newbie scraper question

[david brum]

Hi all

I'm just finishing some walnut bowls that I roughed out in the Spring. I'm using my 1/2" bowl gouge at a shearing angle to get close to smooth. Then I'm using a heavy, round nose scraper (also held at a shearing angle) to get the finished surface. This works fine, but the problem is that I have to sharpen the scraper very, very often to keep it functional. I just leave the grinder on, so I don't wear out the switch. Does this sound normal? The scraper is a Benjamin's Best. I get about the same burr life, or less out of my HF scraper (from the HSS set). Is this just the way it is with scrapers?

[David Walser]

David,

Yes, that's the way it is with scrapers. Depending on the wood, you might only get a couple of passes before you've worn away the bur that's doing the cutting. At that point, you need to sharpen again. One option is to use a burnisher to raise a bur. Here is one example from Lee Valley (You don't need an expensive burnisher, the round shaft of a screwdriver will work.).:

http://www.leevalley.com/wood/page.aspx?c=2&p=20266&cat=1,330,49233

[Paul Atkins]

Are you honing the grind and top? What is your grinder grit? Are you burnishing your edge? Sharper is better. Not sharper angle, sharper edge. If you have a coarse grinder grit you might have a rough edge that would wear out faster. I only have 1 BB tool that I don't use very often and no HF tools so I have no comparison, but it seems like you should get better edge life. That's all I have right now.

[david brum]

Yes, that's the way it is with scrapers.

Thanks David, that's what I thought. I did try to raise a bigger burr with a cabinet scraper-type burnisher. It doesn't seem worth the effort for the extra time involved. Do you get a longer lasting edge with the LV jig?


Are you honing the grind and top? What is your grinder grit? Are you burnishing your edge? Sharper is better. Not sharper angle, sharper edge. If you have a coarse grinder grit you might have a rough edge that would wear out faster. I only have 1 BB tool that I don't use very often and no HF tools so I have no comparison, but it seems like you should get better edge life. That's all I have right now.

Thanks also Paul. I'm just grinding on a 120 grit white wheel. No further burnishing or honing. I would love some advice on making the edge last longer!

[curtis rosche]

i dont know about any body else, but it seams to me that the edge stays starper longer when you grind it at a large degree, so the bevel is long, and then change the angle on your grinder to a small degree, and just lightly tough it to the grinder, so that you have a small secondary bevel, im not sure what other people have found, but this grind seems to me to last longer and cut smoother

[Reed Gray]

Well, you seem to be having more of a problem than I do. I have tried a burnished edge on my scrapers, and didn't like it any better than the one fresh off the grinder. I could not raise a burr with a round burnisher, but could with a triangle one.

To raise the burr, I first hone off the old one on a flat diamond stone. I then put it on a plate type tool rest and push, top side up, face/bevel first into the wheel. I do not just kiss the surface. I use this burr for roughing as well as finish shear cuts. The durability seems to be slightly better for the Thompson than for the standard M2 high speed steel, and about the same as for my gouge edges. You do want a fresh edge for finish cuts, but can do a lot of roughing before you need to resharpen. I can make a complete pass down the outside of a 14 inch bowl with a freshly sharpened scraper. If I have to go back over an area a few times, I will touch up the edge. I also use a swept back grind more than the round nose because I can rough with the nose, and then shear cut with the swept back part.

I seldom use a negative rake scraper. I do know that the burr on one of them is much more delicate than the one on a standard scraper.

robo hippy

[Kyle Iwamoto]

I have the BB bowl gouge set, and I use a diamond hone and a burnisher if that helps. Yes they get dull rather quickly. Although I use it flat on the tool rest. I just got a Sorby scraper, (with the chatter tool) and it has a round shank, so I'll try that next.

If you're grinding a new edge that often, it won't be too long before you don't have a chisel anymore.

[David Walser]

... I did try to raise a bigger burr with a cabinet scraper-type burnisher. It doesn't seem worth the effort for the extra time involved. Do you get a longer lasting edge with the LV jig?
...

Yes and no. The burr raised with a burnisher is larger (as a general rule) than the burr from the grinder. The burr from a burnisher is also more uniform and less ragged than one from a grinder. All these factors should result in a longer lasting burr, but I've not noted much of a difference. I think the reason to use the burnisher is it should make your scraper last longer. (The larger burr might make the scraper more aggressive -- that's a difference I've noticed!)

The biggest variable seems to be the wood. Some woods seem to dull a tool more quickly than others. Cocobolo seems harder on tools than maple, for example. It can even vary from one tree to another within the same species. I've had walnut that would dull your tools just by bringing the wood into the shop; other pieces of walnut cut cleanly and didn't dull tools nearly as quickly. I think you, too, will find that some wood seems to cut more easily and your scrapers will last longer. Still, no matter how easily the wood cuts, scrapers just don't remain sharp as long as other tools.

[david brum]

I can make a complete pass down the outside of a 14 inch bowl with a freshly sharpened scraper.

I'd guess I'm getting about half of that Reed. I'm thinking that experience counts for a lot here.


. I've had walnut that would dull your tools just by bringing the wood into the shop.

This walnut is spalted, so maybe that caused faster wear? My next bowls will be madrona. Hopefully that will be kinder to my scraper.


If you're grinding a new edge that often, it won't be too long before you don't have a chisel anymore.

I know!

[Reed Gray]

I have found green walnut to dull all my tools from the chainsaw to my turning tools. I figured it was the acidic nature of the wood. I was playing around with some today, to see how far I could get with the grinder raised burr. I can make one pass all the way down a 14 inch bowl, but, if I have to make a couple of passes, I tend to use the whole area of the swept back design, from nose to wing. I also honed the burr off for a few passes, and it worked just about as well. I should try to hone a burr on and see what that does.

David, you should love the madrone (madrona in Washington, arbutus, the latin name in Canada). Smooth even grain, cuts like butter when green, very difficult to dry as it warps more than anything else I have ever seen. Usually there are 2 ways to do it, turn to final thickness and wrap the rim with 6 inch stretch plastic film, or turn thick and boil it. Any other way, and it will probably crack. Paper bags don't work well, plastic either. Some times keeping it in shavings helps. If you turn it thick and try to dry it, it can move so much (if it doesn't crack first) that you can't return it.

robo hippy

[david brum]

Thanks for the advice Reed. I can imagine Madrone behaving badly. I'm thinking I'll do some segmented bowls, especially since I have a bunch of flat odds and ends left over from other projects. I really love the stuff as well. It grows everywhere around here, but it's hard to find sawyers that want to mess with it. Got to follow those tree trimming crews around...

[Reed Gray]

David,
What part of Madrone country are you in? If you are ever coming through Eugene, look me up.

robo hippy

[curtis rosche]

if you want a burr that lasts really long, make your own tool using a peice of 10% cobalt or higher stock. the burr on them lasts really long, and you can get them really really sharp

[david brum]

David,
What part of Madrone country are you in? If you are ever coming through Eugene, look me up.

I'm west of Seattle on the Kitsap peninsula. I don't get down there often these days. It would be fun to meet if I do though. I could sure stand to gain insight from someone with experience.


if you want a burr that lasts really long, make your own tool using a peice of 10% cobalt or higher stock. the burr on them lasts really long, and you can get them really really sharp

Thanks Curtis. Is cobalt difficult to grind into the initial shape?

[curtis rosche]

when i grinded mine for the first time i burned the bit a little, you just have to make sure that if you are doing heavy grinding that you cool it off well. it sharpens really easy and about the same as a regular tool, just that it holds a burr longer, it takes an edge really well, i bought a bag of 10 bits off ebay 10% cobalt 3/8x3/8. the edge that was on it from the company when they cut the bit, was sharp enough that it cut through the bag and into my hand when i was unwrapping them.