Thread: Scraping epoxy

as i'm a picture framer i have an endless supply of glass so used glass as scrapers,
but only at the end of my build.
someone i know who builds boats told me this is the method he uses with epoxy and very rarely uses sand paper, it would have been handy if he had told me this earlier it would have saved me a bit of time and not so much sanding

Your point about glass is interesting because I have found that having the traditional 'hook' or wire edge (ie slightly turned over edge) on the scraper improves it immensely - though I know some scrapers seem to work well enough without. The other problem with using something like glass is the way you have to hold it which is immensely hard on your hands when doing a big area.

I have a Stanley 91 (dedicated scraping tool) which is very ergonomic but really only good for flatter areas. My personal favourite though is a Mujingfang smoother with the blade reversed. You need to grind up the edges so they dont dig in, but I do that for cabinet work anyway.

Arron

For specific lumps and bumps a scraper can be very useful in terms of tidying up, But it is waaaay too slow when you have area to cover.

A random orbit sander will eat up the job in a fraction of the time. However there are always some areas where a sander will not be effective or there is a specific problem that a scraper will do much, much better.

One example is when there is a thick build up of epoxy glue in the wrong place .. a sander will take forever and probably cut through the adjacent wood, while the scraper will fix it in seconds. Also tight in corners and places like that a sander cannot do anything worthwhile.

If you can do it green a scraper is much more effective than doing it fully cured. So if you have a choice ... get in early.

MIK

When I was a young man I was fortunate enough to see real craftsman working on boat hulls. One in particular stood out at our local yard. Everyone stood around admiring this beauty. The old timers of that era called her a scrape job.

You see when this boat was built (1930's) they had a crew of "hull joiners" come in and smooth up the planking. The hull at this point was still raw wood, but had it's seams paid. The joiner crew would use a seemly endless number of planes to knock down the seams and high spots, then the whole hull was hand scraped to perfection.

This technique on bare wood produces a much better finish then sanding. It's also hard work. Another benefit is the tubules in the cellular structure of the wood fibers are "sheered" cleanly with a scraper, which permits the wood to breath normally and accept stain, glue, varnish or paint much better. When wood is sanded, these tubules aren't cleanly cut, but fractured and mashed into pulp. Coatings don't soak in nearly as well and rot starts faster on these surfaces.

If you ever have a chance, compare a properly scraped piece of wood next to a well sanded piece of the same species. You will instantly see why sand paper never see's the likes of fine furniture, nor Steinway Pianos during construction. They're hand scraped and have hand rubbed finishes.

How this applies to epoxy has been mentioned above. You don't want to use a scraper all over an epoxy coated hull, but it is a tool that has get benefit in many situations. On raw wood, it'll produce the best finish you can have, so think about it on bright work.

The first time you try to scrape fully cured epoxy, you'll understand why you do it green.

Richard

thanks for the perspective, guys.

Arron

One thing that hasn't been mentioned about scrapers is they're tools that you can easily make and sometimes the only thing that works well.

I've found the older I get, the more often I end up making a tool to suit my needs. I've got dozens of wrenches that have been cut, bent, had things welded to them, just to access something, often only once. This is also true of shaper blades, router bits and of course scrapers.

My last "custom" scraper was to shape the forward end of a rub rail. This rub was live oak (hard, dense, interlocking grain, rot resistant and lovely stuff) and it had a bull nose on the top edge and a chamfered lower edge. Where it landed on the bow the bull nose kind of tapered to nothing and the chamfer angled down, both because of the angled cut to match the rake of the bow profile. Most would have left this and called it done, but it looked crappy to me so I wanted to whittle it down to a pleasing shape.

The chamfer was easy enough with a sharp chisel and some hand sanding, but the bull nose needed to round over neatly, blending into the bow, rather then just terminating at the bow. I had an old, bend scraper blade that I ground a slight hollow into. I used this to work down the bull nose until I needed more curvature, so I ground some more out of the blade. With this freshly shaped scraper I was able to pair down the bull nose to match the decreasing size of the rub as it met the bow. A sander wouldn't have fit without also tearing up paint on the hull, no power tool that I know can make a diminishing radius round over, nor any hand tool that comes to mind that would do a nice job of it.

In short, these are easy things to make, assuming you have some nice grades of sheet steel laying around the shop. Putting and edge on them is quick and reasonably painless with just a little practice. Most importantly of all, with careful use, you don't need any additional finishing after the scraper has done it deeds, just move directly to coating (bright in this case).

Everyone that plays with wood should take a sharp scraper to a raw piece of mahogany, teak and softwood of some sort, just to see what happens to the surface after a few strokes. Teak looks so nice after a good scrape that you'd hate to apply any kind of finish to it. Mahogany takes on a luster that just has to be seen and softwoods finish better then you've ever seen with a sander.

Care to give an explanation on sharpening a scraper the efficient way? I've seen a few things over the years and have never found myself tempted to try ... bit like most yarns about sharpening blades.

Richard

There are a few things that you need to do to sharpen a blade and they're all the same. You have to "true" the edge. This means make it straight and square most of the time, though I have several that are concave or convex. Next is the preliminary bevel, which makes the cutting edge uniform, but not razor sharp. Then comes the under cut. This is the key to a fine edge. If you cut the rough bevel at say 25 degrees, then you hone the cutting edge at 26 or 27 degrees. This is the actual cutting surface. For most edged tools, you'll want to remove the curled over, paper thin portion of this final honing with a strop (leathering), but on a scraper, you don't. Also with a scraper, I just use a fine file, rather then a stone to put the cutting edge on. On all other blades I'll use a stone and strop it afterwards.

this is taken from a site i have just bough some scrapers from

Sharpening is not difficult

Sharpening, or burnishing, a scraper is actually a simple process. It takes a little trial and error to create a usable burr, but you have to learn it only once, and there are a few basic keys to success. Without a squarely honed edge to start with, for example, you won't get a razor-sharp burr later.

Whether your scraper stock is square or curved, large or small, the sharpening technique is the same. The first step is done on any previously sharpened scraper but should be unnecessary for a new one. With the scraper lying flat on the bench, the burnisher is forcefully dragged back and forth to flatten the previously turned burr.

The burnisher is made of hardened steel and ideally should be free from nicks and polished to a mirror finish. Burnishers come in a few shapes and sizes. I prefer a cylindrical shape with a conical point, but I believe it's no longer available. These days I suggest the triangular style that tapers to a point.

Levelling and honing the edge -- The next step is to place your scraper in a vice with the edge to be sharpened parallel to the bench top. Draw-file the edge using a mill file, directing your strokes along the length of the scraper. Hold the file at roughly a 45° angle in the horizontal plane. Give thought to filing the edge straight along its length and square to the sides.

Honing the edge follows. This achieves two things: It removes any file marks and brings the edge to a polished surface, square to its sides. Honing and polishing are done on three surfaces: the narrow edge and the two flat broad sides. I suggest starting with a coarse stone to remove file marks followed by a finer-grit stone. The finer these surfaces are polished, the sharper the edge.

To joint a scraper's edge, first level the edge with a mill file (right). Hold the file at about a 45° angle to the direction of the cut. Take care to keep the file square to the work through the entire stroke (below left).
Then hone each surface (below right). Start with the thin edge of the scraper, moving from a coarse stone to a fine one. Then lap the sides flat.



Burnishing
At this stage the scraper is placed back in a vice with the edge to be burnished parallel to the top of the bench. Begin by drawing the burnisher across the edge, holding the tool at a right angle to the sides. Start with light pressure and increase it with each pass. This flattens any scratch marks left on the surface, again helping to achieve a sharp edge. After four or five passes at the 90° angle, tilt the burnisher slightly for the next pass, which compresses the corner, mushrooming it out along the edge. Do this to both sides of the edge, creating two working burrs.
You might ask what the correct angle is for the burnisher while creating the burr. Think of it this way: The greater the angle of the burnisher, the more you will have to tilt the scraper to get it to cut.
Your burnishing should be firm enough to feel a distinct edge on the scraper. If the edge gets rolled over too far, it can be straightened to a better cutting angle by placing the point of the burnisher behind the burr and dragging it along the inside of the hook, bending it back to a more pleasing cutting angle. This is why I prefer a burnisher that comes to a point.

Thanks for reproducing that Richard it de-mystifies scrapers a lot.
In my trade we use small curvy scrapers, made for all sorts of specific shapes, but I was taught a different method of sharpening. For these we sharpen and hone the (curved, but not necessarily curved) edge just like you would a chisel or knife, maybe paying particular attention to the back of the blade, getting it flat and shiny, then burnish a burr by pushing the edge over a bit. So you only have a single edged tool, not double like in the method you outlined. That means you go back to the burnisher more often, but that's no big deal.
This method also means that you can use many edge tools as scrapers in a pinch; I often resort to an old plane iron, as long as you remember to reset the edge before you plane with it again!
To make special scrapers I prefer little sheets of Swedish steel made for the purpose and easily available through guitar part suppliers (like Stewart MacDonald in the US of A) These can be cut to any shape you need with tin snips or whatever, cleaned up with a linisher or sander, then the edge sharpened on one side for my method above, or squared for the method you outlined. Being flexible, they can be bent slightly in use to give a comfortable 'angle of attack' for the edge, slicing a little instead of pushing.

Because the edge is generally longer and finer, this method is better for fine work, but the square edged ones are sturdier for aggressive work. (in my humble opinion)

Alternatively, for burnishing, use one of these. I can recommend it - quick and idiot proof - and I dont feel like I'm about to slice my fingers.

Not really great for scrapers with a radical curve, though.
Arron

Your method sounds much like mine Rob. I don't bother with double edged tools, preferring the fast and easy straight edge (or curved) that's been rolled.

Par, another little trick for a special finish I love is burnishing the timber after scraping, with (and this is a trade secret so don't tell anyone) Egyptian Horsetail grass. This stuff looks like a certain other greenish weed but has another, altogether different purpose. It is full of silica, so it abrades and burnishes all at once. I don't know if you've ever gotten itchy from rolling in the grass (for whatever reason) but it was from the silica (glass)on the leaves of the grass. Particularly couch grass. This horsetail has been used by guildsmen of several kinds for over a thousand years, although hardly ever in the last two hundred. I import the stuff in 2kg plastic bags and they are always checked by Customs, with a little note from them included. Anyway, it helps get a mirror-like finish before any coatings go on and it helps refract the light around the grain of the timber and the layers of varnish. The technique was brought to Italy from Byzantium before the renaissance. Sorry if I waffle on, just love traditional things...