Official Luthiers Forum!

If you have the space and can spend a little time on Craigslist, grinders are out there. Just don't be afraid to walk away if the price is too high, another will come along.

I made this rest for an old Delta grinder out of L-channel, some flat stock & a Bosch jig saw w/metal cutting blade and another grinder to take the burrs off but a file will work too.

Old Delta & Baldor grinders are pretty simple animals. If you can secure one for $50 it's a no-brainer IMO but YMMV.

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I guess that sharpening these is 'tacit knowledge', just as sharpening a card scraper is: it's something you can learn but maybe not describe. I wish I could help.

Part of the 'trick' is to keep the straight edge straight. Grinding it on a wheel tends to make dips and bumps which get worse over time. That's why sharpening it in between sessions on the wheel with a flat stone helps; you find out where the high spots are.

Always lap the faces on a flat stone to get rid of the old burr before you sharpen. I use a diamond stone for this. Feel the edge to make sure you got the old burr off.

I'm obsessive about getting the tool rest angle right, so that the grinder hits the edge exactly in the center. You check this by touching the edge to the grinder and then flipping the tool over and touching it again right next to the first one. If both marks are not centered, adjust the rest and try again. Somebody always seems to want to mess with my grinder, so I do this a lot.

Take light passes, keeping the whole face of the wheel in contact all the way across the cut. Flip the tool after every pass, and look at the edge to see when you've taken off all of the flat from the previous hand sharpening on the flat stone. Feel the edge for the burr.

You could use a hand skate sharpener to make a hollow edge on the scraper. The one I have has a carbide cutter, and will take material off the scraper nicely. The problem is that it has such a small radius that it would take a lot of work to get all the way out the edges with it. Once there it should work well.

As with riding a bike, another example of tacit knowledge, this may be one of those cases where you simply need to persist until you 'get it'. Once you do, you'll have it.

What Alan says works. I flatten mine on a diamond stone, make sure the edge is flat (on the diamond stone) then I mark the edge with a marker so I can easily see where I'm at when grinding. I use the fine wheel on a slow-speed grinder (Woodcraft) with the tool rest set up as good as I can. I use very little pressure when grinding the edge. Where I depart from Alan's method is that I carefully grind the edge until the marker is gone on one edge then I flip the scraper over and do the same thing for the other edge.

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Steve Smith
"Music is what feelings sound like"

One thing that is critical with this....
This scraper is a burr tool like a card scraper - it's not a finely honed edge tool like a normal chisel....

When you are dressing the edge on the grinder - the goal is to create a very fine burr on the edges... You can kinda feel it catch with your fingernail. That's the part that cuts.

So you start by honing the sides to remove the old burr on a good flat stone. Then you use the grinder to make new burrs on either side.

One advantage to honing on a fine flat stone in between grinding sessions is that it gives a finer, and very sharp, burr. I use this for the final scraping of the outside of fiddles, which are traditionally not sanded. This gives a very smooth surface, the right 'look', and preserves some of the detail that tends to get lost when sanding.

Quick question Alan or anyone else getting good results- do you use a 6”, 8” or 10” grinder. Or is the grit of the stone more of a concern?


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My grinder is an 8" but I think any of the sizes you mentioned will work. Grit of the wheel will determine how fine the burr is.

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Steve Smith
"Music is what feelings sound like"

Right; it's more a matter of the grit of the wheel than the diameter. I don't know what the grit is on the grinder I use: I just use the finer of the two wheels it came with.

I was comparing the Dewalt *" grinder to the Grizzly 10" wet grinder with leather strop wheel as well. Grizzly is bigger, wider and a finer grit so looks like that's the winner. Should also work better with other sharpening tasks as well.

I tuned up one of my scrapers on my Tormek once - cuts smooth but doesn't cut much, the wheel is too fine, I think. I have better results using the fine wheel on the grinder.

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Steve Smith
"Music is what feelings sound like"

I use scrapers turning bowls when cleaning up. This seems to be similar. I have a piece of 5/16" by 1 1/2" tool steel about 12" long. I am inspired to cut off 4" and make one. Seems sharping would be just like a bowl scraper. My card scrapers last about 15 min and then need re-sharpening.

Should work just fine. There is a hollow in the store bought version that makes it easier to flatten the side otherwise shouldn't be much difference at all. Maybe Al will chime in, if I recall he used to make these with or for his students.

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Steve Smith
"Music is what feelings sound like"

I keep ignoring this idea in the back of my head to make a long straight version of this with an old file. I would, in theory, use it to scrape the sides flat on the closed box. I'm just not confident I could get a straight and sharp edge over 5 - 6 inches of steel. Someday maybe. . .

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

In the blacksmith course at JC Folk School 10yr ago we learned to take steel from car spring and shape it into tools. I made a chisel but the interesting thing is how we shaped it with a regular belt sander with 40-60 grit paper. They use it for everything and it does a great job. You first put ear protectors on and flatten it with a hydraulic hammer, which none of use have. But you get to the same place with purchased tool steel or in your case an old file. Anneal it in a charcoal fire, and flatten the edge on a belt sander. Knife makers are everywhere. Look for some around you. They have worked this out and may help you. The key I saw was in the advertised hardness of 62 c of the AC scarper. That is very hard and brittle, but must work for this purpose. O 1 tool steel is tempered by baking for one hour at 250degrees. I've no idea about steel in a file. I do think it is water hardened. You may just shape, and sharpen , it still
hardened.

You have to enjoy making tools to do this. Might make the cost of one look really cheap.

6" planer blade would make a nice one...

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I/ve recycled 6in jointer blades, it is HSS I used a jet wet wheel sharpener to grind a 45 deg bevel. Personally prefer just regular tool steel scrapers like bahco. HSS is hard to sharpen, file, and put on a burr for me.

I made my first one out of a power hacksaw blade; M-2 steel. It was already fully hard, so I 'just' ground it from there. It took some time, but I've been using that one for about twenty years. It holds an edge longer than the commercial ones.

We used to make them in the shop using either O-1, A-1, or D-2 steel. I have an old dental investment furnace, just big enough for a 4" long scraper, that we'd use to heat them. You buy the stock annealed, cut and file it to shape, and then harden by running it up to temperature and quenching it in the proper manner depending on the alloy. We gave up on the oil hardening steels, since the oil tends to catch fire. Even fully annealed this stuff is pretty hard. The big problem is that they warp when you quench them. Normally you'd temper the steel by heating it up a little, which makes it a bit softer and relieves the stress, but you want his to be fully hard so that it will hold an edge. You have to lap the surface to get rid of that, and the hollow helps with that. One of my students made one out of A-10, iirc, which was not so exotic that it taxed my little furnace. He took it home to lap on his belt sander. He touched the belt with the tool and it didn't leave much of a mark, so he leaned on it. The belt was as smooth as a baby's bottom, but the tool was hardly marked.... It took him a while to get that one lapped on a diamond stone.

When one of the students said that his brother-in-law could make them in his machine shop I offered to help him get things going so that we would not have to make them any more. We went through a few iterations on the design. They chose the alloy in part because they could do the heat treating in house, which meant that they could meet the target price. We didn't want it to be so expensive that folks would be scared off by the price.

They wrap the tools in stainless steel foil when they heat treat them, to keep the air from reacting with the carbon on the surface and softening the steel. We used to get lots of scale that had to be ground off. Since then I've taken to putting small steel parts to be baked into a lump of charcoal to prevent decarburization. You learn...

A 6"planer blade would be a natural, and I've thought of that one often but never done it.

ernie:
Part of the point of these scrapers is that you don't file them and turn a burr. The cutting edge is the burr left from grinding. My students all had trouble learning how to turn the burr on a card scraper, but they learn how to sharpen these relatively quickly. I find there are several other advantages as well. I still use card scrapers, but not much.

On a recent remodeling project we had new kitchen cabinets that were finished poorly and with the wrong poly finish. The new finish had to be stripped off and refinished. The painters started using chemical stripper and sandpaper to remove the thick poly off the large number of cabinets. I took a couple of the Ultimate Scrapers (square style) over for the painters to use on various parts of the cabinets, especially the stiles and rails. These guys were amazed how well and how quick they could remove the finish compared to sanding. The scrapers would last all day and I took them home at night to resharpen them. This probably saved us several days on the project. Thank you Alan for this amazing tool.

I've showed them to folks carving chair seats, and they love them. Old cabinet makers know about scraping with glass; some will buy boxes of microscope slides for the purpose. This works the same way, but you can sharpen it more easily.

I wish I could claim credit for devising this thing, but the fact is I got it from Carleen Hutchins, who learned about it from Saconni, and he claimed that Strad used these, making them from broken saber blades. All I did was get lucky in finding a machinist who would make them, give him a little help with the design, and introduce it to the folks as Stew-Mac. The square one, BTW, came about when a a friend droppped by the shop of a student of mine. The friend works in the Steinway shop, and when he got back they ordered a bunch. He suggested the corner for getting in and cleaning out glue squeeze. I'd sharpened up an old plane iron for that years before, so I didn't think of it when we made up the new design. Anyway, I don't get any commission on these; I'm just happy I don't have to make them any more!

Years ago when I first got interested in woodworking I was talking to a friend of the family who was a pattern maker by trade. I was telling him that I was trying to learn how to turn a hook on a cabinet scraper. He said something about not having much use for those flexible scrapers and that, at his shop they used to grind and shape old files for whatever shape they needed. At the time, I didn’t really understand what he meant. Years later I read what Alan was saying about these scrapers but I didn’t make a connection to that old conversation. It wasn’t until they became available and I got one that it finally clicked. This is what he was trying to tell me to do. I wish I had spent more time talking about woodworking with him before he died. I wonder what else I didn’t get a chance to learn from him.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Thanks alan , with the upcycled HSS 6in blade I just put on a 45 deg angle on the jet, wet grinder For the O1 steels which are 1/8in I do put a burr on them tempering some to straw and leaving them straight or 45 deg with a burr , For chair seats and other projects. Thanks for your suggestion.Also another potential source of excellent scrapers are old putty knives I/ve found at yard sales .You can easily spot them with ebony , brazilian rosewood , or other exotic hardwood, polished , flattened on a belt sander, and with a small bevel and burr they excel at getting into tight corners. an scraping small instruments like ukes where one does not need a large 6in scraper.

The advantage of grinding the edge perpendicular to the face is that you get two cutting edges for the price of one.

I may try honing the face like Al says .. but since I have had these (rounded and the square one) all I do is do a quick grind on the fine wheel (120 150 ? - no idea, its whatever came with the Delta grinder) and its good to go ... I never really set the tool rest either .. once it starts grinding all the way across the scraper edge (without flipping - if its not, you will see a line in the middle of the edge as to how far its hitting), I get a sharp edge on both sides .. I also made a couple 5 and 6 inch wide ones from old HSS jointer blades .. put them into UHMW handles, and sharpen them the same way ... haven't used a card scraper since .. 7-8 years now

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"