Width tool. How to use the width tool in Illustrator CC 2019 2018 2017 2015 CS6 etc ? Select the width tool (halfway down the toolbar) - it is grouped with a number of tools. Goto to a path with a stroke (weight such as 10pt etc). The width tool can be used to create all kinds of amazing designs in Illustrator with a path with a stroke. It can be used with all kinds of paths such as closed paths and open paths as well as circles, curves, etc.
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Options. There are no options available via the width tool icon. You can double click the width tool icon and nothing will appear. It is interactive tool in the main part but you can double click at any point in the line and a panel will appear. If there is a point already there then the values will be already set and you can manipulate the side 1 and side 2 (as well remove the link between them to make an asymmetric design) and you will see a total value also. You can also check the adjust adjoining points (which will then re-adjust all the other points). If you just enter a value in the total, the value will adjust for both sides so if you set the width to 100pt then side 1 and side 2 will be 50pt. Set it to 120pt and the side 1 and side 2 will be 60pt. If you remove the link and set the side 1 to 40px and side 2 to 60px then the total will be 100px. You can also use the same panel to delete the point by clicking delete. You can use the panel as a great way to manually create the width instead of interactively. Simply go up and down the line and double click at any point and then add a total of 100pt (or 50pt). You can then go to another part of the path and double click again and set to 50pt and then to another part of the line set it to 100pt and so on and you can create all kinds of wavy lines using that approach. It is a pity that the tool does not interactively show you how far along the path it is (such as 5%, 10% etc so you would then know where to add the points but it can be done quickly by eye).
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Hover over stroke. You can modify the stroke by hovering over parts of the 'stroke'. You can hover over a path with a stroke of 1pt or 20pt or 60pt, it does not matter as the tool will manipulate the stroke to the distance you set. If there is no stroke then it will not work and you will have to add a stroke via the stroke controls. As you hover over the stroke, you will see a little dot and the cursor will change to a '+'. If the dot does not appear, it may be that the stroke setting for the align is not correct. Go to the properties panel and then change the stroke setting by clicking the stroke dropdown and then setting the align to the 'align to stroke center'. You should then be able to change the width for that stroke. Click and Drag outward (hold down the alt / option to just drag one side of the stroke). Go to another part of the path and see the '+' appear again. Drag out the stroke again with the tool.
Selecting multiple points. You can move and modify multiple points at the same time by simply clicking a point and holding down the shift key and then going to another point and clicking that and then clicking another and then you can move them up and down equally as well as increasing the stroke or decreasing the stroke at the same time. For example, create a path with a stroke of 60pt. Click on the stroke and drag out to add a point. Repeat with another point further down the line. Repeat again and again. Now go to the first point and click and then hold down the third point added and then fifth point added and seventh etc. Now move the selected points up and down and you will see the stroke change. Now drag out from the center and all the selected points will change equally. Great for create interesting wavy designs.
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Delete points. You can quickly delete the points by simply selecting the point and deleting and then starting again (the line does not disappear but it will just go back to the default). You can select any of the points and delete them by pressing the del key while they are selected.
Move points. You can also move the generated width point for each of the points added. Click the center of one of the added points with the width tool. Drag the point and move back and forth along the path (or up and down). You will notice that the point can only be dragged so far and will be blocked by the other points (as well some internal maths used to format the stroke).
Tweak. Once you have your width set, you can manipulate it without going to the center point, just click on the outer part of the stroke and move it towards or away from the center point. You will notice that as soon as you drag one side, the other side will symmetrically move so if you move outwards, the other side will also move outwards (this does not mean the 'actual' display outline is symmetric but just the control lines are equidistant (the likely result of all these changes will be a fairly distorted stroke). You can click on the curve at any point and hold the alt / option key and then shift the curve and you will notice then the result is asymmetric so one side can now be further or closer to the center point than the other of the stroke.
Multiple widths. You can use the width tool on a single stroke but with the use of the appearance panel, you can add multiple strokes to a design and each of those strokes can have a different stroke added and you can manipulate them all via the appearance panel. Go to the appearance panel and add a new stroke via the right side menu. Select that stroke entry and go to the tool and manipulate the stroke. As you drag out the points, you will see the width at that point change (you can see the side and width settings as you hover over any point of the path whether or not you have added a point to the stroke). If you use the same color of stroke then the end result will be just the combination of two or more of the strokes but if you change the color of the strokes then you will see a set of wavy strokes from each of the strokes in the appearance panel. The visibility of the stroke (for each entry) depends on the width at that point, you will only see the underlying strokes if the width is greater than above entries. As you can change the entries in countless ways, many combinations of colorful curved lines can be generated (and they will be curved as there is no corner point feature)
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Add points. You can continue adding points as well as modifying existing ones (I don't know if there is an upper limit to the number of control points you can add to the path's stroke).
Expand. Note, the path itself does not (at this point) have any additional anchor points visible, you can only see the end result by expanding the artwork. Go to the object menu and use the expand appearance command to expand the path generated with the width tool. It should also be noted that the keyword here is appearance and the appearance panel can be used with the width feature. Simply select the path and go to the appearance panel and right side menu and add a new stroke (say in a different color) and that stroke can also be manipulated with by the width. You can repeat that multiple times to build up a fairly complex path with multiple strokes added to the design. Once you have expanded you can then manipulate the artwork as a normal path and use curvature etc to manipulate the anchor points and segments.
Cleanup. One of the key issues with the width tool is that it generates a lot of excessive points when you expand the design. You can remove the points by using a variety of tools in the application as well as third party plugins. I would suggest using a plugin like smart remove brush from Astute graphics or perhaps use the in built smooth feature to remove some of the points.
Frames. You can select a rectangle or circle and you can create amazing frames simply by clicking on the path with the width tool and shifting the generated curve and adding points (you can click anywhere on the stroke or where you see the + indicated.
Save as symbols. Once you have created your amazing designs you can then save the artwork generated by the width tool to the symbols panel and use them as a new symbol. You can then re-apply the symbol instances multiple times and also tweak the work multiple times as well as re-color the work if saved as a dynamic symbol.
Save to library. You can also save the artwork to the CC library and then use the wonderful designs in applications such as Adobe Photoshop as well as Adobe After Effects and Adobe Premiere and Adobe Indesign. You can also save the artwork as an AI file and then use the designs in apps such as Painter. You can also save the artwork as vector designs by saving them as PDF files as well as SVG files and using them directly in web pages. You can also use the file export command and save the artwork as a PNG or PSD or JPG raster format file.