Making a Rounder Plane: Part 1

This post is part 1 of a short series on making a rounder plane.

I've been experimenting with making a rounder plane, something I've wanted to do for quite a while.  I've made plenty of round sticks for various projects, typically using hand planes.  But there are times when I want more precision.  That is, I want more consistent cylindricity, er ... cylinderness, er ... cyl ... (oh, what the hay) roundness.

I have some homemade tapered tenon cutters from projects where a round tapered mortise receives a round tapered tenon.  I wrote about making these a few years ago.  The taper was created using a tapered reamer with 6 degree included angle.

This one, sans blade, tapers from 15/16" to 11/16"

Here's another, with iron affixed, with smaller diameter of 3/4"

You would think that if you keep working a tapered tenon through this cutter, when the stick gets to the small end of the tapered hole, it'll come out the other end a cylinder, and you'd be right.  But that cylinder is not anywhere near as nice as I would like.  The surface can be very rough and the stick might not come out straight.

There are some things you can do to help this along.  The first is to feather out the far end of the iron.  In the top-view picture below, the iron is bedded bevel up.  The arrow points to where the edge starts to angle back.  This makes a HUGE difference in the smoothness of the dowel being made.

Arrow points to where the edge starts feathering out

The second thing that helps is to have a backing piece with a hole the diameter you want your stick to be.  In the photo above, the red oak piece on the left is attached to the tapered tenon cutter with screws.  Its 3/4" hole is aligned with the conical hole in the main tool.

Here's the backing piece from a different angle

This backing piece helps form a straight stick.  In some other experiments, I created a round end on a stick, but the round end was at an angle to the rest of the stick.  Because the entrance hole to the tool is larger than the exit hole, it's easy for the stick to be aligned at an angle to the central axis of the tool.  

This entrance hole is nearly 1" diameter.

When the tool is used on a stick that is held in a vice, you can't see whether or not the stick is aligned with the central axis of the tool.  Without the backer piece, it would be especially easy to angle the beginning of the stick.

Rounding a stick that is held in a vice

But when the stick starts getting through the backer piece, it helps it stay in proper alignment.

Finally, it helps to start with a stick close to (but smaller than) the diameter of the entrance side of the tool.  This helps to keep the stick aligned with the conical axis so that you get a straight stick of consistent diameter.

Having figured out a few of these things, I made several 3/4" sticks from various woods.  They all came out at exactly 3/4" diameter (within 1/128" - the resolution of my digital caliper when in fractional inches mode).

A maple stick

Pine stick

An unknown hardwood stick
Yowzah!  And it measured 3/4" everywhere I tested it!

They all fit nice and snug in a 3/4" hole bored into a test piece.  I'm not thrilled with the surface finish that it leaves.  I can always scrape it smooth, but I'll have to be careful not to reduce the size of areas that fit into holes.

One thing to note.  When using the rounder with the backer piece, the resulting stick is a tight fit in the backer and it can make a dog-awful squeak in use.  Make sure to wax the inside of the holes to ease that a bit (and sometimes wax doesn't seem to help).

More on rounder planes coming soon.