Mini-reel for SMD components
The mini-reel is a reel for SMD components on cut tape. It is compatible with the standard 7" reels, only smaller. Its capacity is therefore also much smaller: about 1/4th of what a 7" reel can hold.
Most importantly, the design follows the standard for reels for the essential dimensions (EIA-481). The mini-reels that were once on the market had a diameter of 100mm, and this design inherits that size.
That said, the mini-reel is designed in OpenSCAD and all dimensions can be configured (with the OpenSCAD “Customizer”). You could even use this design file to generate standard 7" reels.
The suggested (and preset) dimensions of the mini-reel are: outer diameter = 100mm (nearly 4"), hub diameter = 50mm, spindle diameter = 13mm (the spindle is also called the “arbour”). There are presets for tape widths of 8mm, 12mm and 16mm, and the design adds a 1mm to that for tolerance. The “wall thickness” of the flanges is 1mm (meaning that the total thickness of a mini-reel is the tape width plus 3mm).
The mini-reel is printed in two parts, which are then glued together. One side is almost closed; this is the side on which you would put a label with the part information. The other side has three holes, to make it easier to stick the tail of the cut tape into one of the three slots. These three slots have varying widths, and this is because cut tape has varying thicknesses. The narrowest slot that the tape still fits in, typically holds the tape best.
The side for the label also optionally has a slit that runs from the hub to the edge, with a scale next to it. Its purpose is to allow you to estimate the amount of components left on the reel, see below.
Estimating the quantity left on a reel
Especially when a reel holds a small quantity of components, you will want to know whether there is enough for the batch at hand. And a mini-reel holds a small quantity almost by definition.
The most accurate estimate is when using a Reel Quantity Calculator. For this calculator, set the hub diameter to 50, and the “material thickness” to 0 (zero). You can accurately measure the “roll width” (the R-value in the calculator) with calipers through the slit with the scale and you need to measure the thickness of the tape with calipers as well.
For a rough estimate, you do not need calipers or a calculator. The roll width can be read directly from the scale of the mini-reel, and it helps you “guestimate” the thickness of the tape as well. The three slots for holding the tail of the tape have a different sizes (see the table). Since you pick a slot that has the best fit, this gives you an upper and lower bound. A visual inspection then also tells you whether the tape thickness is closer to the upper or to the lower bound.
|Mini-reel Tape Size||Slot sizes|
|8mm||1, 2 and 3 mm|
|12mm||1.5, 3 and 4,5 mm|
|16mm||2, 4 and 6 mm|
With the estimate of the tape thickness and the value read from the mini-reel scale, you can read the quantity on the reel from the graph (with the caveat that this assumes that the tape is tightly wound on the reel). In case the components are spaced by 8mm instead of by 4mm, you have to devide the result by two.
At the turn of the century, when SMD components were not as ubiquitous as they are today, you could get parts in a quantity of 1000 on a mini-reel. It made sense, especially for prototyping and the smaller manufacturing services: you could often not re-use left-over parts of one project in another, because SMD parts were still special. So for a small series, you would rather buy mini-reels instead of standard 7" reels (that hold 4000 or 5000 parts).
This changed as SMD parts became more and more common. Sales of 7" reels increased and those of mini-reels decreased, up to the point that part manufacturers decided that mini-reels were no longer commercially viable. Mini-reels all but disappeared from the market.
While mini-reels may not be commercially viable, there is still a use-case for them. The fact that several distributors offer a “re-reeling service” proves that there is still a market for smaller “package quantities” than a full reel, but yet have the parts on a reel.
When it comes to storage, small reels take less space than large ones. That, in a nutshell, is my rationale for the mini-reel. For a small company, with a small stockroom, but still a large selection of different components, all those barely filled 7" reels are a waste of space. The scale for estimating the component quantity left on the reel is a nice bonus.
|Mini-reel for 8mm tape, STL file|
|Mini-reel for 12mm tape, STL file|
|Mini-reel for 16mm tape, STL file|
|Design file for the mini-reel||OpenSCAD|
I recommend that the parts are printed on a smooth surface (so not a "textured" steel sheet). You will want the top side of the reel to be smooth for the label to stick well.
Supports or a brim are not needed.
When starting my design, I was aware of a similar mini-reel design on Thingiverse. After the fact, I also stumbled upon another, even smaller design, also on Thingiverse. Neither design appears to be parameterizable; they are both for 8mm "paper-tape" style cut tape. I wanted a configurable design, both to support several tape widths (at least 8mm and 12mm tape), and to support various tape thicknesses (embossed carrier tape is usually thicker than paper carrier tape).