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Old 08-04-2014, 12:17 AM   #1
carpetbagger
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Default silk experiment . . .

I have Thai silk and Dharma silk and have ben having fun covering with it. But I kept getting wrinkles. Okay, Thai is supposed to be preshrunk and a yard of Dharma I had dyed was preshrunk after soaking in hot water and drying out, so I'm guessing peshrink is the problem and after wetting it down to cover I need to really pull and stretch it out, but wait! I notice the wrinkles are crossways - chordwise on a wing.

With silkspan and Esaki one aligns the grain longways, and I assumed silk, if it had grain, would be the same. I did an experiment: Made three 3" frames out of 3/32" balsa and covered them. Thai, Dharma, and Dharma dyed, All samples were marked with "grain" direction along the roll direction.

Result: all three samples seemed to shrink a similar amount but the shrinkage was across the roll, not along the roll. Not scientific grade test, all I did was shrink and dope samples and then measure across the balsa sticks where they had bowed in.

My wrinkle problem was cured with a few rubbing alcohol 70% spray downs and a few coats of dope, but next time I will apply the silk crossways.
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Old 08-04-2014, 01:06 AM   #2
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From the Dharma web site:

"• We found that this shrinks 8% in Length and 1% in Width

Shrinkage is a factor in planning how much fabric you need for a project. To help you, we took a 1/2 yard of every one of our fabrics, measured the length and width, washed it in a machine with very hot water, dried it in a dryer set on very hot setting, and then measured it again.
Then we calculated the % shrinkage in length and width which we are reporting to you.
Please be absolutely clear!
We think it's the worst case scenario.
This is only our experience and yours will vary.
Please do not take this as some sort of guarantee about how much the fabric will or will not shrink in your circumstances.
Most fabric shrinks when washed and dried, especially undyed fabrics such as the ones that Dharma sells. Fabrics that go through a dyeing process will also go through a shrinkage process. Dyed fabrics that you would normally purchase in a fabric store have already gone through a dyeing process and therefore have gone through a preliminary shrinkage process. So when you buy undyed fabric from Dharma, you're buying fabric that has never been shrunk."

I run the seam lengthwise on wings to get the silk as tight as possible.
This orientates the grain spanwise not chordwise.
If the grain is run front to rear, chordwise, the silk will sag between the ribs of open structures, because it won't shrink enough to prevent the sag.
Don't ask me how I know.

You do have to stretch the silk while wet to get it to shrink properly.

Don't rely on just the shrinkage of dope to get the covering tight.
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Old 08-04-2014, 02:21 AM   #3
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yeah, yeah, I read that blurb when I ordered the silk. Test: of course the shrinking silk had to pull on the frame and 8% probably would have busted the frame as that would be close to 1/4" shrink.

Figured on frame distortion:

Dharma - long shrink a tad over 1%, cross shrink about 3.5%

Thai - long shrink 0%, cross shrink 2.5%

Dharma dyed (obviously preshrunk) - long shrink 0%, cross shrink 2%

Now 0% is how much frame distorted but it did shrink enough to tighten up the covering.
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Old 08-04-2014, 04:39 AM   #4
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Default

Originally Posted by carpetbagger View Post
yeah, yeah, I read that blurb when I ordered the silk. Test: of course the shrinking silk had to pull on the frame and 8% probably would have busted the frame as that would be close to 1/4" shrink.

Figured on frame distortion:

Dharma - long shrink a tad over 1%, cross shrink about 3.5%

Thai - long shrink 0%, cross shrink 2.5%

Dharma dyed (obviously preshrunk) - long shrink 0%, cross shrink 2%

Now 0% is how much frame distorted but it did shrink enough to tighten up the covering.
8% is probably a relaxed shrink rate, or the maximum possible if a piece of fabric was shrunk while laying on a table. Iron on coverings can shrink much more that that, but they stretch while being strunk and thus don't crush frames unless a person is careless with shrinking it on open framework. The same shrink/stretch principle would hold true for a fabric, to a lesser extent.
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