Stu - Convex Grind?

Brent Dowell

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Stu,

Just thinking out loud here, but I just got one of those little HF 1x30 belt grinder for doing knife sharpening. In another post you suggested I could use it for Lathe tools.

That got me to thinking. (I know, a dangerous thing), but one of the things they talk about with knives and belt sanders is the ability to do a convex grind on it for knives.

On my first try with an old camping axe I have, without hardly trying, I noticed that it had a convex grind. The belt gives just enough that it gives a nice convex shape. The added bonus is that with the give, I find it much easier to get a uniform edge along the edge of the tool.

So, I'm just thinking this could be a great way of getting razor sharp skews with a convex grind, or do you think I'm missing something?

Would there be any advantage to having a convex grind on say a roughing or bowl gouge?
 
The convex grind I've shown on the skew is just for the skew, well the parting tool as well, but for a bowl gouge, you want a flat grind, not a convex grind.

That said, I know that a number of top turners advocate using a belt grinder compared to a stone grinder for their turning tools for a number of reasons, one of the biggest is that because of the length of the belt, it is much harder for the tool to get "Hot", as the belt is a much cooler system for grinding :dunno:

Cheers!
 
A bowl gouge, specifically for hollowing, BEGS for a convex grind. I've been advocating that grind for years. Lots of folks use the fingernail grind, though, and that's really hard to make convex.

A roughing gouge really wants a flat or very slightly concave (as on an 8" or larger wheel) bevel, though, as does a bowl gouge used for "outside" work.
 
Played around with sharpening one of my cheapy HF Skews today on the belt sander. Nice convex grind, sharp enough to scrape (I wont say it sliced them off exactly) hairs off my forearm.

That's with a 120 grit belt and some of that green polishing compound.

Can't wait till the finer grit belts and the leather belt from LeeValley get here.

And no, I didn't get to try it on the lathe. Too many other projects piled in from of it right now... :rolleyes:

skewconvex.jpg
 
I think the curved edge is what he was shooting for - it helps to keep that tip out of the work... or so it's said. I've never tried a curved skew so I can't say whether it makes a difference.

Seems like a convex bevel on a skew might be counterproductive - not much bevel to ride. It might work OK, though. One way to find out... :)
 
Tim, my large 1 1/4" skew is has the lower part of the skew slightly curved, but the top part, leading to the long point is straight.

I think you will find that the convex grind on the skew work really well.

Brent, having the skew curved to the long point is a bad idea, when you go to use the long point, the point you want to use will be behind the curved portion, not good.

Try it again and make it strait across, well at at 15 degree bevel, but straight.

Cheers!
 
Interesting. I've got other skews that are straight across. This is just a cheap HF skew that I use for sharpening practice, basically.

The curve on the skew came from somewhere on the interwebs. If I recall, it was supposed to reduce the likely hood of a catch.
 
Interesting. I've got other skews that are straight across. This is just a cheap HF skew that I use for sharpening practice, basically.

The curve on the skew came from somewhere on the interwebs. If I recall, it was supposed to reduce the likely hood of a catch.

Yes, if the curve is on the bottom half of the skew, from just shy of the middle to the short point, but NOT from the middle to the long point. IMHO :wave:
 
So Like this, so its basically straight, with the bottom part rounded off.

honing_skew_2a.jpg

Got it. Will practice on my 'sharpening practice' skews! :thumb:
 
Brent,
My only method of sharpening tools for the lathe is on a HF 1" belt sander using a 100 grit belt... I get nice clean edges and pretty sharp tools. Haven't tried the convex grind yet, will have to give that a try.
On bowl gouges, not sure what the proper name for the grind I use... is not quite square across the end, but I don't have long wings on the grind... I"m thinking it may be closer to the Ellsworth?? I do have a 3/8" (I think that is correct) that has a long grind... probably the fingernail... don't use it much except for little detail work.. almost like a spindle gouge. I have more luck with the shorter wings and closer bevel on the gouge.
 
Just thought I'd add to this. That little 1x30 belt sander does a bang up job on kitchen knives. I got some pretty fine belts and a leather belt from lee valley. Spent more on the belts than I did on the durn sander!

Anywho, put a fine belt on the grinder, run a kitchen knife across it 1 or two times per side, then run it on the leather belt with a little green compound? Man, I can slice soft tomatoes thin enough to read through. The bonus is that it takes very little time.
 
Among knife aficionados, the convex grind, better known as 'apple seed' is a long hotly debated subject.
My observation, and experience, says that an apple seed edge can be very-very sharp and effective indeed.
Downside is that few people are able to properly achieve this edge. Those who can are held in a sorta 'god like' status.
Other downside is that the edge doesn't hold very well. Dulls quickly compared to straight or hollow grind sharpenings. This on knives, I can't speak for the comparison on lathe tools.
I have used my belt grinder for sharpening lathe tools and it was OK.
But you would start a war if you tried taking my Wolverine set-up and 120 grit slow wheel from me. ;)
 
Well, don't know if I got a convex grind on my kitchen knives exactly, but they cut like they've never cut before!
 
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