Olesia

Hi idraw,
Here's a quick way to draw consistent wavy lines. The same technique can be applied for springs.
This isn't intended to devalue your request for a precise geometric tool for this kind of needs, which i agree it's quite useful.
It's just a way to help you solve the problem with the available tools/resources we have at the moment.
waves.mov

I've been using Affinity Designer since its inception. 
 
Sometimes it really does help with illustration-based tasks, making it faster to work with than Adobe Illustrator. 
 
However, the "Expand Stroke" function is still terrible even after several years of development. Has this feature been entirely ignored?
 
This is an example of what I'm talking about:
After creating a stroke with the Stroke Pressure modified, I attempted to use "Expand Stroke." 
 
As you can see, the nicely rounded stroke converts into something pointy like a dagger. 
 
I searched through the forum for help, but all I found was a trail of complaints regarding "Expand Stroke" going back to 2014. 
 
With 2017 almost finished, it would be GREAT if this got fixed.
 
Looks like my "timesaving" approach by using Affinity Designer rather than Adobe Illustrator is actually going to cost me a bit of time. 

Red signifies the starting node. The shapes indicate the type of node; round for Bézier (smooth), square for Sharp, & round with a dot for Smart.
 
There are some illustrations of this in the included help system: open Affinity Designer Help from the Help menu (Mac); click on "Drawing Lines & Shapes" > "About lines & shapes" to see them.

you're welcome! happy that I could help you

Thank you a lot for such comprehensive  explanation . I follow your instruction and done it in my project. Also it is great tip from you to divide and delete the small pieces. Thank again  :) 

because you need a transparent image at the end, I think you have to cut out the spaces. I don't know if it is the right way but you can achieve it like this...
 
(since we still don't have an offset tool, we have to use expand stroke)   1. write your text, set stroke width and align stroke to outside (stroke width will determine the space between your text and your lines later)   2. convert your text to path and go to Layer -> Expand Stroke (I've switched off visibility of the black text in the screenshot)   3. draw your lines with your appropriate stroke width; highlight your lines, go to Layer -> Expand Stroke and set Geometry -> add, now you have one "line-shape",     make sure your line-shape is underneath your text   4. highlight the line-shape and all the expanded strokes -> Geometry -> Subtract    5. now you have a cutted line-shape   6. Geometry -> divide and delete the small pieces   7. you're done ;-)

Hi Olesia,
Welcome to Affinity Forums :)
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