Tunnel Tents Tutorial and State of the Market Report – Part 2: Details and Commercial Models

Curved parts of bicycle frames and especially forks – given their price, I think a lost-wax process is likely. OK – a lost wax process is the only way I can possibly imagine!
Any parts which are straight and tapered can be done on a steel mandrel of course.

Cheers

I can think of a few different ways you could remove a curved mandrel. Wax or polymer that you could melt out as suggested already; some sort of inflatable tube; a material that has a sufficiently different coefficient of thermal expansion from carbon, (perhaps aluminium?) that could be heated and then cooled (or just cooled). Basically anything that can be made even just a little bit smaller so it'll slide out.

The more I think about it the more I think an inflatable bladder would work well. At high enough pressure it would be solid enough to form around and then you could just deflate it and remove it.

Hi Jeremy

> I think an inflatable bladder would work well
Well, yes, but what do you make the bladder out of, so it does not burst and it holds its size at the very high pressures needed? Sounds a bit like Unobtanium to me, but I am very open to suggestions.

Chilling aluminium down to -40 C might work. Wonder what that does to the CF and the plastic or epoxy?

Cheers

The author expresses concern about the Stephenson Tent having only one rear stake. We have two tents, 2R for high cold climbs and the 2X for light backpacks. Both have side window ventilation. The 2X weighs just over 2 lbs.

Our Stephenson Tents have been used more than a hundred times over the past 30 years on many of the highest mountains and never had a pullout of the rear stake. It is a case of using the right stake for the job. Even with two stakes, if one comes out a tent will not be stable.

Normally, we use an eight inch tubular aluminum stake. It holds well in everything but rock and snow. On high altitiude climbs in snow, we often use an ice axe. On Aconcagua we used nothing but large rocks (over 70 lbs.) for the entire two week trip. We have experieinced winds up to 85 mph and snow storms up to 6 inches in our Stephenson tents without difficulties.

During many base camp discussions, others have expressed that they had heard that the Stephenson does not have enough guy-outs, stake down points, it doesn't offer enough ventilation, etc. All these comments have seemingly come from those who have never used a Stephenson tent.

Hi Tim

Your comments are welcome. Yes, 70 lb rocks and ice axes are a bit beyond what I was using for the rear stake, and yes, they would work fine.

I remain concerned about the quality of the sewing, as illustrated, the lack of any real vestibule for cooking and gear, and what was for us a distinct lack of 'living space'. The last is of course a personal preference.

Cheers

Clearly you have a good understanding of tents. I hope no one takes my comments as critism of other tents discussed in the article. I can only speak of tents that I have used.

I was concerned about the sewing of the Stephenson tent as well when I first bought my 2R which was in the 70s. I have always tried my best to treat ultralight weight gear with great caution, and I never have had any seam failures with either tent in more than 30 years of hard use. My son also uses a 2X with no seam problems.

Regarding, a vestibule, we were always able to cook in the front part of the tent that Stephenson refers to as an attached vestibule. When weather was better, we cooked just outside the entrance or with the door clipped open. On miserable nights we risked cooking inside with the door closed. Cooking inside is always a risk. People have lost their tent in seconds due to fire. Check out the Wilcox disaster on Denali in 1967.

Room is another issue. The square footages of floor area for the Stephenson tents are higher than most tents on the market. We often slept three in the 2R when weight was a major issue (about 1 lb. per person). The 2X tends to get damper on the inside due to condensation than the double layer 2R so we always limited it to one or two people so we did not touch the sides.

The 2X tent is a bit lighter than the 2R because it does not have the liner. Also,on the 2X I use the smaller 3/8" main pole instead of the 5/8 " pole (saves about 3 oz.), a shorter version of the tent (saves a couple more oz), 2 titanium stakes in front and one 8" in the rear (another oz), and no stuff sack (two more oz). All in all for a tent that is so light and can withstand severe weather, I really like the Stephenson.

So was the workmanship as utilitarian back then, or "better"?

I purchased the 2X about 10 years ago. My son purchased his about 15 years ago. I did not notice much difference in construction quality of the 3 tents. All of the tents were hand made in the USA and looked like home made tents. I can not speak for todays quality.

Just going off the photos Roger posted as part of the mini-review… does the workmanship look significantly different?

I pulled my tents out and took a look at them today. In general, the workmanship is better with straighter stitching than the photo in the minis. However, mine don't look like works of art. Maybe, by experience, they are art that works.

Stephenson has a long writeup on his site about different types of stitching and their inherent strengths. I can say that Warmlite has been very helpful with any questions and they are supposedly good with guarantees. I think that good seam sealing also helps keep threads from coming loose or tearing the fabric.

I have poked holes in my fabric, damaged the end of a pole and worn through some of the fabric where the pole inserts into the sleeve. All of these things were repaired at home with hand tools, urethane or silicone, and stitching. It is good to carry some extra fabric, thread, silicone for sil-nylon, and a muti-tool. I have never had anything happen during a trip that prevented me from setting up the tent properly.

I hope you don't think I am sounding like a saleman for Stephenson, but they make a 3R model that has sitting room at both ends and more ventilation. It is massive inside with some additional weight. On many trips and sometimes sitting out long storms, we have never complained about sitting up in the 2X or 2R unless there was three of us.

Hi Roger,

Just how pressurised would it have to be? Seems to me an inflated bike tube would be sufficiently stiff and strong to lay carbon fiber around, and they aren't exactly made from exotic materials. But on second thought I think creating a custom-bladder out of rubber or whatever would be a bit complicated, but you could easily create a mould for CF out of this stuff:

http://www.plastimake.com

It melts at 60 degrees C and sets hard and strong, pretty sure CF can handle that sort of temperature.

Good question, but …

You are trying to replace a steel mandrel which has CF cloth wound aroung it tightly and then it is wrapped very tightly with PE tape before thermal curing. I dare say a bike tube might withstand the compression if inflated hard, but what diameter would it be when inflated hard withough the constraint of a tyre? And how do you keep the exact curvature you want for the specs? Remembering all along that you are trying to make a tube about 8-9 mm OD.

I'll pass on the problem of finding such a curved tube to start with.

Cheers

Yeah, I am with Roger. I do not believe the the presurized rubber version would quite work. A lot of good thought, though.

As for the requirement that the poles be 8-9mm, I question that. Larger poles could easily be as effective, perhaps more so, in a prebent configuration. As light or lighter, too.

A simple lost wax process is by far much simpler. A split mandrel could work, too. But, you loose some strength over steel mandrels, again, not a big deal. I would guess some designed in curvature will be lost from internal or external forces on the tube. Process design would be different at any rate.

Anyway, carrying curved tubes is not as neat as straight tubes. I would again bring up the Dyads curved tubes which are a bit awkward to pack. Shorter sections of precurved poles also pose an interesting problem of assembly in the field. Like the Stephensons tents they could be placed in odd arrangemens, not at all conducive to sliping through the sleeves…

Well, as I said, on second thought I don't think a pressurised tube would be that effective, but you guys both seem to have missed the second part of my post about the Plastimake stuff, which has a glass transition temperature of 60 degrees C. It would be relatively easy to use this stuff to wrap and set carbon fiber around, and then it would melt out at less than 100 C – a lost wax process I guess but even more effective than using wax?

Hi Jeremy,
I don't think that 60C will have much of an effect. Actually, I don't think that 100C will have that much of an effect. Epoxy is quite rugged. Note that not all would be suitable, though. Nor would all survive steam heat. Anyway, a production problem easily sorted out. Some of the epoxy will stand up to 200C (~420F) easily. circuit boards for instance, used to be floated over liquid solder.

Generally the layers are taped together, along with thermoset epoxy. Then the whole thing is baked for a time. Untaped and de-cored for further processing. The tape usually shrinks a bit applying a tight compression, squeezing excess resin out. This is used for fishing rods where a taper is desired. Fairly easy as it sits. Short lengths are much easier than long lengths. A largish machine can make the whole thing go much faster…continuous. Used for arrow shafts and other mostly "extruded" type pieces. The fabric is usually wrapped, usually hi-linear layers and "square" type tapes and cloths. Varying the layers can achieve your desired result…lots more to this, but in general. High pressure is used to force the resin in and to force the fibers into close proximity to each other.

There is no real constraint to making individual curved pieces for poles. Indeed, one of the problems is getting them straight. I believe that with the low temp plastics (a lot of different types besides the one you mention) the problem would be lack of internal compression strength. The plastic would soften slighly and not be stong enough to support the internal fibers very well in the setting phase. So, you end up waiting…up to a week for many epoxies at room temp. (Though it seems hard after 4-6 hours, the chemical process will continue up to a week till maximum hardness and strength is reached.) The longish lead time will cause some problems in manufacture, supply, storage, etc. Really not conducive to mass manufacture, cheaply.
This is just one manufacture problem, not insurmountable…but costly.

Lost wax is a process using some material (it doesn't have to be wax) that when heated, runs out of the object. It actually started hundreds of years ago, for metal casting (bells?) hence the name.

Hi James

> This is used for fishing rods where a taper is desired.
Dunno about CF fishing rods, but I do know that many fibreglass rods start parallel and are ground down into a taper. Easy to do on a production basis.

Lost wax for curved CF poles? I suspect the wax, or Plastimake, will melt during the epoxy curing process. Um – well before the curing has got very far. Tricky.

Cheers

Do you have to heat-cure carbon fiber poles? I was under the impression that some of the resins used could be air-cured.

Yeah, there are lots of epoxies out there. I was thinking of quick process stuff that requires *some* heat, though. WIthout heat you probably couldn't create a continuous process. Once it is fairly well set, you could cut it and increase the heat melting the mandrel out and finishing the cure. Anyway…just thinking out loud.
As roger says, tricky, but doable.

Roger,
No, Fishing poles are NOT made by grinding them. (Well maybe old ones were.) They use quite fine mandrels, wrapped.Tips are often solid, though.

I think the problem might be finding a pre-preg with the right epoxy to handle the temperatures. Not a big range available commercially.

> Fishing poles are NOT made by grinding them. (Well maybe old ones were.)
Yeah, well, I admit I was talking about Jarvis Walker rods from the 60s and 70s. That was then.

Cheers

It seems to me that making a thin hollow bent CF tube requires a flexible Stainless steel wire inserted into flexible plastic tubing. The tubing ideally needs to be slightly stretched (ie increased in diameter), by the wire. Once the CF is set, removing the wire will allow the tube to shrink to its original size. Further, pulling one end of the tube causes it to shrink still further allowing it to be removed.
A few points:-The tubing needs to be sprayed with a release compound, I am trying silicon lubricant.
The curve of the wire/tubing can be set by clamping each end the required distance apart and allowing it to hang free giving space to wrap the CF around it. Very tight bends not practical.
Strongest results would be to use two layers of tape wound diagonally in reverse directions.

I am trying this out and will (hopefully) advise results. :-

Roger, I finally got around to finishing this- thanks for writing it. I as many here wish I could get a hold of one of your tents.

Congratulations on finding a way to bring these to market !

Can't wait to see some at the 2015 GGG.

Congratulations, I had no idea REI had these in stock. It’s huge, sub 30 lbs, has room for pillows, safe to cook inside of, room for a massive pack, all the things important in the Australian bush. Tired of waiting ? buy now