ChemKnits: Behind the Design of the DNA Covers

Friday, August 2, 2013

Behind the Design of the DNA Covers

When publishing the DNA beer cozy, I mentioned that the knitting project was functioning as a test swatch for the the DNA kindle cover I wanted to make for my Dad. When I realized that the swatch (which I would need to knit in the round) would almost be beer cozy sized, I realized that I should just make it its own pattern and share that with you guys, too. There was a bit more that went into the design than just knitting up the cozy, and I'll share that with you in this post.

The Swatch

I knit the swatch on US size 6 knitting needles. Of course, I did not use the same needles with which I would ultimate knit the cozy (and eventually the case). This could have an effect on the stitch count, but it is likely small enough that things should still work out okay.

15 sts/3"; 13 rows/2"

Calculations for the Beer Cozy

A Samuel Adams beer bottle measures 7 7/16" (7.44") circumference and ~5" high on the flat portion. I wanted to make sure my target gauge for the kindle cover would make it possible to test my swatch on a beer cozy.

An earlier version of the DNA cable. I decided that I wanted to make the cable slightly smaller, so I modified the first version of my chart. Sometimes, when something isn't quite right you need to go back to the drawing board and start again. Even if it means ripping back to start again.

7.5 rows/inch would give 37.5 rows in 5". This made me decide to do 3 rows of ribbing and then start the pattern. I can always add extra rounds of the helix if I want it longer before starting the decreases.

5 sts/inch would give ~37 sts to fit the bottle. The helix itself is 9 sts wide so this works well for my design. I want there to be slight negative ease in the cozy so it has to stretch to fit over the bottle, but you don't want it to be too tight. I also had to keep in mind that the cabled stitches would decrease the flexibility of the cozy a bit (but not a ton.) I therefore settled on 36 sts.

With the new chart - 26 rows of the chart (+ ribbing) = 4" of cozy.

Even though I ripped out my first cozy, I was able to check the fit and see that it did in fact fit well on a bottle. Calculation success!

The final gauge of my beer cozy ended up being a little tighter than the swatch above, but that was perfect because of negative ease. (If i were to be proper, I would have redone the swatch with each yarn on each set of needles... but I knew it would be close enough.

Calculations for the Kindle Cover

Now that I had a completed beer cozy, I new that I was happy with the DNA cable chart I had come up with. I just needed to make sure that I would have enough yarn to finish the kindle cover.

KnitPicks Comfy Worsted (my selected yarn for both projects) comes in 109 yard/50 g balls. The DNA beer cozy consumed 17 g of yarn. I cut out a piece of cardboard that was the approximate size of the Kindle Paperwhite slightly over 6.7" x 4.6" (the cardboard measured 6.75" x 4.625"). I would say from looking at the beer cozy on top of my mockup, that the kindle cover will ~2x as big. Even if the kindle cover uses 2.5x the amount of yarn, this still leaves 7.5 g of yarn (assuming the ball I have is actually 50 g.) I therefore decided to NOT order extra yarn to complete this project. I hoped strongly that I would not regret this decision.

The beer cozy on top of a cardboard swatch the approximate size of a kindle.

The Kindle Paperwhite measures 6.7" x 4.6" x 0.36. (I must keep in mind that the cardboard does not take the width into account!) This means that the circumference needs to be close to 10". The length isn't as important to worry about because it can be a little longer than the kindle itself, and this is something that is easy to adjust during the design process. However, the overall length should be over 6.88" (to account for the width of the bottom).

With a 10" circumference and 5 sts/inch, I would 50 stitches to accommodate the Kindle. According to the beer cozy (which ended up being slightly less than 5 sts/inch), I had 18 sts in 3.25", and by calculation this would mean I would want 27.7 sts/5". This also brings us close to 50 stitches for the circumference of the Kindle cozy. I will try it out with 48 stitches since the ribbing works best with multiples of 4 sts. This should leave us with enough ease to easily fit over the kindle.

Each side of the Kindle Cover will have 24 stitches. The DNA Helix Cable is 9 sts wide. I think for it to be reasonably from the edge, I want 2 sts, +2 sts to account for the side, then 2 sts on the other side.

It fits! With room to spare so it should fit the thicker actual kindle.

After two complete rounds of the helix chart, The piece fit the cardboard prototype perfectly. If I add two more rows, I can close the helix at the bottom, too. I think I will go for this, because I would rather the cozy be a tad too long than too short. Plus, the cardboard doesn't account for the thickness at the bottom which would decrease the length a bit.