Thompson 5/8 U gouge - first impressions

[rsser]

Letzzgo asked me to post on this and I've had a play hollowing an open bowl 25 x 10 cm.

Most folk go for the V gouge as I did with the first bulk buy.

Doug Thompson says the virtue of the U profile is that it readily allows the cutting edge to be oriented in shear fashion when hollowing.

The gouge comes with a 60* bevel angle at the tip. The flute is reasonably clean in terms of milling marks. There's a long even radius cutting profile.

From the bowl edge to about the mid mark it worked well. Then geometry got in the way. The handle end started to foul the bed.

The handle is about a third longer than the steel, and the banjo top on the VL175 is quite high in relation to the swing.

There are a number of options to change this geometry.

My inclination is to shorten the handle.

[Pat]

Send it to me Ern :U

[rsser]

Kind of you Pat.

I've already sent you one gouge. Worn it out already? ;-}

[Pat]

Just trying to help you Ern. The little Glaser is quiet comfie, really only being used to shear scrape smaller bowls.

Any pics of the Thompson?

[Sawdust Maker]

Letzzgo asked me ...

The gouge comes with a 60* bevel angle at the tip. The flute is reasonably clean in terms of milling marks. There's a long even radius cutting profile.

From the bowl edge to about the mid mark it worked well. Then geometry got in the way. The handle end started to foul the bed.

The handle is about a third longer than the steel, and the banjo top on the VL175 is quite high in relation to the swing.

There are a number of options to change this geometry.

My inclination is to shorten the handle.


Interesting

Mine wasn't ground ex factory. I had to grind it to suit myself. Hence my comment that it didn't work too well initially, I'd not fully/properly ground it :doh:
I put a 15" jarrah handle on it. Lovely. In fact after using it to rough down today, I thought the P&N handle on the 1/2" a little wimpy. I'm not sure I'd want a shorter handle, but then I'm still finding my comfort zone. I didn't use it much inside the bowl as I was mainly roughing down and coring.

Your comment on another thread about diamond hones was interesting. I tried to touch it up during the job with a diamond hone to little effect. Seems to be a harder steel then the P&Ns

[letzzzgo]

Letzzgo asked me to post on this and I've had a play hollowing an open bowl 25 x 10 cm.

Yes, Ern, I think I asked for a comparison in performance between the 5/8" V and 5/8" U Thompson bowl gouges. I suppose for a proper comparison both gouges would require the same grind. I'm not sure if this is feasible?
How much shorter would you need to make the handle to avoid fouling on the bed?

John

[NeilS]

My inclination is to shorten the handle.

...or turn outboard where the handle won't bump anything...:D
.

[rsser]

Yes, I'd swivelled the head out Neil but still had probs within the reach of the banjo.

Outrigger would be an option as you say; there are others and I need more time to play.

Pat, will post a pic later.

John, your question depends on the bowl form and I hesitate to speculate at this early stage.

Re comparo with the V, yes indeed, the grinds are different. The V had IIRC a longer bevel. Can no longer recall the wings form as I've reshaped the bevel a couple of times now.

The U has medium swept back wings.

Nick, yeah, you got one with the tip not ground if I recall. Not good.

My comment re polishing the flute and bevel was about Tormek paste by the way, not diamond (not yet).

[Sawdust Maker]

Tip not ground didn't concern me, in fact I didn't think anything of it at the time. It might have been interesting to see how a Thompson grind looked.

By diamond hone I meant a little diamond stone I'm using to touch up the bevel whilst in use - to save a full grind. ie I'm too lazy to walk to the grinder :p


BTW if anyone wants the Tormek setup for the initial Thompson grind on the spindle gouge then I've got them. worked them out when he was here.

[Doug Thompson]

I prefer a V shape flute over a u shape anyday but when it comes to a U shape flute think... Push cut, Stu Batty finish cuts, roll the tool and use the large radius to your advantage to shear the wood. There are a hundred ways to grind that tool so I put a very basic grind on the tool without removing too much steel... IMO - I would free hand the grind like Stu Batty or Johannes Michelsen to 45 degrees to the flute then put a large secondary bevel to remove the extra stock. This is the grind I would use but freehand grinding is not for everyone.

P.S. - I'm working on a process right now to improve the steel... so far it looks good.

[rsser]

Thanks for the tips Doug.

I like a 60 degree bevel for some applications by the way.

I've just been doing some dry runs with the tool as it happens, before reading your post.

One option with this tool as is, is to pretty much have it horizontal and cut along the equator, rolling the tool to maintain the shear angle. (Talking about hollowing just to be clear).

I'm not comfortable with this approach as it isn't the way I normally work. It also requires an open form and my sense when I tried it once live in the first session is that it increased bowl flex. For some of the arc in the dry run I couldn't see what the edge was doing. But I'll play some more and look up 'Stu Batty finish cuts'.

Attached is a pic of the flute as best I could get alongside one of the 5/8 V gouge taken for the previous bulk buy.

[rsser]

Doug: is this what you meant by Stu Batty finishing cut ... ?

pull cut, shaft towards vertical, bevel rubbing up highish on the bowl outside, flute facing direction of pull.

[Skew ChiDAMN!!]

Hiya Ern!

Just meandering OT for a sec... out of curiosity I googled Stu and found this link: Stuart Batty Woodturning Encyclopedia (http://www.woodturning.org/encyclopedia.html)

If he follows through on the promised articles, I can see this site becoming a handy reference! :2tsup:

[rsser]

Hey Andy!

Yeah, I ended up there too.

Turning university?!

Got tickets on himself but sounds like he earned them ;-}

[Doug Thompson]

His finish cut a push cut using the radius, I'll see Stu at the end of the month and will try to get pictures of the grind.

[rsser]

OK. Thanks.

So I'm thinking that that cut must position the cutting edge of the bevel at about 45* to the travel of the wood, or even steeper if poss. in the way that Michael Mouse seems to use a shallow forged spindle gouge.

[robo hippy]

All the different cuts..... So many to choose from.

The Michael Mouse cut: He uses a continental style spindle roughing gouge, or as he calls it a broad sweep gouge, with a nose profile like this ), which is about the same as the depth of his flutes. His finish cut is a push cut, with the gouge at about a 60 to 70 degree shear angle, and he DOES NOT RUB THE BEVEL. It is a push cut. I swore that this was not possible, especially on the inside of the bowl because if you came off the bevel, it would catch just like a skew does. Well it didn't catch, and because of the high shear angle gives a very clean cut. You do need to use both hands to push the gouge. As some one who prefers a bevel rubbing cut, I find this totally freaky, but worthy of more study. I don't have the link for his video though.

Mike Mahoney uses a pull cut. Non bevel rubbing, handle dropped. Again, a high shear angle for a clean cut. He uses a 45 degree bevel, and 45 degree sweep. I think he uses more of a push cut on the inside of the bowl. Can't really see how you could do a pull cut on the inside of a bowl.

Stewart Batty uses a bevel rubbing push cut, both inside and outside the bowl, and again the 45 bevel and 45 degree sweep. Can't remember if he grinds a secondary bevel for doing the inside of the bowl or not, even though I took a 3 day workshop with him and his father about 2 years ago.

I used to use the swept back, 45 degree bevel. Now, gradually happening to evolve as I turn more, my grinds are steeper bevels, a more rounded nose, and less sweep. The 45 degree grind is more of a universal grind which will do a lot of things well, especially if the bowl form is more open. As the bowl gets steeper, as in radius is the same as or less than depth (12 inch diameter bowl 6 inches or more deep), it becomes impossible to make the cut from the side through the transition, and across the bottom without having your handle and gouge run into the bowl rim and/or the tool rest. This is where steeper bevel angles come in. Mine are closer to 60 degrees now.

An ongoing experiment.

robo hippy

[rsser]

Here's a link to MM and his finishing cut, the 2nd tool in the vid: click (http://s35.photobucket.com/albums/d160/GoodOnesGone/?action=view&current=Outside.mp4)

[robo hippy]

It does look normal on the outside of the bowl, but when done on the inside, it still gives me shivers even though I know it works. You really can't see it in MM's video, but there is no bevel rub.

robo hippy

[RETIRED]

He is actually shear scraping with a spindle gouge with a thumbnail grind.

It is my preferred method as well, as I find it easier than a bowl gouge because the cut is not hidden by the upper edge.157715

The angle of presentation is easier also than a bowl gouge because it has not got the wings that a bowl gouge has.

Very safe for outside and inside open bowls provided you keep the bevel at right angles to the bowl face and keep the cut in the lower half of the gouge.

[rsser]

, forgive me if I've missed something, but as I said, the 2nd tool he uses in that vid is a (shallow) forged spindle gouge with as far as I can see a straight across cutting edge.

There are other, clearer, vids he's linked to on the AAW forum. I couldn't find them in a cursory search this morning but if you have the time ..

[RETIRED]

Ern, if you look closely it is sharpened with a thumbnail grind like these:157737

[robo hippy]

,

You touched on one of my personal pet peeves.

The term "shear scraping" baffles me. The cut shown with his broad sweep gouge is a good slicing cut. Scraping to me is the tool flat on the tool rest, and cutting edge at 90 degrees to wood rotation. Can be done with both the gouge and scraper. The "shear scrape" can be done rubbing the bevel or not. The wood fibers cut the same. Some say the difference is bevel rubbing or not. The wood fibers don't know the difference between the tool used or the shear angle of the tool.

Scraping cuts, yes.

Shear cuts, yes.

Shear scrape? Well, maybe a cut with a deep fluted gouge where the nose is at a shear cut angle, and the wings are at a scraping angle. Can not be done with a scraper or broad sweep gouge.

Maybe better defined as roughing cuts (bulk stock removal cuts), shaping cuts (lighter final form shaping cuts), and finish cuts (very fine clean up the tool marks and tear out cuts).

Maybe this is a topic for another thread.

robo hippy

[RETIRED]

Good point RH.

I define it thus: A cut is when the bevel is rubbing. A scraping action is when the tool has no bevel support no matter what tool is used.

[robo hippy]

That is what I find so confusing, and I don't need any help being confused. Whether the bevel is rubbing or not makes almost no difference in how the steel cuts. The angle of the cutting edge relative to the spin of the wood (shear/angled vs scrape/flat/perpendicular) makes a huge difference.

robo hippy

[NeilS]

The term "shear scraping" ......

Maybe this is a topic for another thread.



Agreed, it was covered extensively here (http://www.woodworkforums.com/f8/tutorial-shear-scraping-113991/#post1118469).
.

[rsser]

Heh heh.

, thanks.

robo hippy, actually for the tip of the tool to penetrate (to cut at all), there's a tiny part of the bevel just from the tip back that is in fact supporting the tool. So you have the shaving coming into the flute pushing the tip down, and the small length of bevel helping to keep the tip up. A balance of forces.

When folk talk about the bevel rubbing I guess they mean more than a smidgen from the cutting edge, and I also guess that this rubbing is pushing the fibres down and is burnishing the wood (which is what has said about the action of a skew in spindle turning if memory serves).

Sorry if this is trying to teach you to suck eggs.

[rsser]

Back to the Thompson 5/8 U gouge ...

Just used it to shape the outside of a bowl of Euro Ash and it worked very nicely.

The 60* bevel angle (flute to bevel included) means that compared to the more common 45* bevel more of the pounding goes to the tool rest and less to the hands.

The wide arc at the edge means that lots can be hogged out and the tool readily rolled to get more of a shear angle for cleaner cutting. It did that to about 3/4s up the side from the base and from there a 3/8 Superflute finished the job.

It's quite like my old 17mm P&N Supagouge but the flute curve is more regular running up the walls.

So as a bowl rougher, partic with the high Vanadium content to resist sand and other crap that might be in the bark, on this bit of wood at least it performed very well.

This role has been played by the Thompson 5/8 V gouge so far and I've progressively been grinding more off the tip to get a wider cutting arc, but can easily see the two swapping roles. However, I'll continue with it as is in order to determine more clearly the hollowing advantages.

Meantime, I'll need to determine the settings for the Tormek gouge jig cos the edge needs a lick on the grinder now. Diamond wheel and BGM first, then the big T.

[NeilS]

I used to use the swept back, 45 degree bevel......

Mine are closer to 60 degrees now.



I settled on 60 deg for all of my bowl gouges a few years back and haven't felt any need to vary from that, but my roughing and spindle gouges are all over the place.

RH, I understand that you put a secondary bevel on the heel of your bowl gouges. If so, that must come into the consideration of which primary bevel angle you settle on?
.

[robo hippy]

I do grind off the back of the bevel on my gouges. Main effect is that when turning the inside of a bowl, the bevel will rub closer to the cutting edge. Not a problem on the outside (convex shape) of the bowl, but more of a problem on the inside (concave shape). Stewart Batty explained that if you are rubbing the heel of the bevel on the inside of a bowl, it does 2 things. One, it can bruise the wood because it is a rather sharp edge. Two, it actually pushes the gouge into the cut, which is part of why you can some times see concentric rings on the inside of the bowl. Ever notice how much easier it is to turn the outside of the bowl than it is to turn the inside? It isn't all due to just being able to see the outside shape/form better than you can see the inside. I don't grind a second bevel, but round it over by rolling and raising and lowering the handle so it is rounded.

Again the bevel rubbing/not bevel rubbing. By definition, cut = bevel rubbing. Scrape = no bevel rubbing. So, if my scraper is flat on the tool rest, then it is a shear scrape? If my scraper is at a 45 degree angle, it is a shear scrape? If my gouge is on its side, no bevel rub, pull cut it is a shear scrape? If my gouge handle is dropped and flutes rolled over, and no bevel rub it is a shear scrape? My rock hard Irish head just can't seem to get around this as there are 3 different cuts here to me.

robo hippy

[rsser]

Yeah.

My post #27 was harking back to the point about MM's forged spindle gouge not rubbing on a bowl outside. Sorry, should have made that clear.

...

I've taken shear to mean anything done by an edge at an acute angle to the direction of the travel of the wood.

[RETIRED]

Ern is partly right.
I've taken shear to mean anything done by an edge with no bevel support at an acute angle to the direction of the travel of the wood.


Again the bevel rubbing/not bevel rubbing. By definition, cut = bevel rubbing. Scrape = no bevel rubbing. So, if my scraper is flat on the tool rest, then it is a shear scrape? No. It is pure scraping.

If my scraper is at a 45 degree angle, it is a shear scrape?Yes provided that the included angle is less than 90 degrees to the wood.

If my spindle gouge is on its side, no bevel rub, pull cut it is a shear scrape? Yes provided that the included angle is less than 90 degrees to the wood. Similar to what Michael Mouse does.

If my Bowl gouge handle is dropped and flutes rolled over, and no bevel rub it is a shear scrape? Yes provided that the included angle is less than 90 degrees to the wood.

My rock hard Irish head just can't seem to get around this as there are 3 different cuts here to me. The type of tool and the way it is presented to the work denotes a shear scrape.

[NeilS]

I've taken shear to mean anything done by an edge with no bevel support at an acute angle to the direction of the travel of the wood.

So, 'shear' cuts with bevel rubbing are something else...:?
.

[NeilS]

I do grind off the back of the bevel on my gouges. Main effect is that when turning the inside of a bowl, the bevel will rub closer to the cutting edge. Not a problem on the outside (convex shape) of the bowl, but more of a problem on the inside (concave shape). Stewart Batty explained that if you are rubbing the heel of the bevel on the inside of a bowl, it does 2 things. One, it can bruise the wood because it is a rather sharp edge. Two, it actually pushes the gouge into the cut, which is part of why you can some times see concentric rings on the inside of the bowl. Ever notice how much easier it is to turn the outside of the bowl than it is to turn the inside? It isn't all due to just being able to see the outside shape/form better than you can see the inside. I don't grind a second bevel, but round it over by rolling and raising and lowering the handle so it is rounded.



Rounding the sharp heel to minimise bruising is understood.

On the second point, I've always found that sideways thrust as you lean into the inside cut is one of the nice things that happens when hollowing out a bowl and, if necessary, a finishing cut will tidy up any irregularities... :rolleyes:

Anyway, I did experiment at one stage with easing back the heel on some of my bowl gouges and found that it felt more comfortable with the primary bevel ground back to an even higher angle than my normal 60deg. I guess this is what I had in mind in connecting a higher grind angle on a gouge with a 'secondary' bevel.
.

[rsser]

Some more comments about the Thompson U 5/8 gouge after roughing a good size lump of green Elm (starting size about 40cm) ....

Of course lumps of timber vary but I'm inclined to think now that Doug is right, that it's harder work roughing the outside with this gouge than with a 5/8 V. But anyone at home with a P&N Supagouge will find this works similarly.

As for hollowing, yes, the wide even arc of the cutting edge means you don't quite have to be on the ball with presentation to the same extent as the V gouge. As you go deeper and wider you can readily roll the tool increasingly using the left wing at the rim and rotating through to the right wing as you come to centre.

There was more tool chatter than I'd expect as the overhang increased and it was easily dealt with by swinging the rest in closer. Normally I'd lower the tool handle and 'climb' the wall more but the VL175 banjo top is too high to allow this.

So is there a compelling reason to opt for a U gouge over a V gouge if you can only have a quiver of one? I don't think so.

But one snowflake does not a winter make.
.