NOT overheating when grinding

[dm65]

Hi all

Having read the post about an overheated plane iron - overheated-plane-iron-t71200.html - I have questions (as ever)

If overheating is bad (as I now understand it to be), how is it best avoided ?

I have some old plane irons that need some serious grinding which inevitably means heat

Is it enough to dunk the iron in water when too hot to hold comfortably or is there a better way ?

 

[Random Orbital Bob]

get a Tormek....water cooled whetstone. No overheating...ever.

 

[custard]

Sometimes woodworkers get a bit too worried about overheating an edge. With a high speed wheel it's almost certain to happen occasionally, but it's not the end of the world. Just grind away the discoloured bit and you're good to go. And the better the quality of your grinding wheel the less likely it is to happen.

I like my Tormek a lot, but "serious grinding" might take twenty or thirty minutes, maybe longer. I'd rather risk the occasional bluing mishap with a dry grindstone and be done in about two minutes!

 

[Paul Chapman]

I'd also recommend water-cooled grinding with a Tormek or similar. No risk at all of overheating. Another advantage is there are no sparks so you don't have to use spark guards. This makes it far easier to see precisely what you are doing. Some people say that water-cooled grinding is slow but I don't find it so. In fact I find a dry grinder slower because you have to keep stopping to dunk the blade in water.

Cheers :wink:

Paul

 

[dm65]

get a Tormek....water cooled whetstone. No overheating...ever.

Oh, I wish I could

Sometimes woodworkers get a bit too worried about overheating an edge. With a high speed wheel it's almost certain to happen occasionally, but it's not the end of the world. Just grind away the discoloured bit and you're good to go

But from the thread I referred to, it sounds like the metal gets noticeably softened ?

In fact I find a dry grinder slower because you have to keep stopping to dunk the blade in water.

That implies more than a dunk, do you have to keep in water till cold again ?

 

[Paul Chapman]

In fact I find a dry grinder slower because you have to keep stopping to dunk the blade in water.

That implies more than a dunk, do you have to keep in water till cold again ?

You have to do it quite frequently is what I meant. Frankly, I found grinding using a dry grinder a bit of a hassle and virtually gave up using mine years ago. In comparison, using a Tormek is quite enjoyable and completely stress-free. I wish I'd bought one years ago.

I wouldn't take any notice of those who imply burning a blade doesn't really matter. It does. And the adverse effects usually go beyond the blue part of the blade.

Cheers :wink:

Paul

 

[CHJ]

If using a dry grinder then selection of wheels and keeping the wheels unglazed and sharp is very relevant to material removal and heat generated.

I keep an odd grinder set up with coarse 40-60 grit wheels for faster cooler bulk material removal.

If money was no object or I was starting again from scratch I think I would just do with the Blue Micro-crystalline Ceramic Wheels for dry grinding, they certainly do what it says on the tin so to speak, and a wet grinder for finishing.

 

[Corneel]

Get a coarse wheel and one of the diamond dressers. Keep the surface of your wheel fresh. Keep a light touch when pushing the blade against the wheel and move it constantly left to right, right to left. Keep your fingers on the back of the blade just right behind the edge, don't worry the grinder won't bite you. And cool the blade in some water for a few seconds when it feels warm (not hot). I grind almost to the edge, just a fraction will still be blunt, then I move to a coarse waterstone to finish the job.

A Tormek might be nice but it is way out of my price range. Taking care I never color a blade.

The colors tell you something about how soft the steel has become. Blue is about RC 52 which is very low for a planeblade. It would still cut but might fold over and it dulls quicker. But if a small bit gets blue, don't fret it too much. Grind back a bit and use the blade. If it still functions you're lucky. If it seems too soft, grind back a bit more. The blade in the other thread was pretty extreme.

 

[custard]

But from the thread I referred to, it sounds like the metal gets noticeably softened ?

That was a near terminal case, someone probably held the iron hard against the grindstone without moving or cooling for quite a time, I'm talking about the tiny bit of bluing that's bound to occur now and again while you're learning the ropes, that's nothing to worry about.

The problem with a Tormek is that a major reshape can take a long, long, long time. I use a Tormek and like it very much, but for a big grinding job I use a dry grinder every time...life's too short to Tormek everything!

 

[dm65]

Thanks everybody - useful info for me as I've never done anything like this before

I think what comes out of this is 'slow and steady', but above all, these blades are very sensitive to heat when it comes to edge retention

I (wrongly) assumed that this sort of metal needed much more heat to alter their properties

Thanks again - I hope to post when I do my first one (gulp)

 

[JohnPW]

The only real grinding I've done so far has been on the coarser side of a combination oil stone. No risk of overheating but a lot of manual work compared with a machine!

One was a wooden rebate plane laminated iron when I had to remove about 2-3mm to get rid off pitting on one of the corners. That also removed some pitting on the flat side. It seemed quite quick to get a thick rolled edge. Perhaps being narrower helped.

The other was a Stanley 4 1/2 iron which was really off square. I only removed one corner ending up with a big camber.

 

[xy mosian]

If I might add to Corneel's words. Working with two blades, during the same session, allows one to cool while warming the other on the grinder.
xy

 

[dm65]

The only real grinding I've done so far has been on the coarser side of a combination oil stone. No risk of overheating but a lot of manual work compared with a machine!

One was a wooden rebate plane laminated iron when I had to remove about 2-3mm to get rid off pitting on one of the corners. That also removed some pitting on the flat side. It seemed quite quick to get a thick rolled edge. Perhaps being narrower helped.

The other was a Stanley 4 1/2 iron which was really off square. I only removed one corner ending up with a big camber.

Currently about 1 1/2 hours into a not too badly cambered no5 blade using the same method, but already done one the same size but not as bad as this one

If I might add to Corneel's words. Working with two blades, during the same session, allows one to cool while warming the other on the grinder.
xy

In my case, as I have a few to do, this makes absolute sense

 

[James-1986]

Grinding with a tormek?! Some of you have a LOT of time on your hands

With a good quality grinder, decent wheels (that are maintained) and a bit of practice you shouldn't have any trouble with overheating.

For anything that is delicate I use a coarse oil stone.

 

[Steve Elliott]

My best tip for not overheating while dry grinding is to start with the blade already cold. I like to keep ice water next to the grinder and cool the blade down before I even start. I put the back end of a plane blade in the water so that even if the cutting edge should be hot it won't suffer thermal shock.

I've recently gone from using a Tormek for all my grinding to using a 60-grit Norton 3X wheel on a low-speed 8-inch grinder. The dry grinding is MUCH faster and with a little care burning isn't a problem. The Tormek is still better for stress-free, controlled grinding right near the edge.

 

[longinthetooth]

Assuming that you are stuck with the grinder you've got - the place of highest risk is at the blade's tip - where it's thinnest. The heat just can't get away so fast. For a big grind (nicks, etc) do the first phase of grinding with the blade squareish to the wheel (as if you are grinding a flat end on it). Do this till the nicks or whatever have gone, then re-present at the bevel angle and proceed to produce the bevel - you can go relatively fast without 'burning' until you approach the last phase when the edge is getting fine - so you progressively slow down (and dunk).

I use a 180mm white wheel on my home made grinder. Wheels are coded, mine is WA-46-J-6-V. J is hardness of bond, 6 is density (less dense = cooler) ... I have a top-mounted gravity water feed and the wheel runs at circa 1200 rpm, belt-driven from a salvaged washing machine motor. Burning is possible, but it's fairly quick. I built it back in the 1970's!

 

[Duncumb.fc]

Personally, I dry grind all the time when I get old tools in and want to get them going quickly. I also made a knife recently and even after hardening and tempering I still dry grind. I switch to the tormek when I want a good clean bevel, as with the guide it's much easier to get a nice grind.
My method is to have a tray of tap water, and to make one sweep on the grinder, then dunk the blade in the water. It only needs to be in the water for a second or two. Leave the water on, because you'll see it dry up through heat way before the blade "burns". Tempering the blade only happens around 180˚C, and actually a light brown is nothing to worry about, as that is where the blade is already tempered to. It's when you go beyond this that it becomes a problem, and light brown can turn to blue very very quickly.
Sweep, dunk, sweep, dunk, sweep, dunk. Just remember that and don't forget, you'll never get near the burning temperature.
As with anything like this, go slow and you won't have a problem.

Fraser

 

[Aled Dafis]

I use a Norton 3X 60G wheel which grinds cooler than any other I've ever used, they really are worth the money. One thing to remember is the thinner the section of steel, the quicker it will reach and pass it's tempering temperature (~200 degrees C for O1 high carbon steel).

If you have a lot of heavy grinding to do, I'd advise that you grind a blunt edge first at around 90 degrees until you reach the dent/nick that you're grinding out and only then should you start grinding the bevel, this will definitely help with reducing the risk of accidentally over tempering your blade. Ad your bevel becomes progressively finer, I'd go with the previous advice of quenching in water as often as you see necessary, definitely as soon as you feel the section near to the edge becoming hot to the touch - even with a Norton 3X wheel it's still possible to blue a fine edge if you're not careful.

Reagrds
Aled