Finding the cut - Thompson gouge

[Aaron Craven]

A wonderful friend recently gifted my my first Thompson bowl gouge (5/8" V-shape). Wonderful tool, and I'm very impressed by it's ability to hold an edge. But I'm having a little trouble transitioning to it.

As background, I have in the past used a 5/8" Sorby gouge (a hand-me-down that was also quite nice, but was reaching it's end of life before I had a catch and broke the handle) and a Benjamin's Best 5/8" gouge that I bought as a short-term replacement until funds could support a higher-quality purchase (as a side note, I've been pretty impressed by the BB gouge -- though it doesn't hold an edge nearly as long as the Sorby and even more so the Thompson gouges).

I recreated the grind on my previous gouges on the Thompson gouge (as closely as I could anyway), but I'm having a bit of trouble finding my cut with it when doing push cuts (especially on the inside of bowls). I get a lot of vibration and my curly shavings start turning to dust (yes, this is with a freshly sharpened tool). I can switch back to the BB gouge and find my cut pretty quickly. I refuse to believe it's the quality of the tool itself, so it's either the grind or my presentation (or both). Looking at the flute on the BB gouge in comparison to the Thompson gouge, I think the flute on the Thompson is slightly more V-shaped, so that may have something to do with it, but not sure.

Any tips? I was thinking maybe I should grind the nose a little blunter (without changing the angle -- just take off a bit more material), but I hate to grind away steel needlessly if this is just a problem with presentation.

[Robert Henrickson]

Differing flute profiles can have dramatic effects on how a gouge cuts, even with the 'same' grind. I'm happier with some flute profiles than others.

[Prashun Patel]

Can you post a picture of your grind?

I wonder if you are cutting more with the tip than the side wings. I was having this problem recently. Rolling the flute to about 45 degrees reduces the risk of catching with presenting more of the wing to the wood.

If you are cutting green wood, beware with that 5/8". I find it super aggressive. It will often dig a channel on one pass which creates troughs that subsequently cause the tool to bump along instead of cut.

[Aaron Craven]

Can you post a picture of your grind?

I'll try to get some pics tonight.

In this case it was green wood, though I had a similar problem the other day on some really dry hickory. In that case, I had trouble cutting it with anything, though... dry hickory is like cutting cement :-o

What you're saying make some sense though. As usual, I did find that as I had trouble I tended to add pressure (which of course is the wrong thing to do). That would make the "troughing" you described worse.

When you say "rolling the flute", I assume you mean along the axis of the tool, correct?

[Prashun Patel]

Yes, along the axis.

[Aaron Craven]

Yes, along the axis.

Okay. Yeah, I thought I tried that, but I'll give it a go again next time I get a chance. It's not really that I couldn't find the cut at all... I would just have to hunt for it, and then I'd lose it pretty quickly. The wood (red oak) was also starting to warp on me, so I'll try with some mostly dry soft maple. I usually find it pretty easy to work with.

[Dan Forman]

Sounds like you are cutting with the tip and losing contact with the bevel, which is essentially scraping, based on the vibration and sawdust rather than shavings that you describe. Cutting with the tip in not really the problem, so much as losing the support of the bevel.

It also sounds like your grind may be close but not identical to what you are used to, which might require a different approach. Do you have a grinding jig, or do it freehand? A V flute will cut a little differently than a U flute, so you may have to just play with it a while, and find a different approach, making certain you are keeping the support of the bevel.

Dan

[Aaron Craven]

Sounds like you are cutting with the tip and losing contact with the bevel, which is essentially scraping, based on the vibration and sawdust rather than shavings that you describe. Cutting with the tip in not really the problem, so much as losing the support of the bevel.

It also sounds like your grind may be close but not identical to what you are used to, which might require a different approach. Do you have a grinding jig, or do it freehand? A V flute will cut a little differently than a U flute, so you may have to just play with it a while, and find a different approach, making certain you are keeping the support of the bevel.

Dan

That's what I'm gathering from other comments. I do think I was cutting with the tip and I know I was losing bevel contact (with the vibration I was getting, there was no way to keep it except to back up and try starting a new cut).

I'm using a Wolverine/Varigrind setup to sharpen. I actually sharpened my old gouge first to set the grind and then used that to repeat it onto the new one (including resetting the depth on the varigrind before my final passes to ensure I accounted for the change in length as I set the initial grind). That said, I know that a crucial part of the process is the amount of time you spend on the various areas, so it's very possible the grind isn't identical.

Incidentally, the BB gouge isn't really a U gouge either. It just has a less severe V than the Thompson. The difference is actually rather subtle (at least in appearance).

I'll post photos later, but mostly it sounds to me that I just need to practice. More time playing at the lathe? I think I can live with that

[Mark Greenbaum]

Not sure if this will help, but I grind the very bottom of the heel on my WoodRiver Gouges at a freehand 45 degrees. A mentor showed me this trick, and it helps when making that transition from wall to bottom.

[Aaron Craven]

Not sure if this will help, but I grind the very bottom of the heel on my WoodRiver Gouges at a freehand 45 degrees. A mentor showed me this trick, and it helps when making that transition from wall to bottom.

I actually just did that to try out on my older gouge. For the bowl in question, it wasn't a problem, because it had a fairly even slope, but I think this is something I will eventually be doing on my new gouge as well. It does seem to help -- especially if I do a somewhat more abrupt transition.

[John Beaver]

The flute on the Thompson gouge is generally not as deep as it is on a Sorby. This leaves more meat below the flute for strength but also leaves more length on your bevel. I would try grinding away the bottom of the gouge to shorten the bevel and see if that helps. I think Mark Greenbaum is suggesting the same thing.

[Aaron Craven]

The flute on the Thompson gouge is generally not as deep as it is on a Sorby. This leaves more meat below the flute for strength but also leaves more length on your bevel. I would try grinding away the bottom of the gouge to shorten the bevel and see if that helps. I think Mark Greenbaum is suggesting the same thing.

I liked this when I tested it on my BB gouge, so I think I probably will.

Also I do recall the problem got gradually worse as the bowl thinned, which makes me wonder if it wasn't simply a matter of the wood moving. By the time I finished sanding the piece (I decided to single-turn it and let it warp), it had already gained about a 1/4" difference between the long and short widths. Then again, the problem seemed at its worst as I neared the bottom of the bowl where the warping should be relatively small.

*sigh* Stinks to be stuck at work when I'd much rather be out in the shop.

[Kyle Iwamoto]

I have several different brands of gouges, and sharpen them all on the same jig (Tormek). I find that the different brands "cut" different. I don't know why, but it's obviously due to the shape of the flute, since they all come from the same jig and have the exact same angles. It takes a couple seconds to go back and find "the cut" as you say. As mentioned, grinding off that heel does help finding that bevel and getting the gouge to cut. Try going back to the basics, run the gouge back all the way off the bevel and slowly come on to the bevel and see if that helps. I also found the Thompsin V's, they cut very different.

[Doug Ladendorf]

Good info above. For inside the bowl cuts you might also try lowering your tool rest a bit. Could be that you are just cutting a bit too high on the inside.

[Dan Forman]

If you are mainly having trouble at the bottom of the bowl, it could be that your bevel angle is too shallow to allow full support of the bevel at the bottom of the bowl, especially if the bowl is relatively deep. Some turners use different gouge for the bottom third, with a steeper bevel, and often times a traditional grind. These are generally called "bottom feeders", named after a Mike Mahoney signature gouge. Somewhere on the web is a series of drawings showing how bowl shape effects the required grind to maintain bevel contact, but I can't seem to find a link to post - maybe someone else can do that.

Dan