Sharpening techniques

[rsser]

With the paw in a splint and turning limited I've turned my attention to this issue.

A while back I had to eat half a humble pie contesting Derek C's promoting of the honing of turning tools.

It seems to me most turners in Oz and North America take their tools straight from a dry grind wheel to the wood. An alternative is to wet grind on a Tormek or similar and hone.

There appear to be very few systematic studies of either the effects of sharpening approaches or of variations in tool steel in woodturning.

Here are two: the first relates only to cutting between spindles, and the second to the durability of various tool steels:

http://www.tormek.com/en/leaflet/pdf/wet_or_dry_en.pdf
(This is only a summary of a piece written for issue 70 of the mag Woodturning - thanks to Ray White for providing a copy).

http://www.morewoodturning.net/woodturn.htm (http://www.morewoodturning.net/woodturn.htm)
Scroll down for the link.

Since Farrance's tests only applied to cutting tools I've decided to (a) do some photomicroscopy on scrapers, at what the edge looks like after dry grinding, burnishing, or top lapping, at 200X, and (b) look at the efficiency of cutting with these treatments. I'll stay with between centres to begin with and try to control as many of the other variables as I can.

It would be interesting to do these tests with the timbers Farrance used - English Ash and Grade 1 Radiata.

I have only a couple of bits of English Ash and if anyone is willing to donate some more I'd be happy to pay postage.

There are some common views about scraping that would be worth some closer examination: (1) the burr does all the work, (2) the burr should be broken off by ramming the tool into a lump of wood, (3) the burr works on medium density timber but not on hard or soft wood (Len Smith), or (4) a turned-up (aka burnished) edge works best (Veritas).

And to summarise Farrance, wet grinding on a Tormek followed by honing produced a sharper and more durable edge on a gouge applied to spindle turning. Scrapers or bowl turning were not tested.

[NeilS]

Good project Ern.


Two comments on the Farrance article.
He specified the grit size of the dry grinding wheel (#80), but not the grit size of the wet grinder. Not that I know anything about them, but according to the Tormek website their grinder come with a #220 grit stone as standard. If that is the case, the test wasn't comparing apples with apples. Of course a #220 grind is going to give a finer long lasting edge than #80.
The relative sharpening times was not reported. In the article Farrance attempted to dismiss the slower sharpening time of the wet grinder by claiming that it was only slower at achieving the initial bevel profile. But without being precise, a significantly slower wet grind may discount the longer lasting edge (subject to point 1) that it produces.
I look forward to your results.

Neil

[Cliff Rogers]

Watching. :2tsup:

[rsser]

Yes indeed Neil.

Lyn Mangiammeli in his response to Farrance's work, on Woodcentral, rather dismisses it on the grounds that the test setup was actually measuring other variables.

So the Tormek runs slower, runs wet, and runs in the reverse direction to std grind wheels. As you say, apples and not apples.

That said, my take-out from his test is that dry grinding wheels produce a hard compacted burr on the gouge which in spindle turning reduces its effectiveness.

No, he doesn't provide data on overall effficiency (taken as output from a given level of input); that should take into account time for setup, grinding and honing of the tool ( and if you wanted to be an economist, the cost and opportunity cost of a Tormek setup), not to mention on the other side of the ledger, steel lost in dry grinding and time and cost involved in improving the finish of the wood.

I think it's a very complex business, involving a heap of variables many of which we have little or no systematic empirical data on. Some of the other variables would include bevel geometry, tool edge to woodgrain presentation (radial v tangential), cutting edge clearance angle, friction/heat generated and so on.

Anyway, I'm resurrecting a laptop to connect the digiscope to and have lapped the top of a 1" HSS scraper on a 25 micron diamond stone. That will be the reference shot at 200X. Will then dry grind with a BluMax wheel, which IIRC is around 54 grit (Cliff?), photo the edge and try to estimate the size of the burr. Then lap and turn up an edge on the Veritas burnisher and again try to estimate the size of the burr.

Then the fun part starts - trying to measure tool effectiveness on spindle blanks. Farrance is not v. clear about how he measured this. Best guess is progress of depth of cut per second (but it could be length of ribbon cut per second).

[hughie]

:U this thread is gonna be a can of worms!

My two bobs worth.

Ern,
Thanks for both articles, they have some interesting points that are worth taking on board.

For me, this is how I see it.

To start with the structure or grain of the tool steel is very important. The finer the grain the finer the edge.

A good example would be silver steel. This is the steel was used to produce cutthroat razors.As a carbon steel it is not as durable as HSS
At the other end would be tungsten carbide, much more coarse and there fore will not produce a fine edge,yet it is very durable.

Horses for courses some what perhaps.

Honing etc. In general honing will or should produce a very fine edge ie the leather strop of a barber using the cut throat razor.
As to the longevity of the edge, then angle at which the tool is ground has some say in this. The cutthroat will have the fine edge but very little steel behind it to support the edge. Conversely the TCT tip has a more blunt angle and there fore have more material to support the edge.

In practice it is a balance or trade off between these and many other factors. That produces a optimum tool for the job at hand.

I notice that wood turners like the ragged of edge of some tools ie the scraper. So the upturned edge area of a rough or 80 grit grind can be useful. But because of what it is, it wont last. It is essentially a burr produced by the grinding.The burr has little strength and so will break away easily.

What is hard for wood workers, is that its a general practice on many different, but similar types of wood. So we try an find the optimum steel to do every thing...bit of a challenge I suspect.

For me I have chosen to do things a little differently, and it is definitely horses for courses here.

I have silver steel finishing gouges for that final fine series of cuts. For the rough out I have a series of tungsten tips tools along with a few hefty gouges. But my heavy bulk removal is often done with TCT tools.

They are all sharpened on my old inherited grinder with a fine stone. Grit grade? Dunno its covered in gunge and cant be read [50+years old]. But I suspect its around 120grit. On top I have a slow revving flat hone, probably around 50rpm, couple that with a rub over by a diamond medium grade file. Produces some very fine edges when I want them. Only the finishing tools would be put through the lot, to do all tools this way is alot of time lost or spent depending on your point of view.

[Pat]

I am in the grinder to the lathe group, 120grit wheel I think. My scrapers get a quick burnish on the Veritas scraper burnisher as it on the same bench as the grinder.

Can of worms, I think Pandora's box has been opened and the earth shall tremble at the responses:U

[rsser]

Yes, when thinking through all the tests that could be done, and the complexities of controlling all the variables bar one at a time, I got the cold sweats.

Thanks for that run-down Hughie.

Though the full Farrance article showed that the burr produced by a dry grind wheel was hard and it took something like 3 minutes constant turning before that tool approached the efficiency of the honed tool. The implication is that the burr had then started to break away leaving a smoother - though still comparatively rough - edge.

I've been corresponding with Brent Beach (of handplane blade tests fame) and Jim Staley.

Jim said the Ring Master maker sharpened their various bits of tool steel but would not say how they did it. When you look at Figure 8 in the paper, clearly there are burrs there so prob. the tools were dry wheel ground.

Pat, Brent suggests that the burnisher might in fact weaken the edge by stretching it. But we have no data.

[NeilS]

To start with the structure or grain of the tool steel is very important.

Hughie your right, but if Ern fixes on one HSS scraper as a constant in his test, then the steel type will be one variable eliminated from his results. I expect he will have enough variables to contend with without the various steel types.

Should anyone be particularly interested in the cutting performance of the different commonly available blade types/brands, (Edit: As Ern is already aware,) Brent Beach has done extensive testing on the performance of different wood plane blades. His results are reported at:

http://www3.telus.net/BrentBeach/Sharpen/bladetest.html

Of course, the slow cutting action of a hand plane blade is somewhat different to the high speed cutting action of a woodturning scraper, but there should be some transfer of applicable findings.

Neil

[rsser]

Yes, heat's an interesting issue.

With M2 steel I've thought that even blueing at the grind wheel won't reduce durability - an item of received wisdom - but maybe there is a gradient.

The Farrance study showed a straw-coloured halo develop at the tool tips during testing but didn't speculate as to why.

And Brent Beach feels that his method of testing plane blades prob. generates more heat than the av. user would do, and this might matter. (Of course, CS is more susceptible to heat degrade than HSS, which I guess is why we're nearly all using the latter in our turning tools. Brent was testing HSS as well though.)

[hughie]

.



With M2 steel I've thought that even bluing at the grind wheel won't reduce durability - an item of received wisdom - but maybe there is a gradient.



most likely not to serious on M2 HSS, as it has what they call a 'red hot hardness'. That is, it can sustain temps up around red hot for brief periods...[not sure how long]
with out effecting hardness. This is one of the important characteristics of HSS.
Before TCT tips etc where common most machine shops used HSS that was ground by hand. The tool bits were routinely ground hard and often went deep blue on on occasion dull red. Then dunked in the water to cool them off, not allot of attention was given to the effect of rapid cooling. In fact it was a generally held belief that little of no harm was done doing this.




The Farrance study showed a straw-coloured halo develop at the tool tips during testing but didn't speculate as to why.



The most likely cause it heat generated during use. In tempering steel by eye "light straw" colour is one of the first colours to appear when heating the steel.

[littlebuddha]

Well my 4p is that i have sharp tools, have been sharpening tools for 40yrs be it with a grinder or stone. with my lathe tools then its a ruby wheel and to the lathe, i use a wolverine type jig homemade it gets one pass and done, i dont grind for the sake of it, and enjoy keeping the metal, if i wated sparks i would buy sparklers.
i use a small dimond file to touch up the edge as i go when needed, then back to the lathe before i finish a piece, i do not do much sanding as my tooling is pritty good.
I think guys that write long articles about the type of metal and heat processes is fine if you want to get into that stuff, but i would rather just get on and sharpen my tools in the way its been for years it works. there is always another metal, another machine, and another tool to by which states its better and better. Its called biz they need the money, simple basics are all that are needed. Even cheap steel tools will cut great if sharpened, might have to sharpen more, but it takes seconds to sharpen a tool. get a good jig and you get it right everytime. To turn is to do. As they say less talk more work.:D and hey im not getting at anyone. its a bit like the washing powders this one will get you whiter than white. sharpe is sharpe, and there are more varibles than there is powder particles in the washing box..have fun guys ..LB :2tsup: iTS RAINING IN THE UK , and i have a leak right over my lathe. got to get the brolly.

[rsser]

Of course there is the wisdom of practice and we all develop our own, but sometimes it's plain wrong. Eg. as Hughie points out, dunking of a hot tool was common but we now know it doesn't do much good to the steel.

Yes, I agree that the data from studies can be used to push an expensive sharpening system (and I won't be buying a Tormek) but I don't think that was Farrance's motivation and it's not mine.

It seems both Brent Beach and Jim Staley were motivated in part to test tool makers' claims about how good their ubeaut triple tempered whosits were. As a result of Brent's comparative testss, one maker no longer claims things like 'lasts 5 times longer than ordinary plane blades'. In fact the cheap and cheeful Mujinfang blade was one of the better performers.

Jim's work shows you'd be wasting your money on cryo treated tools (assuming no variation of consequence between his steel and treatment method and those of cryo tool makers).

So systematic study can debunk conventional wisdom (or confirm it while giving a reason why) and help you save money.

[jmk89]

Ern

I agree with your points and would add that once we know what is fact and what is not, we can also work out what is required and what is just personal preference. Sometimes people try to dress up what is in reality a harmless personal preference as being a scientific necessity.

I look forward to reading how your investigations proceed.

[JDarvall]

What I've gathered from the turning I've done, better off just going straight from grinder. Speeds a important factor for me.

What I'm going to do with my new shed is have a grinder bolted to the wall, near eye level, as close to the lathe as possible. Ideally so I don't even have to move my feet, and do the majority of lathe cuts just using the burr from grinding. When it dulls just grind it a touch with the grinder, back to it without turning the lathe off.

Maybe could do this with a tormac type machine.......but in anycase the hollow ground I've found is important for turning, to get that bevel rub, and tool burr is sufficient for most cuts. Even found its adequate for scraping tools. ie. grind at 70 or 80 degrees and no burnish nesecessary. As long as you can regrind quickly without having to move far.

The main problem I have with honing to something finer than what you get straight from the grinder is that because of the lathes RPM you'll loose that extra hone pretty quick. So all the time spent fiddling to get it extra shinnys really a bit of a waste. Depends on what time restrictions you've got though I spose.

On the wall grinder I'll have 2 AlO wheels. a little rest for parting tool. 25 degrees set permanently..just eye it off looking from the side........and no rest on the other wheel. Just a stick on a universal joint attached to the wall. The stick will plug into a hole in the handles of my spindle gouges that I've drilled, so I can grind them spot on. A more primative and practical version of those grinding jigs. Fast to setup. Just plug it in. Found it important to get that grind right. And I'm hit and miss doing it by eye.

[rsser]

Well I had views similar to yours Jake, but Farrance's article forced me to qualify them. He doesn't make an overall assessment of efficiency (taking into account the cost of a Tormek and the value of one's time) but in terms of effectiveness a wet-ground honed gouge is acc. to his findings clearly superior to what you and I are doing (added: he was honing btw with a compound on a powered wheel which is of course different from a lick with a diamond hone).

There are limitations to his study: the principal ones are that bowl turning and scrapers weren't covered, so I'm starting modestly with scrapers.

So here's the first pics - the s/w is unclear but the magnification is somewhere between 60x and 200x - I'll have to check with the scope supplier to be sure.

I took a HSS 1" scraper and lapped the top in order to get rid of the burr. The first pic is of the top of the scraper, the lapping scratches from the 25 micron stone. I guess that provides some mag'n reference - if a scratch was the full depth of the particle (prob. not likely) then each scratch in the pic is 25 thousands of a metre.

The second pic is the bevel. It was ground before the lapping, on a BlueMax wheel which is 54 grit IIRC.

What these and other pics show, I think, is that the burr hasn't in fact entirely been removed. The dark line at the top of the bevel suggests it's in part been flattened and pushed forward over the bevel. The pics don't capture it well but in real time the edge is pretty jagged with points well over 25 micron at a guess.

Anyway, lots more work to be done.

(btw, with abrasives, what does 'grit' refer to? Particles per square inch I have assumed.)

[Groggy]

Jake and Ern, interesting reading, but I suspect you each turn differently. Recent work I have seen from Jake showed fence post tops and some other work was chair parts.

Ern on the other hand has been doing bowls and deep hollowing plus a bit of other 'show' work. By 'show' I mean it would get picked up and examined at close range.

What I am getting at is that the type of grind depends on the finish you need doesn't it? For fence work I reckon straight off the grinder would be perfect, not sure about chair work but I suspect Jake would be getting a pretty good edge to his tools anyway. For work that will be touched and viewed closely, a finer finish on the tool may help. Particularly if you don't want to get into a lot of sanding. However, if doing chair spindles that are easy to sand, maybe they are easier done that way than fiddling with fine sharpening and trying to support a scraping cut?

Interesting stuff :2tsup:

[rsser]

Sounds logical Greg, resoning from plane and chisel blade performance. Isn't the principle there that the keener the edge the finer the finish?

Certainly with a well prepped blade iron I've got a finish on some woods that just about shines and would be like the finish left after say 240 - 320 grit sanding on a bowl. Something approaching that shine on a bowl is achievable on the outside by rubbing the bevel carefully - (though maybe that's just the bevel heel burnishing the wood). Rarely do I get that on the inside of a bowl which is prob a result of my crappy technique.

[NeilS]

(btw, with abrasives, what does 'grit' refer to? Particles per square inch I have assumed.)

Ern, a complex topic in itself, which I don't pretend to understand. But in simple terms, the numbers refer to the mesh/sieve size measured in holes per lineal inch through which an abrasive grit will pass through. However, there are different US and Europeans standards which start to diverge significantly above about #240. This variation comes from the limitation of finer meshes than that. The following reference provides a useful comparison table across various abrasive types.

http://users.ameritech.net/knives/grits.htm

Neil

[rsser]

Ah, thanks Neil.

Well, couple more pics of the edge after having at it with the BlueMax wheel to produce a burr. It can be felt but is smaller than what I normally raise - maybe harder HSS on this tool, I don't know. Any case, it gives you something of an idea of what a burr looks like close up.

[JDarvall]

Sounds logical Greg, resoning from plane and chisel blade performance. Isn't the principle there that the keener the edge the finer the finish?

Certainly with a well prepped blade iron I've got a finish on some woods that just about shines and would be like the finish left after say 240 - 320 grit sanding on a bowl. Something approaching that shine on a bowl is achievable on the outside by rubbing the bevel carefully - (though maybe that's just the bevel heel burnishing the wood). Rarely do I get that on the inside of a bowl which is prob a result of my crappy technique.

makes sense . I'm not a bowl turner. sortof more interested in copy turnings between centres.

I think it depends how much time you want to save I spose. I believe one needs to only sharpen to a degree thats necessary for the job at hand. Or else you could double the workload unnecessarily. wear your stones unnecessarily.

I feel that there's a huge difference in control between a plane blade or chisel thats been sharpened off the grinder only to one thats been honed further (buffing wheels, stones or whatever). everybody must see that. feel that.

But its a different kettle of fish if your using power IMO. You see it in most powered blades I suppose. routers, planers etc You can get by quite well with something less sharp.

Bevel rubbings burnishes the timber. makes it shine.

So many variables anyway...give an example of what I've noticed with these tools. Why it makes me feel that in general honing beyond the grinder is unnecessary.

Parting tool....... just size with it eh. straight off the grinder, about 25 degrees both side, no problems using it that way. easy to control. I have honed it further before by lapping off a stone just to see what would happen, but then I lost my curvature grind, which gives you that good control.. I even tried it with a buffing wheel. Similar problem.
When it was much sharper, it cut cleaner definetly, but it didn't lend results any faster. because after the time your done honing you would have finished a dozern sizings on the lathe if you'd just left it straight from the grinder. And the finish it leaves generally is not important anyway really. And to start sizing you take it straight in to stop fraying before dropping the handle. That highly honed edge would be just ripped off after a couple of rev's wouldn't it ?

spindle gouge......found if its ground nicely centred to burr, and at 25 degrees, bevel rub, cut with the grain etc, it will cut cleanly into all the valleys. If it hits 35 degrees I risk having problems getting it to cut into tight areas. As long as its profile is maintained it works well I feel. How would you hone this blade sharper than the grinder anyway ? ....its wouldn't be easy. Unnecessarily fiddly I'd imagine.

Roughing gouge.....use that ruffly eh. Would one bother honing that ? I wouldn't. As long as its burred from the grinder.

Scrapers........I've got a broad chisel I use as one, with a slight curvature on the end. I set the grinding tool rest at about 70 degrees and burr it. And use it like that. I have tried lapping it and honing the 70 degrees then burnishing the edge with about 5 degrees I think it was. The shavings were beautiful ......but then it wore out pretty quick. scrapings generates plenty of heat on hardwood......reached the conclusion that it was better to avoid grinding/honing/burnishing and just re-establish the burr off the grinder. But ! I haven't mind you, used a good quality scraper, but the action doesn't suggest it be much better.

Skew....For planing cuts definetly helps to have it sharp. But I prefer to use a roughing gouge for long cuts like that, or my trap plane, cause dig ins still scare the crap out of me. For V cuts, or anything where you want to sharpen up some profile in the wood I definetly don't think the skew needs any more work than what you get from off the grinder.

Sandpapers good stuff ! :D......found orbital sandpaper best. The holes in them stop streaking marks I've noticed. And the velcro backs seem to make them last longer.

[woodwork wally]

Gidday Ern There are some intresting theories and I have found that the burr on the tool doesnt last as long as a well sharpened and honed edge:2tsup: but will invariably seem sharper at the start:) so which way do you go???:doh: By the way I hope that "lunch hook" get better soon :U:U. I hope it wasn't a turning malfunction:no: . Get well soon Regards WW.Wally

[rsser]

Thanks Wally, and Jake.

How do you hone Wally?

If I had to speculate as to why the burr edge feels sharper at the start than the honed then it's prob. because it's rougher and the points are standing up like bent-over saw teeth - so they catch your skin.

[rsser]

Couple more pics: close-ups of the burr. Mag'n prob. 200 x.

[Elbow]

With the paw in a splint and turning limited I've turned my attention to this issue.

What have you done to yourself Ern?

Allan

[rsser]

Allan, see the last post at:
http://www.woodworkforums.com/blog.php?b=289

[TTIT]

Seems an awful long way to send wood that came from just near you but I've got some Ash up here I could send for your 'experiment' Ern. What size/shape were you looking for???

[rsser]

Kind offer Vern. Thanks.

Looking for spindle blanks obviously in English Ash. 4x4 or bigger in whatever lengths you've got.

What do you reckon about this thinking for the test:

With each of the three edge treatments (burr, no burr, burnished), turn till dull, on a blank part-parted into sections a wee bit wider than the scraper. Stop each minute to photograph the edge. Measure the time til dull and the number of sections cut.

Farrance's dry ground gouge died after about 10 minutes. My hunch is that a dry ground scraper wouldn't last that long but a burnished or merely lapped version might match or exceed it. That's prob. going to go through quite a lot of blanks.

I'm not wedded to Ash. That's really only a conceit. Any other hardwood would do so long as it had a consistent grain and density for the three tests, was capable of being cut rather than just shredded, was cheap and readily available. Hmm. Redgum varies a lot (though could perhaps be controlled if sourced from the one trunk), Jarrah and our Euc. 'ash' varieties are coarse grained. What else is there? Blue gum? Brush Box if cheap salvage (though the silica introduces another variable). (Stares vacantly into space :rolleyes: )

[rsser]

K, here's another pic.

There is a view, perhaps mainly held by darksiders, that you can remove a burr by smacking the edge into a bit of wood.

Maybe that's right for tools with a more acute bevel angle. Dunno.

Any case, here's the result of smacking the scraper into a bit of hardwood. See what you think. It's the same burr as pictured above.

[hughie]

wet grind, dry grind.From my understanding...:U

Generally speaking a wet grind should produce a better finish due to the fact that it acts like a lubricant and so keeping the wheel from clogging prematurely.As a coolant in assisting the cutting action by slowing down the degrading of the grit.

The act of sharpening or refacing the grinding wheel,literally rips the grit out of the bond,leaving new sharp grit on the face.

[rsser]

Yes, and as Neil pointed out, the Tormek uses a much finer grit than the typical Alox wheel.

And the Tormek runs 'backwards' so if it raised much of a burr the honing would take it off.

[rsser]

Next: the result of turning up an edge with a Veritas burnisher. It's clearly smoother and taller than the dry-ground burr (pic 2; top view max mag'n).

The black line on the bevel just below the edge is back (pic 1, mid zoom). I now think this is a mark left by the burnisher post.

(Veritas recommend lapping the top first to remove any existing burr or turned edge and this was done).

Added: ref pics of 1 mm markings; the first ostensibly at 200x and the 2nd at 60x - still to verify.

[orraloon]

Sharpening as a topic will always draw a wide range of views and this thread has. This is only my view and it is how sharp does a tool need to be. As has been said most turners just use a dry grinder with whatever wheel they think best and right back ti the lathe. This is to save time. A carver would cringe at the edge but it works on the lathe. I also have a wet grinder and jigs for gouges and chisels but the time to set up and sharpen the much better edge is not worth it. I use it to do plane irons and things where a good edge is required but the turning gouges get a 2 second trip to the dry grinder and back to the lathe. Skews I give a quick rub on an oilstone as I think they require a better edge than gouges and also parting tools. This is still quite quick to do. I grind them sometimes when the bevel is getting out of shape. The better edge will not last on the lathe longer than the grinder one so how much of you're turning time do you want to spend sharpening. I have cut ironbark with a dry grind edge so it seems to work. There are sometimes when a good last cut is required to get rid of tear out then more time to get an edge is worth it.

Regards
John

[rsser]

Yes, I've played with fine peel cuts with a skew on a blackwood bowl exterior, and unless carefully honed with a fine diamond paddle, the feel was grabby, and a little on the scary side.

So I wonder what was causing the grabby feel, and what it would have done to the wood if continued.

What sense John would you make of Farrance's graph on hardwood cutting performance?

.... a wet-ground honed gouge will last 2x as long as a dry-ground one when spindle turning English Ash: almost 20 minutes as against 10 minutes.

[rsser]

Well, there's now some test wood courtesy of DJ. A heavy lump of 4x4 yellow box.

Meantime, the test tool has been prepped. It was a 3/8" Sorby beading tool, now reground as a scraper.

Jeff kindly sharpened the bevel with his Tormek and I lapped the top with 15, 5, 0.5 micron abrasives. The scratches from the 15 are still visible but I don't think that's material with a scraper.

The side is arrissed from its former life but I'll be setting the test wood narrower so it doesn't interfere.

Mag around 60x.

Next 2 tests will be with a dry-ground burr and a hook turned up with a burnisher.