In my shop, travishers are an intermediate tool in the seat carving process between initial shaping with an inshave and fine-tuning the surface with a card scraper. Travishers remove the gross irregularities and they do it in a hurry. They are the jack plane of seat carving.
Hold the travisher between thumb and forefinger, with your fingers as low as possible (without them rubbing on the wood you are cutting). The blade is facing away from you — travishers are usually pushed. Skew the travisher, so that you get curlicue shavings. You want to push the tool with a medium amount of speed – not too fast and not too slow.
If you want to take a thinner cut, roll your wrists forward very slightly so the back of the blade no longer touches the wood. If you want to take a more aggressive cut roll your wrists backwards slightly. However, if you roll your wrist too far in either direction you will pull the edge entirely out of the cut; having this level of control takes practice.
As mentioned above, these travishers are meant to be used in a way that gives you control over the depth of cut as you are using the tool. However, if you need to increase the blade exposure, inserting pieces of paper between the blade and the body will raise the blade. Evenly scraping the sole will have a similar and more permanent effect. Carefully filing the shoulders which the blade seats on, will lower the blade. It doesn’t take much. A single thickness of paper will have a noticeable effect.
Sharpening most tools is the same basic process. You sharpen the bevel with a coarse enough stone to be expedient. Work up through the grits to polish the surface and make a longer lasting edge. Then remove any burr you’ve created by working the burr back and forth with your finest stone until it breaks off, leaving a crisp edge. There are many ways to do this, most of which work. Here are some thoughts:
The Bevel: The cross-section of the blade is the same as a chisel: flat back, hollow-ground bevel. I sharpen the bevel with a slip (diamond, Japanese waterstone…). A 1″ wide flat diamond paddle works fine.
The bevel can – but does not have to be – polished on a felt or leather wheel. Skew the blade on the wheel to give maximum surface contact. Start with the heel of the bevel in contact with the wheel to give yourself a frame of reference. Then roll the blade towards the edge until you see a very slight feathering of the polishing compound curling up off the edge. This indicates that you are right on the edge. A heavy curl indicates you have tipped the blade too far, potentially changing the shape of the bevel and blunting the edge.
The Back: The back of the blade must be kept flat. If the back is rounded over or made convex, however slightly, the tool will be hard to control. If the back is rounded over a lot, the tool won’t cut at all. Therefore, only sharpening stones should come in contact with the back — no strops and definitely no buffing wheels. The back comes flattened and polished, so unless you run the tool into a nail, your finest grit stone should be enough to remove the burr after sharpening the bevel.