Woodworking on the web

[Gary]

Some of these cold days when its too cold in the garage (ie shop), after viewing this nforum, I will surf the web looking of clairification and explinations of some of the things read here. Its amazing what is available.

this
was found which has more information about scrapers than I imagined existed; I wonder how much of it is applicable to the scrapers used in woodturning---Hmmm.

Some of the discussions about food safety came to mind when i saw this statement wood - a naturally anti-bacteria material


(Underdog, feel free to correct the spelling, since I freely admit to being the worlds worst speller)

 

[MichaelMouse]

Well, scrapers for woodworkers are a bit different. If you check the literature, you'll see that they are made of softer stuff than even our high-carbon turning tools, not to mention harder alloy stuff like HSS.

Having said that, I will confess to lathe-off use of a gooseneck and a spoon scraper. Mostly to get that last button off the bottom. You know, the one that rips out a divot every time you try to cut all the way to center? I have given up and gone to sanding or scraping as the best alternative. Leave it proud and scrape for a good surface.

Here's a good tip. You know what a thrill it can be getting that last part-off piece neatly blended to the bottom (or top) of things? Part it off and you're likely to twist and pit, so you saw and trim. Only problem is, you want a concave bottom so the piece will sit properly, and it's tough to hold things while you maneuver a gouge or chisel. Use one of these. That way you can hold the piece one-handed and still pare concave. This is one I got years ago for spoon bowls, but you can use a hoof knife effectively as well.

As to anti-bacterials, I dare say that if some wood like tropicals and cedars were a manufactured material, they'd have to put warnings on them about chemicals.

 

[Gary]

Thanks for the reply Mr. Mouse.
But lets look at what I percieve as the similaraties between the flat-world and the turners scrapers

• They produce the same kind of shavings
  they depend on a burr to cut
  the burr needs to be turned back
  they do not stay sharp for very long

What I'm wondering is - might some of the techniques used for sharpening, such as "squaring the edge" and honing (to get a really sharp edge) and burnishing to create the burr and then putting a hook on the burr, might give a better quality burr and hence a better result than simply going to the grinder to "raise a burr" on the scraper.

As to food safety, I think it is a given that when making items that will come in contact with food, wood toxicity must be taken into consideration.

 

[MichaelMouse]

Malleability is the first answer. A softer malleable alloy will take a burr which is finer and more continuous than a brittle alloy. Then there's the angle of attack, which you consider in two directions when scraping a board. You tilt the opposite side of the scraper forward to engage the burr, then you belly the tool to gain some shear as you push. You vary the angle at which you turn the burr to vary the aggressiveness. Big burrs for glue, the smaller (lower angle) for finer shavings. You compensate by changing the angle of attack.

Heat and force are the enemy of a good scraper edge. Heat builds fast, thinner edges don't carry it away as rapidly as thicker sections. The lathe also presents with a lot more force than you moving a scraper smoothly and slowly over a board, which means that warmer and more malleable edge is likely to deform into nothing pretty rapidly.

Then there's the problem of end grain. You can scrape end grain, but it has a tendency to grab the edge and stutter, same as when you try to scrape close to perpendicular to the rotation of your "normal" cross-grain bowl. With us, of course, the scraper is sturdy and the wood is weak, which means a less than a consistent entry angle stutters the wood. You also have two places where you are trying to scrape (actually cut broadly) against unsupported grain. Old boys used to do it, complete with turning a burr and holding the tool nose down to gain a planing angle, of course, but their standards of finish were considerably below ours. It wasn't "art" then.

Your objective should rather be to cut across the fiber on a narrower face, what we call shear scraping. Since this can also be done with a gouge, which has benefit of a steadying bevel, I think you'll find it a much more useful technique.

 

[Steve Worcester]

Malleability is the first answer. A softer malleable alloy will take a burr which is finer and more continuous than a brittle alloy. Then there's the angle of attack, which you consider in two directions when scraping a board.

You can always temper most any steel to a lower, less brittle Rockwell, that's done in the tempering stage. The other consideration is the grain of the steel. Many steels M2 and below have an inconsistent grain pattern, or grains of different sizes, so that the burr can fracture (on a "microscopic" level) and take varying size pieces with it. Powdered metal have a finer grain,I don't know if it would hold up to the small thicknesses of a plane blade. but work real well with turning tools. This is also why you are starting to see cryo tempering in planer blades and soon it will be the big thing it turning tools. It will allow a more average steel to maintain a burr longer.

To cryo temper, you still have to heat temper, but then you temper with liquid nitrogen afterwards to tweak the molecular structure a bit more.

 

[MichaelMouse]

Steve's post brings to mind the word I should have used in regard to drawing and turning a curl - ductility. Even malleable alloys can make poor scrapers of the cabinet variety if their structure will not allow drawing.

As you can see by the writeup on Lee Valley's site, they use a carbide burnisher, and say nothing about drawing an edge. http://www.leevalley.com/wood/page.aspx?c=2&p=20266&cat=1,330,49233

 

[Steve Worcester]

Burnishing is just "smashing" the edge against the carbide post. On a small level the metal of the scraper curls up because it is the "softer" of the two materials. Until you try to burnish something harde I guess.