hollowgrindin' virgin

[thetyreman]

I'm new to hollow grinding,

any tips? I have got a krenov style hock blade, it's pretty thick, want to get rid of the bulk of the steel so I can just sharpen the very edge, but don't want to ruin it.

Found this video, do you think it's overkill?

 

[Bm101]

I clicked on it Ben and I have to say I'm a couple of pints in after a long day so I turned it off really quickly. Sorry mate. Bit tired.
I have a sorby but the principle is the same with any grinding. Temperatures are no issue until you get to a thin edge. Thinner the metal, the faster it heats. Heat a thin edge for just a second and it blues, so it's soft and need's regrinding. That's why you see the likes of Custard (I only mention Custard because he has taken the time and effort to detail his sharpening setup and added photos), use mechanical sharpening to regrind a serious amount then switch back to hand at the last stage on stones etc...
I tried to get round it with trizact super fine belts at 2000+ grits. It's possible to finish an edge but it's a big risk if you spend a second too long. Ruined an edge and a regrind.
I've been doing some metal grinding today for a project and I keep a bowl with iced water in it next to the sorby.
I'd like to have the money to invest in that Axminster slow speed sorby copy. I'd put a trizact belt on that and never think about sharpening again.

 

[Tony Zaffuto]

Heat is your enemy and the wrong wheel on a too fast grinder is your ticket to problems!

180 grit CBN wheel on a slow speed grinder, with a good rest and some experience, will get you started. With experience, it can be quicker than other methods, but you will still have time on your stones.

 

[Cheshirechappie]

Well - for a start, don't run a high-speed grinder without the wheel guards! The risk of a wheel burst is quite low (provided the wheels are treated sensibly), but if it did happen the guards would contain most of the flying bits. In addition, there's a fair bit of dust and metal particles flung around, and the guards catch much of that. Don't forget eye protection - a metal particle on the eyeball isn't funny.

Dressing a very slight crown on the periphery of the wheel and keeping the work moving sideways helps to avoid overheating. Toolrest to taste; the minimalist ones supplied with most budget bench grinders might be enough.

It's not a bad idea to stop grinding 1/2mm or so from the edge. All power grinding tends to cause very localised high temperatures, which on cooling leave micro-cracks, which weaken the finish-honed edge and cause early dulling. It can take two or three honings to remove the micro-cracked metal, so not grinding right TO the edge reduces the chances of micro-cracks AT the edge. You'll still have micro-cracks further up the bevel, but they don't affect the edge or it's life.

Other than that, the video gave pretty sound advice. Coarse grit wheel, kept clean with frequent light dressing, light touch, keep checking progress. For a tool in good order but honed a few times, one or two passes might well suffice; heavy reshaping only really needed to restore a badly chipped edge or a beaten-up vintage beauty.

Darn sight quicker than rubbing up and down a coarse oil, water or diamond stone, that's for sure!

 

[D_W]

put a wet paper towel folded over between your fingers and the iron if you're that worried about heating the edge. If/when the paper towel contacts the grinding wheel, it doesn't catch - it'll just spritz your face.

More realistic for day to day (wet paper towel is good for heavy angle adjustment, especially on something that doesn't spark much and therefore doesn't discharge much heat) is to make a light pass across the wheel and then see how fast you have to move the back of a chisel or plane iron across your palm. If you can pull the iron across your palm and stop it or nearly stop it, it's not that hot. The hotter it is, the faster you need to pull it. you won't burn your palm unless you try intentionally do it.

 

[custard]

I have got a krenov style hock blade, it's pretty thick, want to get rid of the bulk of the steel so I can just sharpen the very edge, but don't want to ruin it.

Two points.

Firstly, you're very sensibly planning on grinding away the bulk of the steel, but not all of it. In other words you don't want to "break through" and create a burr. As long as you stick to that plan you're unlikely to overheat the blade. The problem of overheating normally occurs if you're grinding out a nick, or some other task where you will grind right through past the edge. A good way of monitoring your progress, and ensuring you don't too far with the grinder, is to use an indelible felt tip pen to shade in the bevel before grinding. That way you can clearly see how close you're getting to the edge, I try and stop about half a mill from the edge, which also allows you to protect the plane iron's camber that you'll eventually have sunk a lot of effort into shaping so it's just perfect for you and your style of working!

Secondly, there's a tendency to overstate the risk of bluing an iron, some people seem to think it permanently ruins the tool. It doesn't. You just grind more sensitively next time and remove the problem. It's not something you want to happen, but it's actually not that big a deal if it does happen.

Good luck!

 

[Ttrees]

I suggest you make yourself comfortable as you will have more patience to do the job well.
You might consider a place to put it which could be better, if its just pulled out from a shelf occasionally.
If your taking your time stooping, by the time you get close you might be getting a sore back and not be in as good a shape as you were when you started.

At the same time as being comfortable, you need to dunk the tool in water quickly .
Get used to the flow, under 2 seconds off of the wheel would be what I'd shoot for.
I could be half that though I've not thought about it.
If you can't do a dry run in that time, somethings not right, get better situated.

Laminated irons seem to blue quicker for me, so watch out for that down the road.