DCF X-Mid Clone

[Eric Blanche]

Great post Stumphges! I concur with your thoughts and statements regarding “deformation” near tieouts for dcf mids. More noticeable with the lighter weight .5oz dcf as well in my experience.

 

Maybe I am in the minority here, but what kind of life expectancy does everyone here think they should be getting from their tents/tarps?

[Jerry Adams]

“In my opinion, this type of construction would be stabilized with the application of ~1 inch DCF tape (typically available in thickness equivalent to 0.8 DCF) to the underside of the ridge seams. Reinforcing all the seams this way should provide dramatically improved dimensional stability with very little weight increase. Doing all the seams on a Duomid-sized shelter might add 1-2 ounces.”

That’s sort of what I’ve done on silpoly mid

Ridge seams are on the bias.  So they stretch a lot.  In the wind the tent flaps.

I don’t know if there’s long term creep, I’ll have to think about that, but there’s short term stretch

I just took a 3 inch strip of fabric.  Fold over to make a 1/2 inch wide, 6 layers, along the grain.  Sew to ridge.  Tent flaps less in the wind.  I think you could use a 1/2 inch grosgrain strip or some other stiff material.

I haven’t had to put up my tent in months, 60 nights of backpacking.  No rain.  Next time it rains I’ll have to look at it to see if there’s long term deformation.

[Stumphges]

Thanks, Eric. I haven’t used my DCF tents long enough to gauge life expectancy. I think there are various estimates out there made by through hikers, who probably have the best visibility of this subject.

Jerry, it was one of your earlier posts that gave me the idea of using DCF tape to stabilize ridgelines. You’d written that reinforcing the ridges with stiff material had reduced ridge deflection. I think that you could use 0.8 DCF tape (like this stuff: https://dutchwaregear.com/product/single-sided-dyneema-tape/) as a ligther option than grossgrain or similar. Expensive, but very light and stiff as hell in that orientation. Doh, I guess you’d have to first put a layer of siloxane tape on, then the DCF tape. Darn slippery sil!

I’ve also noticed that the ridges sewn bias/bias will deflect more in a mid. I have a rectangular mid in silnylon that has the four corner ridges sewn bias/bias, and the other four seams (which in this rectangular octagon are also ridges) sewn selvedge/selvedge. Here’s a photo of the tent:

The door seams are selvedge/selvedge and don’t stretch. The two seams orthagonal to them (in line with the orange apex guy lines) are also selvedge/selvedge. The corner seams are bias/bias. In the pitch shown, I walked all around the tent and pressed inward on the ridges with my palm, trying to similate the blunt force of the wind. The zipper seams don’t really deflect; the selvedge orientation of the fabric there, combined with the zipper fabric itself, makes for very stiff seams. The other selvedge/selvedge seams also do not deflect very much – a little, but not much.

However, the four corner seams deflect significantly with pressure. Now, I took care to tension those ridges as much as I could without damaging the fabric, so I’m not certain how much of that deflection is actually coming from the ridge seams proper. I suspct that the bias orientation of the panel fabric adjacent to the seam is actually what is stretching – the panels are stretching along their biases towards the seams, allowing the seam itself (and the panels adjecent to the seam) to deflect inward. But the seam itself may not actually be lengthening.

That hypothesis runs counter to yours, and it could be a combination of the two – some panel stretching, some stretching of the actual seam – at play. I would prefer that your hypothesis of seam stretching is correct, as that is more easily countered with stiff tape:)

 

[Jerry Adams]

we will eventually figure it out.  When we’re done with this we can move on to uniting quantum mechanics and gravity : )

Your tent is pitched with very taut sides

[Stumphges]

Deleted due to unsecure method of sharing a video:(

[AG]

nice mid. what kind is it?

[Stumphges]

AG, it’s the “Mini2″ by a Chinese company called Knot or Knot Gear, aka Ice River, aka Aricxi – Aricxi seem to be the owner of the Knot “brand.” It’s a rectangular octagon, comparable in rectangular dimensions to the Duomid or Khufu, but with an octagonal shape rather than a true rectangle. This creates two vestibules, so like a Khufu with two vestibules and two zippers. The 20d silnylon is of decent quality and quite light, making the shelter a good weight/volume proposition despite the dual zips. I would prefer a higher quality silnylon and would pay more for it, but there’s nothing else on the market like this with two vestibules and two zips.

On the other hand, the silnylon on this tent is higher quality than a larger, true octagon tent we’ve been using for family trips for three years, and that tent has done really well for us. But if I could get the above tent in the 20d sil MLD uses I would be all over and pay good money for it. And if I were to make a mid with DCF myself, I would copy this design.

In addition to the two vestibules, it is my opinion that this type of octagonal mid performs better in wind than a true rectangle. The footprint and cross-sections are larger, but the octagonal shape tensions into an elliptical cone that seems to spill the wind better. The cat cut hems look goofy, and prevent a winter-worthy seal with the ground, but they make it easier to pitch with very taut panels; one can focus on ridge and panel tension, since the tension on the hems does not need to be perfect.

The overall shape is similar to the MYOG mid described in one of my favorite BPL forum posts, here: https://backpackinglight.com/forums/topic/mid-set-up-issues-got-advice/page/2/#post-3443441

Despite the B-grade silnylon, I rate the fly highly enough that I just bought a Locus Gear Khufu Full Mesh inner for it, which cost nearly three times as much as the fly! (The Khufu inner is 15 cm wider and about 5 ounces lighter, but the inner that comes with the fly at the link above is actually excellent quality with tough 40d floor, and has two zips, though it’s only ~120 cm wide.)

To get back toward topic, I feel that this design offers something of the function of a two-pole mid like the X-Mid, namely dual zips and vestibules, but with better wind performance. The downside is that you still can’t get the dry entry of the X-Mid with this type of fly if used by two people. The footprint might be a little larger than an X-Mid, too, not sure, although the cat cut hem allows for some maneuvering in relation to rocks and stuff in the camp site, so the footprint is functionally a bit smaller.

[Stumphges]

Jerry, I have a nice video of the wind playing on that tent (the images I’ve posted in this thread are actually stills from that video) but I can’t find an anonimized way to post video online.

So below is another still from that video, showing a ~30 mph gust pressing into the near corner seam. I’d purposely pitched the mid broadside to the wind to study this bias-stretch corner issue, so the wind is having its way with that corner seam.

To my eyes, it looks like the seam is hanging in there, but the panel fabric adjacent to the seam is stretching on the bias and deflecting quite a bit.

I mentioned above that I also have a larger, truly octagonal tent by the same company. I have not observed this seam behavior with that tent, and I think this is the reason why: I think that radially symmetrial mids are very easy to tension such that the stretch is “pulled-out” of the bias. One reason I think this is because that larger, true octagon mid, does not sag in the cold and wet. This smaller, rectangular octagon does sag, despite being made with higher quality silnylon with more silicone coating applied to it. And I believe the lack of sag is due to the bias stretch being tensioned out of the panels, so when the fabric expands when cold and wet there is little movement possible in the fabric, or it’s almost been over-tensioned on the bias. This also means that when the wind hits the bias/bias ridgelines, all the stretch has been taken out of the panels already, and so the panels don’t deflect as they do in the photo above.

If this is so, I would predict that a truly octagonal mid in DCF would tend to deform at the corners over time, because that shape so naturally loads the panels along their biases (i.e. orthagonal to the Dyneema filament orientation, with respect to DCF). So maybe not a great idea to build an octagonal tipi out of DCF. But this rectangular octagon does not seem to naturally load the panel biases as much, so the above design might be dimensionally stable if made with DCF, and the panel stiffness of DCF might better prevent the type of deflection seen in the photo above. So maybe I should make one of these with 0.8 DCF.

[Stumphges]

A follow up to the posts above about the Knot Min2 pyramid tent pictured. I compared its silnylon fabric to several other silnylons and I think it has too much bias stretch to make a truly great tent. Compared to the 30d silnylon used by Locus Gear, for example, the 20d Knot stuff has probably 3 times as much bias stretch. I think the design is great, price is great, and it’s a good way to try out a pyramid tent without breaking the bank, but I would not recommend this tent for expedition use, the fabric just isn’t stiff enough.

[Sam Farrington]

It seems we are conflicted by Roger’s emphasis on strength through the elasticity of silnylon and others’ emphasis on strength through stiffness, or lack of elasticity.  As Jerry suggests, there must be more to it.

[Roger Caffin]

Just so. You have to ask ‘strength for WHAT?” before you can answer the question.

Does your design need stiffness? If so then Sil/PU Poly might be the go. Ir even the old spinnaker fabric. But if your design needs the ability to handle violent weather and to snap back without damage, then (I say) sil/sil nylon is the go.

Always remember that (imho) the design may be more important than the fabric. A fine-weather design is not a high-altitude storm design. And my UL silnylon tunnel tent took 100 kph wind all night even while missing some guy ropes (they frayed on the Ti pegs in the storm).

My 2c.
Cheers

[Stumphges]

Roger, I don’t know about tunnels, but for both pyramids and domes, it seems to me that too little stiffness is obviously a problem, for if the tent fabric stretches too much, its panel will deflect too much, become concave, catch the wind like a sail, and then the wind will, if fast enough, overload the pole/stake strength that’s holding everything up.

Consider this video, which is interesting in that it appears that Nordisk sprayed the silnylon fabric with water before cranking up the windspeed to simulate the effect of rain and wind coming to camp at the same time. No time to re-tighten the fly after the wet has caused it to sag. Even at 30mph (15 m/s) the panels are starting to scoop and catch the wind; at that point the wind is not yet strong enough to overload the structure, but it already has the purchase it needs to do so. All the wind needs is a little more force, and even at 40 mph nobody could sleep in that thing.

Clearly, this tent would have done better had its panels not been saggy, but tautness would only delay the inevitable. If the panels had been taut, but made of precisely cut DCF, which is far stiffer than silnylon, would it have done even better still? And what if the little  tunnel had been made of carbon fiber of sufficient thickness to not deflect at all?

 

[Jerry Adams]

Interesting topic.  Nice looking tent at 30 MPH Stumphges.

I have a ~1975 tunnel tent from REI.  5 pounds?  I think tunnel tents may do better in heavy wind.

If you put poles on ridges it holds up better in wind but it weighs more. Like a tunnel tent.  Or you could have 4 poles for the mid ridges (or 8 for octagon).

If you have one (or two) vertical poles there’s an engineering advantage, the pole weighs less to get the same strength.  My silpoly mid weighs 14 ounces, plus 4 ounces for stakes and 4.5 ounces for the center pole.

[Roger Caffin]

Would a pyramid tent made of DCF or PU/Poly be better than one made of silnylon? That is possible. Distortion in the design of a pyramid does not look good. Yes, the fabric has to suit the design.

The testing in the Nordisk video is a bit of a disgrace imho. That is not really a tunnel tent anyhow, with only two poles, but it was pitched really poorly. There was far too little tension along the length – if indeed there was any at all. The length of the unsupported sides was huge. You need a lot of lengthwise tension in that sort of design. You could see the sides flapping in and out: that was disgusting.
Was it a competitor’s tent, with the testing designed to look bad?

We are on the shoulder of Le Brevent and the massif in the background is Mont Blanc in Europe. The tent site is a bit exposed, as you can see. There was a high wind blowing. My blue tent looks stable enough, but there was a very high tension along the length (and the side panels between poles are short). We spent a quiet night.

But note that even a tunnel tent can be made to look bad in a high wind IF you don’t have the lengthwise tension. I have a very sad video of one like that. So fabric matters, design matters, but so does pitching!

Cheers

[Dan @ Durston Gear]

Interesting thread. Did the DCF X-Mid 1P ever get built?

Regarding bias, we had a good thread on this recently in the gear forum. With the X-Mid basically all the stress is running along corner seams and ridgeline. If you do have these on the bias (diagonal to the dyneema strands) then slapping some 1″ DCF on the top or bottom will do a lot to stabilize that and avoid permanent stretch issues.

[Erik G]

Looks like I have some catching up to do on this thread!

Unfortunately I have not constructed my X-Mid clone yet, but I have ALL the materials, have the tie outs designed, and am ready to go as soon as my twins grow up… ;)

I read the thread on bias considerations – good stuff. When you say corner seams, do you mean the vertical seams or the perimeter? I’ve planned for 1″ seams at the corners and ridgeline, and 1/2″ taped hem along the bottom edge/perimeter. Certainly will be stronger/stiffer than a plain sewn hem. That plus the catenary cut along the edge should aid in reducing flappy edges. Would you recommend a 1″ taped seam around the perimeter?

RBTR took some liberties with my patterns and oriented them differently than I had planned. Original design was essentially at 0/90 deg, but now they’re…not that. I’m pretty confident it won’t matter much, but there’s not much I can do about it now!

[Dan @ Durston Gear]

The bottom edge doesn’t matter as much. If you imagine trying to extend one of the hiking poles, the height would limited by the 4 lines of tension running to the nearest 3 corners plus the ridgeline. Similarly, if you push on the pole tip sideways it’s those 4 seams bearing the load. Where the bottom edge can see strain is when wind is pushing on the side panels. That loads the entire panel so it’s pretty spread out though, and pragmatically wind speed is lower in the lowest foot or so, so my subjective perception is that forces are quite a bit lower along the bottom edges compared with the seams running between the peaks and corners.

So a 1″ taped seam is overkill IMO for the bottom edge. Just folding the DCF and sewing is probably good enough, but bonding is nicer so I’d probably fold it with a 1/2″ double sided tape. Since there are two layers and less stress, I’d feel pretty good about that but if you were wanting to make it bomber then tossing a DCF backed 1 sided tape onto the inside would reinforce the edge. I’d only do that if the bias is very close to 45 degrees and you are more worried about severe storms than saving grams.

For the seams between the peaks and corners, I’d would likely bond a narrower seam (0.5″ or 3/4″) with a double sided tape and then put a slightly wider (3/4″ or 1″) DCF backed single sided tape over top (likely on the inside for a cleaner appearance) to reinforce. You can skip the latter if the DCF is oriented parallel to the seam, but adding that DCF to higher stress seams like this is just good practice.

[Erik G]

I appreciate the feedback!

[California Packrafting]

I’m interested in making one as well. Please let us know how it goes and how much less it would be now that you have paid for the setup.

 

Thanks!

[Stumphges]

Zpacks sells DCF tape in .75 and 1 inch widths. The spec 3.8 g/meter but don’t say which width that refers to. They also don’t specify what variety of DCF is on the business side of the tape.

Conversely, Dutchwear have tape made with 0.5 oz DCF but don’t specify the weight.

For reinforcing seams that are uncomfortably near the bias, as Dan has described, I would think 0.5 would be adequate. But maybe the weight difference between 0.5 and 0.8 tape is so small that it wouldn’t matter. It might be that the majority of the weight of these tapes is actually the transfer tape the DCF side is bonded to, in which case ‘investing’ in the burlier DCF would be worth the ‘cost’ of the adhesive.

[Erik G]

Construction has finally started…

Getting pretty close! Just need to finish up a few details around tie outs and peak reinforcements.

I feel compelled to bring it to life before the X-Mid Pro! Lol. But seriously, hoping to get it done by mid-April. More to come!

[David Gardner]

Looking good Erik! I hope you’ll bring it and your family to the NorCAl GGG April 15-17! I’d love to see your tent, but even more it would be great to see you again. If you’re there by 2 p.m. on Friday y’all can take my place and ride in with the support vehicles.

[Stumphges]

Good luck, Erik!

[Erik G]

Well…It’s been a loooong time coming, but it’s finally done. Had to wrap it up in time for the arrival of the real DCF X-Mids ;) and my upcoming first backpacking trip in two years! Two. Years.

HUGE shout out to my awesome mom – I would not have succeeded at this without her. She’s an OG master seamstress and really helped me with patterns and little details. The second pair of hands was also invaluable. Love you, Mama!

Final weight including all tie outs, guy lines, and stuff sack is 13.8 oz.

Here’s the inaugural pitch:

 

 

The only stitching on the whole tarp is the tie out reinforcements to the grosgrain; everything else is taped. Just after taking these photos I finished adding 1/8″ shock cord to all the mid-perimeter tie outs and doors, and made a couple of magnetic door toggles. I got lazy and didn’t attach the toggles permanently to the tarp, and later realized I actually really like the ability to move them around as needed and they can be used for various other odds and ends like holding up a head lamp, or raising a portion of the perimeter hem to allow airflow while reducing/eliminating flapping.

It got dark before I could take any more pics (more to come!) but the peak tie outs really help achieve a taut pitch. With those and all the perimeter tie outs staked, it is SOLID.

Super happy with the results, and can’t wait to take it on my upcoming trip!

[Dan @ Durston Gear]

Wow nice job! It looks great! This is essentially a fly only right? And a 1P?

I’ve never seen zippers installed on a tent with just tape before. Interesting.

Is that 1″ tape? Might want to be a little careful with those bottom hem stake points near the center of the end walls because they look to be pulling on a bit of a diagonal up to the peak (rather than fully in line with the fibers) so they’ll work well but if you really cranked on them it could distort the material.

Enjoy that camping trip!

[Author]

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