Heat damage to blades when grinding...

[Mike Holbrook]

Derek,
Did you buy an extra Tormek rest or are you using the same rest and jigs, moving them between the two grinders? I figure there are two wheels, so I still have to figure out what I will do at the second wheel. I thought i would rig something like Derek has at my second wheel, with the Tormek rest and jigs I have and see how I like using them on the CBN wheels.

[Derek Cohen]

Hi Mike

The kit from Tormek comes with a single arm and (I am not sure about this) a single base. I have a vague memory of purchasing a second base for the other wheel.

Tormek BGM 100: http://www.tormek.com/en/accessories/bgm100/index.php

I have toyed with the idea of purchasing a second arm so that both sides may be set up independently of one another. In this photo the second arm is borrowed from my Tormek ...



In practice it does not work well to have two arms as, being coplanar, they get in the way of one another when removing or replacing either the blade holder or tool rest. So the simple solution is the cheaper one: a base for each side and one arm.

Regard from Perth

Derek

[ian maybury]

Just to say that i've done the deed and ordered the 80 and 180 grit pair of CBN wheels (chickened out on betting whether one or other alone would do the job) from Ken Rizza at Wood Turner's wonders - the key point for me being that they have the previously mentioned roughly 1in wide strip of abrasive on each side which should permit face grinding flat bevels, and the grits will hopefully enable rapid metal removal (e.g. re-angling bevels) and/or finer re-cutting/finishing of bevels as required.

I enquired about the durability of the aluminium wheels, Ken confirmed that they have never seen a problem and that the wheels are guaranteed for life against failure of the bond holding the grit - but obviously not against normal long term wear and tear in use. He also indicated that they are manufactured to an overall tolerance of significantly less than 1 thou (e.g. in terms of runout/eccentrictity and side to side wobble) which sounds excellent - the grinder is unlikely to match that.

Flat grinding requires moving the tool across the face of the wheel as on a disc sander - with a bar/miter slot/something to guide whatever is holding the work. Re. Derek's use of the Tormek fixtures. I have most of them from years ago - hopefully they will prove useful off a bar placed at right angles to what Derek has and be able to handle this face grinding situation also. (need to think it through) One fallback if it proves problematical might be a cast iron table and tilt adjustment from a deceased 10 or 12in disc sander...

[Derek Cohen]

Hi Ian

I am still trying to work out what advantage you find with a flat ground primary bevel over a hollow ground primary bevel. Why? It certainly complicates matters - possibly unnecessarily.

Regards from Perth

Derek

[ian maybury]

I agree entirely that it complicates matters Derek, although if the face grinding CBN wheels and Tormek accessories work out as hoped for it won't once the method has been sorted be by very much. It's more that using CBN wheels to grind flat bevels is not a standard and well proven set up (at least not a widely published one) as in the case of hollow grinding - so there is some risk of unexpected issues arising.

My primary driver is that I have two sets of Japanese chisels in white steel. There's those that argue that they need the bevels ground flat to avoid the increased risk of breaking the hardened edge off that supposedly arises with hollow grinding, and those that argue that it's no problem whatsoever.

I guess I chose to take the conservative/safe route, and grind them flat. Having done so I really like the look and feel - and so have (somewhat pig headedly/against some very well intended advice) persisted in searching for a method of grinding that handles heavy metal removal entailed in re-angling bevels on wide baldes better than a disc sander. I'm also aware that for whatever reason it's traditional, and that there is a perhaps smaller but definite population out there that prefers for whatever reason to grind them flat.

My disc sander method was getting the job done, but tends to put a lot of heat in which slows metal removal right down. Which is a pain when e.g. re-angling plane irons. One alternative was to switch to a belt sander like the Sorby system, but the reports from yourself, David and others (and my own short trial) of the CBN wheels were so good (that they were doing such a remarkable job in terms of rapid metal removal for minimum heating) that it seemed a pity not to seek a way of using them. Especially since the cost is similar to the Sorby system, and it was proving tough to establish just how cool running it is.

Mike's posting of the availability of the WTW side/flat ginding wheels was the key enabler.

PS The fallback is that if for whatever reason it's not working out the same hardware (bench grinder + CBN wheels + Tormek accessories) can easily be set up for hollow bevel grinding...

[Derek Cohen]

Ian, I have hollow ground my Japanese chisels for years now. Never experienced any issues at all. Neither has David Charlesworth, whose lead I followed. Another was Jim Krenov.

My only caution has been to avoid overheating the hard steel in the lamination. The 10" wet wheel of the Tormek never was an issue. I suspect - and will soon find out! - that the 8" wheel of the CBM wheel is also fine. After all, Krenov ground his Japanese chisels on even smaller wheels.

Test this out for yourself on a wider chisel first. Just go slowly ...

Regards from Perth

Derek

[paul cottingham]

So here's a question. I am now grinding my blades with a 42" belt grinder. Is there any benefit to using a microbevel? As I see it, a microbevel basically is a way of not needing to waste energy regrinding the whole bevel every time. I realize it also may save some metal, but that is not as important to me.

[bridger berdel]

When you say grind, do you mean that you follow the belt with honing on stones? If so, hone the microbevel. If you are using the belt as your final abrasive, don't bother.

So here's a question. I am now grinding my blades with a 42" belt grinder. Is there any benefit to using a microbevel? As I see it, a microbevel basically is a way of not needing to waste energy regrinding the whole bevel every time. I realize it also may save some metal, but that is not as important to me.

[paul cottingham]

When you say grind, do you mean that you follow the belt with honing on stones? If so, hone the microbevel. If you are using the belt as your final abrasive, don't bother.

Yes, i should have been clearer. My final belt is around 2000 or so. I can strop as well.

[ian maybury]

Thanks Derek. I knew you were hollow grinding your chisels, and working hard woods too - which is one reason why i know it's fine. Then there's the advantage when hand sharpening too - the solid lock in of the honing angle. All of which and more being reasons why I'm maintaining the option to fall back to doing so.

Don't mind my peculiarities in trying for an effective flat bevel grinding method, especially one also capable of removing lots of metal when needed - the intention is not to promote it as better or as a mainstream technique...

As a part of the above Paul I've been using a waterstone honed microbevel over a flat primary on plane blades. It's pretty incredible how quickly the honing goes in this situation (a hollow ground bevel would be similar) - just a few strokes are required on each stone to get an edge, and maybe only 10 or 12 on each side to add a moderate camber. Add the precision of a honing guide and work down to a very fine stone and the result (as i only recently discovered with help from especially David) is a spectacularly sharp, polished and flat but only about 0.5mm wide working micro bevel.

The single bevel sharpening i've been using on the Japanese chisels once an initial edge has been established while still quick takes a little longer. It's quick provided the set up (I'm using a dialled in Veritas Mk 2 honing guide) can return very accurately to the original bevel angle and blade alignment - even a slight misalignment makes it necessary to remove material over the entire area of the bevel which can be quite slow. The Mk 2 guide works well in this regard, but isn't perfect in that a tiny amount of misalignment can creep in on occasion.

One very big advantage of using a microbevel is that it's much less sensitive to variations in honing or grinding angles. It's got to make hand sharpening much easier than it would be done single bevel/Japanese style.

I've not tried fine belts, but if doing so would want to take care to avoid overheating (if the belt was running at a typical sander sort of speed - the Sorby ProEdge runs at about 700ft/min which is relatively slow). While it would be influenced a lot by the set up, another caution would be the risk of the belt not lying flat/of a ripple forming and running ahead of the tool - which if it happened might result in less than flat honing. Plenty of tension, and a flat platen underneath would seem advisable...

[Mike Holbrook]

I think some of these issues are very much related to relative amounts. Hollow grinding that causes an extended very fine edge may be functional for straight razors that need to be very sharp but do not cut thick hard materials. Tools like straight razors are also hollow ground on both surfaces, making a much finer edge. I understand why this degree of hollow grinding will cause a problem on a chisel. Certainly the small amount of hollow grind Derek puts on a single side of his chisels is not the issue that deeper hollows may cause, especially double hollows.

For those who may not have Derek's penchant for invention:
Checking out the Tormek site I find the new BGM-100 Bench Grinder mounting set Derek mentions above. This kit offers all the hardware one needs to build a Tormek tool support/holding jig for 6-10" bench grinders, user supplies wood/material for base. The kit also contains a booklet with specific instructions on how to fit and adjust this jig to fit different size grinders. The kit includes a two piece height adjustable block that allows the user to set the tool bar at exactly the correct distance from the grinder wheel, both vertically and horizontally. The kit also contains rubber feet to be placed on a customized wood surface, supplied by the user, The rubber feet raise the bolts protruding through the wooden platform above the surface. The rubber feet may also dampen grinder/wheel vibration. The kit can also be mounted on a bench top. The kit contains profile labels, designed to be placed on the tool, which allow one to record the three settings necessary to replicate the profile/bevel in the future. Or we could use a Sharpie on the blade or handle.

Set up correctly using the Tormek Turning Tool Setter TTS-100, one can match settings on their Tormek tool rest to those on their bench grinder's Tormek BGM-100 tool rest. The user can then grind, even turning tools, on their grinder and hone on the Tormek without creating all those slightly off micro bevels.

[David Weaver]

Ian, I have hollow ground my Japanese chisels for years now. Never experienced any issues at all. Neither has David Charlesworth, whose lead I followed.

I've done it from time to time with white steel chisels (the most temperature sensitive) and no problems, either. I only don't do it all the time because of a preference for seeing an attractive bevel on the chisels that I have.

Temper temperature for white steel is somewhere in the range of 275 degrees. Not much of any chisel I have ever gets that hot.

It'll be interesting to see how you guys get on doing it with CBN, which I wouldn't allow to get to the edge of very hard steel if I were grinding (because of the severity of the grooves cut), not because I think there will be a temperature issue but more if you notice whether or not the soft backer causes any issues (since all of the CBN wheels come with a specification to use them only on hard steel).

[ian maybury]

There seeems to be some blurring on the issue of steel grade and CBN David. Some suggest that mild steel is OK, others that only hardened steel should be ground - and others that it's not a big deal since a touch with a hardened steel will clear any clogging caused by a softer steel. I did ask the question of one supplier about CBN on Japanese chisels, and the answer was no problem - but not of WTW. Hopefully it will prove OK, but mild steel sounds like its sailing close to the wind and these wheels are definitely not for general purpose use.

Build up on cutting edges when machining metal is a common problem. It usually happens when the metal is soft (e.g. a soft aluminium), and the rake angle (as in the pitch of a plane blade) is too steep. It's like it causes enough heating and pressure when the chip impacts the face of the tool to partially weld it to it, and to other chips. So chances are that the build up when grinding soft metals on CBN could be to do with the geometry of the cutting edges on the abrasive.

Agree from the trial earlier in the week that CBN definitely cuts deep grooves. Hopefully (again) if not the 80 the 180 grit wheel will get close enough to make for trouble free honing.

One confusing aspect of the whole situation seems to be that woodturners regard the edge that comes off 180 grit as sharp - they don't in general seem to go for polished cutting edges as we do on a plane for example… So its very possible that we could run into issues when honing...

[Mel Fulks]

Is there a reduction in the grooves and roughness of the bevel with CBN if you move the chisel laterally? Seem to help when using the white wheels.

[ian maybury]

It was only a fairly quick trial Mel, but looking at the blades manually ground earlier this week by slowly moving them on a tool rest across the (curved) face of the wheel the 180 grit is slightly lined, but getting close to a visually uniform satin finish. The surface left by the 80 grit (or maybe a bit coarser) wheel is quite deeply lined/grooved - more than enough to catch a thumb nail drawn across it….