Hollow grind question

[Phil Mueller]

I’m finally set up to be able to put a hollow grind on my edge tools. Slow speed grinder and 80 grit CBN. Here’s a picture of one of my first grinds (60 1/2 block plane).

391595
I know I need to work a little more on the micro-bevel. Question is, the 80 grit scratch pattern...it’s ok as long as the micro bevel has no scratches right? Being used to polished bevels, the scratches kind of bother me...but is there a reason it should? Do I need a higher grit CBN to smooth it out some?

Thanks!

[Brian Eaton]

I’ve recently gotten set up to hollow grind bevels and have left the primary bevel as it is off the wheel. Between hollow grinding and stepping up to some good quality 3m lapping papers from wet/dry stuff I’ve gotten far sharper edges than I had previously been getting. That being said, your scratch pattern looks a bit more aggressive than what mine seem to end up with. Could just be how close the blade is to the lens though!

[lowell holmes]

I would hone the bevel smooth and put a micro bevel on the edge. Google micro bevel.

[Stewie Simpson]

Phil; I purchased the #80 and #120 grit cbn wheels over 12 months ago.

The #120 cbn supplies a finer scratch pattern that's better suited to follow up work on the honing stones.

[Phil Mueller]

Thanks all. Appreciate the input on the 120 grit, Stewie. Sounds like a good use for the $ sitting in my paypal account.

[Chris Parks]

I’m finally set up to be able to put a hollow grind on my edge tools. Slow speed grinder and 80 grit CBN. Here’s a picture of one of my first grinds (60 1/2 block plane).

391595
I know I need to work a little more on the micro-bevel. Question is, the 80 grit scratch pattern...it’s ok as long as the micro bevel has no scratches right? Being used to polished bevels, the scratches kind of bother me...but is there a reason it should? Do I need a higher grit CBN to smooth it out some?

Thanks!


The way I do it is to grind the hollow until all defects are removed then it all gets done on the stone(s) after that. I usually make the first stone 1000, place the blade on the stone and feel for the heel and toe touching then slightly lift the heel and start honing until the grind marks are gone and the bevel has been established, being very small this does not take long. Rinse and repeat for each stone you want to use. I do not worry about angles, just a small lift and the more you practise the better the muscle memory. Lock your arms to your side to prevent any change of angle caused by arm movement and then move your whole body back and forth to move the blade along the stone.

[alan west]

Leaving the scratch marks in the hollow grind works just fine. In fact, you will have less surface to remove when you need to re-sharpen this way. If you are lucky you will not need to grind again and just use your stones.

[Chris Parks]

Ignore the scratch marks in the hollow, you can't do anything about them with a flat stone and if you want a blemish free full bevel hollow grinding is the wrong method to be using as the primary bevel has to be flat for that to happen. The beauty of the hollow grind is the speed it can be done at, five minutes and you have a sharp blade from go to whoa.

[Derek Cohen]

I’m finally set up to be able to put a hollow grind on my edge tools. Slow speed grinder and 80 grit CBN. Here’s a picture of one of my first grinds (60 1/2 block plane).

391595
I know I need to work a little more on the micro-bevel. Question is, the 80 grit scratch pattern...it’s ok as long as the micro bevel has no scratches right? Being used to polished bevels, the scratches kind of bother me...but is there a reason it should? Do I need a higher grit CBN to smooth it out some?

Thanks!

Hi Phil

Scratches on the hollow are expected. Scratches on the secondary or micro bevel are not.

I recommend that you get a 180 grit CBN wheel for refreshing the hollow. 80 grit is too coarse to allow for one to quickly remove scratches. 120 grit is too close to 80 grit.

I wrote about this a few years back: http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp.html

180 grit CBN and honed ..

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp_html_71b2c2d0.jpg

Regards from Perth

Derek

[Stewie Simpson]

Phil; Derek's correct. I went and checked the finer grit rating on my CBN set up. (The 180 grit CBN wheel is on the right hand side of the grinder.) My apologies for the confusion.

Stewie;

http://i1009.photobucket.com/albums/af219/swagman001/bench%20grinder/_DSC0159_zpsatnwy36d.jpg

[Phil Mueller]

Thank you both. No apologies for confusion necessary. Actually, Woodturners Wonders does not have 120 grit, so I made a wild assumption that it probably was 180. Order sent and looking forward to using it.

[John K Jordan]

Thanks all. Appreciate the input on the 120 grit, Stewie. Sounds like a good use for the $ sitting in my paypal account.

Why stop at 120? At the moment I use 80, 220, and 600 grit CBN wheels on 1/2-speed bench grinders and a 1200 grit CBN on a Tormek. I like the edge I get with the 1200, great for my lathe spindle gouges with a minimal amount of honing. I use the 600 for scrapers and some other tools.

[Derek Cohen]

180 grit is for bench chisels. Lathe chisels are different since one may use them off a grinder.

Regards from Perth

Derek

[John K Jordan]

Lathe chisels are different since one may use them off a grinder.


That's certainly true for some, especially those turning bowls green wood. I prefer to turn hard, dry wood so I hone/strop nearly all lathe tools from the grinder, some lightly with the leather wheel of the Tormek, some with polishing compound rubbed on a piece of resawn MDF, and some with very fine diamond and/or a ceramic stone.

Turners often use scrapers and rely on the burr directly from a coarse grinding wheel. I prefer use a finer wheel, hone away the grinder burr, and raise a burr with a carbide burnisher.

I'm not as experienced with sharpening bench chisels and plane irons. After reading some of the sharpening threads here I'm sometimes amazed that I can get an edge as sharp as I do with my crude techniques!

JKJ

[Phil Mueller]

I​t just occurred to me that I’ve spent another $200 on sharpening, and based on another post where Derek mentioned a medium Spyderco may just add a bit more to that. When does this slippery slope end! :eek:

[John K Jordan]

I​t just occurred to me that I’ve spent another $200 on....
When does this slippery slope end! :eek:

My best projection, based on long observation of the woodturning, other wood endeavors, metalworking, pottery, motorcycles, boating, and a variety of passion-inspiring pursuits - the slope ends when you finally slide off the Big Slope of Life.

JKJ

[bridger berdel]

I like to follow a bench grinder with a few strokes on a similar grit stone, then move on up the grits.

[Derek Cohen]

I like to follow a bench grinder with a few strokes on a similar grit stone, then move on up the grits.

Hi Bridger

This is an interesting issue.

If one is using a vitreous silicon carbide grinding wheel - the recommended white wheels are typically 46 grit - then the resulting bevel is quite coarse and serrated. Your suggestion to follow with a coarse stone is one I would follow when I used such wheels. In fact, it was recommended that one did not grind to the edge of the blade ... not just because of the resulting heat, but to preserve as much of the old smooth bevel as possible. Unfortunately, leaving this edge comes complete with a rounded wear bevel. It needs to be removed.

The advantage of a CBN wheel is not just they are great at keeping their shape and grinding quite cool; the advantage is also that one can use a reasonably smooth grit, such as 180, and that this produces a smoother surface at the end of the hollow. Indeed, one can grind safely to the edge (enough to raise a fine wire, and no more than than).

I have recommended a step beyond this, and that is to use the Tormek BGM-100, since this will enable the grind to be dead straight. It is not just that the resulting hollow grind is super clean and straight, but when ground to the edge of the blade, it is possible to move directly to honing with higher grits. I start with 6000 grit. This requires about 3 strokes to raise a smooth and straight shine with a wire to the back of the blade. A couple of strokes on a 13000, and you are done. The hollow will remain this friendly for quite a long time. Grinding like this means less grinding.

As before ...

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp_html_71b2c2d0.jpg

Regards from Perth

Derek

[bridger berdel]

If you are grinding with a fairly fine grit on a jigged grinder you can likely forego the first stone being of similar grit. I grind and hone freehand, and have multiple grinder options. The first stone being near the grit of the grinder needs only a few swipes before moving on up the grits- in my hands this is quicker than jigging the grinder. However, i don't have a tormek, so i'm not in a position to address the amount of time spent fiddling with those particular sets of gizmos. What i do works for me, is quick and efficient in my shop. YMMV.

[Charles Guest]

None of this matters, much, since you rarely grind tools all the way to the edge. If you are under the impression that you do, you have a fundamental misunderstanding of the process. There's little need to spend a lot of money on grinding wheels.

[bridger berdel]

Grinding to or past the edge mostly happens when repairing a damaged edge.

[Stewie Simpson]

Grinding to or past the edge mostly happens when repairing a damaged edge.

imo; its not sound advise to grind away the damaged edge from the bevel side of the tool.


https://www.toolsforworkingwood.com/blogimg/1/repair_6_1200.jpg



https://www.toolsforworkingwood.com/blogimg/1/repair_5_1200.jpg

[Chris Parks]

None of this matters, much, since you rarely grind tools all the way to the edge. If you are under the impression that you do, you have a fundamental misunderstanding of the process. There's little need to spend a lot of money on grinding wheels.

Charles, can you expand on this a bit more please for those of us who don't understand the process. Thanks.

[Kees Heiden]

Charles, can you expand on this a bit more please for those of us who don't understand the process. Thanks.

Stewie just posted a few pictures how you repair a nicked edge. Present the chisel perpendicular to the grinding stone to grind out the damage. Only then remove metal from the bevel at the usual angle, only doing this until just a little remains of the obtuse grind done previously. That little bit is quickly removed on a coarse flat bench stone, if you dare to go close enough.

It does take some decent skills to do that evenly and accurately on the grinder.

[Chris Parks]

Stewie just posted a few pictures how you repair a nicked edge. Present the chisel perpendicular to the grinding stone to grind out the damage. Only then remove metal from the bevel at the usual angle, only doing this until just a little remains of the obtuse grind done previously. That little bit is quickly removed on a coarse flat bench stone, if you dare to go close enough.

It does take some decent skills to do that evenly and accurately on the grinder.

I have never found the need to do that with a CBN wheel as it cuts so quickly and the wheel absorbs much of the heat produced is absorbed by the mass of the wheel and the edge never gets hot enough to suffer any damage at all. I had a chisel handed to me as a challenge where the owner had deliberately driven the edge into a nail several times and I took those deep nicks out by grinding it to the edge and the chisel blade was still cool enough to touch right at the bevel. CBN wheel sharpening has been a game changer in this respect for anyone who uses one.

[Derek Cohen]

I've been grinding to the edge of blades for over a decade, and without any damage to the steel. For several years this was with a Tormek, which is a wet grinder. For the past 3 years I have done so with a CBN wheel on a half-speed bench grinder. So far I have not damaged a blade on this either.

The edge is not weakened by this method. I have used 25 degree hollow grinds (to the edge) for shooting end grain, and never chipped nor rolled an edge. I have hollow ground to 30 degrees bench chisels, and chopped with them. Also no chipping or rolling of the edge. In short, in my experience, the method is perfectly safe when the grinding is cool.

The trick is to keep the edge cool. This is not for the heavy-handed or impatient. Take it slow, light, and with a cool-running wheel, and she'll be right (https://www.urbandictionary.com/define.php?term=she%27ll%20be%20right).

Regards from Perth

Derek

[Kees Heiden]

When my current grinding wheel wears down too much I'll certainly think about the CBN option. But that'll take a few more years, and in the mean time I use the method posted above to grind a nicked edge without overheating on a conventional coarse wheel.