Arunda

[john verge]

I bought a used Woodmizer LT40 bandsaw a while back and will be selling it. I plan to reinvest the money back into my business which is contracting/timberframing. One tool that appeals to me is a jig and router set-up by Arunda.ca . I'm curious as to what people might think of this system, so any postings would be appreciated. Most of my tools consist of mafells line of timber framing tools which are pretty effective when trying to join heavy timbers, however this Arunda system looks as though it would nicely augment my current approach to working with timbers.

[Chris Hall]

In case people were wondering what it is:

A-dove-0-b.jpg (46.72 KiB) Viewed 3553 times

A video showing the system in use:

https://www.youtube.com/watch?v=7RNo0ESFsl4

[john verge]

Thanks for that Chris. The picture certainly conveys a clearer message.

[john verge]

Of course i probably won't be operating the system in the pristene swiss alps; more likely to be grinding it out in some shop somewhere or rain infused site! All good though.

[Chris Hall]

John,

I thought you were in the pristine west coast alps?

[john verge]

Ha, ha, right again chris. A few days ago i was out walking (in shorts-sorry to all those who have been locked down in the grips of winter) and as i looked over towards vancouver is. It did appear to be a pretty special place.

[Chris Hall]

Since no one has chimed in, I guess I'll do so.

I've never used the Arunda system, however it amounts to an aluminum machined jig and that's about it, so function-wise it is like a lot of jigs, serving to improve uniformity of the result and obtain tight-tolerance fits. I'm sure the jig succeeds on those levels.

I would not purchase such a jig myself as I am not a believer in single dovetail connections, except when the single dovetail is quite long, as in a sliding dovetail joint on a cabinet. I avoid the use of dovetails in timber frame work.

Why, you might ask? Maybe you didn't ask, but I'm on a roll here so i may as well rattle on...

Well, firstly, consider the two parts of the connection: you have a male dovetail, the angled sides of which are comprised of radial or tangential grain, depending, and you have the dovetail mortise in the receiving timber, the sloped sides of which are comprised of end grain.

In a 'showdown' between radial/tangential grain and end grain, the harder and denser end grain wins every time. What this means is that if the dovetail joint is actually loaded in tension, the flared sides of the dovetail male will be compressed as the timber is pulled in withdrawal. Pull hard enough and the dovetail male will crush and shear, and the connection will pull apart. That's why you will see, in Japanese timber construction, where the single dovetail is used it is both housed and reinforced with a metal threaded rod connector.

Even if the joint is not pulled apart far enough to separate, any amount of pull will compress the grain on the dovetail mail, and when the load is relaxed, the joint will be loose.

A single dovetail is also highly dependent upon a close fit for good mechanical performance, irrespective of loading. Too tight and the joint can bind in assembly, too loose and it is useless. Even if perfectly fitted though, most of the time the timbers in which the joint is cut are not perfectly dry, and if the frame sees central heating, the timber will shrink- meaning the dovetail male portion will shrink, and the fit will be loose.

The Arunda jig makes the dovetail tapered from top to bottom, which suggests that even if the dovetail male shrank, the timber could drop down slightly and maintain a good fit. The problem with this idea though is twofold;

1) there must be a gap at the bottom of the mortise so the male tenon has space to drop
2) if the timber with the tenon on it is connected to much else, like flooring, or adjacent posts, then it won't be able to drop down regardless.

What that jig promises, and delivers, is simplified assembly and consistently good fits when assembling, and those fits are accomplished without having to reference off of the dimensions of the timbers involved. But I think the long term performance of such connections is suspect - I don't think it adds up to sound long term constructional practice. Aren't people buying into timber frame buildings at least partly for the promise of solid, long term, beefy construction? Finally, the Arunda jig does not seem to house the dovetail, so even if there were never any moisture change to the wood and the joint fit perfectly, it is a weak connection without a housing. You can get away with it in furniture work, but not timber framing.

Finally, after watching the video I have a couple of points to raise:

-don't these guys know about hearing protection?
-hogging out the dovetail female in one pass is a bad idea and is both hard on the router and the tooling.

[john verge]

Appreciate the critique. Jigs are alluring for sure and kind of hold a promise of effortless, high production resulting in the $'s just rolling in. Yes, the shrinkage issue would definitely make those joints look less than appealing 2 to three years down the road and although housings are primarily for structural purposes they do often help to hide the shrinkage issue.
I noticed that a lot of european material is glue laminated thus making the material less prone to shrinkage and as a result these connections might be more suitable here. They sure know how to market well though, we could really take a page from their book. I half expected that router to produce wings, fly to the stick and run itself.
Here in BC where we are waiting for the big one to hit, i hate to even speak it, would probably do well not to employ such connections, but if we did, not doubt they would also recieve a heavy dose of steel fasteners and then what would be the point of the exercise you might wonder? Just for fun i'll run the system by an engineer and see what the commentary is, and will post it when that happens.

[Chris Hall]

I noticed that a lot of European material is glue laminated thus making the material less prone to shrinkage and as a result these connections might be more suitable here.

That's a very good point. Still, I would choose other forms of connection in most instances though.

Engineers, you will find, will generally prefer glue-laminated stock to solid wood, but some customers do not. One happy medium is to face the glue laminated material on all four faces so it presents an appearance very close to the solid timber.

[john verge]

I believe my take n ess ( cool word i thought) with the jig system came out of a place of need for speed. The competition with the handworkers and the cnc-ers is heating up. It would appear that a blend of the two approaches might be closer to the answer; much like many woodworking shops i would imagine.