Question: How do you sharpen curved scrapers?

[Darrma]

Hello!

I've a question for anyone who knows: How do you sharpen your scrapers effectively? I've not done too badly with a standard, straight-edged card scraper, but I've yet to find a good and reliable method for sharpening my curved scrapers and I know they're not cutting anywhere near as well as I would like them too.

I'm just coming up to preparing my kit violin for varnish and I've love to know how to get a good edge on my scrapers before I begin the task  

I've found a lack of information in this regard when looking previously so maybe this can be useful to other amateurs as well 

[uncle duke]

Depends on what you have for scrapers shape wise.  Some of my smaller ones I'll just put them between two pieces of wood in a vice and file the edge first, if they need filing.  

 If you have the three piece scraper set from a place like Woodcraft then for that particular round scraper that came with that set I put a file that I know will cut metal smoothly into a flat piece of wood via a groove for a side edge of the file to be set in.

 Then starting from one edge of the scraper I just move the scraper across the surface of the flat wood with the scraper edge making contact with the upright file.  After a series of passes a glove can be worn now because the scraper edge starts to become sharper, it could cut skin if one is not careful.  

Regardless of which way I use to file the edges first the second step is to smooth the filed edge with a honing stone manually without turning the edge, maybe a few passes with 400 grit soon after.  Then it's edge burnishing time with the scraper put back into the vice after flattening the burr on a flat, hard surface.    

[Darrma]

Thank you for the reply uncle duke. I was late in saying thank you because I didn't fully understand your reply the first few times I read it and so it seemed better to keep having a look. I'm pretty sure I understand your method now though.

I don't have a good metal file, would it be sufficient to use my diamond sharpening stone? And even to use it in the grooved piece of wood as you have suggested?

Thanks again!

[uncle duke]

  I've never used a diamond sharpening stone.  The idea is to what would seem to gradually remove metal from the scraper edge by filing when actually you are forming a burr.  It won't be a 1mm burr but should be noticeable.  Whichever side you get the burr to show up on will be your business side.  Work with that side only, maybe mark/scratch the scraper so you know which side is which.

  You could use a wood file.  The file I'm using stays in the groove, it's been there for a couple of years now and it may be a wood file,  I'm not sure  

  The plank of wood is about 6" wide x 14" long and maybe 1/2 or 5/8" thick with a kerf put in it lengthwise - like run the plank over a shallow set tablesaw blade about 5mm deep or so - just so that a file will fit down on the groove.  The groove I have is about an inch from the edge of the plank.    ex.  if the file is 1/8" thick then the groove in the wood is too.   

Some of my files just glide over the top of the scraper edges without accomplishing anything helpful for sharpening.  I found what I think is a 8" or 10" smooth mill that works for curved scrapers so that one is now delegated for that use only - stays in the groove.

Check around for videos and such that explain the use of burnishers.  What works for me may not be good enough for another, and his way may not be good enough for others, etc.  Find a burnishing method that will work for you - very important.

 

[Don Noon]

My method might not help...

Grinding wheel and rest initially if it is dull

Fine sandpaper on a surface plate or fine diamond sharpening plate to refine the surface

Power buffer (lightly) to polish the surfaces, making sure not to round over the edge

Finally put the scraper in a vise and turn the edge with a burnisher.

 

Metal files are really cheap.  If you don't have the power tools, get one of those to do the rough shaping.

[not telling]

Grinding wheel if needed, then several wet sharpening stones of increasing grit, then burnish to turn the edge. Good times. 

[Jeffrey Holmes]

17 hours ago, Darrma said:

Hello!

I've a question for anyone who knows: How do you sharpen your scrapers effectively?

Water-bath grinding wheel (fine) with table (on bevel), leather buffing wheel on bevel (or water stone if you're a masochist ) , water stone on the flat side, strop (optional), burnisher. 

[Jim Bress]

I do it like Jeffery (probably not as well).  I've not tried it, but I've read that some people find it helpful to move the sharpening stone over curved scrapers, keeping the scraper stationary.  Always more than one way to skin a cat.  You also have to decide if you're going to use a 45 degree angle or a 90 degree angle for your scrapers.  There are good makers in both camps.

-Jim

[Darrma]

Ah, this looks more complicated than I had thought, haha.

I don't have access to a grinding wheel and, honestly, they do intimidate me quite a bit 

Maybe it would help if I explained my current (and unsuccessful) method for sharpening a new scraper:

• Flatten both faces of the scraper completely on a 300 then 1,000 grit diamond stone.
• Flatten the edge to as perpendicular as possible using the same stone (I have done this previously by holding and rotating the scraper over the stone, but the idea of clamping the scraper and moving the stone seems to make much more sense).
• Alternate for a short while between those two processes to make sure I have the faces and the edge completely flat without any unintentional burr -to be clear: my goal here is to end up with a scraper that is completely flat on both faces and completely flat on the edge; as if it it been cut with a very fine laser from an elliptical cylinder-type shape.
• I then place the scraper flat on my workbench, nearly overhanging the edge and, using either a specific TCT scraper burnisher or a regular 'big, old screwdriver shaft' type, I proceed to apply pressure in a smooth but heavy motion across as much of the perimeter as I can realistically get to (repeatedly) before rotating the scraper and carrying on. I do this slightly off-level, with the handle of the burnisher slightly down which, in my mind's eye, creates a small burr close to parallel to the face of the scraper, going off over the edge. I do this for some time... (I should point out that, by this time, the ineffective nature of my method is beginning to reveal itself to me).
• Eventually, I stop and, holding the scraper vertically, run the burnisher nearly perpendicular to the edge I've burnished in a fast, smooth motion, in order to (I imagine) fold the burr over. (I am now fully aware that last 10-15 minutes have largely been spent in vain).
• I then face my disappointment as the scraper is only questionably sharp at best.

Is this even along the right track, or am I simply going about this is completely the wrong way? 

Is the use of a file on the edge, rather than a diamond stone, what I'm mostly missing? Am I simply getting my wires crossed and the process of filing the edge isn't meant to leave no burr at all, but to perhaps start a burr that will be refined later with the burnisher?

Sorry, and thanks for all the replies so far -your patience is appreciated  

[Jim Bress]

I use very little pressure and check the burr on my thumb nail to see if it grabs.  If you are using 90 degree bevel a different method may be needed.  I believe Davide Sora has a video of him sharpening scrapers at 90 degrees.  His scrapers are certainly sharp.  They will cut (Doug Marcaida voice).

-Jim

[Michael_Molnar]

I dress the scraper edges on a water stone block that rests on the bench. A wood block sits on top of the stone to keep the scraper vertical while I move the scraper along the stone. I watch the shiny edge develop as I work the scraper. I apply light pressure to avoid marring the stone.

I also have a hollow-ground set for which I use a round stone, 

If the scraper needs a burr, I use the Stew-Mac tool I mentioned elsewhere.

 

[Jeffrey Holmes]

3 hours ago, Darrma said:

Ah, this looks more complicated than I had thought, haha.

I don't have access to a grinding wheel and, honestly, they do intimidate me quite a bit 

Maybe it would help if I explained my current (and unsuccessful) method for sharpening a new scraper:

 

• I then place the scraper flat on my workbench, nearly overhanging the edge and, using either a specific TCT scraper burnisher or a regular 'big, old screwdriver shaft' type, I proceed to apply pressure in a smooth but heavy motion across as much of the perimeter as I can realistically get to (repeatedly) before rotating the scraper and carrying on. I do this slightly off-level, with the handle of the burnisher slightly down which, in my mind's eye, creates a small burr close to parallel to the face of the scraper, going off over the edge. I do this for some time... (I should point out that, by this time, the ineffective nature of my method is beginning to reveal itself to me).

I only sharpen my straight rib scraper at a 90 degree angle.  All my curved scrapers are beveled.... but what ever you do... as mentioned...you might try punishing the edge a little less when you burnish.  It doesn't take all that much pressure, and repeatedly drawing the burnishing tool across the sharp edge may turn the burr too far (as might be evident by noting the angle the scraper needs to be held to get a clean cut). Play with it a bit and see what works for you.  If I am using a scraper to level fill varnish during a restoration, the scraper will have a very tiny burr, or none at all.

[Evan Smith]

8 hours ago, Darrma said:

• Is this even along the right track, or am I simply going about this is completely the wrong way? 

Is the use of a file on the edge, rather than a diamond stone, what I'm mostly missing? Am I simply getting my wires crossed and the process of filing the edge isn't meant to leave no burr at all, but to perhaps start a burr that will be refined later with the burnisher?

Sorry, and thanks for all the replies so far -your patience is appreciated  

I use scrapers without a burr,, or with a burr. Light burrs or heavy burrs, 45, or 90 degrees.

It sounds like you have the methodology down fairly well. After using all kinds of things for burnishers that were recommended to me, I noticed that there were always marks on the burnishers, and being used to metal work I have always been a bit unsatisfied with the result. Some of these were expensive things made for scraper burnishers, some others  I've used,, bearing steel, high speed steel, chrome plated, and chrome moly , hardened 0-1 and hardened w-1,and I thought they all failed miserably to produce an edge that I thought possible. Not that they won't or can't but they get beat up and are no longer perfectly flat, so after a while I get mixed results. The final result has a lot to do with the material that the scraper is made from, and what it is being worked with. Different materials has it's advantages and drawbacks and that is learned through practice.

But I did find the perfect  material to use for a burnisher,,,and it should be really obvious ,as it is so simple as to be flat out stupid,, that is,,,

Tungsten carbide, it has a grain structure that is coarse like a very fine file and it is much harder than anything that you will ever have another scrapper made out of except another piece of tungsten carbide, it it so much better at pulling a burr as to have no comparison. I have used it a lot and it has no marks on it and it is perfectly flat. I actually use a piece of  tungsten carbide to fine grind steel, no need to put teeth on it.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=carbide+rod+drill&_blrs=spell_check

For shaping the edge of the scrapers I use 400 grit aluminum oxide sandpaper on a table top belt sander with a flat graphite table, and I use a bit of chrome oxide buffing compound with that to polish, it is real fast and does a nice job if you're good at holding things straight, it will keep things flat and straight, and it is great for the curved scrappers, it keeps the curves nice and smooth,,,as curves should be.  But you need to grind the belt overlap to get rid of the bump in the belt.

 

[Evan Smith]

Here's a rough exaggerated drawing of the Idea, the smoother and sharper the first edge is before you roll it,,,,,will determine how perfect the edge can be..

The prep work before the edge is rolled,,,,,,,, is as good as it will get. I polish them like a mirror before they are rolled, and many are just polished at 90 degrees and not rolled at all, I use then just that way, like Mr Duke said,, they will cut you.

 

Notice that you hold the burnisher at 90, or close to,, to finish the edge, I think that a common mistake is to try to roll the corner over. That is not necessary, just push the burr back out to the side.

The # 5 pic is actually wrong, the side edge of the scraper would extend straight out to the cutting edge, I show a bevel then the cutting edge,,,, just in a hurry!

[Berl Mendenhall]

My system is so simple. I lay on a flat surface and remove the burr with a two different grits of diamond stones. I use the credit card size stones for scrapers. I then chuck the scraper in a small vice and hold the diamond stone horizontal and run it over the edge. It doesn't take much and you have a square shiny surface. Then I turn the burr or leave it flat. No mess with water or oil. The whole job takes only minutes. Also, the stones I use have lasted for at least fifteen years.

[Darrma]

Hi again folks, thank you all very much for the replies -I've got plenty of variations to try now, probably tomorrow evening.

And thanks Evan for doing the illustration. I think I understand what you mean about no.5 too.

So, just to make I'm on the right track:

• Using the diamond stone to square of the edge isn't necessarily a problem (so long as you can keep it square), but some people prefer to use a file.
• Once the faces have been flattened and the edge has been squared, as above, it is not necessarily necessary to do anything further; the scraper should cut in this state (and you all seem to be saying that is should be a very fine cut too, which is probably what I'm looking for in this instance).
• If I do choose to put a burr on my scraper after the above two stages, then try burnishing using a 45º angle as apposed to a nearly 90º.
• don't use anywhere near as much pressure when burnishing and try going over the same spot fewer times.

Thanks everyone, if wasn't quite so late I'd have a go now! I'll let you all know how I get on   

And, Evan, here is the TCT burnisher I have https://www.workshopheaven.com/arno-carbur-2-solid-carbide-burnisher.html . I'm was more used to using the sort that you posted, but made of steel, so it's interesting to know that you can by TC rods too.

[Julian Cossmann Cooke]

If you want to go ueber-geek, get one of these from Micromark:  http://www.micromark.com/MicroLux-5-Inch-Mini-Disk-Sander

Works great with blue steel.  You can get a very fine adhesive backed paper (if you're dork enough, let me know and I'll look up the source),  But you'll also need to spend for a regulator to control the speed (dial versus pedal -- more control).  Otherwise, you'll find the scraper whizzing past your ear and sticking with a boyoyoyoyng into the wall (that's the official sound of the knife lodging in the target next to the young lady's ear in the knife-throwing act at the carnival).  You can also use it to square blocks, using heavier grit paper from a big box store.

Makes some sense if you don't already have a disk sander -- mine is manual --, but may also be overkill.  The $200-odd just as easily could go toward a Tormek, a more important investment.

[Evan Smith]

4 hours ago, Darrma said:

• If I do choose to put a burr on my scraper after the above two stages, then try burnishing using a 45º angle as apposed to a nearly 90º.
• don't use anywhere near as much pressure when burnishing and try going over the same spot fewer times.

Thanks everyone, if wasn't quite so late I'd have a go now! I'll let you all know how I get on   

And, Evan, here is the TCT burnisher I have https://www.workshopheaven.com/arno-carbur-2-solid-carbide-burnisher.html . I'm was more used to using the sort that you posted, but made of steel, so it's interesting to know that you can by TC rods too.

I think that you are still misunderstanding me,,, you do not want 45 degrees, you do want close to 90.

And depending what I am burnishing, I will use a lot of pressure,, or a little bit, just barely touching.

That is a nice burnishing tool.

[David Beard]

The other thing is that burr scrapers aren't the only kind.  A good number of my scrapers are simply sharpened blades.  For these, I like blades with plenty of solid strength behind the edge, that is lots of hard metal.

[Darrma]

I'm sorry I didn't get back to this sooner -I'm a couple of days late.

Early experiments have seen me really enjoying using non-bevelled scrapers, just with the flat faces and a square edge that many in this thread recommended. 

I think I've finally got my kit fiddle to a point where I'm very close to applying the ground and varnish I purchased from Nunzio (Vernici Liuteria). He's currently completing a .pdf file to instruct in the application of his varnish and ground and, when that's complete, I'm sure I'll be read to start applying!

Thanks again everyone for all the useful help and advice.

[Berl Mendenhall]

If I still had my old computer, I would make a short video on how I sharpen my scrapers. If you remember I did this with spirit varnishing, it was easy and fun. The computer I have now is not much and not capable of this type of thing. If any of you folks have the capabilities of doing a short video and uploading it to youtube that would be helpful to some folks. Scraping is a difficult thing to master, properly sharpened scrapers are a must. I believe Davide Sora included scraper sharpening in one of his videos.

I also use scrapers with a burr and scrapers sharpened at 90 degrees. I have some thin scrapers i like to do at 90. These work very well around purfling channel and the relief of f hole wings. Maybe it's just me but the thick scrapers Stewart- MacDonald sells just din't seam to work well for me. They seam to dull too quickly. An old laminated plane iron works better for me, just sharpened regular to a razor edge. One last thing, Woodcraft sells leather finger guards for woodcarvers. I use one on each thumb when I'm scraping ribs. Keeps from burning your thumbs. I hold my rib scraper with both hands and use my thumbs to put a small bow in it. 

 

 

 

 

 

 

[Darrma]

On 3 June 2017 at 11:01 PM, Berl Mendenhall said:

I believe Davide Sora included scraper sharpening in one of his videos.

Ah, I haven't come across this yet -a good excuse to keep watching them!

[Davide Sora]

On 5/6/2017 at 10:04 AM, Darrma said:

Ah, I haven't come across this yet -a good excuse to keep watching them!

 

You can see the sharpening of scrapers in videos "Bombatura del fondo - Lavorazione a rasiera Parte Prima / Parte Seconda / Parte terza" (Back arching - Scraper working Part one,two and three).

http://davidesora.altervista.org/videos/belly-back/

It's just sharpening with the steel burnisher, not the complete shaping and sharpening with stones.

If I find the time I will try to put together the shooting on scrapers sharpening I made for those videos to make it more specific.

[Darrma]

Davide, you illustrate it very well in those videos. I have never been able to sharpen any scraper to cut as well as that.

I am definitely putting far too much pressure onto the burnisher when I do it -no question, and the same is true of the final step of folding the burr as well.

I have a couple of unused rectangular card scrapers and I'd like to make one in the same shape you use. I cannot find 0.5mm scrapers though and only have 0.4 and 0.6, would the 0.4 be the better choice for this type of scraper?

Thanks again, it's always a treat to watch and learn from your videos!

[Davide Sora]

On 5/6/2017 at 0:27 PM, Davide Sora said:

 

You can see the sharpening of scrapers in videos "Bombatura del fondo - Lavorazione a rasiera Parte Prima / Parte Seconda / Parte terza" (Back arching - Scraper working Part one,two and three).

http://davidesora.altervista.org/videos/belly-back/

It's just sharpening with the steel burnisher, not the complete shaping and sharpening with stones.

If I find the time I will try to put together the shooting on scrapers sharpening I made for those videos to make it more specific.

 

Done!