Sewing tolerances – inaccuracy in cutting and seam width

[Eric Blanche]

Just wanted to add that the basting tape from sailrite can definitely be peeled off after usage if not sewn through.

Although, if doing a Faux flat felled seam, depending on how you do your initial line of sewing seam allowances, you can reuse the tape when folded over. I find that sewing through the tape is generally not an issue but the needle WILL gather some degree of adhesive and eventually need the needle cleaned or replaced.

[Sam Farrington]

I use only very fine pins for seams.

First, the fabric pieces are tailored over the framework that is used to support the tent.  At this point, the fine pins are inserted parallel with the seam, right where the seam will be kept taut.  Then the center of the seam is marked very lightly.

Next, the joined seam is removed from the framework and placed flat on the table (a rugged ping-pong table that holds its shape).  The pins are then removed, one-by-one, and rotated 90 degrees and reinserted under the seam line, keeping the fabric taut.

On a flat felled seam, the seam allowance is trimmed to leave just enough to re-pin while forming the seam with the pin reinserted again to insure that the pins stay right under the marked seam line.

Next, the work is sewn with the pins removed one-at-a-time just before the work goes under one side of the seam.  This is when adjustments are made if the seam line is not dead center over the pin holes.  Then the other side of the seam is  sewn.  Note that the sewing is done with one hand held before the stitch, and the other hand held after the work on the other side, in such a way that the work is held taut while the work is moving under the needle and the presser foot.

This approach is used only for very light tent fabric; hence the extra care must be taken.  Granted, it is cumbersome; but not being a trained seamster, this is necessary to insure the tent will pitch taut.  Since only one tent is being done, the extra time is found acceptable.  Also, the most difficult seams are only used for the overlapping flat felled seems, and hems and the like are much quicker.  But speed is avoided, because having to cut out the threads to redo the work is a bummer.

[Roger Caffin]

sewing is done with one hand held before the stitch, and the other hand held after the work on the other side, in such a way that the work is held taut while the work is moving under the needle and the presser foot.
Exactly! Essential.
Not needed when sewing quilts with ‘heavy’ cotton fabric.

Cheers

[Paul McLaughlin]

So, I’m wondering what types of basting tape would work best for the 1.8 Airwave Hybrid Nylon Ripstop?

Cannnot say on the tape, but I have experience with that Airwave, and it is squirrelly stuff. I would pin it. I had to put a pin at each end of the seam, carefully line things up with no tension on the fabric, put a pin in the middle of the seam, line up again, put a pin in the middle of each half, etc., until I got them close enough together for my tastes. Very easy to stretch that stuff out of shape unless your seam is straight and precisely aligned with the grain.

[Jerry Adams]

Sam, Roger, Paul – exactly!

I do sort of like Paul.  A mark a line on both pieces of fabric where I want the first row of stitches to be and line them up as I sew along.  Except I use a hand stitch.  Ideally, I’d put the hand stitch 1/8″ away from the line so it doesn’t weaken the fabric.  Put one at each end, one in the middle,… Make sure you’re taking all slack out of both pieces of fabric but don’t stretch.  Sometimes, I remove the hand stitches after I do the first row of stitches.

Yeah, since I’m doing just one tent I go slowly.  If I had to do a bunch of tents and minimize labor cost, I wouldn’t spend so much time marking lines and doing hand stitches.

[Roger Caffin]

If I had to do a bunch of tents and minimize labor cost, I wouldn’t spend so much time marking lines and doing hand stitches.
I wonder what would happen to the quality?

Cheers

[Jerry Adams]

You could cut the fabric with a laser computer controlled cutter.

Make the fabric exactly 1/2 inch (or whatever) wider than the seam and then use the marks on the machine to do exactly 1/2 inch seam allowance.  You would get equally good quality as if you marked lines on the fabric…

Maybe a skilled seamster on a good machine would keep both pieces of fabric aligned and not stretched relative to each other without pins.

On clothing patterns they have these little notches to show where the fabric is supposed to align.

I wonder how the commercial product makers on this site do it

[Roger Caffin]

Be warned: biased opinion follows!
I have made clothing (usually Taslan fabric) and silnylon tents.
The notches on the side of bits of dress-making fabric work for two reasons:
* the fabric is (usually) not at all slippery
* the distance between notches, corners etc are small

When making a tent, neither of these applies (imho).

Cheers

[Sam Farrington]

In reading this thread several times, it occurred that maybe some fabrics are subject to being more “sticky” than others.   If the fabrics generally vary in quality, the ‘stickiness’ probably varies as well.  So selection of non-sticky fabrics should receive equal attention.

Result:  Some of the silpoly I’ve found is not sticky at all.  Granted, it may be necessary to cannibalize a tarp or two to find the best quality.  An expenditure of around $200 compares favorably with the cost of TNT.   There is one concern, arising from a note received from the owner of Yama Gear.  I felt perhaps he did not like the cannibalizing of his excellent tarps.  All I can say is that it would be for one tent only, used only by this one poster.  Hope that helps.

[Dan]

Some things I’ve learned.

Get lots a practice in on smaller project (eg mini taps) ground sheets. Where making mistakes won’t hit so hard in your pocket. Or leave you without shelter.

Check several times then sew once.( Less likely to slip sideways or bunch or crease so a seam doesn’t end up in the wrong place).

Sewing through double sided tape is possible. Wipe the needle with silicon spray (silicon polish works). Do as frequently needed. ‘gold’ ti-nitrate (TiN), if available are good as well.

I roll panels lengthway, it makes them more manageable. See above check twice  sew once.

You will be  skilled at sewing or seamster (rather than seamstress(?)). If you prefer you could be a Thread Insertion Technician , as the hammock forum guys would have it. They DO NOT SEW (macho). But I think they are being T.I.T.s

Take your time& best of luck.

[Dan]

1. Correction :smaller  projects ( eg mini tarps),

[Roger Caffin]

Well-known phrase:
‘Measure twice, cut once’.

For engineers, an alternate version is
‘Measure, cut, weld back together, repeat’. :)

Cheers

[Jerry Adams]

Or, practice on scrap pieces

You want to include strips that are like 6 feet long

And make sure one isn’t slipping relative to the other. Make a mark exactly 6 feet distant on each piece, then when you’re done sewing the seam, the marks should line up

[Roger Caffin]

And they will line up if you use LOTS of pins.

Cheers

[Sam Farrington]

Alex,
Looking at your diagram again (the one in your first post), it occurred to me that it is not quite the way I make a lap felled seam, in several respects.  I think of your diagram as a cross view with two internal flat hooks overlapping each other. Fine pins can then be used to hold the whole seam including the ‘hooks’ inside, in place before sewing.  The pins are placed across the seam, so each pin penetrates all four layers; and most important, is pinned far enough inward to keep well inside any of the two edges further inside. In other words, so that there is plenty of internal overlap held by the pins (and later by the threads).  Note that unless you have a machine that does two parallel threads at a time, the whole process must be done for each side of the seam line.

The pins are then held in place in both hands, front and back, and each pin is  removed one at a time just before that pin hole goes under the presser foot sewn parallel to the seam. Some prefer to leave the fine pins until just AFTER they go under the presser foot; but with tents I do not in order to be sure the seam remains the desired shape. That preference may be affected by the thickness of the seam; for example, whether it is very thin, or heavier.  When making a tent, as opposed to a pack, the fabrics are thinner and lighter, and must be much more carefully done.

Also, some prefer to have more folds in their seams, or include more than two panels joined in a seam.  But seams may be designed to limit the additional weight resulting.  With MYOG, you can design a tent to minimize the weight occasioned by seams; thus producing a superior product.

From reading the posts, there are a lot of ways folks refer to seams, not to mention how they create them.   And some confusion is naturally the result.  Even diagrams often don’t help, because they are one dimensional, and don’t show all three dimensions as seen by someone observing from different angles.  But the bottom line is to keep a seam as light as possible without weakening it, including the fabric around it.  So sealants can be narrow, just to protect the thread; and not bury a seam with a lot of glop. And I also try to figure ways to avoid seams altogether in order to reduce weight even further.

Hope all this is helpful.  As one member recently posted, the whole process can be very frustrating.  But ‘practice makes perfect’.

Happy Trails.

[Dan]

Hi guys, an  alternative to ‘sail’ double sided adhesive seam tape is Double sided cellulose adhesive tape it’s is double and less tacky so doesn’t bind the needle. It is certainly very useful when sewing very light or net as it temporarily gives it enough structure to feed without issue with fine needles or gather under the foot/ into the needle hole/slot.

It might be work silpoly. But has less strong tack, As it no film adhesive carrier layer  so tears  out after stitching along it quiet easily.

Also a Bright in the base of the sewing machine can highlight where to sew. I pre-marked the seam line, with a biro, on the wrong side of the fabric. (Red, blue green or blue not black. Thermal pens are also available, cool iron to fade away.)

I used marked seam lined to sew up a ram aerofoil kit where seam placement was critical to the 1milimetre on each panel.

[Sam Farrington]

Dan, re some thoughts about silpoly:

> It might be work silpoly … But has less strong tack, As it no film adhesive carrier layer  so tears  out after stitching along it quiet easily.

As regular readers may have noticed, my reliance on silpoly is based largely on tests of a number of popular tarps.  The clear winner was silpoly from Yama Gear’s tarps.  Water could barely be forced through the tarp.  Even better, I could not tear it. Yet unlike DCF, TNT and other laminates, the silpoly has some elasticity that can retain a stable and taut shape in a windstorm.  Also, the Yama tarp measured a fabric weight of 1.08 oz/sq/yd, so is well below that of its competitors, as most of the samples of other tarps had fabric weights over 1.2 oz/sq/yd.

Granted, the laminates can provide a solo tent weighing around a third of an ounce less per square yard.  But only at much greater prices, and not much longevity; and what sticks most in my mind are the photos published in BPL of laminates torn to pieces in a severe windstorm.  Gear that is more resilient when pounded by the worst nature can dish out should be a must.

So I plan to use the Yama fabric for most of a solo tent, including a floor, a fly, and vestibules.  The side-entry front vestibule will have no obstructions, and only one full zipper; but is designed to be opened on either the right side, left side, or on both sides together.  The rear vestibule has no entry to save weight and will block wind from the rear. So only the front zipper will be used, and the rear can be used for pets and/or storage, as well as wind protection.

I was amazed with the quality of the fabric used by Yama, and will use it for all but a lighter colored inner ceiling that will not only support the fly, but also keep the inner dry for a few minutes while the tent is being pitched.  The tent will be completely self-standing;  so unlike the tents supported by numerous heavy cords and stakes, only four pegs will be needed to anchor it in place, not to support it.

There have been a lot more steps designed to reduce the tent weight ; but it should come in well below 2 pounds, including the 4 alloy pegs.  For more information about the design, BPL members can go to the BPL Dashboard, select “Research and Learn” from the righthand list; then select “Search the Site”, and enter “XX”, which is an abbreviation for the “Double-Crossed” design.  And as always, please note that I have no connection with marketing.

Much remains to be done on this project; but hope that more details from the BPL archives will provide a better idea of the design.  Please feel free to post or email.

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