Bowl Gouge sharpening question

[Lee Alkureishi]

Hi everyone,

I've been having some difficulty with my bowl gouge recently, and wanted to ask here if I killed the gouge, or it's just a technique problem (or both!). As a result, the bowl I showed on my other post was turned using mostly an oland tool and carbide insert tools.

I've been experimenting with different variations on an irish grind for the 1/2" Benjamins Best bowl gouge. My jig setting wasn't easily repeatable, so the gouge shape has been changed significantly a few times. I've previously been able to get a nice sharp edge on it, and was able to get good long ribbon shavings on a few occasions.

Recently, though, when I sharpen in on my grinder, I'm finding that the cutting edge develops multiple paperthin wisps of steel which trail off the edge (like short coat tails hanging off the edge) - I don't get a nice straight edge. When I go to turn with the gouge, it doesn't act like it's sharp. I struggle to get a cut started, and when I look at the edge, the edge has bent back ever so slightly toward the bevel, so much so that it's easily palpable. It's like my tool edge has softened.

I know HSS is not supposed to be affected by heavy grinding and bluing the edge in the same way that Carbon steel is, but I'm wondering if I killed the steel by all the heavy grinding I've done? I also realize that the BB tools are not top shelf quality, but it was previously much better than this, and others do swear that they're reasonable tools...

Thanks for your input,

Lee

p.s. I ordered a proper jig to help remedy these issues; waiting for it to arrive :)

[Scott Hackler]

I wouldn't think that you could easily take the temper out of HSS tools with a grinder. There are a lot of folks that "re-shape" gouges when they first get them, to their own preference. That can and often does take a substantial amount of grinding. Now if while your grinding the steel turns bright red or yellow for an extended amount of time....well a lower grade of steel (even marked HSS) might loose its temper.

Are you using a slow speed grinder and a Aluminum Oxide (180) wheel? A regular grinder with a regular wheel would generate a whole lot more heat than the previous meantioned set up.

The jigs are great to get easily repeatable results, but don't discount the "heat" factor. I have and use a BB small hollowing set and its marked HSS and sharpens just like you would expect (although they aren't the same as my Sorbys or Thompsons). Maybe a bad batch of steel???

[Brian Brown]

I have the same problem. The remedy, Take a dowel that is slightly smaller in diameter than the gouge flute. Wrap a piece of 400 automotive sand paper around the dowel (I use rubber cement to hold it on), and draw it through the flute a few times, sanding off the burr. Sometimes this just folds the burr the other way, but you can easily scrape it off with your finger nail. This works so good, that now I do it as a matter of course, whether there is a burr or not. I find that when the flute is milled at the factory, there are some very small grooves in the steel (you can see them with a magnifying glass), and the sandpaper helps smooth them out, making for a cleaner sharper grind. While I am sure that there is a difference in the quality of steel with cheaper tools like the BB's, I think that much of the quality difference is in the final "fit and finish", kind of like the difference between a Chevy, and a high end BMW.

[Steve Schlumpf]

Lee - both Scott and Brian bring up valid points but this is one of those times where a photo or 3 of your gouge would help all of us out in offering advice.

[Faust M. Ruggiero]

Lee,
Everything you are saying tells me two things. First, I believe you are sharpening or at least shaping with too fine a stone. I shape with 46 grit and until I recently bought a CBN wheel, I sharpened with 80 grit. The finer the grit, the more heat builds up during grinding. Is it possible you lost your temper? I suppose so but you can easily grind past the damaged area but not with a fine stone.
The real problem sounds like you are grinding to too steep an angle. Sharpening always produces a "wire edge". However, the steeper you grind, the thinner the wire edge becomes. Go on Doug Thompson's web site and look at the angle he shows for grinding his tools. I suspect your angle is producing an edge that is too "long" and literally falls apart. If you must regrind, get a coarse wheel and lay the entire cutting edge on the grinder and lightly grind away 1/8" or so. Then reset your jig to a more obtuse angle, I use 55 to 60 degrees and reshape your edge. Finish with light passes on your finer wheel.
faust

[Lee Alkureishi]

Hi everyone,

Thanks for the tips. You all pretty much nailed it. I'm using a 100 grit white alum oxide wheel, which is probably too fine for the heavy grinding. Once I got my rough grind set, the touchup sharpening went better. Sanding off the burrs also helped.

Now, can anyone fix my bowl gouge technique?

:)

[Thom Sturgill]

Hi everyone,

Thanks for the tips. You all pretty much nailed it. I'm using a 100 grit white alum oxide wheel, which is probably too fine for the heavy grinding. Once I got my rough grind set, the touchup sharpening went better. Sanding off the burrs also helped.

Now, can anyone fix my bowl gouge technique?

:)

Find and join a turning club. Nothing beats having an experienced turner watch you and help you correct your posture, angle of attack, and movement. Clubs will usually have members more than willing to give a new turner plenty of help.

[Rick Hutcheson]

I have found that the BB tools seem to work good for the first 1" - 1 1/2" of the tool. After that there seems to be just mild steel and they don't hold an edge very long. I still have, buy, and use BB tools but realize that only the tip has good steel. To me, the shorter they get the milder the steel gets.

[Reed Gray]

The wire edge that forms during grinding/sharpening is usually fragile, and breaks off quickly. I have found if I do the dropped handle high shear angle non bevel rubbing cut (called shear scrape by some) if you remove the burr with a hone, it helps on that cut, but not so much for generally cutting and roughing. I have never had any of the Benjamin's Best tools, but they are not of the highest quality, and that quality can vary a lot from tool to tool. The metal heads claim that it it impossible to get the HSS tools hot enough to lose their temper on standard grinders. If the steel does get red hot, and some blueing occurs, the edge can be a bit more brittle though, so it may dull more quickly, but I am not positive on that one. The main thing you want it for it to be a simple, easily repeatable process. Jigs can do this as well as platform sharpening. I have found that my grinds are never perfect, but most of the time, they will still cut, and the next time I sharpen them, I just have to remember to spend slightly more time on the problem area.

I guess there are two parts to sharpening. First it to grind to the profile you want, and second is to sharpen/touch up the edge. The first removes a lot of steel, and does require a bit of pressure. The second involves a quick brush against the grinding wheel. Keeping your wheels clean and true is a huge help in touch ups. I use the CBN wheels exclusively. They cut with a lot less heat, are spin balanced, never change shape, never need cleaning, and there is zero risk of them ever blowing up. They cost more, but they will out last by far any other grinding wheel available.

As to how coarse, or how fine of a wheel to use, I don't know. Most of the time I prefer the 180 grit wheel for gouges, and the 80 for my scrapers. Mostly the 80 raises a better burr on the scrapers. Some turners prefer a coarse wheel (40 grit) for gouges saying that the more serrated edge cuts better, and the more 'teeth' provided, the more cutting surface there is. The other school, Tormek and other wet wheels claim that the finer edge cuts better and lasts longer because there are fewer teeth to wear down. I can tell little difference between either, though I did have a 320 grit CBN wheel for a while, and eventually discarded it because I felt that it did not remove enough steel to 'refresh' the edge.

robo hippy

[Dick Strauss]

Lee,
If you're ever in passing through OH, stop in for a lesson.