negative rake scrapers

[Phil Pascoe]

Semantics?
I'm surprised someone hasn't come along to enlighten us. :lol:

 

[Random Orbital Bob]

that's why I asked the question

It appears to me to be rather shrouded in mystery, opinion and nomenclature confusion. I'm not sure I'm any the wiser to be completely honest but I appreciate the discussion.

Mike Waldt's Youtube does give a very clear and definable approach which you can take to the grinder. Also it shows that the practical results are there too. Jon's (Chipmunk) point about the transition from wall to base inside a bowl was what got me started thinking about this. That cut is obviously increasingly tricky with the depth of the bowl and though I've become reasonably proficient at taking very light cuts with all manner of tools including regular scrapers and the same in sheer cut mode at circa 45 deg, a more forgiving tool would always be welcome. So I thought it worth exploring anyway. The input is appreciated.

 

[Mark Hancock]

I did some research on this topic a while ago when a new range of negative rake scrapers appeared on the market and the conclusions I came to were:

1. the rake angle is the angle between the tool and the work
2. negative rake is an angle less than 90 degrees
3. a standard scraper (no top bevel) when presented in trailing mode presents a negative rake angle
4. negative rake scrapers (with a top bevel) are usually presented horizontal hence the need to have a top bevel

The whole issue of negative rake scrapers is somewhat confusing because IMHO of the use of terminology and techniques from metal turning being applied to woodturning.

I can see a use for negative rake scrapers in confined spaces such as the inside of a box but I just don't understand the need on a bowl when simply lifting the handle on a standard scraper gives exactly the same presentation angle to the work... maybe it's just me :roll:

Edit: re the link someone put up to the Sorby scraper instructions....That is the first time in 25 years I've ever seen the advice to rub the bevel of a scraper :?:

 

[woodfarmer]

I did some research on this topic a while ago when a new range of negative rake scrapers appeared on the market and the conclusions I came to were:

1. the rake angle is the angle between the tool and the work
2. negative rake is an angle less than 90 degrees
3. a standard scraper (no top bevel) when presented in trailing mode presents a negative rake angle
4. negative rake scrapers (with a top bevel) are usually presented horizontal hence the need to have a top bevel

The whole issue of negative rake scrapers is somewhat confusing because IMHO of the use of terminology and techniques from metal turning being applied to woodturning.

I can see a use for negative rake scrapers in confined spaces such as the inside of a box but I just don't understand the need on a bowl when simply lifting the handle on a standard scraper gives exactly the same presentation angle to the work... maybe it's just me :roll:

+1 it is my take on it also. To my mind a scraper HAS to have its "cutting" edge at most 90 degrees to the work ie scraping, and not on a bevel. Although boning the cutting edge does turn it temporarily into a cutting tool as opposed to a scraping tool.

I use the skew because it came in my only set of tools and that set did not include any scrapers.

 

[Phil Pascoe]

That's what I thought. The ability to drop the handle would only really be an advantage (as you say, exactly) in the bottoms of boxes, although for outboard turning of bowls it might make for more comfortable working. I did a small box on Monday, and as my eyes don't work around corners, I was acutely aware of the proximity of the scraper handle to my jaw. I was wondering what a scraper made from a leaf spring would be like - irrespective of grind - would its curve drop the handle too far?
Just thinking aloud.

 

[Mark Hancock]

I was acutely aware of the proximity of the scraper handle to my jaw.

That was what put me off scrapers over 20 years ago.....in my case I got a catch and a nice bash on my jaw :roll: Now very rarely use a scraper as I prefer a shear scraping action.

 

[CHJ]

I have tried a Negative Rake Grind so that a stiff scraper could be held horizontal on the rest but not found any significant advantage in the way I work, there again 'professional' turners would probably say I do it all wrong anyway.

One aspect I suppose is that presented as such (horizontal) there is less chance of a catch if the handle is inadvertently dropped slightly as the cutting edge may still be in trailing mode.

I can see the advantage on inside curves with a curved sweep scraper with negative rake top face giving a stable tool rest location as opposed to tipping a normally ground scraper.

To me trying to use a negative rake scraper with bevel rubbing would be a very limited application, can't think of any instances in recent past where I would have been able to apply such a tool, perhaps there is more application in spindle work, a rare occurrence for me.

What happens if a novice tries to use a negative rake scraper in bevel rubbing mode inside a piece?
Cutting edge would have to be on centre at best, more likely below centre so very prone to dig-in.

 

[woodfarmer]

What happens if a novice tries to use a negative rake scraper in bevel rubbing mode inside a piece?
Cutting edge would have to be on centre at best, more likely below centre so very prone to dig-in.

It would be virtually the same as using a skew chisel... scary