Sharpening tungsten carbide gouges with diamond

[Neil S]

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One of the drawbacks for gouges made from tungsten carbide (TC) is that it is best sharpened with diamond. Many of us now have CBN grinding wheels for sharpening our HSS turning tools and although those could be used to sharpen TC that would be both inefficient (something like only 67% efficient as diamond) and would also shorten the life of the CBN wheel for use with HSS, which is its primary purpose.

With their wider use, the cost of CBN wheels have progressively come down in recent years at the same time as diamond wheels have gone up with their lesser use. With the exception of the diamond wheels made specifically to fit on Tormek style machines, quality diamond wheels that will run on a bench grinder are now costing upward of twice to three times more than a similar sized CBN wheel. So, few of us are going to go to the expense of having a diamond wheel in our workshops, in addition to our CBN wheels, for just sharpening TC.

Of course, if you happen to already have a:

• Tormek with a diamond wheel on it then you are good to go… :~}
• Diamond wheel for your bench grinder, as some still do, ditto!
• Sorby ProEdge sharpener or similar, just swap in a diamond belt on that…
• Using one of those diamond belts on a DIY belt grinder is another option.

However, few of us do have those options, so that leaves the challenge of finding an economical way of sharpening TC tools with diamond.

Most of us do have a few handheld diamond plates that we use to freshen an edge on our turning tools and they will also do a good job of doing that on TC, albeit slowly and without the benefit of being able to use jigs and attachments to maintain angles, etc. The thin single sided diamond discs that are used in lapidary for shaping and polishing gems are made in the same way as the handheld diamond plates we have been using and compared to diamond wheels are relatively inexpensive. In lapidary they are mounted horizontally on a platen and grind with water. I experimented with mounting the discs vertically on the side of my 8” CBN wheel and set up my gouge jig to sharpen against the discs in two ways…

With the first method I attached a cleat with a jig leg pivot point to the back of my sharpening platform…

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The sideways position of the cleat determines the correct sharpening angle against the disc. Once the cleat is fixed in position, that sharpening angle will be maintained regardless of how the platform is swung in and out, which will be done to get a position where the gouge tip won’t intersect with the wheel retaining nut or flange while being sharpened. The platform can be swung down out of the way or back into position for platform sharpening after using it this way and the correct setting will be maintained for when it is needed for sharpening TC next time.

Any of the swing away sharpening platforms could have this method added to them. If you don’t already have a sharpening platform on your grinder you could rig up something similar for just this purpose. Ensuring that its axis at the pivot point is square to the grinder axis is the key requirement.

This method has the advantage of allowing a TC tip if mounted on a longer shaft to swing unimpeded to get the full grind back along both wings. This method will produce a different grind pattern on the bevel to what you will get with wheel grinding, but as far as I could tell that didn’t affect the performance of the gouge edge.

The other method I tried was to use a slide with a pivot point mounted on the bench top square to the end of the grinder with the grinder raised (I needed to do that by 2”) to accommodate the length of the jig leg that I normally use. Here is that setup…

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Both the left and right sides of the disc need to be used to fully grind back both wings.

This setup works well with shorter gouge bars like the one shown in the above photo, but if a longer shaft is attached to the carbide tip the overall length of that is restricted with that setup. The maximum length of shaft + TC tip was 10” with my setup doing a 42° bevel grinding using a Tru-Grind jig. This overall length could be extended by raising the grinder further off the bench and also raising the height of the slide so that the grind contact point is maintained at grinder axis height. I found that grinding at axis height was necessary with a 6” disc to allow my jig to swing past the outer diameter of the 8” wheel when grinding the wings.

Another way to setup so that the length of the gouge shaft will not be an issue is to position the bench grinder so that the side of the wheel hangs out over the edge of the bench, but I couldn’t find a way of positioning the slide that I used so that the pivot point for the leg of the jig was away from the side of the bench without the clamp on the slide being located somewhere underneath the grinder. I have an idea of how to get around that, but haven't implemented it as I don’t have a need for longer shafts at this stage.

 

[Neil S]

The grind pattern on the bevel with this end on to the axis setup will be similar to that off the face of a grinding wheel, but with a #1k diamond disc you don’t see much of a grind pattern…

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My tests showed that a #1k diamond disc gave my TC bowl gouge the best edge endurance, so I currently recommend using at least a #1k diamond disc for refreshing edges. A higher grit may do better yet again, but I haven’t tested that yet.

Green silicon carbide wheels have been used in the past for sharpening TC. They have the advantage of being able to be shaped for profile grinding, which isn’t required for gouge bevel sharpening, but they are also far less efficient than diamond and have all of those issues with having to regularly dress them and the associated mess that comes with that. They also don’t come as a wheel in the finer grits that diamond does.

There is one other economical option which I haven’t used specifically for re-sharpening TC gouges, but have had some experience with it for other purposes with TC and that is to use loose diamond grit that can be added to a wax buffing compound and applied to a hard substrate like High Density Fibreboard (HDF). It is quick and effective. Loose diamond grit comes in a wide range of grit sizes and is reasonably economical from some sources. The HDF disc or wheel must rotate away from the cutting edge or it will dig in (big time!) if the HDF is used with it spinning in towards the cutting edge!

One option with this method is to use a thick HDF wheel mounted on a bench grinder and use it from the back of the grinder where it is rotating upwards. Or, if you have a spare old or underutilized bench grinder (say an old 6”) you can detach the motor from its base, rotate the motor around 180° and then reattach the motor to its base so that the switch will be at the front and the HDF disc rotating upwards away from the cutting edge, see second part of this video...

View: https://www.youtube.com/watch?v=isWzcFBlNmU

Some of the wax/diamond charge applied to the circumference of the wheel will be flung off during use if run at bench grinder speeds, so some form of guard/hood is a good idea to capture that and also to reuse that diamond, which will still be good. I presume that a slow speed bench grinder would be better for this purpose and also the lower peripheral speed of a 6” grinder, but not having done it I’m only guessing about that.

I have used something similar mounted on my lathe where the speed can be controlled and that worked well…

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That’s it other than raising the all important safety issues associated with all of this. Like many of our turning tools, TC contains stuff like Tungsten and Cobalt and the fine dust coming off the abrasive while grinding is full of it. But, unlike some of the other woodturning tool metals we use, TC doesn’t have sufficient magnetic iron in it for magnet capture to help. According to my particle counter it only remains suspended in the air for a number of minutes after I stop grinding, but leaning over the grinder as we do we are going to breathe in and ingest a lot more of that stuff than I would care to get inside me, so I go in for heavy duty respiratory protection whenever I’m grinding it.

I have been experimenting with a dust extraction hood prototype on my grinder for capturing the TC metal dust as close to source as possible and will post what I did there when I'm a bit more satisfied with that.

The second safety issue is that TC is brittle, very brittle! And, when it shatters, which it does at the least provocation, it can come at you with very sharp shards. I always wear the best eye protection I have whenever I'm using it at the grinder or on the lathe.

 

[hughie]

This I have always considered to be the hard part of owning a TCT tipped tools and especially as a few years ago a local supplier brought out a range of TCT tip tools and it didnt go well as and in the end they sold them off greatly reduced to get rid of them. The new lapping discs are a simple and very cost-effective way around the problem. There might be a question of durability but pricewise and the fact you won't need to grind the tip anywhere near as often as the conventional tips I dont see it as an issue.

 

[Doug Rasmussen]

Neil & Hughie, You're aware of significant health concerns with grinding TC. The lapping discs may run slow enough to minimize dust in the air though. The ideal machine for sharpening would have been the Accu-Finish, I believe the company no longer offers them. They were fairly expensive too. Lapidary type horizontal wheel machines might be adapted for sharpening with water flooding the disc.

Aside from the TC cutting tips your testing results should be a wake up call for users of M42 and other exotics as to the benefits of fine grit wheels for touch up sharpening.

 

[hughie]

Neil & Hughie, You're aware of significant health concerns with grinding TC. The lapping discs may run slow enough to minimize dust in the air though. The ideal machine for sharpening would have been the Accu-Finish, I believe the company no longer offers them. They were fairly expensive too. Lapidary type horizontal wheel machines might be adapted for sharpening with water flooding the disc.

Aside from the TC cutting tips your testing results should be a wake up call for users of M42 and other exotics as to the benefits of fine grit wheels for touch up sharpening.

Doug, Yes and most of us have a DC that would help with the dust and I admit the slower, the better would be the way to go. I have a horizontal hone that can take these discs, it runs much slower than the CBN wheels and I have used it with kero in the past as flushing agent more than an aid to cutting, so the dust hasnt really been of concern. What we are finding is the amazing edge holding ability of TCT and the only drawback is another grinding system, as you mentioned dust is of great concern. But the slower disc speed is proving a great help there at minimal cost as well.

 

[Neil S]

I should have added the following to this thread, which I have posted to the companion thread on testing TC gouges...

Note: Gouge flutes should be taken down to as fine a grit as that used on the bevel side of the edge. I took the flutes on the TC gouges that I used in my tests runs down to a 5micron finish with loose diamond powder suspended in wax, which is equivalent to #1,200 grit. This is what gave them that mirror finish you can see back in post #4. You wouldn't need to use loose diamond for the HSS flutes, but it is much cheaper than you would expect if you look for a reasonably priced source.

I power hone the flutes on all of my gouges and in the case of TC the abrasive just needs to be diamond rather than chromium oxide, etc...

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Stacked High Density Fibreboard held in a chuck can be profiles to match your various flute profiles. The small light coloured piece of wood against the hone is the template I use for making my 1/2" parabolic No 1 flutes being used there to check the profile on the hone.

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[Neil S]

I'm responding here to the following comments on sharpening made over in the the companion thread on testing TC gouges because they relate more specifically to this sharpening thread...

Terry Martin wrote "Rethinking Sharpening" in the June 2014 issue of Am Woodturner. He describes his own experience with using the Tormek, which I believe is similar to a 1000 grit diamond finish. He is convinced that polishing a gouge to a higher finish lasts longer. He also refers to an article by R Farrance with sophisticated tests that show a finer edge lasts longer.

only logical if you are starting finer that it takes longer to get to dull—just like if you are driving faster, it takes longer to get to zero.

Michael and Alan

I think you are both right up to a point (pun acknowledged!) with exotic HSS. But, I think there may be an additional factor with TC sharpened on diamond, which may or may not apply to HSS.

The 'sharpologist' David Weaver maintains that fine diamond powders slice through the carbides without dragging them out of their matrix, which would weaken the edge and also reduce their durability. To quote him...

these powders are both fine, but also extremely strong cutting, and will cut through carbides of anything - including...well, carbide, but more importantly, through tungsten and vanadium carbides.

For the TC that I'm using it seems that the grit needs to be somewhere finer than #800. I went down to #1,000 diamond for grinding the bevel and #1,300, which is about 5 micron) for honing the flute to get the best results.

The same may apply to the lesser amount of carbides in the HSS that we commonly use (eg A11/V10 only has 16% carbides), but I will leave any testing on that for now for others to pursue.

 

[Neil S]

Michael Nathal said:
Terry Martin wrote "Rethinking Sharpening" in the June 2014 issue of Am Woodturner. He describes his own experience with using the Tormek, which I believe is similar to a 1000 grit diamond finish. He is convinced that polishing a gouge to a higher finish lasts longer. He also refers to an article by R Farrance with sophisticated tests that show a finer edge lasts longer.

For reference, here is that article by Terry Martin, which contains a precis of Farrance's piece... https://www.sharpeninghandbook.info/Images/AW2903p18-19.pdf

Having never gone finer with bevel grinding than #360 on a full speed bench grinder with HSS I'm unable to comment myself. I've talked to a few turners like Glenn Lucas who uses the slow speed Tormek with he diamond wheel who prefer it, but I never had the patience for a slow speed grinder!

The diamond lapidary discs mounted on the side of the CBN wheel is not slow cutting, but with the #1k I found it sharpens at just about the right rate for me for refreshing an edge.

 

[hughie]

Having never gone finer with bevel grinding than #360 on a full speed bench grinder with HSS I'm unable to comment myself. I've talked to a few turners like Glenn Lucas who uses the slow speed Tormek with he diamond wheel who prefer it, but I never had the patience for a slow speed grinder!

My thoughts and opinion on this is a slow diamond wheel immersed in a fluid be it water or kerosene etc, would be extremely beneficial as it would control the dust, lubricate the process and add life span to the wheel and offer maximum control for the operator albeit slow for some. I have always preferred slow speed grinders as heat is the enemy and industrially the wheels are lubricate and cooled by a stream of cutting fluid, most often water based soluble oil.

 

[Neil S]

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My tests showed that a #1k diamond disc gave my TC bowl gouge the best edge endurance, so I currently recommend using at least a #1k diamond disc for refreshing edges. A higher grit may do better yet again, but I haven’t tested that yet.

I subsequently acquired a #1.5k diamond disc and compared that with the performance off the #1k diamond disc. I did two test runs on the previously used very hard and abrasive redgum sleeper and swapped the TC gouges around for the second run to eliminate any differences there. Both test runs gave a slightly better endurance off the #1k diamond disc. So, the recommendation based on my testing remains the same with the #1k disc sitting in the sweet spot.

 

[Neil S]

Doug Rasmussen said:
Neil & Hughie, You're aware of significant health concerns with grinding TC.

Revisiting this thread I saw that the photos in my last post to it had a technical meltdown, so that has been deleted and here it is again now with its photos

To address the health concerns with grinding the TC, I knocked up the following cardboard box prototype dust shroud, connected to a vacuum cleaner, to go around the end of my bench grinder where I attached the diamond disc. I just screwed the box onto the grinder motor housing where the safety shield previously attached and stuck the vacuum hose through the back of it so that the end of the nozzle was level with the position of the diamond disc. The vacuum cleaner has its own filter so that the dust isn't recycled back into the workshop.

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According to my PM2.5μm particle counter the improvement was surprisingly good. The first reading below is with the dust hood attached and the vacuum cleaner going (I rigged it up so the cleaner fires up when the bench grinder is turned and then stops a set time after the grinder is turned off) with that in place I'm getting almost no PM2.5μm reading…

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That reading is very good. I then removed the dust hood and got a PM2.5μm reading of over 50 particles per square meter after I stopped grinding. IMO, that is too high to be breathing in, but of equal concern is that it took 30mins for the fine metal dust to drop out of suspension in the workshop air and for the reading to fall below 10 particles per square meter of PM2.5μm sized particles. Some form of effective fine dust mitigation is a wise measure when grinding TC and any of the other tool we grind that contain heavy metals like cobalt, chromium and vanadium.

 

[Neil S]

Having tested the effectiveness of the cardboard prototype I replaced it with the following arrangement to make it more durable. I also rearranged the position of slide for the gouge jig to give better clearance for my longer gouge bars …

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I’ve also made a prototype extractor hood for my diamond wheel. Not that too many of us have diamond wheels on dry bench grinders, but keep in mind that M42 tool steel has over 8% cobalt and 4% chromium in its composition, while V10 has 10% vanadium and 5% chromium in its composition, which are all heavy metals you might like to avoid breathing while grinding those on CBN wheels. This is also working well and I will make something more substantial at some stage…

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[Neil S]

More recently I have changed my side mounted diamond disc arrangement. I came by 6” grinder and as I have been using 6” diamond discs I decided to add a 6” x ½” aluminium lapping platen to the 6” grinder and run the thin diamond lapping discs mounted on that. The advantages of this change is that I have better manoeuverability around to the side of the disc with my gouge jig, which was restricted by the larger 8” wheel, and also better dust capture with the shroud.

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I have found that the 6” grinder is more than adequate for the finer grit (#1,000) grinding that I'm using on my TC bowl gouges.

It has also freed up an 8” grinder for other tasks that will benefit its extra power and wheel diameter...

 

[Neil S]

There is one other economical option.... and that is to use loose diamond grit that can be added to a wax/oil and applied to a hard substrate like High Density Fibreboard (HDF). It is quick and effective. Loose diamond grit comes in a wide range of grit sizes and is reasonably economical from some sources. The HDF disc or wheel must rotate away from the cutting edge or it will dig in (big time!)

I experimented briefly with this again today and confirmed that it works very quickly and very well. I made a disc out of HDF mounted in a chuck and added 20 micron diamond paste.

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It took only 10 seconds to refresh the bevel to a super sharp edge. If I was to adopt this method of resharpening the edge I would pair it with a hard buff shaped to the match the flute profile, which I would use before touching up the edge on the bevel side. This is the hard buff for the flute that I turned from a soft dense wood....

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[Bill Alston]

For reference, here is that article by Terry Martin, which contains a precis of Farrance's piece... https://www.sharpeninghandbook.info/Images/AW2903p18-19.pdf

Having never gone finer with bevel grinding than #360 on a full speed bench grinder with HSS I'm unable to comment myself. I've talked to a few turners like Glenn Lucas who uses the slow speed Tormek with he diamond wheel who prefer it, but I never had the patience for a slow speed grinder!

The diamond lapidary discs mounted on the side of the CBN wheel is not slow cutting, but with the #1k I found it sharpens at just about the right rate for me for refreshing an edge.

Thank you for posting the link.

I had a wet grinder many years ago and found it far too slow for general use. I’m been a firm advocate of belt grinders. One of the obvious advantages is that you can shape tools with a 60 grit belt quickly then sharpen with a 120 or 240 grit belt. More recently I’ve been honing tools with an 800 grit belt and have been very pleased with the results.

You can get a sharp angle with many different grinders but is it really a sharp edge if it’s done on anything lower than 320 grit? I think not, but I’m aware many if not most disagree. Although I don’t agree with all the comments in the article you linked, I most definitely agree about the honed edge. I wish I had the space and funds for another grinder like the Tormek. I’d definitely use it for a final honed edge on some of my tools.

I appreciate though that some turners may not notice too much of a difference between a 240 grit ground edge and one done at 1000 grit. We all have different lathes, tools, etc and turn different woods.

Thanks again for changing my mind about the Tormek. I think I was heading there anyway after using 800 grit belts on my grinder but you’ve accelerated my thinking! 🙂

 

[Bill Alston]

This may be of interest Neil? Some time ago I bought and modified a small 6” bench grinder for use with 4” diamond cup wheels.
It’s for sharpening small tool bits for various jobs. I made the shield from a soil pipe coupler and end cap. The modified end cap is fixed to the grinder with two screws whilst the coupler is simply a push fit and can be rotated. I still need to attach some type of extraction for it.

 

[hughie]

Thank you for posting the link.

I had a wet grinder many years ago and found it far too slow for general use. I’m been a firm advocate of belt grinders. One of the obvious advantages is that you can shape tools with a 60 grit belt quickly then sharpen with a 120 or 240 grit belt. More recently I’ve been honing tools with an 800 grit belt and have been very pleased with the results.

You can get a sharp angle with many different grinders but is it really a sharp edge if it’s done on anything lower than 320 grit? I think not, but I’m aware many if not most disagree. Although I don’t agree with all the comments in the article you linked, I most definitely agree about the honed edge. I wish I had the space and funds for another grinder like the Tormek. I’d definitely use it for a final honed edge on some of my tools.

I appreciate though that some turners may not notice too much of a difference between a 240 grit ground edge and one done at 1000 grit. We all have different lathes, tools, etc and turn different woods.

Thanks again for changing my mind about the Tormek. I think I was heading there anyway after using 800 grit belts on my grinder but you’ve accelerated my thinking! 🙂

From an engineering perspective the finer the better when it comes grinding and Neil I have proved to ourselves that on the carbide tips that were finished with 1000grit diamond lasted considerable longer. History is also verifies this with edged weapon development, the blade were judged on how sharp they could made and how long they lasted. I run 140 and 800 grits on my CBN for all same reason you have alluded to, yes, I have friends, associates, fellow turners who think Im a bit pedantic on both sides of the water.