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Bowl gouge dulling quickly

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Forum topic by JoshNZ posted 09-05-2018 08:33 AM 679 views 0 times favorited 16 replies Add to Favorites Watch
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JoshNZ

118 posts in 1189 days


09-05-2018 08:33 AM

Topic tags/keywords: sharpening

Just wondering if anyone can shed any light on why my bowl gouge dulls so quickly when hollowing out. I read something in a wood turning book last week about a guy saying he sharpened once or twice a day in a production workshop =/. Sometimes I’m lucky to get two passes before im really needing to push on it.

I’m guessing my problem is that I’m scraping the wings as the photo shows. Ive tried varying the openness of the flute and nothing seems to help. Is this just not a suitable grind to be hollowing with or am I doing something else wrong? It’s a 1/2”, U-flute, HSS, and quite a swept in fingernail grind.

It’s lovely to use right off the grinder, in my position shown I get a nice hissing with good shàvings. But it doesn’t last long. Wood is wet walnut.

Thanks!


16 replies so far

View Wildwood's profile

Wildwood

2408 posts in 2255 days


#1 posted 09-05-2018 12:19 PM

What brand bowl gouge do you have? Do you have the same problem with other wood species?

Looking a gouge picture looks like you are sharpening correctly.

-- Bill

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Nubsnstubs

1369 posts in 1850 days


#2 posted 09-05-2018 01:57 PM

I do a lot of Mesquite, and a bunch of Palo Verde, both local desert woods. From one tree, I can turn maybe 5 large plates before sharpening. Wood from another tree, sometimes I have to sharpen after 2-3 passes. I’ve heard that it depends on how much silica the wood sucks up while the tree is alive. My gouges are Thompson’s. ........... Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

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Kirk650

549 posts in 868 days


#3 posted 09-05-2018 04:16 PM

I assume you have HSS gouges. As for rapid dulling, the first thing that comes to mind would be that you may be making a semi scraping cut rather than slicing.

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Aj2

1662 posts in 1918 days


#4 posted 09-05-2018 06:33 PM

This also seems weird to me. I don’t do much turning lately but when I did the edge on my bowl gouges lasted very long time. I used a Tormek to shape and sharpen.
Maybe your grinder is too course and the steel is getting to hot?

-- Aj

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Woodknack

12338 posts in 2500 days


#5 posted 09-05-2018 07:22 PM

It can really only be 2 things, the steel isn’t very hard or the wood is full of an abrasive like silica. Change one variable and see what happens.

-- Rick M, http://thewoodknack.blogspot.com/

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JoshNZ

118 posts in 1189 days


#6 posted 09-06-2018 12:28 AM

The steel is HSS (so it says), it’s a fairly cheap set I got while I was in Canada. That said I was once stuck for a parting tool on my metal lathe and I formed one out of my round scraper from the same set and clamped it in the tool post. If it cut mild steel it should cut wet wood!

I tried some mangeo today a native NZ wood, still the same problem. Also tried a woodcut chisel with the replaceable hss tips, 3/8” and narrower flute, same problem across all so I think it must be my technique.

I’ve tried varying the flute angle as I said, I can’t see any way to present it to the cut that won’t make some of the edge scrape. The cut is clean because the last part of the edge is at a slicing angle but higher on the wing is definitely a more scraping angle. Is this normal?

The chisels are ground with a jig on a normal bench grinder fine grit wheel, I can touch the tip after the pass just barely. One or two strokes with 600grit out of the flute to remove the burr and then I get cutting, and it’s definitely sharp at that point.

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Wildwood

2408 posts in 2255 days


#7 posted 09-06-2018 10:26 AM

Looking at shavings on the floor don’t think gouge is the problem. Already mentioned about same species of wood can be both blessing or curse. Bottom line once you start forcing the cut, time to re-sharpen your tool!

Bevel angles are a compromise depending upon bowl design. If go to page 13 of link will find good info on bevel angles and see what am talking about!
http://s12166.pcdn.co/wp-content/uploads/2015/09/Woodturning_Notes.pdf

You already discovered even cheap steel tools will cut cleanly if sharp! So when in doubt re-sharpen your tool (s)! High carbon, any variety of HSS, exotic steel tools won’t cut cleanly when dull.

Yes some bowl gouge bevel angles work better than others for different designs. Then again a degree or two won’t matter much. So once find one stay with it, or will end up wasting lot of steel at the grinder and not accomplish much!

-- Bill

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Nubsnstubs

1369 posts in 1850 days


#8 posted 09-06-2018 02:25 PM



The steel is HSS (so it says), it s a fairly cheap set I got while I was in Canada. That said I was once stuck for a parting tool on my metal lathe and I formed one out of my round scraper from the same set and clamped it in the tool post. If it cut mild steel it should cut wet wood!

I tried some mangeo today a native NZ wood, still the same problem. Also tried a woodcut chisel with the replaceable hss tips, 3/8” and narrower flute, same problem across all so I think it must be my technique.

I ve tried varying the flute angle as I said, I can t see any way to present it to the cut that won t make some of the edge scrape. The cut is clean because the last part of the edge is at a slicing angle but higher on the wing is definitely a more scraping angle. Is this normal?

The chisels are ground with a jig on a normal bench grinder fine grit wheel, I can touch the tip after the pass just barely. One or two strokes with 600grit out of the flute to remove the burr and then I get cutting, and it s definitely sharp at that point.

- JoshNZ


Leaving the burr on the tool end is supposed to give a good cut until it wears off. Try turning with the burr on and see if it extends the turning time between grindings. ............... Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

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JoshNZ

118 posts in 1189 days


#9 posted 09-07-2018 10:36 PM

Great little attachment thanks Bill I’ll read through that again.

I will try leaving the burr on the tool too. It is paper thin usually I can flex it over with my fingers I couldn’t imagine it making a difference.

I think I’m getting better results holding the flute more open. So that more of the edge is presented at a slicing angle and less at a scraping.

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LeeMills

587 posts in 1421 days


#10 posted 09-08-2018 12:27 PM

I keep looking at pics 1 & 2 and can’t decide. This may not help at all but the tool should not dull that fast.
It appears you may be trying to cut (scrape) directly into the end grain by the “dust” shavings in pic 1.
About minute 5.5 Lyle shows hollowing with the push cut. Note he is cutting about 45° toward the headstock.

www.youtube.com/watch?v=1HF9IGdHCTA

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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JoshNZ

118 posts in 1189 days


#11 posted 09-09-2018 12:10 AM

I keep referring back to that same video as well I learned a lot from Lyle’s stuff. He’s what prompted me to try opening the flute a lot more which helps a little.

It’s probably been a combination of cheap steel, scraping, and silica rich wood.

Let me ask you this how long would your edge last if you scraped a whole bowl?

View Wildwood's profile

Wildwood

2408 posts in 2255 days


#12 posted 09-09-2018 12:38 PM

So many things can determine how long a tool stays sharp, type of steel, wood species, how you hold the tool, bevel angle on that tool, whether using a push or pull cut, etc..

Nice video explaining shear scraping. Reed loves his scrapers but does use his gouges too!

https://www.youtube.com/watch?v=xeOhPqOsORs

Have to learn difference on what you are turning whether push or pull cut is better on the piece working on.

Mike almost the same info as Reed but worth a look!

https://www.youtube.com/watch?v=77Yyd7PGMCA

Tool buying advice:
https://www.youtube.com/watch?v=ZM4ak8ygzS4

Both Reed & Mike will talk about using scrapers inside a bowl and extending over the tool rest if pay attention heavy duty scrapers a must!

-- Bill

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LeeMills

587 posts in 1421 days


#13 posted 09-10-2018 12:41 AM



Let me ask you this how long would your edge last if you scraped a whole bowl?
- JoshNZ

I’m going to assume you mean with a bowl gouge. I have only used a scrape or sheer scrape with a bowl gouge as the final cleanup. Your earlier comment on the burr being able to be easily bent is normally true with a bowl gouge;
with a scraper the angle is usually 70° or greater so there is a lot of steel even when the burr is gone in just a couple of minutes.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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JoshNZ

118 posts in 1189 days


#14 posted 09-14-2018 10:01 PM

I changed the profile of my gouge yesterday, taking on more of a V with a radius tip than a fat U like it was. Also increased the bevel angle a bit and I took more of the bevel off the wings so it’s not quite so swept in as it was and it has helped tremendously. I roughed a whole bowl with only one sharpen in between.

Will have to keep playing around I might purchase a Thompson gouge. Any idea what size I should be after, if I’m only going to have one at this stage and already have a 10mm and 1/2” (diameters not flute width) in other brands.

Cheers

View OSU55's profile

OSU55

1834 posts in 2109 days


#15 posted 09-16-2018 12:38 PM

Might not be time for an expensive Thompson yet. If you saw a big improvement with changing wing sweep and bevel angle, it tells me you have a long way to go yet in determining the sweep and bevel angles that work well. Better to grind up cheap tools while figuring this out vs expensive tools.

5/8” tool dia not flute is by far my most used bowl gouge size and is the only size I buy in expensive steel.

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