Thread: shear scraper

Hmm, ditto for me on the tungsten the tips in question are for glass or tiles, for steel its a different configuration

The very cheap and crudely made carbide masonry drills will cut some fairly hard steel. A friend recently gifted me with a piece of metal-cutting bandsaw blade (1/16" x 1") to make a thin parting tool, and suggested use of the masonry bit. Just like drilling mild steel. Contrary to popular opinion, these bits can be sharpened with an ordinary gray grinding wheel (light pressure and motor gently). It's a little tough on the wheel, but I do it so rarely that it doesn't matter. Not sure how well the cheapie drills would work on thicker and/or harder material.

Originally Posted by TTIT

Can't really answer that except that the Sorby 'shear' scraper has a rounded back to the shaft so that when you roll it to an angle, you are still supporting the tool below the cut. With a normal scraper, if you angle the edge to 'shear' scrape, the cut is not supported directly below and can be difficult to control - or at least that's my take on it if it makes any sense .

Makes sense to me, and has switched on a light bulb, thanks .

You also get a similar effect to shear scraping with a 'long' ground bowl gouge right up on its side but I'm not going to try and explain that one - it just works

Yes, found that out myself by trial and error, it's another piece of the puzzle in the right place.

A bit more research and I should be able to work out what is going on from a mechanical perspective. I think I might be on the verge of starting a new war on what cut is what.... This post will be presented as evidence.

"Normal" or "conventional" scraping is done with the tool flat on the tool rest with the handle slightly elevated, and the cutting edge on a line horizontal through the centre. Shear scraping has the handle down, with the blade tilted so that the left hand edge of the tool is supported on the tool rest. The process is a finishing cut and will produce nice fine curls. The term "shear" scraping refers to the process rather than the tool.
For what it is worth, that's my interpretation and practice.
Jim

Sounds good to me. I am picking up some 5/8 steel round hopefully this week finally, got some metal scrap in hand for the cutters. I have noticed that Sorby, maybe others, have a flat ground on the tool to register it at the 45. Why not just use a round bar and roll the tool over to the desired angle?

Originally Posted by Daddy3x

Sounds good to me. I am picking up some 5/8 steel round hopefully this week finally, got some metal scrap in hand for the cutters. I have noticed that Sorby, maybe others, have a flat ground on the tool to register it at the 45. Why not just use a round bar and roll the tool over to the desired angle?

The flat side is what the teardrop scraper actually attaches to so it is parallel to the cutter. The flat is placed on the toolrest for stabilty when using the hollowing cutter and flipped over/rolled when shear scraping with the teardrop - which isn't necessarily at 45 degrees - a higher angle will give you an even finer cut etc which is why a round back is better

After-thought! That is unless Sorby have added another one or 2 flats to it since I bought mine

I've got some steel from garden sheers and pruning cutters which have holes and all! Just a matter of grinding the right shape around the hole and mount on suitable handle.
Haven't done it yet but will report on result when done.

If anyone else has used such steel before, please let us know how it went as a scraper.

Cheers,

FrankG

Originally Posted by efgee88

I've got some steel from garden sheers and pruning cutters which have holes and all! Just a matter of grinding the right shape around the hole and mount on suitable handle.
Haven't done it yet but will report on result when done.

If anyone else has used such steel before, please let us know how it went as a scraper.

Cheers,

FrankG

Don't know about turning tools but I once made a skinning knife out a set of garden shears - took and held a fine edge pretty good too - might even still have it somewhere ................ gawd knows where, 'twas about 30 years ago

My take on 'shear' is that it refers to the angle of the cutting edge to the travel of the wood, not the tool per se. So rotate a curved edge scraper edge up at 45 degrees or so and you're shearing.

The effect is prob going to vary in hollowing a bowl say; depending on what section is coming down on the edge: end-grain, long-grain, cross-grain or the transition from one to another.

I was trying out 's and Cliffs bowl-gouges at Prossy and got to show me a technique to remove the tearout on open-grain stuff like this White Cedar. (Turns out I've been doing a similar cut all along but with a very 'unique' method of handling the tool ) While testing the different techniques I also tried shear-scraping (my way!) to compare the results. On this particular wood, shear-scraping did reduce the tearout considerably but still fell short of 's fine-slicing cut with the wing of the long-ground bowl-gouge or a similar slicing cut with my spindle-gouge.
Anyway, got young Nev (another forumite) to take some shots of the shear-scraper in action - unfortunately the shots of it working the inside didn't really show the 'presentation' of the tool as well.

Interestink.

Been turning a bunch of Deodar bowls which has distinct grain diffs. Best result with a gouge was clean cut on late growth but some tear-out on the softer early growth. When cleaning that up with that Sorby tear-drop scraper the early growth finish was better but the late was worse. Sigh.

I'm also playing around with a burnished scraper edge. Harder to control than a burr since presentation is more critical and there's a self-feeding effect. I'm not as yet sold on it.

Originally Posted by rsser

My take on 'shear' is that it refers to the angle of the cutting edge to the travel of the wood, not the tool per se. So rotate a curved edge scraper edge up at 45 degrees or so and you're shearing.

The effect is prob going to vary in hollowing a bowl say; depending on what section is coming down on the edge: end-grain, long-grain, cross-grain or the transition from one to another.

Ern, IMHO "the angle of the cutting edge to the travel of the wood" is relevant because the direction of the fibres, albeit rotating, is more or less always on the same plane orthogonal to the spindle and, because the best cut is not with the grain or across the grain, it is at an angle, that's what tilting the blade is aiming at. It can't be the defining element of the technique, though, because that angle changes when the turner's position moves from being orthogonal to the spindle (outside of the bowl) to parallel to the spindle (inside of the bowl).

I am still convinced, from all the photos (including Vern's above), that the purpose and justification of "shear scraping" is to pull the top surface of the scraper to the surface of the wood at the appropriate angle (acute in the direction of pulling, obtuse if one refers to the penetration of the wood) for eliminating gouging, thus producing fluff and not a shaving. If a shaving is produced, IMHO it is not "shear scraping". Hence most of the confusion, probably.

This should be fairly easy to check, can any of the gurus confirm?

Originally Posted by TTIT

Anyway, got young Nev (another forumite) to take some shots of the shear-scraper in action

That's a useful photo. When it comes to shear scraping, a great number of words can be written to explain what is plain obvious in a single photo.

Thanks, Vern

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Originally Posted by Frank&Earnest

....thus producing fluff and not a shaving. If a shaving is produced, IMHO it is not "shear scraping". Hence most of the confusion, probably.

This should be fairly easy to check, can any of the gurus confirm?

Frank, will leave it to the gurus to speak for themselves, but heavy enough shear scraping would produce a sort of shaving, not fluff, and still be shear scraping, although the resulting finish would be rougher and not a good use of the tool.

The fluff has more to do with the lightness of a finishing cut than the angle of tool presentation. A light horizontal scrape (eg inside the the bottom of a bowl) will also produce fluff.

Hoped that helps you to sort things out a bit more.


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