Author Topic: Negative rake  (Read 3825 times)

Offline Bill21

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Negative rake
« on: November 22, 2021, 01:13:51 PM »
I bought a large, and rather expensive round nose scraper some years ago. I resharpened it to negative rake but it doesn’t work as well as a smaller conventional scraper I have. I’m wondering if I should grind it back the way it was. Included angle is under 80°, maybe I should reduce it further. Any ideas?

Offline bodrighywood

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Re: Negative rake
« Reply #1 on: November 22, 2021, 04:35:41 PM »
Must admit I tried the negative rake and didn't see a lot of differenmce myself. Worls for some though.

Pete
Turners don't make mistakes, they have design opportunities

Offline BrianH

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Re: Negative rake
« Reply #2 on: November 22, 2021, 11:31:15 PM »
I must be one of the ones it works for because I've converted almost all my scrapers. Best to remember that even though the cutting edge looks the same either way up the tool cuts better when it is the same way up as it was ground. Also negrake scrapers lose their edge quicker than conventional. One of my grinder wheels has a semi permanent 40* jig attached ready.
Brian

Offline Twisted Trees

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Re: Negative rake
« Reply #3 on: November 22, 2021, 11:34:12 PM »
Must admit I tried the negative rake and didn't see a lot of differenmce myself. Worls for some though.

Pete
This may sound daft... but I think they work better for taller people, or very short people, it is all about angle and vision lines, having watched a bunch of people using them and puzzling over the mixed results I have concluded average height on average lathe height often do at least as well if not better on a standard scraper design.

That is of course the joy of worn out tools, you can try any strange configurations of wing / angles that you have heard about see if it suits you or not.
TT, AKA Pete, but that name is taken :-)

Offline The Bowler Hatted Turner

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Re: Negative rake
« Reply #4 on: November 23, 2021, 08:13:23 AM »
I used to use a negative rake scraper when I was turning bone (and many years ago Ivory).It is only recently that I started to use neg rakes on wood. With a traditional scraper you have to be careful to make sure you use a trailing edge but with neg rakes not so much, they are more forgiving than normal scrapers. I have found that they perform better if the top angle is the last one sharpened, I also think you get a finer finish from neg rake . Be gentle with them (and all tools come to that) and you will get better results.

Offline bodrighywood

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Re: Negative rake
« Reply #5 on: November 23, 2021, 08:58:14 AM »
Must admit I tried the negative rake and didn't see a lot of differenmce myself. Worls for some though.

Pete
This may sound daft... but I think they work better for taller people, or very short people, it is all about angle and vision lines, having watched a bunch of people using them and puzzling over the mixed results I have concluded average height on average lathe height often do at least as well if not better on a standard scraper design.
I am 6'4" (shrunk a bit with age LOL) and afraid that my height doesn't seem to help, maybe I am the odd one one out.
Pete
Turners don't make mistakes, they have design opportunities

Offline BrianH

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Re: Negative rake
« Reply #6 on: November 23, 2021, 10:02:15 AM »
Pete perhaps if you stood on a box while wearing high heels it might help!!!
Brian

Offline Twisted Trees

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Re: Negative rake
« Reply #7 on: November 23, 2021, 11:45:07 AM »

I am 6'4" (shrunk a bit with age LOL) and afraid that my height doesn't seem to help, maybe I am the odd one one out.
Pete

That kills that theory  :) back to the "some things work for some turners" theory.  ;D
TT, AKA Pete, but that name is taken :-)

Offline BrianH

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Re: Negative rake
« Reply #8 on: November 23, 2021, 01:44:33 PM »
I love the way this forum just occasionally throws up a thread which gets my brain cell excited and leads me to look closer at a subject that I had previously just taken for granted. This thread is a case in point and here are my morning's conclusions.....

My negrake scrapers are ground with twin bevels ,each at 40*. The tools business end looks rather like a blunted skew. This means that the burr, which is going to do the cutting for us, is thrown up at the same angle and is, in fact, forward of the apparent cutting edge so it is almost immaterial what angle you present the tool to the workpiece. It also carries the added advantage that one tool can do the work of two 'handed' shapes, it will cut either left or right according to which bevel was last ground.
A trad scraper, on the other hand, is likely to be ground much closer to a right angle so the burr will face upward. To obtain a similar cut to the horizontally presented negrake the handle will be up amongst the the rafters or the cutting edge well below the works centreline.

So, in Brian's world anyway, the 'big boy/little boy' theory does, in fact, hold water!
Now that's what I call scientific ......
Brian

Offline Bill21

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Re: Negative rake
« Reply #9 on: November 23, 2021, 05:34:21 PM »
Thanks for your thoughts folks. I have a bowl project coming up so I’m going to resharpen the scraper and give it another try. As I mentioned, it was expensive at the time so I want to get my moneys worth!


Offline Bill21

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Re: Negative rake
« Reply #10 on: November 23, 2021, 09:34:13 PM »

Offline Twisted Trees

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Re: Negative rake
« Reply #11 on: November 24, 2021, 12:14:50 AM »
I found this interesting.

https://www.sharpeninghandbook.info/WW-Scraper-NRS.html

I am not a regular scraper user, so my method and advise is of limited value, but my method for negative rake is the second one, I knock back the top by 20° then just sharpen the bottom face. I think if I did 2 faces the same it would be upside down 60% of the time.
TT, AKA Pete, but that name is taken :-)

Offline The Bowler Hatted Turner

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Re: Negative rake
« Reply #12 on: November 24, 2021, 09:34:37 PM »
Pete perhaps if you stood on a box while wearing high heels it might help!!!
Brian
Or put the box on your head!! ;D ;D ;D

Offline The Bowler Hatted Turner

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Re: Negative rake
« Reply #13 on: November 24, 2021, 09:40:52 PM »
It never ceases to amaze me how clever some of our members are. I don't have the brain power to workout the whys and wherefores that has happened in this thread. I have always said that I don't do anything clever and it is true. If I find one of my tools is not cutting right I assume it needs sharpening, if it still doen't cut I assume that my technique needs to sharpen up or the tool is ground wrongly in which case example no 2 still applies. It is all about sharpening correctly.

Offline Twisted Trees

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Re: Negative rake
« Reply #14 on: November 25, 2021, 12:03:25 AM »
It never ceases to amaze me how clever some of our members are. I don't have the brain power to workout the whys and wherefores that has happened in this thread. I have always said that I don't do anything clever and it is true. If I find one of my tools is not cutting right I assume it needs sharpening, if it still doen't cut I assume that my technique needs to sharpen up or the tool is ground wrongly in which case example no 2 still applies. It is all about sharpening correctly.

So now you know, if the tool is sharp and the cut still isn't flowing.. you need a box and high heals  ;D ;D ;D
TT, AKA Pete, but that name is taken :-)