How do you keep curved flat-felled seams in thick, bulging fabric straight?

Industrial machine with a compensating foot will keep everything in line and set distance from edge. It also helps to reduce the bulk when possible similar to how you do zippers in a hem.

What kind of fabric or material are you using?  Is this just for a pack, or are you making tents or tarps as well?

Assuming you are making a pack, and using DP materials, that may be why you want a true, not a faux, flat or lap felled seam, as the faux seam will expose needle holes on an exposed single layer of material –  needle holes that will enlarge over time and require sealing with seam tape.  This is but one of the reasons I do not use DP materials for packs.  If I did, I would not attempt to create true flat felled seams, and would simply join the curved edges of the two fabric pieces with a line of stitching, add an extra line of stitching for strength right next to the first line, and then sew a strip of binding or seam tape as a cap over the exposed material edges.  Seam sealing the initial lines of stitching is a good idea before adding the binding or seam tape, which will be on the inside of the pack and not show. This is how much lower cost gear is made, but can be quite durable.

Lester, What are you sewing with currently? Since I started using a walking foot machine, this is a non-issue.

Regarding Sam stating that DP fabrics have stitch hole elongation issues, I am very curious to hear more about this, as it isn’t anything I’ve seen as significant.

Thanks Sam –  this is for sewing UL backpacks, using mostly DP X-21 RC (210d face) and LS-07 (70d backing), with a little VX-21 here or there for hight wear or stress areas as needed. Using flat felled seams is preferred mostly for looks, plus it does add some strength and finishes the seam nicely too.

For UL packs (i.e. used with moderate care), a single stitch (plus second backup stitch line next to it) seems to work just fine as you said, and it’s quick and easy. On my last pack, I simply cut the excess fabric from the double stitched seams and singed the edges briefly with a torch. MLD does this with their Burn backpack (210d Dyneema-X grid) and it seems to hold up fine with minimal fraying.

Your method of binding the seam with tape (with or without seam sealing tape) is something I’d like to try. My GG Gorilla pack (70d Robic nylon mostly) uses this finishing method and it’s nice and clean and looks easy to do. But for an UL pack with material not overly prone to fraying, I wonder if binding all the seams is a little overkill?

Nathan – I’m sewing with a new Singer 4423. Most backpack long stitches are made with Gutermann Mara 70/Tex 40 with size 90 Microtex needles and 2.5mm stitch length. To get started with MYOG in the Fall, I just wanted an economical new machine that would work great out of the box. A walking foot machine seems popular for these kinds of projects, but they are pricey and there are many kinds to sift through.

Even with thick fabric with bulges to the side, I can hold a straight top stitch pretty well so long as both pieces of fabric can lay flat. However, I’m having some more trouble with the contoured side panel of my packs, where the panel edge bends to conform to the contour of the upper back or shoulders. The fabric has to be continuously pulled away from the seam to keep the seam snug while sewing, but that pulling force deflects the needle, causing intermittent seam wondering. I would be so much easier with 4 hands!

Would a professional walking foot machine really be that much different? Sounds like the walking foot would also help with thin DWR and silnylon fabrics too. It would also be helpful to have more space under the presser foot for sewing thick shoulder straps – mine barely fits two layers of fabric and webbing plus 3/16″ foam. Another thing that would be nice is a more well-governed foot control pedal. The sewing speed quickly races from zero to full speed with minimal deflection of the pedal. And annoyingly, the needle always seems to stop in the needle-up position when I take my foot off the pedal.

Lester,

Luckily, my first machine was a Kenmore  steel Zig-Zag ca. 1970.  Luckily, because it has high penetration power, and can sew really slowly.  Found a well preserved one in Northern Maine on Craigs List recently, so have a back-up.   The foot control pedal makes a sound like it is about to short circuit, but doesn’t, and you can make the work just inch through the machine or go as fast as desired.  This provides a lot of control that it sounds like your machine lacks.  A wheel on the right side of the machine gives more control of the needle also. Suggest doing a search on BPL and reading some of the older threads on machines, then bringing your own fabric to a machine store (used if you can find one) and trying some out.  Don’t know if Sears still takes old machines in for repair, but our local Vac’n Sew store does, and does it better for less.   I was almost totally self-taught, so probably do everything wrong, but have done a lot of successful projects with these old machines.  Know I will never be able to sew like a pro, and that is OK.

Maybe the DP ‘fabrics’ have improved by now, but my impression of them when they first came out was that they lack the elasticity and flexibility of woven nylon fabrics that are much easier to work with, and mold to sew into different shapes.  It is just common sense that something inflexible is going to abrade sooner than something not.  Check in every now and then, and have not seen much improvement, but maybe there has been some.  It is also just common sense that an unwoven dyneema matrix bonded in a very thin mylar and/or very thin polyester sandwich, whether talking X-Pac or Cuben, are going to present problems with expanding needle holes resulting in loose threads.and open seams.  Bonding seams was the first answer I noted on BPL and there are many good posts on threads about this.  Have probably read most of them, but none left me satisfied and was never bitten by the Dyneema bug.  It is just so much simpler and easier for me to work with nylon fabric and quality thread.

And as for advantages, the first Xpac I bought that was under 3 oz. leaked like a sieve. Didn’t even have to obtain an HH test, water just pushed easily through it.  Whereas some of the better nylons, like Robic, have great potential if finished with a quality HH coat, and are so much easier to work with.  And I think they will last.  Made a pack from 4.8 oz. spectra gridstop nylon in 2007, and it has proven indestructible.  The coat is starting to wear a bit, and could be better, although it is much better than the coats on the Dyneema gridstop that  is availalbe from various sources these days.  Maybe those ultra thin sheets of mylar on Cuben and Xpac are better at waterproofing, but the evidence to the contrary on this site is troubling.  Now that Roger is making packs of the laminates I’m encouraged to give it another try, but am not inclined to discard materials that work well and put in a lot of work pack or tent building using materials that have not proven themselves, to me anyway.

Also think it is wise to be aware that much of what we see on the internet is marketing with a lot of hype, fad-chasing, and BS.  But it is encouraging to see young people thinking critically and learning how to ask the right questions these days.

Sam, I would absolutely encourage you to try DP laminates again if it’s been over ten years.. Not sure what sub 3oz material you’re referring to, but for packs I think using a 200 denier or higher woven nylon base is a good starting point. Im happy to send you out a yard of X21 or V21 to play with if you’d like.
Yes, Cuben has stitch hole elongation issues because it is nonwoven, but DP recreational fabrics use woven nylons as a base fabric and I haven’t noticed that the stiffness that comes from mylar backing to create significant stitch hole elongation issues. I could see this as potential for lighter materials say sub 70 denier base.

I personally find the stiff hand of these materials a real pleasure to work with as they hold creases well. I also have more trouble with slippery silnylons under 40 denier than I do Cuben fiber in sub 1oz weights.

YMMV

As a disclosure I have made over a hundred packs from Xpac laminates and also sell the material.

Nathan,
Re: “but DP recreational fabrics use woven nylons as a base fabric”
& “haven’t noticed that the stiffness that comes from mylar backing to create significant stitch hole elongation”

Thank you for sharing some of your experience with the DP materials. The first one I tried was around 5 oz with a V prefix, and the second just below 3 oz with a T prefix, both less than 10 years ago. Both had a thin, woven fabric layer, but the layers were too thin to limit stitch hole expansion. The mylar did stiffen the materials, but it was the thinness of the mylar layers, like the woven fabric, that weakened the material at the stitch holes.

Although you as well as Roger have had good experience with these materials, I’m still concerned with their durability and water resistance in hard use compared with better nylons, particularly nylons with a spectra or dyneema grid and a high quality coating if such can be found. Sourcing for DIY is often more of a challenge than the DIY itself. Congrats to you both for mastering these newer materials.

Workng with the low denier nylons is less difficult now that they often come with a PU coating on one side that reduces both elasticity and sag a bit, but could not do it without using short, fine pins and a large foldable table made for table tennis but quite suitable for cutting fabric and laying it out for pinning.

Lester, Yes an industrial walking foot machine will change your entire sewing experience for the better. But also likely cost over $1000 new, which for some is considerable investment. I used a $200 craigslist found Pfaff 130 for years and maybe two dozen packs before a Sailrite LSZ-1 Then a proper industrial Juki  with servo motor. The Juki sews like butter through everything Ive thrown at it including 1/2″ closed cell foam with multiple layers of webbing. Control is there too, it stops when you want it to. Currently saving my pennies for a computerized barrack machine.

Sam,

Based on your descriptors, is sounds like you’ve only worked with 70 denier Xpac laminates. 200+ denier stuff is what I recommend to folks for packs.

There was at one point in the early 2000’s a Dyneema-X faced Xpac laminate. I bought some from a cottage company I can’t recall to build a pack I used to hop freight trains in my early 20’s.

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