Scraper Sharpening

[Thomas Smith]

Hi folks,

I have a wolverine jig and feel very comfortable sharpening skews, spindle and bowl gouges. I have the various attachements to sharpen different gouge profiles.

What I don't have much confidence in, is sharpening scrapers. I have started to like using a huge Crown scraper, but my understanding of the tool and how it cuts seems to interfere with my understanding of how I sharpen other tools.

I've seen the LV Scraper Burnisher and was wondering if that's what I need, or is there a grinder technique. I have gotten my scrapers so they cut pretty well, but not very consistent and I'm just looking for revised information.

Thanks!

Tom in Alberta

 

[Ken Grunke]

A large grinding rest, wide and deep, is best for scrapers. Especially for a round-nose scraper where you need to swing it around to grind the whole edge. Absolute minimum of 3" wide and deep in my opinion. Mine are 3" deep and 5" wide on my shopmade grinder setup.
Most grinders come with a dinky little thing less than 2" wide and deep. Does the Wolverine have a good-sized flat grinding rest?
Most turners use a scraper fresh off the grinder, when the burr is sharpest, and grind often. I have not experimented much with burnishing a hook edge on a scraper, but I think it can be a useful technique also. It probably lasts longer than a ground burr.

P.S. I'm moving this thread to the main forum, since it's not a how-to posting but a question. (See the sticky messages in the How-to section about posting there)

 

[Fog Tanner]

I have and use one of the Lee Valley burnisers. It can put an edge on a scraper which is much more agressive than the burr from a grinder. It is also longer lasting. You can also put a "ticketed" or brunised edge using a the shnk portion of a gouge. You would do this the same way as you would a cbinet scraper, just using the gouge for the round tool steel.

Either way you lap the top of the scraper flat and get a sharp corner on it. Using the LV unit, which you mount to something stationary, it is a matter of pivoting the scraper against the "cone" and applying a little pressure as you pull it along. The more pressure the more and aggressive the hook.

For grinding, Ken pretty much outlined what you need. You would keep the scraper flat on the rest and apply a light amount of pressure until sparks are coming over the edge and swing it around. You should be able to feel a small wire edge rasied on the upper surface.

And if you are doing endgrain work and want a clean surface. You lap the top of the scraper and don't raise a wire edge burr. You still have to have a square corner. It will not cut as agressive or as fast as the LV or burr edge, but will give you a cleaner surface on endgrain. And on some woods if you shearscrape, you won't need to sand.

 

[robert davis]

i do not grind my scrapers,too aggressive. iuse a smalldiamond stone as a burnish tool .gives afineburr for shear scraping

 

[john lucas]

I do both, grind and hone. Some of my scrapers sharpen with a better burr using the grinder but most work better using the diamond hones. What I like about the diamond hones is you can control the burr size. The fine hone leaves a finer burr than the medium hone and they cut differently.
I always polish off the old burr by running the diamond hone over the top and then run the hone up the bevel to raise the burr. Usually after quite a few of the honing style burr raisings I'll go back to the grinder to re-establish a good bevel and then raise the burr with the hone again.
Now bevel angle is a different matter. I've been playing with everything from 45 degrees to 80 degrees. I really like the 45 degree bevel on the John Jordan shear scraper but prefer a steeper angle for my 1/2" flat scrapers. My big roundnose heavy scraper is sharpened at about 65 or 70 degrees.

 

[cypher]

I use the table that came with my wolverine jig to sharpen all my scrapers. I normally tilt the table to the angle of the grind on the scraper and rotate the scraper by hand. This has worked very well for me. I use a 120 grit wheel so as not to take off to much steel. To ensure i have the grind angle the same i color the end of the scraper with a sharpe marker and turn the wheel by hand and then adjust the table angle to match the scraper grind exactly.

 

[Thomas Smith]

Thank you for your replies.

Ken, sorry about misplacing this post. I realized after I posted it that I had done a bad thing.

 

[Ken Grunke]

No biggie, Tom, it happens occasionally and is easy enough to correct.

 

[hockenbery]

Tom,

I generally use the wolverine platform to get the proper angle.
Then use a hone to remove the burr and strike a fresh burr with the hone.
This is something Al Stirt showed me a long time ago and lots of folks do something similar.

HOW IT CUTS??
scrapers are NOT CUTTING TOOLs and I never let the bevel ride when using one.
ridding the bevel of scraper invites the wood to drive down onto the cutting edge and tool profile allows no escape except and a big catch results.

happy turning,
Al

 

[MichaelMouse]

The burr you leave or the burr you turn is a cutting edge. With a turned burr you'll get more consistent angle and no embarrassing gaps. It rides on its own "bevel", the back of the curve, but it's still relatively easy to dig in save with the lightest of cuts, because there isn't much to guide on that can't be pushed back into a too-steep to cut curl with a bit of overpressure. Shearing puts more in contact, but the control you gain on the far side of the edge is more than compensated by what you sacrifice by not providing a firm guide on the rest.

Check the principles of burrs, angles, and angles of attack on any flatwork site. You can even scrape without a burr, as indicated, but it won't produce as fine a surface as a cutting burr unless you're downhill and downgrain the whole time.

 

[Bob Chapman]

sharpeneing 'scrapers'

Hi Tom,

I don't sharpen, or use, scrapers like other turners. I grind them to an angle of around 45 degrees (not critical) and then I turn them over and rub the top surface on an oilstone to remove any burr that might have formed. Yes, I do know that this burr is supposed to be essential, but bear with me.

By the time I've done this, the 'scraper' is as sharp as any of my other tools, and i use it in the same way i.e. angled upwards, cutting edge at around centre height, bevel rubbing. It cuts beautifully, leaves a superb finish and is wonderfully controllable. Because it's not a scraper anymore I actually call it a 'flat gouge', (but who cares about the name).

The closest I get to scraping with my scrapers is when I use a very broad one to smooth the inside of a bowl or vase. I arrange the rest so that the cutting edge of the scraper is exactly on the centre line, and I keep the tool perfectly horizontal while I use it. I can't remember when I last had a dig-in (but having said that, we all know the next one is just around the corner ) I never use it angled down (negative rake) in the manner recommended for scrapers sharpened with a burr.

Bob

 

[Mark Mandell]

Grinder Burr

The burr pushed up by a grinder is actually what's referred to as a "wire edge" that is as sharp as the wheel's grit but is inherently weak and short lived because the bond to the main piece of steel is weak. If, however, you hone the wire edge off and then use a burnisher to bend back a uniform burr, you'll do a lot less grinding because your cutting edge will last much longer, and your cuts will be smoother because the cutting edge will be smoother and sharper. I use a large curved cabinet steel to shear-scrape the interior of my bowls and it does a great job of refining the surface and taking out torn grain.

This is also why I hone the flute edge of my gouges to take off the wire edge and put a slight back bevel on the edge. Just a single pass with the hard Arkansas slip is enough to refine the edge.

 

[Marc Himes]

Scrapers in general

Bob C. in the UK. Your technique sound interesting and I may have tried something similar in presenting my scraper to the inside of my vessels . They seem to do a reasonable job of hollowing when presented at a 45 degreee angle coming from the inside out. Are there good videos demonstrating different techniques for using scrapers which would include shear scraping? When you angle the scraper do you round off the edge to avoid damage to the tool rest? (similar to a round edge as opposed to round nose skew)
I like to use a scraper on the inside of a bowl to get a better curve at the bottom but I still get catches and need to learn more. The care and use of the scraper sounds like a good demo for our local AAW chapter.