Files and scrapers

[Dr PR]

I often see comments about using sandpaper to smooth wood hull and deck planking. Sometimes files are used to shape pieces for deck furniture and such. Occasionally someone will mention scrapers, but not much more is said about them. But files and scrapers can be very useful for shaping hulls, especially on the concave (inward curving) surfaces where flat sanding blocks are of limited usefulness.

 

Here are four tools I find indispensable for putting the finishing touches on the surfaces of a planked hull.

 

I bought the top two blades and the handle decades ago in a set, along with several more common blade shapes. I could see how the curved knife blade could be useful for cutting things, but I had no idea how the loop blade should be used.

 

The two files are fairly common shapes. The top one has one flat side and the other side is curved, forming a flattened "D" shape. I could see how it would be useful for cutting "U" shaped grooves in pieces. The flat rectangular file is useful for just grinding away material, as is the flat side of the other file.

 

But I have learned there are other ways to use these tools.

 

 

First consider that curved file. You can use the curved side to shape concave surfaces with an ordinary back and forth motion along the length of the file. But this can cut grooves into the wood if you are not careful.

 

The long curved edge of the file can also be used to cut much gentler curves more closely matching the curvature of the hull. Move the file at an angle to the length of the file, holding the edge in contact with the wood.

 

By rotating the file around its axis you can change the curvature where the cutting edge contacts the wood to match subtle changes in the curvature of the hull.

 

 

 

If you use the file flat side down, and rotate it a bit, you can change the cutting angle from straight (flat against the wood) to the full curvature of the file edge.

 

The tip can be very useful for removing small imperfections. Again, move the file from side to side, holding the edge of the tip against the surface.

 

You can see in the picture where the hull surface has an "S" curvature where it goes from a convex shape around the hull side through a concave curve to meet the keel and deadwood near the stern of the boat. You can use curved sanding blocks in these concave areas, but the curved files are better suited for working in these tight varying radius curves with neighboring surfaces.

 

 

 

OK. Now what about the scrapers? You may have seen posts about the very specialized (and expensive) scrapers used by luthiers (stringed instrument makers) and furniture makers. These often have specially prepared curved cutting edges to allow the same curves to be repeated over and over. But just about any reasonably sharp knife blade can serve as a scraper.

 

First of all, scrapers usually produce a cleaner surface with less raised wood fibers and none of the parallel scratches that sandpaper leaves in the wood. And the scraper blade can work in tight spaces where a sanding block isn't suitable.

 

A straight or square-ended blade (like a single edge razor blade) is very good for smoothing deck planking. A curved blade is useful as a scraper on concave surfaces.

 

As shown here, hold the blade perpendicular to the surface and drag it sideways over the wood. The blade will scrape material from the high spots only, bringing them down to the level of lower areas. This is especially useful where you have planks of varying thicknesses, or plank edges that rise above the surrounding planks.

 

 

 

I finally figured out how to use this strange cutting loop. By holding the cutting edge at an angle to the surface and dragging along it will make a shallow "U" shaped cut. The greater the angle of the blade to the surface the shallower and broader will be the cut. But you must use only slight pressure so the blade doesn't cut deep into the wood!

 

Sand paper and sanding blocks sometimes just remove the edges of raised planks, leaving the surface rippled with smooth surface between higher and lower planks. This loop scraper will remove the "crown" of the higher plank.

 

You can also drag it at an angle to the plank length to remove small bits at the highest points. I was surprised at how useful this tool is for removing very small amounts of wood in small areas.

 

 

The trick to getting a very smooth hull surface in curved areas is to hold the surface at an angle to a bright light so low spots show up as slight shadows. I use these files and scrapers to remove material from the high places surrounding slight depressions until the shadows disappear.

 

An even more sensitive way to detect slight imperfections in the surface is to drag your finger back and forth over the wood. You may be surprised that you can feel imperfections that don't appear as shadows. And this is the way to detect slight irregularities in the curvature that are never visible. In these cases you must remove only very tiny amounts of wood while smoothing the surface. Cut a bit, feel a bit, and continue until you cannot detect anything amiss.

 

After you have used the files and scrapers to get the "perfect" surface it is best to go over it with very fine sandpaper or steel wool to remove any tiny scratches.

 

CAUTION: Be careful to avoid repeated shaping in a single spot (with files, scrapers or sandpaper) until you have removed all of the wood and make a hole in the planking. If you have a deep dent or plank edges that rise very high it might be best to add material to the low spots before you start removing the highest parts. I sometimes glue thin wood shavings (made with a plane) into low spots and sand them down flush with the surrounding areas before starting the final shaping.

 

Edited 6 hours ago by Dr PR

[Thunder]

A great and helpful article, thank you.

 

I almost exclusively use the permagrit tools for the roughing down and tools 'stolen' from wife's nails beauty kit for the finer aspects. Have a set of french curves scrapers but sometimes, although can be dangerous, i piece of broken glass as a scraper.

 

I have reground old swann mortan scalpels to make shaped scrapers but have used for making small moulding. Not sure why not occurred to me to use for the hull and decks as you describe. I will certainly be trying that. 

 

Thank you,

 

Adrian