DIY Differential Cut UQ Calculator

[GadgetUK437]

Less is probably more....

Have you been raiding the fortune cookies again?
Well, yes the fewer baffles the better I guess. But there is a point where few is too few!
Hence my thinking there should be a ratio between baffle spacing and loft. IE, for a given loft (Hc), there would be an ideal IWB.

[FJRpilot]

Have you been raiding the fortune cookies again?

Darn... Busted again..... I agree there may be an optimum ratio, but with the popularity of designs like the Karo Step.... I just wonder what the benefits of the optimum would deliver....


Sent from my iPad using Tapatalk

[GadgetUK437]

Is there an ideal ratio between chamber width(IWB) and chamber height(Hc)?
In my head, thinner quilts would have narrower chambers

My wheels don't seem to be getting any traction on this one, so perhaps I need to ask this question in a different way.
My HG Phoenix has 9 chambers, 5" wide and approximately 2" high (2" of loft). If I were to make a UQ with 1" of loft, would it make sense to have narrower chambers?



--
Gadget

[MAD777]

My wheels don't seem to be getting any traction on this one, so perhaps I need to ask this question in a different way.
My HG Phoenix has 9 chambers, 5" wide and approximately 2" high (2" of loft). If I were to make a UQ with 1" of loft, would it make sense to have narrower chambers?



--
Gadget

You are correct.
To answer your original question, there is no ratio that works for all thickness.

Sent from my SM-G900V using Tapatalk

[Junebugdawn]

If you are using less down and 1" baffles, having more baffles (narrower channels) will provide more loft. You could do 12-15 baffles instead of 9.

Sent from my SM-N920T using Tapatalk

[GadgetUK437]

As loft increases, the radial difference between the outer and inner shells becomes larger. This means the arc length of the shell material between the outer shell and the inner shell has a larger differential.

Have been thinking about this recently, and after a little testing, I've come to the realisation that the calculator does not account for difference in arc length (between inner and outer shell). No matter what the thickness of the quilt!
To test this, this is what I did;

• First I made Hb and Hc the same in each case (I know it is conventional to have Hc larger, but it would only add confusion)
• I then tried different values for quilt thickness, from 1" to 1000" (ridiculous I know, but it proves the point)
• I noticed the Outer Shell Fabric Width per Baffle (OWB) does not change in relation to the Baffle Height (Hb), as it should, because the arc length would increase on thicker quilts.

2017-02-19 (8).png
2017-02-19 (5).png

[Tacblades]

Have been thinking about this recently, and after a little testing, I've come to the realisation that the calculator does not account for difference in arc length (between inner and outer shell). No matter what the thickness of the quilt!
To test this, this is what I did;

• First I made Hb and Hc the same in each case (I know it is conventional to have Hc larger, but it would only add confusion)
• I then tried different values for quilt thickness, from 1" to 1000" (ridiculous I know, but it proves the point)
• I noticed the Outer Shell Fabric Width per Baffle (OWB) does not change in relation to the Baffle Height (Hb), as it should, because the arc length would increase on thicker quilts.

2017-02-19 (8).png
2017-02-19 (5).png

Maybe the arc length over standard sizes is so insignificant that it reality it doesnt make any difference, as long as the delta between the baffel height and the peak height is within an inch or two.

[Tacblades]

Also this is the version i did with metric conversions
https://goo.gl/wQJPC4

[MAD777]

In my opinion, the difference arc length vs thickness is insignificant. Also, if one wished to account for that, the baffle material would need to be cut in an arc. No thanks, LOL.

I believe this is nothing to worry about, as the quilt building process is very forgiving.

Sent from my SM-G900V using Tapatalk

[GadgetUK437]

I disagree that it is insignificant. In fact, as a quilt gets thicker, the more significant it becomes.
An easy way to compensate for the error, is to add a fudge-factor, i.e. puffyness. Adding a inch or so of puffyness (Hc - Hb > 1") adds a lot of forgiveness.

But, I have trudged through the sums, to add a bit more precision -
Firstly I worked out the differential between the inner and outer shell without puffyness;

As you can see, with a small baffle height the difference between the inner and outer is small, but when you get to around 3" baffles, the difference is over 10"!
2017-02-19 (15).jpg

Then I looked at adding a catenary curve to the outer shell of the baffle chamber, but ran screaming from the equations. So I compromised, using a section of an circular arc (much easier formula, and a fair approximation) -

2017-02-19 (16).png

Lastly I added the puffyness to the previously calculated differential -

2017-02-19 (14).jpg
I haven't added seam allowances, or added 2 x baffle height for the side walls, but it is interesting to compare with the calculator.
Above 1.75" baffle walls the calculator does not add enough to the outer shell, so it becomes more important to add puffyness to the chambers to maintain loft. When you get up to 3" baffles and above, you need to add more than an inch of puffyness (Hc - Hb > 1") to maintain 3" of loft.