brackets are the easiest to make. As you get into pan shapes and “U” shapes expect to pay more for the time spent forming the part.

        Other items to consider when designing a part:

        Rolled parts with large radius (above ½”) need special tooling or must be rolled. This is normally an added expense. An example of a rolled part can be seen below:

        Example of Rolled Part

        On a “U” bracket when the height of the part is larger than the brake then this can be an added expense because most brakes can not form this so it has to be welded. The part below gives you an idea of this design where the sides are much higher than the bottom causing special tooling or an additional operation to be done. Try to avoid this if possible.

        Example of Larger Height Flanges

    • Welding
      • We discussed adding gussets and other features that may require welding. Although a great way to improve strength it adds cost. Welding is an expensive operation for most people. Make sure you need to weld a part before designing it this way. If at all possible avoid the process of welding. In the end it is important that you minimize any special feature to ease the manufacture of the bracket. Anything you add special you will have to pay for



    Conclusion

    Designing a bracket is actually pretty simple and straight forward. If you follow the simple approach as shown above you will develop an easy to manufacture, cost effective and very function bracket. Short Run Pro has developed the necessary calculation tools to make the job simple.

    By Bruce Toal
    Technical Advisor
    SRP
DD
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