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Numerical angle measurment for scrapers........

odie

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I try to get all my scrapers to grind at the same angle......simplifies things at the grinder to keep the same setting for everything. (Although there are a couple applications where this isn't possible.)

Was wondering........where does everyone else measure this angle? From the top edge to the grind, or from the bottom edge to the grind. One would be an obtuse angle, while the other would be acute.

Seems to me, that since the scraper is actually contacting the grind table from the bottom surface......then the only logical conclusion would be to record angles from there.....or, use the obtuse measurement.

I recently made a slight adjustment to my universal scraper angle because of a slight application problem specific to a particular use. The angle is now 120 degrees.......but I suppose some of you would view this as 60 degrees?

I have a feeling I'm measuring everything exactly the opposite of what everyone else is doing........?

Any comments about this?

ooc
 
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Sigh. It would be a lot easier to discuss these things if there were some agreement on terminology. It seems to me that the cutting edge is the proper point of measurement; the table angle is a consequence of both the cutting angle AND the thickness of the tool. To make matters worse, the cutting angle is sometimes defined two different ways: Plane irons usually define the angle of the included metal, e.g. about 25 degrees, with 155 degrees of air; whereas for metal-cutting, the relief angle measures from the perpendicular to the cutting surface. So, a 30-degree relief angle would produce 60 degrees of metal and 120 degrees of air. Gauges for measuring these usually measure the metal between the top and a chord as long as the gauge's notch; the bottom could just as well be subterranean, which is sort of a compromise.

In any event, up to 5 degrees variation from "perfect" is often acceptable. A constant table angle might be consistent enough; where it isn't, a thin auxiliary wedge could be employed to avoid re-setting.
 

john lucas

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Joe stated it pretty clearly. I measure my gouge angles from the flute down the bevel so I do the scrapers the same way from the top down. I've started using 45 degrees ever since buying John Jordan's shear scraper.
I even converted my flat scrapers to that setting. Mostly because nothing has to change on the grinder. I do have to insert a wedge because I have my table set for 40 degrees to sharpen my stewart Batty bowl gouge grind.
 
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Amazing how an article by one of the "names" has caused the renaming of a tool, when it was simply a case of misunderstanding proper use, yet we can't agree on a framework to measure angles. Get the Management involved, and it can be added to whatever "objective" standards we choose to use to define art, which, it seems to me is a feeling, not a checklist completion.

Could easily use the naming conventions of flatwork, of course, but turners are a perverse bunch. Included angle makes sense to me. How many degrees of steel are there, not gone. That might lead to an understanding of other flatwork nomenclature as it applies to all edge tools - sharpness angle and clearance angle.

Of course if you go with the grinding burr you have no idea what either your actual sharpness or relief "angle" is. If you turn a burr with a burnisher, you might have a better idea. If you go with a clean edge, the terms are meaningful.
 
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I always use the terminology "included angle" or "tool angle" for the angle in the steel and "clearance angle" for that in the air. There should be no doubt what I am talking about, but people still get it wrong.

I see the angle of a scraper as a compromise between a small included angle that gives a very sharp and fragile edge that leaves a better finish (with or without the burr); and a thick included angle that has a lot of metal supporting the cutting edge, but often leaves a rougher surface on the wood. A 45-degree included angle is a fragile cutting edge, while an 80-degree tool is not. The 45 will make a lot smoother cut than the 80.

It follows that it might be better to use the heavier angle for roughing cuts and the shallower angle for the finishing cuts. I compromise at somewhere around 65-70 degrees included angle for all scrapers, but I have a finishing scraper with a 30-degree tool angle that can leave a finish that a skew would proud of.

John, not everyone agrees with you on JJ's shear scraper. I like my scrapers thick and with long handles for better control. Using JJ's shear scraper puts everything in my wrist and reminds me of using a utility knife. Just a difference of opinion on scrapers.
 
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john lucas

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Russ I use John's scraper in a pull cut sort of way. The handle is a little higher than the cutting edge and I'm pulling the scraper with it tilted at 45 degrees. It doesn't need a long handle for this and used this way a long handle would in some cases be in the way.
Of course we both know that there are a million different ways to do things. My favorite scraper for dry work is still my 1/2" flat nosed scraper with a long handle that I use probably the same way you describe. I'm just a fan of JJ's scraper for green work. It's probably a combination of the sharpening angle, the ease that you can roll an edge with his ceramic stone, and the shorter handle that lets me move it more freely. I don't truly understand why his tool doesn't work as well on dry wood as my 1/2" flat nosed scraper that has the same included angle before raising the burr, it just does. It would almost have to be the longer handle.
 
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Six of one, and a half dozen of the other. For me, I opt for the 60 degrees because its fewer numbers to write. As far as which angle cuts cleanest, it doesn't matter which bevel angle you grind on your scrapers. Flat scraping cuts will be much coarser and great for roughing. Angled/shear cuts are for finish work, both on bowls and spindles.

robo hippy
 
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Being relatively unskilled and also not very picky, I measure the angle by the "that looks and feels about right" method. However I define the angle as the included angle at any point along the cutting edge, measured in a plane perpendicular to a line tangent to the cutting edge at that point. Took me a long time to discover that it is usually the included angle, and I'm sticking with it.
 
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What do I know?

I'm one of those people who hones the edge of a scraper without a burr and rides the bevel. All of the famous woodturneers tell me it can't be done that way, but that's the way I learned to do it many years ago and I have never had a problem.
 
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Russ, well, I am not exactly famous (still doing better at getting famous than I am at getting rich), but I had an argument with some one about that very point. I ride the bevel of my scrapers across the bottom of my bowls (the heel has been eased/ground round). He told me you can't do that. Well, I do it on most of my bowls and plates/platters.

robo hippy
 

john lucas

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Why couldn't you rub the bevel of a scraper and us it that way? It's no different than a skewchigouge or any of the tools that don't have a flute. I've made several of the round nose cutting tools that are flat and polished on top. They work more or less just like a spindle gouge when you are rubbing the bevel. If you don't rub the bevel then it works just like a hollowing scraper. If you raise a burr and us it handle high it works like a shear scraper.
In fact now that I think about it the Beading tool is really nothing but a flat scraper (if you'll pardon the term) without a burr, so is a Bedan, more or less. They might be sharpened more acutely than your typical scraper.
Is a Skew laying on it's side a scraper or a cutter? It peels off really clean shavings. There isn't a burr but you sure aren't rubbing the bevel. You get the same cut with a Hunter tool tilted over on it's side (if you don't rub the bevel) I estimate the Hunter tools edge to be somewhere around 25 degrees which is actually a sharper angle than I prefer for my skews which are usually around 35 degrees.
 

odie

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Wow.......I leave you guys for a couple days......!:D

I really don't mean to be soooooo controversial.....! Ha!

All I was really after was finding out if it's more common to measure the grind angle from the bottom or top edge on a scraper. I measure the bottom (the obtuse angle) because it's easier to take a measurement and adjust my Wolverine table with my existing set of measurment tools. It isn't measuring the "air" at all. I can see that it would be in my best interest to revert to the acute angle when communicating with other turners......that way we all are on the same page and everyone understands exactly what's being discussed.

In the end, it really doesn't matter if you measure from the top or bottom......because the sum of the two angles will be 180 degrees. Visualize two parallel lines with an intersecting line. On either side of that intersecting line will be two angles where it meets the parallel lines. One will be the obtuse angle, and the other will be the acute angle......and when you add the two numbers together, it will always equal 180.

I really don't care how others take their measurements......I've been doing things in a way that works for me, and all I'm really interested in is getting my general terminology in agreement with everyone else.......

ooc
 
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After reading all of this I’m still trying to figure out - why even MEASURE the angle? I think it is more common for woodturners and turning literature to describe the angle as measuring from the top surface than the bottom, and if you understand the principal that the pointier you make it the more aggressive the tool becomes, that’s all you need to know in order to move forward. I can’t think of one instance where the actual angle as measured in degrees is relevant to accomplishing what is necessary. And the same goes for gouges. If you understand the above principal you can pick up any tool with any angle, know what it is capable of, and make it work. It is amazing how a group of turners can argue angles and grinding methods all day and at the day’s end still have a rack full of dull tools.

- Scott
 
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I can’t think of one instance where the actual angle as measured in degrees is relevant to accomplishing what is necessary. And the same goes for gouges. If you understand the above principal you can pick up any tool with any angle, know what it is capable of, and make it work. It is amazing how a group of turners can argue angles and grinding methods all day and at the day’s end still have a rack full of dull tools.

Well, not really. Sharpness angle makes a difference in how the tool gets under the shaving with the bevel rubbing (0 clearance angle). Counts in gouges and chisels, but not much, as mentioned above, in tools which are not run with the bevel on the work. The tool may also be limited in the angle of attack to a point where it cannot be used inside a narrow piece in the preferred method because of the bevel angle.

Turners who are observant would indeed know this, and choose the tool which will do the work best from those at hand somewhere else. They will have altered their own grinds at home to do the type of work they prefer already.
 

john lucas

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The only reason I talk about angles is because every single demo I do someone will ask what angles I use. I suppose I could say "whatever works" which is true but can come across as sort of smart elick remark. For that reason I usually do say what it is and might throw in a little about why if I have time.
 
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