Perspectives on different methods of planar knife sharpening

[custard]

Again...the problem is the time it takes to grind HSS...its just a bellyache because the stone keeps glazing and therefore stops cutting. I'm resolved to try a diamond dresser to reactivate the stone quickly.

Bob, I also use the Tormek with the Blackstone Silicon wheel which I dress with the TT-50 diamond truing tool. Unfortunately, even with these measures, the Tormek just isn't a very quick grinding tool, and if I've got a lot of material to remove I use a Cubic Boron Nitride wheel on a regular grinder. The CBN wheels aren't as cool running as the Tormek, but they're much cooler running than other grindstone wheels. They remove material really quickly and with virtually no sparks which feels strange at first. Another advantage of CBN wheels is that they're bonded to a metal wheel, so once that's trued and balanced there's no need for any subsequent truing.

Going back to your Tormek, truing the wheels is an essential step. I pretty much follow the David Charlesworth method for getting the best from a Tormek, true the wheel with the TT-50 (the grading stone is a very crude alternative and you can't get the surface of the wheel parallel with the Universal Support, besides which it doesn't work with the Blackstone wheel), set the Universal Support a fixed distance above the stone using a spacer which you keep for this one purpose, and after truing the wheel don't alter the settings on the Universal Support. Following this method gives good, predictable results from the Tormek, but it's still pretty S....L....O....W and if you don't want to think in terms of 15 minute or longer grinding sessions for a major re-shape then consider a CBN wheel.

 

[Random Orbital Bob]

Appreciate the input Custard. But respectfully I'm very very familiar with all things Tormek. I agree entirely that its forte is not shaping but rather sharpening for which it is extremely useful.

The challenge with the TT-50 is that to re-dress the wheel properly (which I agree the TT-50 does supremely well) you have to dismantle the planar knife jigs settings....so while it cuts beautifully after dressing...you're now out of kilter with the very fine settings.

Bottom line, I agree with you that the Tormek is not ideal for removing large amounts of steel. Like I say, great for sharpening....not so for shaping...but a bit is OK..certainly with plane irons and chisels I have no problem. HSS planar knives however are long, and hard (I'll re-phrase that

So do you grind your planar knives on that wheel CBN wheel then? If so what jigging method do you use?

 

[custard]

So do you grind your planar knives on that wheel CBN wheel then? If so what jigging method do you use?

I'd occasionally grind planer knives when I had a 10" two knife planer block. At the time I had one of those horizontal waterstone wheels that had a decent planer jig, but it was tedious process so I kept two sets of knives and would generally send one out for sharpening while the other set was in the machine.

Now I use a disposable knife system, and if they weren't disposable I'd certainly be sending them out for grinding as it's a 17" four knife block!

 

[custard]

Appreciate the input Custard. But respectfully I'm very very familiar with all things Tormek. I agree entirely that its forte is not shaping but rather sharpening for which it is extremely useful.

The challenge with the TT-50 is that to re-dress the wheel properly (which I agree the TT-50 does supremely well) you have to dismantle the planar knife jigs settings....so while it cuts beautifully after dressing...you're now out of kilter with the very fine settings.

This I just don't get. Your Blackstone Silicon wheel (which is the same one I use) simply shouldn't be glazing anywhere near that quickly. I'll true mine occasionally, mainly if there's been uneven wear due to grinding chisels or turning tools. But that's chiefly to remove unevenness on the stone more than to deglaze it, I'm astonished that you're finding glazing a problem during the course of one set of planer blades.

 

[Random Orbital Bob]

Nope....I also use the blackstone to grind bowl gouges literally every day.....and I entirely understand and agree with the dishing effect the articulated bowl gouge jig causes in the centre of the grindstone. For that reason, like you I true when it gets too bad. I also take considerable trouble to keep the stone wear as even as possible by distributing the focus of the grind across the entire surface of the wheel (not easy with bowl gouges but comes with practice).

If you go on to the tormek forum...you'll find this problem is very well documented with large surface area HSS or exotic metals. Planar knives are the scourge. The simple fact is that to grind the amount of steel necessary to re-energise a 12" planar knife bevel is a hell of a lot and the Tormek really struggles with this task. The engineering of the jig is brilliantly accurate and well thought through. The problem is that so much surface area of High speed steel quickly wears away the abrasive in the binder of the stone and it stops cutting. One is then left with the need to re-true the stone because the stone grader doesn't really activate the blackstone that well. That re-truing whilst activating the stone also denudes it's diameter by a fraction....enough to throw out the jigs sensitive set up leaving you needing the grind more metal (because the jig is further away from the now smaller stone). Its a self stroking cycle of reactivating creates cutting ability but throws out jig setting. Very frustrating.

If you haven't experienced the blackstone glazing then either your planar knives only needed a tiny hair off them or they're not really sharp because they were taken out before the whole bevel was ground (the marker pen across the bevel is the true test for this).

The fundamental weakness of the tormek is its brilliant for sharpening an existing repeatable grind (and it truly is remarkable in the edge it creates and the speed it gets it)...but its slow in removing a lot of hard steel (eg wings to produce a fingernail grind on a bowl gouge or planar knives both which are lots of high speed steel).

So as I said before...good for sharpening (little metal and repeatability needed)...not so good for shaping (lots of metal removal needed but only once in a long time)

 

[Jacob]

......

So as I said before...good for sharpening (little metal and repeatability needed)...not so good for shaping (lots of metal removal needed but only once in a long time)

You could say exactly the same of no-machine hand sharpening, which begs the question; what is the point of a Tormek?

 

[Random Orbital Bob]

LOL...sore fingers for one thing (their avoidance that is). I might be being a bit cruel to the Tormek where planar knives are concerned but its a fabulous tool overall.

The point of it in a nutshell is dead accurate, fast, repeatable, seriously sharp edges on an enormous array of tools. Shaping is fine too, every once in a while, its just not its primary forte....sharpening on the other hand most certainly is. I moan a lot about the really tricky end of its range ie planar knives but I couldn't be without it for turning tools, bench planes and chisels. This spring I also did my lawn mower blades, secateurs, a scythe and some hedge shears. You cant beat it for versatility.

So apologies if I was unduly knocking the Tormek...not so...those Swedes have created a legend with the thing...why would so many clones be trying to copy it were that not the case

 

[custard]

If you go on to the tormek forum...you'll find this problem is very well documented with large surface area HSS or exotic metals. Planar knives are the scourge. The simple fact is that to grind the amount of steel necessary to re-energise a 12" planar knife bevel is a hell of a lot and the Tormek really struggles with this task.

That's disappointing to hear, I'd always had a lot of respect for the integrity of Tormek as a company. But to sell a planer knife jig if the stone's aren't up to the task borders on "not fit for purpose".

 

[Random Orbital Bob]

I made that exact comment on their forum re the planar knife jig. The threads are very mixed on the topic. Some absolutely love it and if you examine their testimony carefully it can be seen that for relatively short knives (less metal to grind) and with knives that aren't that blunt (very little metal to be ground) the results are superb.

Its sharpening versus shaping again you see. My planar knives are 12" so a fair bit of chunk, and they were blunt and dinged when I tried them. It was just a stretch I think....just outside its range.
But the other issue to consider is I may have just cocked it up...you never know...the setup is fiddly and it may have been operator error. I don't think so but....I'm too long in the tooth to think I have a monopoly on the truth!

It did occur to me that I might tip the angle of the bevel forward a little more next time to focus the grind at the very edge. In theory this would alter the angle about a degree or so but it would also guarantee the grinding begins at the edge and not at the bottom of the bevel. Thus you should remove less metal and make the task less arduous. Again, in theory you're meant to grind the entire bevel leaving a single facet as you'd expect. The other poster mentioned he uses a slight back bevel.....perhaps that would also help...though I've never seen a sharpening service recommend that.

I think people shouldn't be put off by my experience and should go ahead and try it themselves....and then report the results....there are too many variables involved to summarily dismiss the jig outright. Also, aside from this one jig I absolutely respect my Tormek for taking the back break out of sharpening...so again, it could simply be me doing it wrong.

 

[dickm]

Don't know if any of the current models of horizontal wet grinders have similar attachments, but the Lion branded one had a very accurate planer blade jig. It has the same problem as the Tormek in that it is really for honing, not grinding, but substituting a MRMDF disk for the existing stone, and sticking coarse wet and dry paper on it makes quite a rapid job of the 8" blades off my Lurem.

 

[Random Orbital Bob]

That's an interesting notion...I wonder if it's possible to manufacture a substitute wheel for the Tormek out of solid wood. Using a similar approach to the way you point out for the Lion....then attach an appropriate abrasive wet n dry for use with the jig. I guess you could manufacture a carefully bandsaw'd circle out of thick oak or another stable hardwood. Create some kind of glued in bearing point for the axle and then maybe even Velcro strip a piece of backing for the abrasive. That sucker would sure cut quick

I'm getting the impression that by far the majority just use disposables or use a service however.

 

[Lons]

Well I have to say I am happy to own a 30 year old Kity universal machine that includes a 535 planer that comes with a grinding jig that fits on the side and I have never had cause to send the blades away for sharpening or had to purchase any expensive system to achieve a sharp edge..

Wow, you've just reminded me!

I have something like that, long forgotten - can't even remember where I aquired it :? I'll dig it out tomorrow to have a look as I always intended to motorise it somehow.

Is it a contraption with 2 offset round bars with a sliding holder and accompanied by a contraption with a cup grinding wheel?

EDIT

Wife thinks I'm potty, rooting around the workshop at 10.30 pom but had to look.

Is this similar to yours?
Bob

 

[dickm]

Hadn't thought of making a wooden wheel for the Tormek. Could be done, but might be better to use something more stable than "proper" wood? MRMDF seemed to work OK, provided it was dried out quickly once the job was done. MIGHT work with several layers of marine ply turned to the right diameter??
Actually, thinking about it, it wasn't MRMDF, but flooring grade chipboard..... cheapskate!

 

[Random Orbital Bob]

Yes...turning laminated marine ply sounds like a really interesting idea. By turning it you guarantee the perfect circle...I never even thought of that....brilliant.