Wednesday, December 19, 2007

Guest Blogger Elia Bizzarri

Here is an image of the finished volute carving. I hope the series was of benefit. I'll describe the gouges I used next.




The next section is by Elia Bizzarri. He is looking for feedback on his essay about reamers. Thanks for taking time to reply here or directly to Elia at www.handtoolwoodworking.com. Elia is a great resource as a chairmaker willing to supply the rest of us with good tools built correctly for the trade. So here's Elia,



I have tried write a non-biased look into the pros and cons of two common tapers used for leg to seat joints in Windsor chairs. That said, I have had a hard time finding many advantages for eleven degree tapers. I would love to hear from anyone who uses eleven degree tapers regularly or has any other comments on this article.

6 degree versus 11 degree tapers

I personally prefer six degree tapers for a number of reasons. Shallower tapers makes a stronger joint because when the joint is driven home it locks tighter, and takes more force to remove, than a similarly sized joint of a steeper taper. Shallower tapers should also theoretically be stronger because the difference between the smallest and largest diameters of the tenon is less; when the seat changes thickness with changes in moisture content the mortise will try to pull away less from the sides of the tenon. All this can be taken too far as shallower tapers are more likely to split a seat during assembly than steeper ones.

Taking this to the extreme, why not use cylindrical tenons like those on the stretchers and spindles? Assembly is easier with tapered joints and the tighter the stretcher joints in the undercarriage the more this will be noticeable. When using hand tools, it is harder to bore a hole at the correct angle then to drill an approximate hole and then ream it perfect. Tapered joints don't squeegee glue off the joint the way cylindrical ones do, thought admittedly this is a minor issue. However, one oft mentioned advantage of tapered joints in my opinion does not hold water; that tapered joints get tighter from the weight of the sitter. A joint is allowed get tighter only when that joint fails and our goal should be to make a joint that will not fail because it is tight to begin with.

Aside from issues of strength, six degree tapers are easier to use than eleven degree tapers for several reasons. Less wood to remove from the mortise means the reaming process goes faster. Also, the reamer is less likely to get started at a drastically incorrect angle because narrower tapers have more bearing surface on the cylindrical hole.

On an aesthetic note, I find that six degree tapers allow me to slim down the turnings where they enter the seat making them less bulky. However, eleven degree tapers tend to be smaller where they come through the seat making the joint less obtrusive.

7 comments:

Jean-Francois Theoret said...

Hello Pete!

Just wanted to thank you again for all your lectures (the knuckle carving information is enlightening). Your blog entries are always read from A to Z (most often more than once)! Thanks a million for your generosity.

I really appreciate them all, and I know I'm not the only one.

Jean-Francois Theoret said...

Hello Elia!

Thanks again for the great tools you built for me last year. I have been a 6 degree convert since my visit to Curtis' shop!

If I may suggest, people might want to have a smaller reamer too (w/ 6 degree taper). I built one for reaming arms.

Keep up the great work!

Anonymous said...

Hi Elia, I bought the emhof reamer and used it once. When I went to Curtis' I bought your 6 degree reamer which I use almost daily. I use the smaller 6 degree reamer for the arm joint and also to taper the holes through the arm where the spindles pass in a sackback or comb back. They are really easy to sharpen (like a scraper) and my angles have been near dead on. I dry fit a leg in a seat using the 6 degree and have customers try to pull the leg back out. To there surprise they can't do it until I tell them to twist it out. Thanks for a great tool.
Greg P.

greg said...

I haven't tried a 6 degree taper, and I really do want to one of these days- but I have the following concern:

What about the aspect of fine tuning for a given length? Say you're trying to get your arm to be exactly 10" from the seat by reaming the hole in the arm. Wouldn't a 6 degree taper be more sensitive than the 11 degree one, making it more sensitive, and hence easier to go past your mark in this instance?

Like I said, I have no experience with a six degree taper so I don't know if this is a factor or not.

Elia said...

Thanks for the compliments. It's good to hear back for people who are using the tools.

Greg, you are correct that the reaming process goes faster with a shallower taper. Once you get used to it, I haven't found it hard to nail the depths of the stumps, arms &c. One advantage of the scraper reamer is the agressiveness of the cut is adjustable (there's an article on my website about useing the reamers).

Elia

Anonymous said...

Hello Elia,

As you know, one weakness of the dowel joint is the end grain to end grain glue areas. Is it possible that the 11 degree taper exposes more surface grain to provide a better glueing surface?

- Wayne

Peter Galbert said...

Wayne,
Elia is traveling this month, but I'll ask him to respond when he gets home. For my 2 cents, I can't imagine that the small gain in surface area could cancel out the fact that the 6 degree taper locks the joint better, as well as the other advantages. But of course, to each his own!