How to sharpen a jamieson ground gouge
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How to sharpen a jamieson ground gouge
The gouge shown on the Jamieson site is made by Doug Thompson (thompsonlathetools.com). I'm not read up on the details of the Jamieson grind, but it looks like the grind that comes on all Thompson bowl gouges as purchased. There are instructions for it on the Thompson website. It's done with a Wolverine system and the vari-grind accessory.
Just doing a Google images search for Ellsworth grind, it looks similar but the bevel seems to roll up more on the wings, and also looks to have a shallower (e.g., more like 45 degrees than 50) bevel angle.
Sharpening bowl gouges is two parts -- the fixture you use to guide it and how much you grind in different areas of the tool. The vari-grind attachment makes it easy to get the bevel to "roll back" on the wings. The rest of maintaining the profile is how much you grind on different areas as you sharpen. If you have a tool that has the grind you want to maintain, take some pictures and make some measurements before you start grinding so you know what the target is. It's common for profiles to drift over time with repeated grinding (though that's not necessarily bad if it's working well for you).
There are videos out on youtube that have Doug Thompson demonstrating how to establish a swept back grind if it's gotten out of shape. I don't know if that's the Jamieson grind in every respect, but at a first glance, it appears to me to be.
Best,
Dave
Here's a link to the sharpening info on the Thompson site: https://thompsonlathetools.com/sharpening/ The video is linked there.
From just a little reading on the Jamieson site, it appears he uses a 2" protrusion from the vari-grind fixture, Doug's site recommends 1.75". I expect that difference would be very subtle.
When trying to maintain a grind over time, I recommend making a jig to get that protrusion consistently. Jamieson actually sells a trinket for this purpose, but just drilling a hole of the appropriate depth in a block of wood will work just as well.
I'd also recommend making a reference block to reproducible establish the distance setting for the base of your sharpening system. I use the wolverine system and have a short stick of wood with a screw sticking out the end (which makes the length adjustable) that drops in between the grinder base and the socket for the vari-grind to quickly get the right set-up. If you have CBN wheels (that don't change diameter) you only have to do this once. If you're using regular abrasive wheels (that wear away) you'll have to adjust the length of the set-up stick periodically or the grind angle will drift a little over time as the wheel wears. If this description isn't sufficient to understand what I'm talking about, reply to that effect and I'll take a couple pictures that will be way more informative than words.
Best,
Dave
From the horse's mouth...
https://www.youtube.com/watch?v=3liDhY_zxSc
https://www.youtube.com/watch?v=5sTx5SbGDJI
That sharpening approach is the same as shown on the Thompson site, except for a steeper bevel on the nose (60 degrees in Jamieson video, 50 on Thompson site). Same emphasis on the side view profile of the wing grind. It was interesting to hear his explanation of why that shape works so well when entering the riim when hollowing a bowl; I knew from experience that it does, but did not appreciate the mechanics of why. I have a 5/8" U flute gouge I use for finish cuts "rounding the corner" and across the bottom on the inside of bowls. I couple times I've tried entering the cut from the rim with that gouge because it was already in my hand. Definitely more inclined to skate, but didn't understand exactly why.
Not to hijack the thread, but watching him sharpen on a white wheel makes me appreciate CBN even more than I already do (if that's possible). I've gone to 600 grit CBN for all maintenance sharpening -- it's so smooth, the tool just glides on the wheel even though it is cutting well, with no sense of impact or bounce. I presume you take less steel off per sharpening as well, though that is so dependent on touch it might hard to assess and might not be the same for everyone. I've also quit honing, except for rare circumstances where the cut is not clean enough off the 600 grit wheel. My 180 grit CBN is only used for reprofiling now.
Dave
Continuing not hijacking this thread, using a 350 grit (I only have 1) I've been thinking I should have gotten the 600 instead, which I do have on my Tormek...... For those of you who may not have invested in a CBN yet. Think about the 600....... You should have the rough white wheels for reshaping/profiling.Quote:
Originally Posted by Dave Mount
I have found the Jamieson sharpening set up to be a bit complex for me, and I don't really understand it. As near as I can tell, it is a swept back grind, then you grind away almost all of the heel of the bevel, leaving maybe 1/16 or slightly more of the primary cutting bevel. There was a thread over on the AAW forum about it and his jig set up for it. The question I asked, was 'isn't it kind of like what you do when platform or free hand sharpening a swept back grind'? The answer appears to be yes. This means you roll the tool more as you sharpen the wings, so the wings have a more blunt angle rather than the more straight up and down wings you get in jig sharpening. This is similar to what happens when you do the 40/40 grind on a platform. You also grind away the heel of the bevel with the 40/40. As for general shape of the swept back grinds, bevel angles can vary from 50 to 70. Don't think any one goes more blunt than 70.
robo hippy
Reed, are you confusing Lyle Jamieson's with Johannes Michelson's Vector grind? Lyle's shaping is very similar to David Ellsworth's with a single hollow ground bevel except that the wing angles are considerably blunter, closer to the 60* nose angle. Maybe a "60-60"? Let's start a new fad. Link to Jamieson https://www.youtube.com/watch?v=3liDhY_zxSc
I think Reed is talking about easing off the heel of the gouge which can be problematic on a Jameson type grind. A secondary or even tertiary bevel is sometimes needed to make it more useful, especially in the transition area. Heel marks are a pain in the ... to remove sometimes.
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I don't think Lyle does that, at least not in the videos I linked to, not that one shouldn't. I mentioned the vector grind because Reed responded to a thread on that subject recently on the AAW forum.
I suspect that Mr. Jamieson could get a decent result with a sharp runcible spoon. He comes close in this video https://www.youtube.com/watch?v=JxgadMxUBcI
I may be confusing them.... Thing is, there are almost as many variations of swept back designs as there are turners. They do function pretty much the same way. Lyle doesn't seem to relieve the bevel. Christian Burshard has a variation he learned from, or figured out from Johannes, where he relieves the entire bevel. I don't use swept back grinds at all any more. No real use for them. I do all my shear scraping with scrapers. I use the 40/40 grind and BOB (bottom of bowl) gouges for the rest, and I have half a dozen or more variations of BOB tools.
robo hippy