Sharpening Floats

Floats, like most edge cutting tools, will need periodic sharpening to get optimum performance.  While our floats will cut out of the box, we would suggest an initial sharpening.  Here is the process for doing so. 

We will need a simple, shop made fixture for holding the float while filing. A scrap of wood about 10" long with a shallow 1" wide rabbet works well. The step is about 1/16" deep.
A 5" or 6" double extra slim taper file will be needed. This one is made by Bahco and is available from Lee Valley.

The fixture is clamped in a vise at a comfortable height for filing.  We are using a patternmaker’s vise with the jaws rotated to obtain more height.  A parallel clamp mounted in a bench vise will work just fine also.  The float then can be held in the fixture with a spring clamp.  The far side of the float should be pressed against the step in the fixture. 

The far side of the float is against the rabbet in the fixture. Filing will need to be done on a slight angle to match the angle of the teeth of the float.
Ready for sharpening.

On a new float, we want to file the entire cutting face and front edge of each tooth.  The float may have distorted slightly during the heat treat process, and often when filing there will be a hollow behind each tooth.  This does not need to be cleaned up entirely as long at the front is sharp.  File with long, smooth strokes and light pressure. Adjust the position of the file up or down and left or right based on where it is cutting.  We want each tooth to clean up as evenly as possible.  Be sure that both the top and front of each tooth is cleaned up.

Hold the file with both hands and make smooth, long strokes.
The first few teeth have been sharpened. Note the hollow area that did not clean up. This is acceptable because each tooth edge has cleaned up nicely.
On push floats, the front of the first tooth also will need to be filed.
Edge floats are clamped directly in a vise without the need of the fixture.

After the first sharpening, we will need to use a machinist layout fluid in order to see where the file is cutting. Dykem is a popular brand of fluid.  It can easily be removed with alcohol.

After several sharpenings, we will want to joint the float.  This process reestablishes the height of the teeth to make sure they are all the same.  First, coat the teeth with machinists layout fluid.  We will then draw file the length of the float using a single cut bastard file.  Draw filing means to hold the file perpendicular to the float and drawing it along the teeth toward the end.

Continue to do this until all the teeth have the layout fluid removed across the cutting edge.

Draw filing. The float is being pulled away from the handle of the float in line with the clamping fixture.
Draw filing is complete. Note that all the teeth have been dressed at the cutting edge.

After draw filing, recoat the float with layout fluid and sharpen as usual until each tooth is cleaned up up to the cutting edge.

Final sharpening after jointing.

Sharpening should be done when the performance of the float begins to suffer.  Often, it will start to chatter or only produce dust rather than shavings.  Push floats tend to dull on the first tooth before the rest of the teeth because that fist tooth does the bulk of the work.  Experience will tell you when it is time to sharpen.

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