Saturday, April 9, 2011

Profiles greater than 60 degrees, etc.

When I was just getting interested in hollows and rounds I read an old Fine Woodworking article that shows the exact opposite of what I teach. The author shows that a round plane is started on a chamfer and a hollow starts on an arris of a rabbet.

Chris Schwarz demonstrated this second method for cutting cavettos (coves) on his blog yesterday. Take a look because it's fun watching people work and because there is more than one way to get from A to B. Chris learned to stick moldings this way and has stated that he has much more success starting on a chamfer than with a rabbet, as I illustrate. You can't argue with success in 5 minutes and that's all that matters.

To the point: in the comment section I had a brief exchange with a woodworker that pointed out a few mistakes that I have made with my illustrations on my blog in the past. I know I've done it, but always thought that my writing would supercede my poor illustrations. (note: I look at woodworking magazines more than I read them so I apologize for assuming the opposite of you.) In the picture frame in this link the chamfers I used were smaller than what I illustrated, but at the same angle.

Let's look at cutting a profile greater than 60 degrees...

But let's first start with a simple 60. When cutting a 60 degree profile the inset corner of the rabbet created can fall nearly upon the finished profile. The reason for this is because the plane will never get rotated. It starts and finishes on the same angle. As the profile progresses the plane will sit in its own profile at all times.

When cutting a rabbet greater than 60 degrees, in this case 90, the single rabbet cannot be upon the finished profile. The round will register upon the two point for the first cut, but not the second. You will have to rotate the plane immediately and then the round will only touch one point, which goes against everything I've taught.
In this situation you have a few options. The first is to start out with a rabbet that is much smaller. Plane down to the level of a single full with shaving, and then start rotating the plane.
In this situation depth and progress can initially be gauged off of the disappearance of the rabbet and then the size of the remaining fillets (the vertical and horizontal flats).

The second method, which is definitely recommended for larger profiles (for me starting around the size of a #10), involves cutting multiple rabbets. With this second method the vertex of the rabbets can again be placed nearly upon the finished profile and much more of the waste is removed.
As the profile progresses the plane will eventually have a surface against which it can register. Then it's just a matter of going to the finished profile that's been drawn on the ends.

As the profile gets bigger, the number of rabbets should increase. The problem that will arise is that as the number of rabbets increase the way that the plane is influenced by the points it follows becomes more difficult to calculate. Calculating this is time wasted. So...what is there to do with errant rabbets made in the name of '5 minutes'? 
The round is not headed in the correct direction in the second picture above. Recognize this mistake early and correct it with a rabbet plane if you have difficulty steering. (note: I am often asked about rabbet plane width. I use a 7/8" for nearly everything...except this. This is when I use my 5/8" because it's smaller, easier to see and easier to fit.)

Then get back to work.

This applies to the chamfers used to guide hollows too.
You'll be on your own to illustrate this.

There are a number of ways to use hollows and rounds. Look at a few, try a few and then practice. You'll find one that works for you. It may even be a combination. I never chamfer before using my #2 or 4 hollow, regardless of what I illustrate.

With the exclusion of mortising, the way you learn a skill or achieve early success is usually the way you'll be most successful. If you are efficient and accurate you are set. There is, however, always a better way to mortise by hand and it's safe to say that it's not the method you use so stop it, abandon it and find another yesterday.

No comments:

Post a Comment