Monday, June 14, 2010

Poles for A frame Tents

My concern with wood top poles is they tend to snap under high winds and heavy rain ... So I am unsure if this is due to the wood typically used or that wood poles just tend to break.
(From NORSEFOLK - Writer deliberately obscured!)

The error almost all modern day re-enactors make is to fall prey to mere ease over following the example of the Norse and selecting the correct materials for tent frame construction.

The ideal material for any ridge pole for a tent is in fact a pole. A complete sapling.
I have a smaller (admittedly) 10 x 10 frame on my tent. It uses a selected spruce sapling for the top ridge pole. This tent has been up in heavy weather any number of times over its roughly 18 year life. This includes a gale force storm out at L'Anse aux Meadows itself.

The sapling started about twenty feet long, about four inches at the base. It was cut green, de-barked and then trimmed to the finished roughly 11 1/2 feet. The thick end is about 3 1/2 inches, the small end about 1 1/2. To get one both naturally dead straight, plus without a lot of side branches to trim, I found a cluster of about 8 or 10 saplings that were growing in a tight cluster together (My guess all the product of the same pine cone. I also let the prepared timber season a full year before I used it, standing upright.

The grain on a complete sapling is naturally evolved to resist sideways force.
Modern dimensional lumber is simply NOT. Cut from ever smaller and faster growing 'junk' timber, the quality of purchased lumber has declined rapidly in North America over the last two decades. (Yes, even here in Canada where most of the USA available lumber grows in the first place.) Grain is wide (weak, less resistant to warping). As saw cut lumber, the grain is cut across , producing diagonal lines of weakness. This leads to both warping and great possibility of breakage under any kind of sideways forces.

In the Viking Age, these same tent beams would have been cut from slow growing northern trees. So very dense grains, producing great strength. This tells you right off the start you should be selecting from even lumber with the tightest grain available - the heaviest pieces.
All Viking Age lumber would have been split - not saw cut. So all lumber would run with the grain, not across it. These straight grain lines produces lumber with great flexibility to forces sideways down the length. A Viking Age tent beam might sag - but it would not break.
The shapes of the three side beam sets on the Oseburg tent frames suggests all were likely cut from saplings, then these trimmed slightly to flatten two sides (with an adze or draw knife).

The best solution to the problem of combining strength with weight on the top ridge pole for a replica VA tent is simply to do exactly what they did - one single length from a complete sapling. Any attempt to use store bought modern (pathetic quality) dimensional lumber will just not give the performance required.

As so many reading are urban dwellers, my best suggestion is for you to make friends with someone who lives in the country. You should be able to arrange to get that single top ridge pole cut and delivered at your next camping event?

I later had this comment sent to me, which I have asked permission to pass along here:

They mostly sleep in tents that would have made a Jarl proud! Giant A-frame tents seem to be the norm these days. In-period, MOST of a ship's crew would have been sleeping cheek-to-jowl inside one of these.
I totally agree with you that modern dimensional lumber is going to pot. As a budding timbersmith, I'm learning to spot the good from the bad -- and a great deal is bad these days. For those who are loath to chop down their own trees, find a friendly local sawyer (many mill lumber part-time using portable equipment) and get him to QUARTER-SAW lumber for you. You'll pay a premium for this as it wastes some of the log, but without a retail operation to support, the local fellow might have reasonable prices overall. Quarter- and rift-sawn wood doesn't cut across the grain, mostly, and is less likely to warp. For a few dollars more, many will even cut your wood to length, plane it, etc. Worth asking about if you don't have a shop.

I'm fortunate to have a friendly sawmill close by that carries the good stuff in their little showroom at fair prices. Using local second-growth oaks (which is about the only thing they quarter-saw for retail), typical board width is a mere 6-8", roughly 1.25" thick. Can't beat the grain pattern though -- the top of my tool chest is quarter-sawn oak:

Michael / Einar - Michigan

Víkingarnir úr Mikillvötnumum


Polymarkos said...

I'm glad to see someone else shares my opinion of the pathetic kindling passed off as 'lumber' these days.

I hate kiln dried pine. Hate it, hate it, hate it.

We have cut our way through so much forest, and preserved so little, this problem will only worsen.

DHBoggs said...

Type of wood is another factor. There is a big difference in structural strength and durability between oak, ash, and other hardwoods typically used in Norse carpentry and the soft firs and pines used today.


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