What are Tabs?
- Tab And Slot Sheet Metal Designs
- Sheet Metal Tab And Slot Design Guide
- Sheet Metal Tab And Slot Design
In this article, we will introduce the 6 types of sheet metal joining process that is often used in product design. Folding / Tab Joints The two pieces of sheet metal connected to each other by folding or bending tabs in the form of a buckle and a clamping slot. For a slot or hole 1' diameter then the minimum distance 'D' = 2.5T + R (see fig. 'C') Form height to thickness ratio – To determine the minimum form height for sheet metal use the following formula: D = 2.5T + R (see below) The height can be less but it required secondary operations and is far more costly. Tabs and slots are commonly used to align interlocking sheet metal components, and the new Tab and Slot feature in SOLIDWORKS 2018 allows for corresponding tabs and slots to be created in one operation. This is definitely easier than using a complicated design library feature or separate extrude, cut, and pattern features. . Slots or tabs widths should be greater than 1.5 X stock thickness. The length can be a maximum of 5 times slot/tab width. These rules can be violated at an increased tooling cost- width as low as 1 X thickness and length as high as 7 X thickness can be achieved. On cutoffs, avoid full radiuses across the width of stock.
In most cases, your precision machined part will be etched from a sheet of metal. Metal parts are held in sheets by several small tabs which may leave a burr when detached. It is important to note that this burr is unlike a progressive die burr. Therefore Fotofab will refer to these 'burrs' as tabs. There are two types of tabs used in the Fotofab Process: External and Recessed.
External Tabs
External tabs formed by precision machining will produce a break-off point that will leave a small part of the metal sheet on the part. If you have one of Fotofab's business cards, you may be able to feel the external burr used on our cards.
Recessed Tabs
Recessed tabs formed by precision machining are similar to external tabs except that the break-off point will be recessed into the part. Use this option if your part cannot have any areas extend beyond its perimeter. Typical applications that use the recessed tab are metal parts such as encoder discs and other circular parts, washers, and shields. RF/EMI shields will use recess tabs so that the tab does not affect the fence's attachment to the PCB.
What are my options if my part cannot have Tabs?
We can produce your metal part without placing any tabs to hold the part to the sheet. This is referred to as having drop-out parts. The benefit of going with drop-outs is clearly losing tab, but since the parts are less stable (they are no longer tabbed into the sheet) we generally have looser tolerances on drop-outs. Additionally, the etching and stripping processes create a higher yield loss. Parts that make good candidates for drop-outs depend on metal thickness (the thicker the better), part design, and most importantly tolerances.
Design Guide to Photochemical Machining: Tabs
To provide the tightest tolerances, we recommend precision machining parts so that they remain within the metal sheet from which they are etched. The small amount of metal that is designed to bridge the part to its metal sheet is called a tab. Parts that are tabbed to remain in the sheet also allow for safer handling and easier inventorying.
Fotofab gives you the option of two different tab designs, depending on the edge requirements of your part. The upper figure to the right illustrates the general appearance and maximum tab dimensions of a part held to the sheet by an external tab after it has been removed from the sheet. The lower figure illustrates the general appearance and maximum tab dimensions of a part held to the sheet by a recessed tab after it has been removed from the sheet.
For thicker metal parts, Fotofab can design a small score line etched into one side of either an external or a recessed tab to facilitate the part's removal from the metal sheet. Casino near mississippi river.
If your part's outside edge requirements are critical, we can produce the part without tabs. We refer to an untabbed part as a dropout part. The benefit of a dropout part is that it will not have a tab because the part does not remain in the metal sheet during etching. However, a dropout part can be etched less consistently than a tabbed part, and therefore has a guaranteed dimensional tolerance of approximately +/-15% of the metal thickness with an absolute minimum of +/-.003″.
Depending on the strength of the metal chosen, typically only a part that is thicker than .010 inches (.254 mm) is a candidate for a dropout part. Note that a dropout part is more expensive to handle, inspect and package than a tabbed part, so consult with us prior to selecting this option.
One of the most popular ways to create a 3 dimensional assembly of waterjet cut parts is via the t-nut technique. In this technique, a bolt or screw is passed through a round hole on the faces of one waterjet cut part, and then through a special slot perpendicular to the cut edge of another piece. The bolt is threaded through a nut which is held in place in a perpendicular slot.
The mating edges of both parts are usually cut with tabs and slots to further secure them together. This is similar to the finger joint or comb joint sometimes found in woodworking.
Illustration : CAD drawing of parts to be joined at their edges with the t-nut technique
Tab And Slot Sheet Metal Designs
Illustration : Waterjet cut pieces joined at the edge with the t-nut technique
Illustration : Another view of the t-nut technique with the same part from the previous photo
The slots cut into the face can be placed along the edge for maximum space savings. For more stability, the slots should be surrounded by solid material. This is analogous to the mortise and tenon joint of woodworking.
Sheet Metal Tab And Slot Design Guide
Illustration : Parts to be assembled using the t-nut technique;
the slots are placed in a location which provides more stability.
Illustration : The t-slot technique in a more
stable configuration: the slots in the center of the part
Illustration : Another view of the more stable variation of the t-slot technique
Note that the slot which holds the bolt extends slightly beyond the nut. This is to make sure that the bolt fully engages all the threads on the nut. It also gives some flexibility in the length of the bolt used.
You might need to consider making the tabs slightly smaller than the slots or overcutting the corners in order to compensate for rounded inside corners due to the waterjet's kerf, as shown below. (More information on kerf can be found in our article on the limitations of waterjet cutting).
Illustration : Inside corner reliefs on tab section to compensate for kerf
Illustration : Inside corner reliefs on slot section to compensate for kerf
Since the cut edge of the part is used in contact with a flat face, you should consider the use of low-taper waterjet cutting for this type of construction.
Sheet Metal Tab And Slot Design
You should decide whether it's more important to have a tight fit or easy assembly.
If you go with 'tight fit', you should design the slots slightly undersized (0.005 or so), and fix it by filing away any excess. Heating the hole section with a torch or heat gun so that it expands will make putting the pieces together easier. You can force the pieces together with a press or even a hammer.
Tab And Slot Sheet Metal Designs
Illustration : Waterjet cut pieces joined at the edge with the t-nut technique
Illustration : Another view of the t-nut technique with the same part from the previous photo
The slots cut into the face can be placed along the edge for maximum space savings. For more stability, the slots should be surrounded by solid material. This is analogous to the mortise and tenon joint of woodworking.
Sheet Metal Tab And Slot Design Guide
Illustration : Parts to be assembled using the t-nut technique;
the slots are placed in a location which provides more stability.
Illustration : The t-slot technique in a more
stable configuration: the slots in the center of the part
Illustration : Another view of the more stable variation of the t-slot technique
Note that the slot which holds the bolt extends slightly beyond the nut. This is to make sure that the bolt fully engages all the threads on the nut. It also gives some flexibility in the length of the bolt used.
You might need to consider making the tabs slightly smaller than the slots or overcutting the corners in order to compensate for rounded inside corners due to the waterjet's kerf, as shown below. (More information on kerf can be found in our article on the limitations of waterjet cutting).
Illustration : Inside corner reliefs on tab section to compensate for kerf
Illustration : Inside corner reliefs on slot section to compensate for kerf
Since the cut edge of the part is used in contact with a flat face, you should consider the use of low-taper waterjet cutting for this type of construction.
Sheet Metal Tab And Slot Design
You should decide whether it's more important to have a tight fit or easy assembly.
If you go with 'tight fit', you should design the slots slightly undersized (0.005 or so), and fix it by filing away any excess. Heating the hole section with a torch or heat gun so that it expands will make putting the pieces together easier. You can force the pieces together with a press or even a hammer.
If you want 'easy assembly', you can get the parts to hold together more tightly using retaining compound (Loctite makes a good one) or epoxy.
Here is a complete box made using this technique. The box sides have been laser cut from clear acrylic, which lets you see how the whole thing is assembled.
Illustration : Box assembled with the t-nut technique