Problems with interpolation

Hello. I’ve been designing a font and decided to try interpolation followings Glyphs’s tutorials. I’ve designed the regular (weight 90) and bold (weight 130) and interpolated the light (weight 70), semibold (weight 110), extrabold (weight 157) and black (weight 190). The way weight was determined was the width of one of the side rectangles on the “H”.
i came to some issues in a lot of the glyphs on curves, shape, distance between components, etc… This is shown on the prints below. I exported each variable and added to a new file so I could have a better view of all the glyphs
The way I designed this font includes two main values on each glyph, the stem (or downstroke generally) value and a smaller value for the upstrokes (generally), I’m not sure that could have interfered with the interpolation and caused the problems I’m facing.
I also made sure all glyphs are compatible between the regular and bold masters.
I could go the somewhat hard way and do each master individually as I did for the bold, but I was wondering if there’s any tips to fix the mistakes that happened.





Any tip will be appreciated. Thank you.


There’s also the black variation

Anything outside the range of your masters (90 and 130) is an extrapolation. Extrapolations are risky because they continue the linear movement of points that happened in the interpolation between masters.

Extrapolations typically only work for a very small range in comparison to the interpolation (I’ve seen 5 or 10 units on a 200 unit interpolation range) because at one point, nodes will bypass each other. You are trying to stretch the extrapolation very far, you’re going 20 and even 60 outside an interpolation range of 40.

What I would do is add the lightest and boldest interpolation as masters, and correct them. That way you avoid extrapolation. And then get rid of one of the two original masters (probably the bolder one of the two), and have a three-master interpolation.

And the distortion of the “y” is due to different starting points in each master.