Tantung gouge tips

[hughie]

Some years ago I came across Tantung steel which according to the blurb is in between HSS and TCT and can be ground by conventional grind stones. Then I ran across a comment by Robbo Hippy about its edge holding ability, something along the lines of “sharpen it in the morning and all turn all day” now that intrigued me. I picked up a piece 6mm square by 75mm and made up a simple Oland hollower out ¾ shaft results were very good. But at the end of the day its was a scraping type action and I was after a more durable slicing edge.
I teamed up with Neil Strong from Adelaide SA in order to make a few Tantung tips like the Woodcut variety for both of us. I would make them and he would run the test regime and write up the results. It had to be done over the net as we live 1500k a part or 850 miles and or about 16 hours drive. I would run a few tests and add to his outcomes where I could. My set up is quite simple I converted the 4” grinder into a tool post grinder for my ancient metal turning lathe and by the look of it, it would be close to 100 years and due to dark green paint I would say it was a veteran of WW2 to boot







In order to get around high speed of the portable grinder, I decided to use the 1mm cutting discs grind a series of 1mm groves close together down somewhere near the finished dia and then change to the grinding disc and finish grinding to as near the required dia as I could. I looked at variable speed drive but on single phase low rpms also means low HP or watts and at the rpm I wanted it would have been gutless. Later went on to use a conventional friable wheel to try and get a half decent finish, all in all the entire outcome wasn’t ideal but under the circumstances it was good enough to do some serious testing.

 

[hughie]

We managed to obtain 4 or 5 ¾” Tantung pieces used CNC machining bits ex USA and it was my job with the new tool post grinder to produce 12mm,16mm and 3/4 “ gouge tips

Showing here mounted on shafts in respect to each tips diameter secured held in place with Loctite 620, the secret with the 620 is to maintain the tolerances for maximum gripping .14 to .25mm or .0055 to .0095” It turned out to be more of a challenge than I realized and had to resort to .003” brass shim on one of the tips

told 3 Tantung tips were ground initially this way 12mm, 16mm and ¾ or 19mm. The rough shape grinding I reset the old friable grinding wheel back on just to save the CBN wheel. I also used this wheel to clean up the tip after reducing the dia down from ¾
.

 

[hughie]

Here we have the 12 and 16mm tips prior to shaping. In the beginning it became very obvious the wing angles needed attention as the gouge suffered damage with chipping and general edge degradation to the working area of the wing. This didn’t surprise me as the Tantung is primarily used for machining various grades of steel and would very good edge support.

This is where I ended up 70’ on the front with 45 on the wings, 12mm tip approx 50mm long in Tantung, still with straight sides although more shape to the bottom. Polished flute with the same procedure as the HSS

 

[Karl Loeblein]

You put a lot of effort into making these tips. Can’t wait to hear how well these work.

 

[robo hippy]

You are having too much fun! I always have to tinker with things. The only problem with the tantung is that it is brittle. You drop it, it will shatter. Not sure how the gouge wings will hold up. I would expect them to be prone to chipping. Let me know.

robo hippy

 

[hughie]

You are having too much fun! I always have to tinker with things. The only problem with the tantung is that it is brittle. You drop it, it will shatter. Not sure how the gouge wings will hold up. I would expect them to be prone to chipping. Let me know.

robo hippy

Yes We had to play around with the wing angles and until we got that sorted it was not looking it was worth the effort.

You put a lot of effort into making these tips. Can’t wait to hear how well these work.

its on the way

 

[hughie]

The anecdotal evidence thus far indicates with an angle combination of 70/45 on a Tantung bowl gouge tip. After an hour of turning Acacia Melanoxylon, very dry and very curly there was no appreciable wear and tare, the edge was sound showing no sign of chipping, it still felt sharp to the touch. Although it was evident by the way it was cutting, it needed a touch up with the diamond stone
.
This is the tip after lightly touching up the edge with a coarse diamond stone

 

[Neil S]

Hughie generously made two bowl gouges from Tantung for me to try, one ½” and the other ⅝”. I was pleased to have this opportunity to test the Tantung on some of the harder woods that I turn at times, which are known to challenge most woodturning tools.

Summary for those that don’t wish to read the details: Overall I found that Tantung performed close to V15 on endurance with push cuts where the leading edge is supported with metal behind it. On the finer cuts, like with shear finishing cuts, where the fine edge is less or unsupported, the Tantung didn't perform as well.

My test protocol: The Tantung bowl gouges were used alongside gouges made of other metals with each being used for a timed 30 seconds, in rotation, and on the same blank for each test run. This ensured as much as possible that each gouge got equally exposed to any variation in the test blank. Unless specified, each gouge was used until it could cut no longer.

Turning until a gouge edge is completely exhausted is not how we turn in practice, so why did I do this on these test runs? We all have slightly different standards on what we will accept as an edge that is still sharp enough to efficiently cut wood. By cutting until the edge will no longer remove wood eliminates some of the subjective element from the assessment of how durable it is. Only the individual woodturner can decide how tolerant they are prepared to be of a dull edge. I have included wherever I could the point at which I would refresh the edge, but then record the performance of the edge from there until it is too dull to cut any longer after that.

On the push cut test runs I limited the cut to the first 5-6mm from the tip back. This was to control the amount of fresh edge engaged in the test runs and to also reduce the time needed to get a result.

I used the hardest woods I had on hand for these performance tests partly because they would reduce the time required to carry out the endurance aspect of these tests, but also that is the particular use I am hoping to put these Tantung bowl gouges to.

Note: I have abbreviated Tantung to Tt in the following posts

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The following are the details of my test run results. Of course, your results may have been different.

My first round of tests used the flutes that Hughie first came up with. Here they are before the bevels were ground on them…

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The first test matched up the ½” Tt against a ½” M42, both with a 55° bevel and using push cuts on very old and hard redgum from farmyard fence posts. These are almost as hard as those stones it is sitting on there...

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After refreshing the edges, the next test run matched the ½” Tt against a ½” V10, both with a 55° bevel and using push cuts on the same very old and hard redgum blank.

Combining those two test run results using the same test blank I got…

I repeated that test run with another V10 BG from a different tool maker and got similar results for that V10. That other V10 gouge is a ⅝” with a 40/40° grind on it, so I also put a 40/40° grind on the ⅝” Tt. Another very old and hard redgum blanks was used. The two V10s performed about the same while the ⅝” Tt cut well for 10 mins and then poorly for just a further 2 minutes. So, the Tt with a 40/40° grind didn’t have quite the same endurance as it had with a 55° grind.

Based on that result I returned the ⅝” Tt to a 55° bevel angle and also widened the flute from 6.5mm to 10.5mm. Turners will play around endlessly with different bevel grinds, but treat the flutes on their BGs as sacrosanct. But, with a DIY bowl gouge you can endlessly customise the flute to suit yourself… :~}

Here is the changed flute profile…

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I then put the ⅝” Tt with the wider flute and 55° bevel up against a ⅝” V15 BG with the same bevel angle of 55°. In my experience V15 performs the best of any gouge that I have used on the tough hard woods that we have down our way. So, this was a better contest for the Tt.

I ran this test three times to ensure that it was a fair test. The first of these test run was on another v. hard piece of old redgum.

Both BGs cut well for 10 mins and 30 secs before both suddenly became too blunt to continue.

In an attempt to separate the two in the next test run I used an old, very hard, Allocasuarina blank…

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Here are the results…

 

[Neil S]

3rd Push cut and other test runs

In the third test run was on a piece of Allocasuarina that I know for certain to be Buloke (Allocasuarina luehmannii). Some specimens of this species have tested as hard as Janka 5060 lbf, which would put it at the top of the list of the hardest woods. The Allocasuarina blank used in the above 2nd push cut test was harder than this piece one, so was also probably Buloke.

Wood Species Janka Hardness Scale/Chart By Common/Trade Name A - E

771 woods listed alphabetically A - E by common trade. The world's top 125 known softest and hardest woods listed in order of softness and hardness.

web.archive.org

As an indication of how hard this wood is, a thick dust cloud comes off the gouge when turning this wood with the ‘shavings’ that settle more closely resembling grit than shavings…

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Here are the results from the 3rd push cut test run off…

I didn’t persist beyond the point where the two gouges had stopped cutting well given the similarity in the results to that point. So overall, the V15 had a slight edge on the Tt (pun acknowledged) in its endurance beyond where both were cutting well, but the Tt was a very close contender in these tough wood tests.

I then moved on to some wing cuts. The first was with peeling cuts where the purpose was rapid wood removal. The test was done on the outside of a piece of cranky grain Bluegum…

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Four different ½” 55° BGs were tested against each other. The V10 took heavy peeling cuts for 4 mins 30 secs and the Tt about the same, then both began to tear out the end grain. The M42 took heavy peeling cuts for 2 mins and an M2 only took heavy cuts for 1 minute before they began to tear out the end grain.

A test run with heavy scraping cuts with the wings off a 55° grind gave the following results on hard redgum…

Dedicated scrapers with a more obtuse edge angles like 70° may have given a different result, but this test was about how the wing edge might perform on this cut while the gouge is in hand and undertaking a variety of other cuts for which a middle of the road 55° grind would be more appropriate.

I then moved on to shear finishing cuts with the wing. This is a David Ellsworth outside finishing cut in which the handle is dropped, the side bevel rubs and very thin shaving are taken off along the wings. This cut is less destructive of the edges on the wings than a scraping cut. I included four ‘steel’ types in this test as I know from experience that the fine carbides in M42 are good for this cut.

The blank was the same cranky grain Bluegum, the bevel angle was 55° on all of the bowl gouges and I recorded when the long thin fine shavings became shorter than 1” for each gouge, which is the point at which I consider the gouge had become too blunt for this cut and tear out likely to happen.

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Here are the results of that test run…

The last test I ran was a light finishing scraping cut along the wings (with a closed flute) on the outside of the same piece of cranky grain Bluegum. The wavy grain in this blank was a good test for this finishing cut. The bevel angle was 55° again on all of the gouges and I recorded the point at which each became too blunt to take a thin fluffy shaving.

As anticipated, none of these test gouges did that well on this test and typically this is where we go to a dedicated finishing scraper where we expect to be frequently refreshing the keen edge required to keep getting those thin fluffy shaving coming off the tool.

Conclusion: Overall my test runs indicated that the Tt performed close to V15 on endurance with push cuts where the leading edge is supported with metal behind it. On the finer cuts, like with shear finishing cuts, where the fine edge is less or unsupported, the Tt doesn’t perform as well.

I did try a 40/40° grind on the Tantung and although not conclusive, I am inclined to think that the metal performs best, at least for my purposes, at a less acute edge angle than that. I settled on a 55° bevel angle, 30° wing relief angle on the wings and a 60° wing edge angle, which I used for most of the tests. It is yet to be seen how prone the brittle Tantung will be to edge chipping in regular use, which has been pointed out by Robo.

I like my V15 bowl gouge for the more demanding woods that I turn from time to time, but the V15 has become a bit scarce to come by lately, so a Tantung bowl gouge with very similar performance is an excellent alternative. And, if you DIY you can have whatever flute profile you prefer… :~}

In collaboration with Hughie I'm about to do a similar side by side test run between the Tantung, a V15 and a Tungsten Carbide bowl gouge. A TC bowl gouge is something that I have not had an opportunity to try before, so I'm looking forward to that. I'll report back on my findings here when I've done that.

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End Note: Like all of the other exotic turning ‘steels’, Tantung is full of heavy metal nasties. I was careful to avoid breathing in the metal dust while grinding it. Unlike some of the other exotics where you can capture the swarf on magnets near the grinding wheel, Tantung is non magnetic, so I set up my vac to capture as much of the fine dust at source as I could, as well as wearing respiratory protection. Tantung has quite a different metal composition (see the following) and you will get quite a different experience with it at your grinder with very few sparks coming off it, so waiting for sparks to start coming down into the flute to know that you have a fresh edge isn’t going to work with this one!

The typical composition of Tantung G is cited as Cobalt 35-40%; Chromium 27-32%; Tungsten 14-19%; Nickel 7%; Carbon 2-4%; and Iron 2-5%. Source: https://www.tttg.org.au/php/DocView.php?DocId=71

 

[robo hippy]

Yup, you are having too much fun! One difference between jig sharpened gouges and platform/freehand sharpening is that with a jig, the wings have a much more acute angle than the platform sharpened gouges. When shear scraping with scrapers, I prefer a burnished edge. The tantung can be burnished, but you want a light touch. Too hard, and you can fracture the edges. I have also wondered about making a skew with the tantung. Sandwich it in between softer metals, kind of like the Japanese plane irons and chisels. Not sure if the edge would hold up or not since the material is so brittle. Can't remember exactly, but just 'feeling' the cutting, I think the stellite would polish to a finer edge, which could be the difference between the metals. Tantung is cast, not sure how they make the stellite. It would be interesting to see a micro photo of the edges to see how they held up.

robo hippy

 

[hughie]

Yup, you are having too much fun! One difference between jig sharpened gouges and platform/freehand sharpening is that with a jig, the wings have a much more acute angle than the platform sharpened gouges. When shear scraping with scrapers, I prefer a burnished edge. The tantung can be burnished, but you want a light touch. Too hard, and you can fracture the edges. I have also wondered about making a skew with the tantung. Sandwich it in between softer metals, kind of like the Japanese plane irons and chisels. Not sure if the edge would hold up or not since the material is so brittle. Can't remember exactly, but just 'feeling' the cutting, I think the stellite would polish to a finer edge, which could be the difference between the metals. Tantung is cast, not sure how they make the stellite. It would be interesting to see a micro photo of the edges to see how they held up.

robo hippy

In the earth moving/mining industry, Stellite is applied via arc welding to bucket walls and cutting edges etc and I believe the early Kelton corers were made this way. So with that I think you/we etc could easily produce a Skew chisel. For those who maybe curious, as to my background I am a retired engineer with a couple of decades in the mining industry up my sleeve. its kinda where all this tinkering stuff stems from

 

[hughie]

On another note, and the Tungsten Carbide gouge tip, performed better than I expected. My test wasn't as exhaustive or well set out as Neil's, but the results were such that I tried to order a set of them, if not a set then 2 or 3 different sizes. Even with the extra cost of a diamond wheel set up, I was prepared to bite the bullet, such was the performance. But alas the project didn't get off the ground and I have been looking at and for alternatives ever since.

 

[Neil S]

I have also wondered about making a skew with the tantung. Sandwich it in between softer metals, kind of like the Japanese plane irons and chisels. Not sure if the edge would hold up or not since the material is so brittle.

I have a collection of hand forged knives from different Japanese blade smiths with HRCs well up in the 60s. Those steels are also very brittle. My experience with them is that they will slice for almost ever but microchip at the edge with any amount of lateral pressure/impact. The softer cladding iron will cushion the harder steel (higane) from a cracking completely through, and will hold it together if it does, but doesn't prevent micro-chipping at the exposed edge.

I wouldn't think a Tantung skew would go too well with roughing down to round cuts, but depending on your skew technique, the Tantung would be worth a go with slicing/peeling cuts.

 

[Neil S]

It would be interesting to see a micro photo of the edges to see how they held up.

robo hippy

OK, here they are, just the afters, didn't think to do before. Apologies for the quality. It is hard to get a good image on my little economy digital microscope. Magnification is at 200X....

Tantung edge near tip after test run


V10 edge near tip after test run


Tantung flute with 4x40 grind
after test run


10V flute with 40x40 grind
after test run​

There are some obvious differences there that explain the relative cutting performances of those two metals.
.

 

[Neil S]

I didn't manage to get a similar edge and flute mag image of the 15V gouge that I used in the test runs, but here is one view from the flute side after the test run and indicates why it performed so well. That grind is off #360 CBN wheel. For reference, the image next to it is with the same 200x magnification showing 0.5mm graduations, so we are looking at a 2mm width here...

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I did do a test run in which I honed all the bevel edges with a #600 diamond plate, but found if anything that the Tantung didn't performed anywhere near as well on the endurance test compared to the V15, which I can't explain...